What formula is used to determine the number of phenotypes in the offspring during splitting?
To determine, the formula 2 n is used, in which n is the number of pairs of allelic genes.
If it happens monohybrid cross, "parents", endowed with a difference in one pair of traits (Mendel experimented with yellow and green peas), in the second generation they give two phenotype(2 1). At dihybrid crossing they differ in two pairs of traits and, accordingly, produce four phenotypes in the second generation (2 2).
In exactly the same way, the number of phenotypes obtained in the second generation is calculated by the method trihybrid crossing- eight phenotypes will appear (2 3).
What formula is used to determine the number of different types of gametes in heterozygotes?
This number is also calculated by the formula (2 n). However, n in this case is the number of gene pairs in the heterozygous state. On the use of this formula, problems are built in the Unified State Examination in biology and the internal exam of Moscow State University.
What formula is used to determine the number of genotypes in the offspring during splitting?
The formula 3 n is applied here, where n is the number of pairs of allelic genes. If the cross is monohybrid, the splitting of the genotype in F 2 occurs in a ratio of 1:2:1, that is, three different genotypes are formed (3 1).
With dihybrid crossing, 9 genotypes appear (3 2), with trihybrid crossing - 27 genotypes (3 3).
Do you want to pass the exam perfectly? Click here -1) population-species
2) organismic
3) biogeocenotic
4) molecular
The infusoria shoe represents both the cellular level of life organization and
1) molecular
2) organismic
3) specific
4) biocenotic
What studies are difficult in humans due to the slow change of generation and small offspring
1) anatomical
2) physiological
3) histological
4) genetic
4. In a DNA molecule, the number of nucleotides with guanine is 30% of the total. How many nucleotides with thymine are in this molecule?
Foreign proteins that enter the human body bind, forming complexes with
1) antigens
2) platelets
3) antibodies
4) antibiotics
Single cell animal cell
1) does not have an endoplasmic reticulum
2) creates organic substances from inorganic
3) has vacuoles with cell sap
4) performs all the functions of a living organism
The daughter organism retains the greatest similarity with the parent during reproduction.
1) parthenogenesis
2) sexually
3) using seeds
4) budding
How many phenotypic groups are formed when two heterozygotes are crossed?
3) twelve
4) sixteen
The essence of the phenomenon of heterosis used in breeding is
1) a multiple increase in the number of chromosomes
2) change in the gene pool of a variety or breed
3) the transition of many genes to a homozygous state
4) heterozygosity of hybrids
Which of the following representatives of the kingdom of fungi does not form mycelium?
1) penicillium
4) boletus
Task 2. "Yes" or "No"?
Remember who are tunicates and lancelets What systematic groups do they belong to? What morphological characters or biological features are present ("Yes") or absent ("No") in these groups. Fill in the table cells.
Task 3. Circles!
Consider the presented drawings, concentric circles are clearly visible on them. Answer the questions.
Questions:
1. What is shown in the pictures?
2. Are they similar or homologous structures?
3. How are they formed? (1 offer)
4. What are the reasons for the similarities? (1-2 sentences)
 |
|
Task 4. Biological problems.
Read the conditions carefully and solve the biological problems. Write down in detail: given, decision, answer.
1. On average, a bee family in summer has 70 thousand bees and collects 130 kg of honey per season. How much honey does each worker bee produce, considering that 1/14 of this family is busy with other things.
2. A lover of pigeons crossed a black male with hairy legs with the same female. And he got offspring - 15 chicks: 8 black with shaggy legs, 2 brown with shaggy legs, 4 black with bare legs and 1 brown with bare legs. The genes for the two traits are not linked.
Define:
1) genotypes of parents,
2) genotypes of offspring
3) the pattern of inheritance of traits.
Task 5. Photo question.
This photo shows a low island, which has the correct ring shape, consists of limestone. Almost its entire area is occupied by unusual lush greenery, outside there is a narrow sandy beach and a strip of shallow water, partially exposed during low tides. Answer the questions.
Questions:
1. What is the name of such formations?
2. What animals created this unique relief?
3. What systematic group do they belong to?
Task 6. Year of the monkey!
According to the Chinese lunar calendar, the new year is celebrated on the second new moon after the winter solstice, which usually falls between January 21 and February 21. 2016 new year corresponds to the year of the monkey!
You need to use your knowledge of monkey biology to come up with three original and tricky questions about biological features these animals and answer them.
Evaluation criteria:
1. Compliance with the task.
2. Biological literacy.
3. Originality.
4. Compliance with technical requirements.
Task 7. How it was ...
Answer the suggested questions:
1. What is your mood after completing all the tasks?
2. What was the most difficult and how did you overcome the difficulties?
3. What can you praise yourself for?
Try to make the answers to the questions interesting for other participants to read. You can write answers in any genre. It can be a story, a note, a fairy tale, a poem, etc.
Evaluation criteria:
· Reflection is not provided - 0 points.
· Reflection was made for this competition and is a formal answer to questions that are not related to each other - 1 point.
· Reflection was made for this competition and is the author's detailed answers to questions - 2 points.
Recommendations that will help you get an excellent result, and we can quickly check your work:
1. The document with the answers must be named Surname_Name_class. Sample file name: Petrov_Ivan_ 5th grade.doc
2. Graphic images are executed in any graphic editor with the extension - JPG or GIF. The document with the image must be named: Surname_Name_class. Sample filename: Petrov_Ivan_1 class.jpg (Unless the task requires otherwise).
3. If the participant's work contains more than one file, then it must be placed in an archive with the name: Surname_Name_class. Archive sample: Petrov_Ivan_1 class.rar
4. The work must be uploaded in the Personal Account, after filling out the list of participants.
5. The size of the uploaded file must be no more than 20 MB
6. Detailed instructions on how to upload the work, download the award material on the site page How to participate.
7. If you have any questions or suggestions - we are waiting for your letters to the mail [email protected] or use our online form on the website.
Useful documents:
1. Regulations on the International Competitions of the Center for Additional Education "Snail"
2. Mass media registration certificate
3. Snail Center license
Read and find out the latest news, communicate and find out the news of the SNEIL Center on the pages of social networks:
PEI "CDO "Snail", 2016
At dihybrid crossing
- two signs are studied, for example, "white short hair";
- two pairs of (alternative) genes, eg AaBb x AAbb.
In a dihybrid cross, genes A and B can be inherited independently or linked.
Independent Inheritance
If genes A and B are in
- different chromosomes;
- different pairs of chromosomes;
- non-homologous chromosomes;
- different pairs of non-homologous chromosomes (all this is the same);
then they are inherited independently, according to Mendel's III law (the law of independent inheritance): "Splitting on each pair of features occurs independently of other pairs of features."
The cytological basis of independent inheritance is independent chromosome segregation in anaphase I of meiosis.
Splits characteristic of independent inheritance in dihybrid crosses
1) No splitting (all children are the same) - two homozygotes AABB x aabb (or AAbb x aaBB) were crossed.
2) Splitting 9:3:3:1 - two diheterozygotes AaBb x AaBb were crossed (Mendel's third law).
3) Splitting 1:1:1:1 - a diheterozygote and a recessive homozygote AaBb x aabb were crossed (analyzing cross).
Linked inheritance
If genes A and B are located in
- one chromosome;
- one pair of chromosomes
- one pair of homologous chromosomes;
then they cannot separate independently, there is a linked inheritance according to Morgan's linkage law: "Genes located on the same chromosome are inherited together".
All genes on the same chromosome form a linkage group. The number of linkage groups is equal to the number of chromosomes in the haploid set (the number of pairs of homologous chromosomes).
How many types of gametes will AaBb get:
- with independent inheritance - 4 types of gametes (AB, Ab, aB, ab) 25% each
- with full clutch only 2 types of gametes (for example, AB and ab)
- with incomplete clutch(due to crossing over) - 4 types of gametes, but not 25% each (not equally).
Choose one, the most correct option. If the genes responsible for the color and shape of pea seeds are located on different chromosomes, then the law manifests itself in the second generation
1) independent inheritance
2) linked inheritance
3) feature splitting
4) dominance
Answer
Choose one, the most correct option. The number of gene linkage groups in organisms depends on the number
1) pairs of homologous chromosomes
2) allelic genes
3) dominant genes
4) DNA molecules in the cell nucleus
Answer
Choose one, the most correct option. What types of gametes are formed in an organism with the AaBb genotype when dominant genes are linked
1) AB, ab
2) Ab, aB
3) AB, Ab, aB, ab
4) Aa, Bb
Answer
RATIO OF PHENOTYPES IN THE ANALYSIS CROSSING OF A DIHETEROZYGOTE
1. Determine the ratio of phenotypes in offspring when crossing a diheterozygous pumpkin plant with white round fruits and a dihomozygous plant with yellow elongated fruits (white color and round shape of the fruit are dominant traits) with complete dominance and independent inheritance of traits. Write down the answer in the form of a sequence of numbers showing the ratio of the resulting phenotypes, in descending order.
Answer
2. Determine the ratio of phenotypes in offspring during dihybrid crossing of an organism homozygous for both traits (aabb) with a diheterozygous organism. The genes are not linked. Dominance is complete. Write down the answer in the form of a sequence of numbers showing the ratio of the resulting phenotypes.
Answer
3. Determine the ratio of phenotypes in offspring in the analysis of crossbreeding of a diheterozygous organism with complete dominance and independent inheritance of genes. Write your answer as a sequence of numbers arranged in descending order.
Answer
4. Determine the ratio of phenotypes in offspring in the analyzing crossing of a diheterozygous black crested chicken with independent inheritance of traits. Write your answer as a sequence of numbers.
Answer
RATIO OF GENOTYPES IN THE ANALYZING CROSSING OF A DIHETEROZYGOTE
1. Determine the ratio of genotypes in the offspring during analyzing crosses, if the genotype of the parent is AaBb with complete dominance and independent inheritance of traits. Write down the answer in the form of a sequence of numbers showing the ratio of the resulting genotypes (without additional characters).
Answer
2. Determine the ratio of genotypes in the offspring obtained by analyzing crosses, if the genotype of one of the parents is AABb. Write your answer as a sequence of numbers in descending order.
Answer
3. When heterozygous tomato plants with red and round fruits are crossed with individuals that are recessive in both traits (red A and round B are dominant traits), offspring with the genotypes AaBb, aaBb, Aabb, aabb will appear. Write down the ratio of these genotypes as a sequence of numbers in descending order.
Answer
RATIO OF PHENOTYPES WHEN CROSSING TWO DIHETEROZYGOTES
1. What ratio of phenotypes will be obtained by crossing two diheterozygotes with complete dominance and independent inheritance of genes? Write your answer as a sequence of numbers in descending order.
Answer
2. Determine the ratio of phenotypes in offspring in a dihybrid crossing of two heterozygous organisms with complete dominance. Write down the answer in the form of a sequence of numbers showing the ratio of the resulting phenotypes, in descending order.
Answer
3. Determine the ratio of phenotypes in the offspring when crossing females and males with AaBb genotypes, given that the genes are not linked to each other and complete dominance is observed. Write down the answer in the form of a sequence of numbers showing the ratio of the resulting phenotypes, in descending order.
Answer
4. Determine the ratio of phenotypes in offspring when crossing two Drosophila diheterozygotes with a gray body and a normal wing shape (the genes are in different pairs of autosomes). Write your answer as a sequence of numbers arranged in descending order.
Answer
RANDOM PROBLEM, DETERMINE PROBABILITY
1. In beans, the yellow color of the beans dominates over the green, and the black color of the seeds dominates over the white. Determine the probability (in %) of the appearance of bean plants with green beans and white seeds when a dihomozygous plant with yellow beans and black seeds self-pollinates. Write down the correct number for your answer.
Answer
2. A person has brown eyes (A) and one of the forms of myopia (B) - autosomal signs. Determine the probability (in %) of the birth of a blue-eyed child with normal vision, if his parents are brown-eyed with normal vision (homozygotes for both pairs of traits). Write down only the appropriate number in your answer.
Answer
3. A woman with long eyelashes and wide eyebrows, whose father had short eyelashes and narrow eyebrows, married a man with dominant traits homozygous for both alleles, a child with long eyelashes and wide eyebrows was born in the family. What is the probability (in percent) of the birth in this family of children with the same phenotype as the mother, with complete dominance and independent inheritance of traits? Write only the number as your answer.
Answer
4. Indicate what percentage of children will have brown hair and normal leg length if the father is Aabb and the mother is aaBb (A - black hair, a - brown hair, B - short legs, b - normal legs).
Answer
Choose one, the most correct option. Scheme AABB x aabb illustrates crossing
1) monohybrid
2) polyhybrid
3) analyzing dihybrid
4) analyzing monohybrid
Answer
Choose one, the most correct option. When heterozygous tomato plants with red and round fruits are crossed with individuals recessive in both traits (red A and round B are dominant traits), offspring with the genotypes AaBb, aaBb, Aabb, aabb will appear in the ratio
1) 3:1
2) 9:3:3:1
3) 1:1:1:1
4) 1:2:1
Answer
Choose one, the most correct option. When crossing Drosophila with a gray body and normal wings and Drosophila with a dark body and rudimentary wings, the law of linked inheritance is manifested, since the genes responsible for these traits are located in
1) mitochondrial DNA
2) different pairs of chromosomes
3) one pair of chromosomes
4) sex chromosomes
Answer
Choose one, the most correct option. In dihybrid crossing (unlinked inheritance), individuals with dominant and individuals with recessive traits in F1 split according to the phenotype in the ratio
1) 9:3:3:1
2) 1:2:1
3) 3:1
4) 1:1:1:1
Answer
Choose one, the most correct option. The genotype of one of the parents will be AaBb if, during analyzing dihybrid crossing and independent inheritance of traits, phenotypic splitting is observed in the offspring in the ratio
1) 1:1
2) 3:1
3) 1:2:1
4) 1:1:1:1
Answer
Choose one, the most correct option. Genes are always inherited together
1) recessive
2) allelic
3) dominant
4) closely linked
Answer
HOW MANY TYPES OF GAMETES WITH FULL LINKAGE
1. How many types of gametes does a diheterozygous individual form with full linkage of the studied genes?
Answer
2. How many types of gametes does an individual with the AaBb genotype form with full linkage of the studied genes? Write your answer as a number.
Answer
3. How many types of gametes does an individual with the AaBb genotype form if it is known that non-allelic genes are linked and there was no crossing over? Write your answer as a number.
Answer
HOW MANY TYPES OF GAMETES IN INDEPENDENT INHERITANCE
1. How many types of gametes does an individual with the AaBb genotype form with independent inheritance of traits? Write your answer as a number.
Answer
2. How many types of gametes does a diheterozygous individual form with independent inheritance of traits?
Answer
3. How many types of gametes does an individual with the AaBb genotype form in case of gene linkage disruption during crossing over? Write your answer as a number.
Answer
4. How many types of gametes does a diheterozygous individual form when the linkage is broken by crossing over?
Answer
How many types of gametes do individuals with the AaBB genotype form? Write down only the appropriate number in your answer.
Answer
How many types of gametes does a dihomozygous individual form? Write down only the appropriate number in your answer.
Answer
HOW MANY GENOTYPIC GROUPS
1. How many different genotypes will the offspring get when analyzing the crossing of an organism with the AaBB genotype (complete dominance and independent inheritance of traits)? Write down only the number of genotypes in your answer.
Answer
2. How many genotypes in offspring can be obtained in an analyzing cross of a tomato plant that is dihomozygous for dominant traits of fruit shape and fruit color with independent inheritance of traits? Write your answer as a number.
Answer
3. How many different genotypes can be obtained by self-pollination of a tomato plant, homozygous for the recessive trait of fruit shape and heterozygous for fruit color, with complete dominance and independent inheritance of traits? Write your answer as a number.
Answer
4. How many different genotypes can be obtained by crossing an oat plant homozygous for the late-ripening gene and heterozygous for the normal growth gene with an oat plant heterozygous for the late-ripening gene and homozygous for the giant growth gene with complete dominance and independent inheritance of traits? Write your answer as a number.
Answer
HOW MANY PHENOTYPICAL GROUPS
1. How many phenotypic groups will result from self-pollination of a heterozygous pea plant with yellow smooth seeds? Write down only the appropriate number in your answer.
Answer
2. How many different phenotypes can be obtained in offspring in an analyzing cross of a tomato plant, diheterozygous for the traits of the shape and color of the fruit, with independent inheritance of traits? Write your answer as a number.
Answer
3. How many phenotypic groups will be obtained by crossing two dihomozygous individuals with different phenotypes (genes are located on different chromosomes). Write down only the appropriate number in your answer.
Answer
4. How many different phenotypic groups can be obtained by self-pollination of a tomato that is homozygous for the recessive trait of fruit shape and heterozygous for fruit color with complete dominance and independent inheritance of traits? Write your answer as a number.
Answer
5. How many phenotypes will appear in hybrids when a diheterozygous pea plant is crossed with a plant homozygous for recessive traits, if the traits are inherited independently of each other, and dominance is complete? Write down only the appropriate number in your answer.
Answer
Choose one, the most correct option. With dihybrid crossing and independent inheritance of traits in parents with AABb and aabb genotypes, splitting is observed in the offspring in the ratio
1) 9:3:3:1
2) 1:1:1:1
3) 3:1
4) 1:1
Answer
Choose one, the most correct option. When crossing individuals with AaBb genotypes with AaBb (genes are not linked), the proportion of heterozygotes for both alleles in the offspring will be
1) 0,75
2) 0,5
3) 0,25
4) 0
Answer
PHENOTYPE RATIO AT FULL LINKAGE
1. Determine the ratio of phenotypes in offspring in a dihybrid crossing of two diheterozygous organisms. Dominant and recessive genes are linked in pairs. Dominance is complete. Write down the answer in the form of a sequence of numbers showing the ratio of the resulting phenotypes.
Answer
2. Determine the ratio of phenotypes in the offspring during the analyzing crossing of a diheterozygous hamster with full linkage of genes. Write your answer as a sequence of numbers arranged in decreasing order.
Answer
RATIO OF GENOTYPES IN FULL LINKAGE
Determine the ratio of genotypes in offspring in a dihybrid crossing of two diheterozygous organisms. Genes A and b, a and B are linked. Dominance is complete. Write your answer as a sequence of numbers in descending order.
Answer
Choose one, the most correct option. How many types of gametes are formed in the parent organism with the AaBb genotype in the case of linked inheritance in the absence of crossing over?
1) 1
2) 2
3) 3
4) 4
Answer
Choose one, the most correct option. When homozygous tomato plants with red (A) round (B) fruits and plants with yellow (a) pear-shaped (b) fruits in F2 are crossed, phenotypic splitting occurs in the ratio (color genes and fruit shape are located in different pairs of chromosomes)
1) 1:1
2) 3:1
3) 1:2:1
4) 9:3:3:1
Answer
1. All of the following characteristics, except for two, are used to describe the linked type of inheritance. Find two characteristics that "fall out" from the general list, and write down the numbers under which they are indicated.
1) genes located on the same chromosome are inherited together
2) phenotype splitting is observed in the ratio 9:3:3:1
3) the number of linkage groups is equal to the haploid set of chromosomes
4) genes located on different pairs of chromosomes are inherited independently
5) as a result of crossing over, gene recombination occurs
Answer
2. All of the following characteristics, except for two, are used to describe the linked inheritance of traits. Identify two characteristics that “fall out” from the general list, and write down the numbers under which they are indicated.
1) one gene determines the development of several traits
3) the number of linkage groups is equal to the number of pairs of chromosomes
4) non-allelic genes on the same chromosome are inherited together
5) the manifestation of a trait depends on the action of an environmental factor
Answer
All the laws below, except for two, are the laws of heredity of G. Mendel. Find two laws that “fall out” of the general list, and write down the numbers under which they are indicated.
1) uniformity of hybrids of the first generation
2) independent inheritance of traits
3) inheritance of sex-linked traits
4) splitting of signs
5) linked inheritance of traits
Answer
All but two of the following characteristics are used to describe a pea dihybrid cross with independent inheritance and complete dominance. Find two characteristics that "fall out" from the general list, and write down the numbers under which they are indicated.
1) the number of linkage groups is equal to the haploid set of chromosomes
2) splitting according to the phenotype occurs in a ratio of 9: 3: 3: 1
3) genes for different traits are on different chromosomes
4) the formation of different types of gametes is due to crossing over
5) four phenotypic classes of offspring are formed in the ratio 1:1:1:1
Answer
All the statements below, except for two, are the provisions of the chromosome theory of heredity. Identify two statements that “fall out” of the general list, and write down the numbers under which they are indicated.
1) the traits of the parents are inherited by the offspring
2) genes are located linearly on the chromosome
3) genes located on the same chromosome are inherited linked
4) non-allelic genes are inherited independently
5) gene linkage is disrupted as a result of crossing over
Answer
© D.V. Pozdnyakov, 2009-2019
Monohybrid cross. |
|||
F1 splitting |
|||
by genotype |
|||
Phenotypes |
|||
The second law, or splitting rule.
Mendel formulated the second law based on the study of the patterns of splitting of hybrids of the second generation during monohybrid crossing. When hybrids of the first generation (F1), heterozygous for the alleles of one gene, are crossed with each other, each of them forms gametes of two types in equal amounts, and among the hybrids of the second generation (F2), individuals appear with the genotypes and phenotypes of the parents and hybrids of the first generation in strictly defined ratios 1:2:1 - by genotype and 3:1 - by phenotype.
Monohybrid cross. Splitting signs.
F1 splitting |
||||||
by genotype |
||||||
Phenotypes |
||||||
Splitting by |
||||||
phenotype |
||||||
Individuals with the same phenotype form a phenotypic class, and individuals with the same genotype form a genotypic class. In
the second generation splits into two phenotypic classes in the ratio 3A_ (yellow): 1 aa (green) and three genotypic classes in the ratio 1 AA: 2 Aa: 1 aa.
The number of genotypic and phenotypic classes when crossing heterozygous organisms that differ in n traits can be expressed by the formula:
number of genotype classes: 3 n number of phenotype classes: 2 n
The phenomenon of splitting is explained with the help of one of the regularities of genetics, which is called the rule " gamete purity". According to this rule, in the process of maturation of germ cells (meiosis), only one of the pair of alleles of a given gene enters each gamete.
When solving problems in genetics, it is necessary to correctly determine and write down the types of gametes that are formed during a given crossing. To calculate how many gamete types an organism with a given genotype will give, you need to calculate and multiply the number of gamete types for each pair of genes. For example, an organism with the AaBbCcDDEe genotype will produce 16 types of gametes.
Mendel's third law, or the law of independent inheritance.
In dihybrid crosses, the inheritance of two pairs of alternative hereditary traits is studied. Mendel took into account the shape of pea seeds (smooth/wrinkled) and color (yellow/green) (Fig. 2-3). When smooth yellow pea seeds (AABB) are crossed with green wrinkled (aabb) seeds in the second generation, four phenotypic classes are formed in the ratio 9:3:3:1 and nine genotypic classes with splitting - 1:2:1:2:4:2: 1:2:1. In each pair of alleles of two genes, individuals were distributed by phenotype in a ratio of 3:1, and by genotype - 1:2:1. At the same time, in the second generation, new combinations of traits appear that were absent in the parents.
Thus, Mendel established that when crossing diheterozygous individuals in the second generation, independent splitting occurs for each pair of traits. Signs are inherited independently of each other, combined in all sorts of combinations.
Independent Trait Inheritance
Wrinkled |
|||||||||
AB, Ab, aB, ab |
|||||||||
Wrinkled |
Wrinkled |
||||||||
Wrinkled |
Wrinkled |
||||||||
genotype |
||||
phenotype |
||||
Quantity |
||||
phenotypic |
||||
If we apply the phenotypic splitting formula from Mendel's second law (3:1), we get the same four phenotypic classes: (3A_: 1 aa) x (3B_: 1bb) = 9 A_B_ : 3 A_bb: 3 aaB_ : 1aabb
If we apply the genotype splitting formula from Mendel's second law (1:2:1), we get nine genotypic classes: (1AA: 2 Aa: 1aa) x (1BB: 2Bb: 1bb) = 1AABB: 2AABb: 1AAbb: 2AaBB: 4 AaBb: 2Aabb: 1aaBB: 2aaBb: 1aabb
Independent inheritance of traits is explained by the fact that the genes responsible for the development of these traits are located in non-homologous pairs of chromosomes. The cytological explanation of this phenomenon lies in the meiotic division of germ cells with the formation of haploid gametes, in which signs can be combined in various combinations.
In polyhybrid crossing, the splitting of characters is based on the same cytological patterns as in dihybrid crossing. The number of classes and splitting in the second generation when crossing heterozygous organisms that differ in n traits are calculated by the formula:
number of phenotypic classes - 2 n number of genotypic classes - 3 n splitting by phenotype - (3: 1) n splitting by genotype - (1: 2: 1) n
Solve situational problems based on Mendel's experiments
1. Yellow color (A) of pea seeds dominates over green (a). Determine the phenotype of the seeds obtained as a result of crosses:
a) AA × aa b) Aa × Aa c) Aa × aa
2. In peas, the smooth seed shape (B) dominates over the wrinkled
(in). Determine the phenotype and type of gametes in plants with the genotype BB, Bb, bb.
3. In peas, yellow seed color is a dominant trait (A), and green is a recessive trait (a). The smooth shape of the seeds is a dominant trait (B), and the wrinkled shape is recessive (b). Determine the gamete type and phenotype of plants with the AAbb genotype; AABB; Aabb; AaBB. Determine the phenotype of pea seeds in the offspring obtained by crossing: AAbb x aaBB; AABB x aabb; AAbb x aabb; AABb x AaBb; aaBB x AaBb; aaBb x AaBb.
Rice. 2-3. The experience of Gregor Mendel (1865) on the study of inheritance in dihybrid crosses [from: http://medbiol.ru].
2. MICRO PREPARATIONS. PHENOTYPICAL FEATURES IN THE DROSOPHILA FRUIT FLY
A convenient model object for genetic studies is the Drosophila fruit fly. Experiments are more often carried out on fruit flies D. melanogaster, D. simulans, D. mercatorum. The advantages of Drosophila are a fast generational change, a large number of offspring, a wide variety of visible phenotypic manifestations of mutations; The karyotype contains only 8 chromosomes.
The fruit fly D. melanogaster (Fig. 2-4) is widely used in scientific experiments, starting with the work of T. Morgan on the genetics of sex and the chromosome theory of heredity. Currently, D. melanogaster is one of the most studied species of living organisms, which is a convenient biological model for studying the interaction of genes, developmental genetics, studying the effects of drugs and pollutants.
Rice. 2-4. Female (right) and male (left) Drosophila and their chromosome sets [from: http://www.cellbiol.ru].
The D. melanogaster genome contains 4 pairs of chromosomes: the sex X/Y or X/X pair and three autosomes, labeled as 2, 3, and 4. The fourth chromosome is punctate and is not taken into account in a number of studies. X (or first), 2nd and 3rd chromosomes are metacentric. Currently, the Drosophila genome has been completely sequenced and consists of approximately 132 million base pairs and 13,767 genes.
The study of the genome and mutations in Drosophila is of great medical importance, since about 61% of known human diseases have a recognizable match in the genetic code of the fruit fly. With the help of Drosophila, genetic models of Parkinson's, Huntington's and Alzheimer's diseases were obtained. The fruit fly is often used in experiments to study the mechanisms underlying immunity, diabetes, cancer, and drug addiction.
1. The yellow body phenotype (Fig. 2-5A). D. melanogaster color define three pigments: yellow, brown and black. The wild type has a brown body and wings. The yellow pigment gene is located in X chromosome inherited in a recessive manner.
2. The forked setae phenotype (Fig. 2-5, B). Drosophila bristles are sensory organs, consist of bundles of actin filaments and contain sensory nerve endings. The wild type has straight, long, slightly curved bristles. As a result of disruption in the formation of bundles of actin filaments during embryogenesis, short, strongly curved setae with bifurcated ends are formed. It is inherited in a recessive manner.
1. Draw and describe the phenotype of a fruit fly.
2. Write down the genotype of the fly and the types of gametes it produces.
3. The serrated wings phenotype (Fig. 2-5, B). Normally, the Drosophila wing has five longitudinal and two transverse veins. With a given phenotype, the number and length of the vein does not change, but notches form between the longitudinal veins along the wing margin. It is inherited in a recessive manner.
1. Draw and describe the phenotype of a fruit fly.
2. Write down the genotype of the fly and the types of gametes it produces.
Rice. 2-5. Phenotypes of the fruit fly Drosophila. BUT - the wild type has a brown body and wings. By recessive type, yellow color is inherited; B - in the wild type, the bristles are straight and long. The recessive type inherits short and curved setae. AT - wild type has a wing with a smooth, smoothly curved edge. According to the recessive type, the wing with notches between the longitudinal veins is inherited [from: http://www.cellbiol.ru and http://www.bios.niu.edu]
TYPICAL SITUATIONAL TASKS WITH ANSWERS AND EXPLANATIONS
The task of determining the types of gametes
Task 1. Determine which gametes and in what ratio an organism with the genotype AaBBсcDd forms, if it is known that all genes are inherited independently of each other.
Solution: An organism with this genotype is homozygous for genes B and c, heterozygous for genes A and D. Thus, the number of genes for which the organism is heterozygous is two. Substituting the number 2 into the formula for determining the number of gamete varieties, we get 22 = 4 gamete varieties. Now let's determine the gamete varieties: the AaBBccDd genotype forms the gametes ABcDABcd aBcD aBcd. With independent combination of genes, the formation of any kind of gametes is equally probable, therefore, in this case, all gametes are formed with a frequency of 25%.
Answer: this organism forms 4 varieties of gametes: 25% - ABcD, 25% - ABcd, 25% - aBcD, 25% - aBcd.
Allelic exclusion task
Task 2. When purebred white chickens are crossed with each other, the offspring turns out to be white, when black chickens are crossed - black. All offspring from crossing white and black hens have a variegated color. What plumage will have a) descendants of a white rooster and a motley hen, b) two motley parents?
Decision: Neither black nor white chickens, when crossed with each other, give splitting, therefore, they are homozygous. Because the offspring from crossing white and black chickens has an intermediate (variegated) color, then we can assume the phenomenon of allelic exclusion (with incomplete dominance, hybrids should have uniformly gray plumage). Let's denote the genotype of black chickens - AA, white - aa, motley - Aa.
Let us write down the schemes of the required crossings.
Answer: a) the offspring have parental characteristics in approximately equal proportions (analyzing crossing); b) individuals appear that have all three types of color, in the ratio: 1 part black, 2 parts motley, 1 part white.
Incomplete dominance challenge
Task 3. In snapdragons, flowers are of normal shape (two-lipped) and pyloric (without pronounced labiality), and in color they are red, pink and white. Both traits are determined by unlinked pairs of genes. The normal form of the flower dominates the pyloric, and the pink color is obtained from crossing red and white individuals. 1) What offspring will result from crossing two heterozygous plants for both pairs of traits? 2) What offspring will result from crossing two plants with pink pyloric flowers?
Decision: Let's write down the genotypes of parental forms: 1)
1) a dark-haired blue-eyed man heterozygous for the first allele married a dark-haired brown-eyed woman heterozygous for the second allele. what arepossible phenotypes and genotypes of children?
2) a person has brown eyes. how many genotypes of this allele and which ones can a person of this phenotype have? what if the eyes are blue?
3) Husband and wife have curly hair. They had a child with curly hair. What are the possible genotypes of the parents?
4) In cats, the black color gene (B) and the red color gene (c) give incomplete dominance. When these two genes (BB) are combined, a tricolor (tortoiseshell) color is obtained. The genes are located only on the X chromosomes. A black cat had one tortoiseshell and several black kittens. Determine the phenotypes and genotypes of the father and kittens.
5) From crossing a white rabbit with a black rabbit, 5 black and 3 white rabbits were obtained. Why did splitting happen in the first generation? What are the genotypes of parents and rabbits?
6) Platinum coloration (A) mink fur is more beautiful and valued more than brown fur. How should one crossbreed in order to get the maximum number of platinum offspring from a standard brown female and a platinum male?
7) 150 smooth pea seeds were bought and sown in the seed shop. Why did 498 peas in a harvested crop of 2032 turn out to be wrinkled?
8) What will be the offspring according to the genotype and phenotype if you cross a pink-fruited strawberry with a red-fruited one?
9) in the offspring from crossing gray Drosophila with black, 290 black and 908 gray individuals were obtained. What are the genotypes of parents and offspring?
10) A dark-haired, blue-eyed woman, homozygous for two alleles, married a dark-haired, blue-eyed man, heterozygous for the first allele. What are the likely genotypes and phenotypes of the children?
11) The rabbit has white fur. How many genotypes and which ones can a rabbit of this phenotype have?
12) From the marriage of a color-blind man with a healthy woman, a color-blind girl was born. What are the genotypes of the parents?
13) A man suffering from the absence of sweat glands married a woman who was healthy on this basis. What are the possible genotypes and phenotypes of children?
14) When crossing gray and black mice, 30 offspring were obtained, of which 14 were black. It is known that gray coloring dominates over black. What is the genotype of mice of the parental generation?
please help me decide :)Line of guinea pigs with black
longhair was crossed with a line having white shorthair. F1 hybrids crossed
among themselves, resulting in approximately 160 F2 hybrids.
Shorthair and black coat color are dominant genes and are inherited
regardless. How many different genotypes can there be among F2 hybrids?
How much theoretically should be in F2 black
long haired guinea pigs?
The color of the plumage in chickens is inherited according to the principle of incomplete dominance, with black coloring dominating over white, and heterozygous organisms have a variegated coloration. what will be the offspring from crossing a motley hen and a rooster?
in dope, the red color of the flowers dominates over the white, and the prickly seed pods dominate over the smooth ones, the traits are inherited independently.