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Ch. 4 - Modification of Mendelian Ratios
Klug - Essentials of Genetics 10th Edition
Klug10th EditionEssentials of GeneticsISBN: 9780135588789당신이 사용하는 게 아니라요?교과서 변경
모든 교과서Klug 10th EditionCh. 4 - Modification of Mendelian Ratios문제 22
4장, 문제 22

Labrador retrievers may be black, brown (chocolate), or golden (yellow) in color (see chapter-opening photo). While each color may breed true, many different outcomes are seen when numerous litters are examined from a variety of matings where the parents are not necessarily true breeding. Following are just some of the many possibilities.
(a) black x brown → all black
(b) black x brown → 1/2 black, 1/2 brown
(c) black x brown → 3/4 black, 1/4 golden
(d) black x golden → all black
(e) black x golden → 4/8 golden 3/8 black 1/8 brown
(f) black x golden → 2/4 golden 1/4 black 1/4 brown
(g) brown x brown → 3/4 brown 1/4 golden
(h) black x black → 9/16 black 4/16 golden, 3/16 brown
Propose a mode of inheritance that is consistent with these data, and indicate the corresponding genotypes of the parents in each mating. Indicate as well the genotypes of dogs that breed true for each color.

검증된 단계별 안내
1
Step 1: Identify the genes involved and their alleles. Labrador coat color is controlled primarily by two genes: the B gene (with alleles B for black and b for brown) and the E gene (with alleles E for pigment expression and e for no pigment expression, which results in yellow/golden color). The B gene determines black or brown pigment, and the E gene controls whether pigment is deposited in the coat.
Step 2: Assign genotypes to each color phenotype based on the known genetics: black Labradors have at least one dominant B allele and at least one dominant E allele (genotypes like B_E_), brown Labradors are homozygous recessive for the B gene (bb) but have at least one dominant E allele (bbE_), and golden/yellow Labradors are homozygous recessive for the E gene (ee), regardless of B gene alleles (B_ee or bbee). Dogs that breed true for each color are homozygous at the relevant loci: black (BBEE or BBEe), brown (bbEE or bbEe), and golden (any B genotype with ee).
Step 3: Analyze each mating scenario by combining the parental genotypes and using Punnett squares for both B and E genes separately, then combine the results to predict offspring genotypes and phenotypes. For example, in a black x brown mating, if the black parent is BbEe and the brown parent is bbee, calculate the possible gametes and resulting offspring genotypes.
Step 4: For each cross, determine the expected phenotypic ratios by considering the dominance relationships: B > b for pigment color, and E > e for pigment expression. Use the combined genotypes to predict the proportion of black, brown, and golden puppies.
Step 5: Match the predicted phenotypic ratios from your genotype crosses to the observed data in the problem (a) through (h). Adjust parental genotypes if necessary to fit the observed ratios, and clearly indicate the genotypes of the parents and the genotypes of puppies that breed true for each color.

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주요 개념

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Mendelian Inheritance and Allelic Dominance

Mendelian inheritance explains how traits are passed from parents to offspring through dominant and recessive alleles. Dominant alleles mask the expression of recessive ones in heterozygotes, affecting phenotype ratios. Understanding dominance relationships among alleles is crucial to predict offspring colors in Labrador retrievers.
추천 영상:
가이드 코스
04:37
Variations on Dominance

Multiple Alleles and Genotype-Phenotype Relationships

Multiple alleles refer to more than two alternative forms of a gene existing in a population, each potentially producing different phenotypes. In Labradors, coat color is controlled by multiple alleles with a hierarchy of dominance, influencing the observed color ratios. Identifying genotypes that breed true helps clarify which alleles are homozygous and their dominance order.
추천 영상:
가이드 코스
05:54
Natural Selection

Punnett Squares and Probability in Genetic Crosses

Punnett squares are tools used to predict the genotypic and phenotypic outcomes of genetic crosses by combining parental alleles. They help calculate expected ratios of offspring traits based on allele combinations. Applying Punnett squares to the given crosses allows determination of parental genotypes and consistency with observed color distributions.
추천 영상:
가이드 코스
07:41
Probability
관련 실천
교과서 질문

Consider the three pedigrees below, all involving a single human trait.

Which combination of conditions, if any, can be excluded? dominant and X-linked dominant and autosomal recessive and X-linked recessive and autosomal

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교과서 질문

Horses can be cremello (a light cream color), chestnut (a brownish color), or palomino (a golden color with white in the horse's tail and mane). Of these phenotypes, only palominos never breed true.

From the results given above, determine the mode of inheritance by assigning gene symbols and indicating which genotypes yield which phenotypes.

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교과서 질문

Consider the three pedigrees below, all involving a single human trait.

For each combination that you excluded, indicate the single individual in generation II (e.g., II-1, II-2) that was most instrumental in your decision to exclude it. If none were excluded, answer 'none apply.'

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교과서 질문

Horses can be cremello (a light cream color), chestnut (a brownish color), or palomino (a golden color with white in the horse's tail and mane). Of these phenotypes, only palominos never breed true.

Predict the F1 and F2 results of many initial matings between cremello and chestnut horses.

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교과서 질문

Consider the three pedigrees below, all involving a single human trait.

Given your conclusions in part (a), indicate the genotype of the following individuals: II-1, II-6, II-9 If more than one possibility applies, list all possibilities. Use the symbols A and a for the genotypes.

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