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Ch. 4 - Modification of Mendelian Ratios
Klug - Essentials of Genetics 10th Edition
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Tutti i libri di testoKlug 10th EditionCh. 4 - Modification of Mendelian RatiosProblema 9b
Capitolo 4, Problema 9b

Given the inheritance pattern of coat color in rats described in Problem 17, predict the genotype and phenotype of the parents who produced the following offspring:
9/16 gray: 3/16 yellow: 4/16 albino

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Identify the inheritance pattern described in Problem 17, which likely involves two genes with epistatic interactions affecting coat color in rats. Typically, such ratios suggest a dihybrid cross with epistasis.
Assign symbols to the genes involved. For example, let gene A control pigment production (A = pigment, a = no pigment) and gene B control pigment color (B = gray, b = yellow). Albino rats result from homozygous recessive at the A locus (aa), which masks the effect of the B locus.
Write down the expected phenotypes based on genotypes: gray rats have at least one dominant A and one dominant B allele (A_B_), yellow rats have at least one dominant A allele but are homozygous recessive at B (A_bb), and albino rats are homozygous recessive at A (aa regardless of B genotype).
Use the offspring phenotypic ratios (9/16 gray : 3/16 yellow : 4/16 albino) to deduce the genotypes of the parents. These ratios correspond to a dihybrid cross where both parents are heterozygous at both loci (A/a B/b).
Conclude that the parents' genotypes are both A/a B/b, and their phenotypes are gray, since the presence of dominant alleles at both loci produces gray coat color.

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Mendelian Inheritance and Dihybrid Ratios

Mendelian inheritance explains how traits are passed from parents to offspring through dominant and recessive alleles. The given offspring ratios (9:3:4) suggest a dihybrid cross involving two genes, where the phenotypic ratio deviates from the classic 9:3:3:1, indicating gene interaction such as epistasis.
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Punnet Square

Epistasis in Coat Color Genetics

Epistasis occurs when one gene masks or modifies the expression of another gene. In rat coat color, certain alleles can suppress pigment production, leading to phenotypes like albino regardless of other color genes, explaining the altered phenotypic ratios observed in the offspring.
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Percorso guidato
13:08
Epistatic Genes

Genotype-Phenotype Relationship and Predicting Parental Genotypes

Understanding how specific genotypes produce phenotypes allows prediction of parental genotypes from offspring ratios. By analyzing the proportions of gray, yellow, and albino offspring, one can infer the parents' alleles and their combinations responsible for the observed phenotypic distribution.
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Gamete Genotypes
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