Textbook Question
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
Ch. 4 - Modification of Mendelian Ratios
Klug10th EditionEssentials of GeneticsISBN: 9780135588789
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Table of contents
- Ch. 1 - Introduction to Genetics16
- Ch. 2 - Mitosis and Meiosis28
- Ch. 3 - Mendelian Genetics37
- Ch. 4 - Modification of Mendelian Ratios53
- Ch. 5 - Sex Determination and Sex Chromosomes32
- Ch. 6 - Chromosome Mutations: Variation in Number and Arrangement37
- Ch. 7 - Linkage and Chromosome Mapping in Eukaryotes36
- Ch. 8 - Genetic Analysis and Mapping in Bacteria and Bacteriophages24
- Ch. 9 - DNA Structure and Analysis38
- Ch. 10 - DNA Replication29
- Ch. 11 - Chromosome Structure and DNA Sequence Organization22
- Ch. 12 - The Genetic Code and Transcription36
- Ch. 13 - Translation and Proteins27
- Ch. 14 - Gene Mutation, DNA Repair, and Transposition34
- Ch. 15 - Regulation of Gene Expression in Bacteria22
- Ch. 16 - Regulation of Gene Expression in Eukaryotes37
- Ch. 17 - Recombinant DNA Technology27
- Ch. 18 - Genomics, Bioinformatics, and Proteomics30
- Ch. 19 - The Genetics of Cancer21
- Ch. 20 - Quantitative Genetics and Multifactorial Traits37
- Ch. 21 - Population and Evolutionary Genetics45
Chapter 4, Problem 9c
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: 27/64 gray:
16/64 albino: 9/64 yellow: 9/64 black: 3/64 cream
Verified step by step guidance1
Step 1: Identify the inheritance pattern described in Problem 17. Since the offspring phenotypic ratios are given as fractions out of 64, this suggests a dihybrid cross involving two genes with multiple alleles affecting coat color in rats. Typically, such ratios come from a cross involving two genes with epistatic interactions or multiple alleles.
Step 2: Assign symbols to the genes involved. For example, let’s say gene A controls pigment production (A = pigment, a = albino) and gene B controls pigment color (B = black, b = yellow). The presence of albino (16/64) suggests recessive homozygosity at the A locus (aa) results in albino phenotype regardless of B locus genotype.
Step 3: Analyze the phenotypic ratios to deduce genotypes. The ratio 27/64 gray, 16/64 albino, 9/64 yellow, 9/64 black, and 3/64 cream suggests a combination of genotypes at both loci. Use the expected Mendelian ratios for dihybrid crosses and epistasis to match these numbers to genotypes.
Step 4: Use Punnett squares to model the cross between two heterozygous parents at both loci (e.g., AaBb x AaBb) and calculate the expected phenotypic ratios. Compare these expected ratios to the observed ratios to confirm the parental genotypes.
Step 5: Conclude the most likely genotypes of the parents based on the matching phenotypic ratios and explain the phenotypes of the offspring based on the genotypes at each locus, considering dominance, recessiveness, and epistatic interactions.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Mendelian Inheritance and Dihybrid Crosses
Mendelian inheritance explains how traits are passed from parents to offspring through dominant and recessive alleles. A dihybrid cross involves two genes, each with two alleles, producing a characteristic phenotypic ratio in offspring. Understanding these ratios helps predict parental genotypes based on observed offspring phenotypes.
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15:24
Punnet Square
Epistasis and Coat Color Genetics
Epistasis occurs when one gene masks or modifies the expression of another gene, affecting phenotypic ratios. In coat color genetics, interactions between multiple loci (e.g., pigment production and pigment distribution genes) can produce complex inheritance patterns, explaining deviations from classic Mendelian ratios.
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13:08Epistatic Genes
Phenotypic Ratios and Genotypic Prediction
Analyzing offspring phenotypic ratios allows inference of parental genotypes by matching observed ratios to expected Mendelian or epistatic patterns. Calculating probabilities for each phenotype helps identify which allele combinations parents likely carry, enabling prediction of both genotype and phenotype.
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Related Practice
Textbook Question
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: 3/16 black: 1/16 cream
Textbook Question
In humans, the ABO blood type is under the control of autosomal multiple alleles. Color blindness is a recessive X-linked trait. If two parents who are both type A and have normal vision produce a son who is color-blind and is type O, what is the probability that their next child will be a female who has normal vision and is type O?
Textbook Question
In goats, the development of the beard is due to a recessive gene. The following cross involving true-breeding goats was made and carried to the F₂ generation:
Offer an explanation for the inheritance and expression of this trait, diagramming the cross. Propose one or more crosses to test your hypothesis.
Textbook Question
In rats, the following genotypes of two independently assorting autosomal genes determine coat color:
A third gene pair on a separate autosome determines whether or not any color will be produced. The CC and Cc genotypes allow color according to the expression of the A and B alleles. However, the cc genotype results in albino rats regardless of the A and B alleles present. Determine the F₁ phenotypic ratio of the following crosses:
AaBbCc×AaBbcc
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Textbook Question
A husband and wife have normal vision, although both of their fathers are red–green color-blind, an inherited X-linked recessive condition. What is the probability that their first child will be (a) a normal son, (b) a normal daughter, (c) a color-blind son, (d) a color-blind daughter?
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