Textbook Question
Flower color may be red, white, or pink, and flower shape may be personate or peloric. For the following crosses, determine the P₁ and F₁ genotypes:
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 9a
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
Verified step by step guidance1
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 = black, b = yellow). The cream phenotype might result from a double recessive or interaction between these genes.
Write down the expected phenotypic ratios for a dihybrid cross with epistasis. The given offspring ratio (9/16 gray, 3/16 yellow, 3/16 black, 1/16 cream) suggests a 9:3:3:1 ratio, typical of independent assortment without epistasis, but with different phenotypes assigned to each genotype combination.
Determine the genotypes corresponding to each phenotype based on the gene symbols. For example, gray might be A_B_, yellow A_bb, black aaB_, and cream aabb. This helps to map phenotypes to genotypes.
Use the offspring phenotypic ratio to infer the parental genotypes. Since the ratio matches a 9:3:3:1 ratio, the parents are likely heterozygous for both genes (AaBb x AaBb). Confirm this by setting up a Punnett square and verifying the offspring ratios.
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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 9:3:3:1 phenotypic ratio in the F2 generation when both parents are heterozygous for both traits.
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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. In coat color genetics, interactions between multiple genes can produce complex phenotypic ratios different from classic Mendelian ratios, such as the presence of cream or yellow colors influenced by gene interactions.
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Guided course
13:08Epistatic Genes
Genotype to Phenotype Prediction
Predicting genotype and phenotype involves using observed offspring ratios to infer parental genotypes. By comparing expected Mendelian ratios to observed data, one can deduce which alleles parents carry and how they combine to produce specific phenotypes in offspring.
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07:52Gamete Genotypes
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: 27/64 gray:
16/64 albino: 9/64 yellow: 9/64 black: 3/64 cream
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
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
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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