Textbook Question
What advantages were provided by Mendel's choice of the garden pea in his experiments?
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Ch. 3 - Mendelian Genetics
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 3, Problem 7
Mendel crossed peas having round seeds and yellow cotyledons (seed leaves) with peas having wrinkled seeds and green cotyledons. All the F₁ plants had round seeds with yellow cotyledons. Diagram this cross through the F₂ generation, using both the Punnett square and forked-line, or branch diagram, methods.
Verified step by step guidance1
Identify the traits and their dominance relationships: Round seeds (R) are dominant over wrinkled seeds (r), and yellow cotyledons (Y) are dominant over green cotyledons (y). The parental cross is between homozygous round yellow (RRYY) and homozygous wrinkled green (rryy) peas.
Determine the genotype of the F₁ generation: Since all F₁ plants have round seeds and yellow cotyledons, their genotype must be heterozygous for both traits (RrYy).
Set up the Punnett square for the F₂ generation by crossing two F₁ individuals (RrYy × RrYy). Create a 4x4 grid with the possible gametes from each parent (RY, Ry, rY, ry) along the top and side, then fill in the genotypes for each box by combining the alleles.
Analyze the Punnett square to determine the phenotypic ratios of the F₂ generation by grouping genotypes into phenotypes: round yellow, round green, wrinkled yellow, and wrinkled green, based on dominant and recessive allele combinations.
Construct the forked-line (branch) diagram by first determining the probability of each seed shape genotype (RR, Rr, rr) from the cross Rr × Rr, then branching each of these with the probabilities of cotyledon color genotypes (YY, Yy, yy) from Yy × Yy, and multiply the probabilities along the branches to find the overall phenotypic 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 Dominance
Mendelian inheritance describes how traits are passed from parents to offspring through dominant and recessive alleles. In this cross, round seed shape and yellow cotyledons are dominant traits, while wrinkled seeds and green cotyledons are recessive. Understanding dominance helps predict phenotypes in F₁ and F₂ generations.
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04:37
Variations on Dominance
Punnett Square Method
The Punnett square is a grid used to predict the genotypic and phenotypic ratios of offspring from a genetic cross. It organizes all possible allele combinations from the parents, allowing visualization of how traits segregate and combine in the F₂ generation.
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18:27Chi Square Analysis
Forked-Line (Branch) Diagram
The forked-line method breaks down multi-trait crosses by calculating probabilities for each trait independently, then multiplying them to find combined genotype or phenotype ratios. This method simplifies complex dihybrid crosses by showing stepwise segregation of alleles.
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06:28Branch Diagram
Related Practice
Textbook Question
Albinism in humans is inherited as a simple recessive trait. For the following families, determine the genotypes of the parents and offspring. (When two alternative genotypes are possible, list both.)
A normal male and an albino female have six children, all normal.
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Textbook Question
Which of Mendel's postulates are illustrated by the pedigree that you constructed in Problem 3? List and define these postulates.