Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

3. Extensions to Mendelian Inheritance

Understanding Independent Assortment

Genetics

3. Extensions to Mendelian Inheritance

Understanding Independent Assortment

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2:11 minutes

Problem 32c

Textbook Question

Three independently assorting genes (A, B, and C) are known to control the following biochemical pathway that provides the basis for flower color in a hypothetical plant:

Three homozygous recessive mutations are also known, each of which interrupts a different one of these steps. Determine the phenotypic results in the F₁ and F₂ generations resulting from the P₁ crosses of true-breeding plants listed here:
colorless (aaBBCC) × green (AABBcc)

Verified step by step guidance

Step 1: Understand the genetic basis of the problem. The three genes (A, B, and C) control a biochemical pathway for flower color. Each gene has a dominant allele (A, B, C) and a recessive allele (a, b, c). The recessive alleles disrupt the pathway at different steps, leading to different phenotypes (e.g., colorless or green).

Step 2: Analyze the P₁ cross. The parental genotypes are colorless (aaBBCC) and green (AABBcc). Since these are true-breeding plants, they are homozygous for their respective alleles. The F₁ generation will inherit one allele from each parent for each gene, resulting in the genotype AaBBCC.

Step 3: Determine the phenotype of the F₁ generation. Since all F₁ individuals are heterozygous for gene A (Aa) and homozygous dominant for genes B and C (BB and CC), the dominant alleles will ensure that the biochemical pathway is functional, resulting in a colored phenotype.

Step 4: Set up the F₂ cross. The F₁ individuals (AaBBCC) are self-crossed to produce the F₂ generation. Use a Punnett square to determine the genotypic combinations for each gene. Since gene A is heterozygous (Aa), it will segregate in a 3:1 ratio (3 dominant: 1 recessive). Genes B and C are homozygous dominant (BB and CC), so they will not segregate and will remain dominant in all offspring.

Step 5: Predict the phenotypic ratios in the F₂ generation. The phenotypic outcome depends on the segregation of gene A. Since gene A segregates in a 3:1 ratio, 3/4 of the F₂ offspring will have at least one dominant A allele (colored phenotype), while 1/4 will be homozygous recessive (aa) and result in a colorless phenotype. Combine this with the fact that genes B and C are fixed as dominant, ensuring no green phenotype appears in the F₂ generation.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Independent Assortment

Independent assortment is a fundamental principle of genetics stating that alleles for different genes segregate independently of one another during gamete formation. This means that the inheritance of one trait will not affect the inheritance of another trait, allowing for a variety of combinations in offspring. In the context of the question, it implies that the genes A, B, and C will assort independently when determining the phenotypes of the F₁ and F₂ generations.

Homozygous and Heterozygous Genotypes

A homozygous genotype consists of two identical alleles for a particular gene, while a heterozygous genotype contains two different alleles. In the given question, the parental plants are homozygous for their respective traits (aaBBCC and AABBcc), which will influence the genotypic and phenotypic ratios in the offspring. Understanding these terms is crucial for predicting the genetic outcomes in the F₁ and F₂ generations.

Phenotypic Ratios

Phenotypic ratios refer to the relative frequencies of different phenotypes in the offspring resulting from a genetic cross. In this scenario, analyzing the phenotypic ratios in the F₁ and F₂ generations will help determine how the combinations of alleles from the parent plants affect flower color. This concept is essential for interpreting the results of the genetic crosses and understanding the expression of traits in the offspring.

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Identify each mutation as either dominant or recessive. In each case, indicate which crosses support your answer.

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Textbook Question

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Textbook Question

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Textbook Question

Three independently assorting genes (A, B, and C) are known to control the following biochemical pathway that provides the basis for flower color in a hypothetical plant:

Three homozygous recessive mutations are also known, each of which interrupts a different one of these steps. Determine the phenotypic results in the F₁ and F₂ generations resulting from the P₁ crosses of true-breeding plants listed here:

yellow (AAbbCC) × green (AABBcc)

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Textbook Question

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Textbook Question

An organism having the genotype AaBbCcDdEe is self-fertilized. Assuming the five genes assort independently, determine the following proportions:

Progeny that are expected to have a genotype identical to that of the parent.

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Textbook Question

An organism having the genotype AaBbCcDdEe is self-fertilized. Assuming the five genes assort independently, determine the following proportions:

Gametes that are expected to carry only dominant alleles.

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