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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2:03 minutes

Problem 27a

Textbook Question

The wild-type (normal) fruit fly, Drosophila melanogaster, has straight wings and long bristles. Mutant strains have been isolated that have either curled wings or short bristles. The genes representing these two mutant traits are located on separate chromosomes. Carefully examine the data from the following five crosses.

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

Verified step by step guidance

Step 1: Understand the traits and their possible dominance relationships. The wild-type fruit fly has straight wings and long bristles, while mutants have curled wings or short bristles. Since the genes are on separate chromosomes, analyze each trait independently.

Step 2: Examine the phenotypes of the offspring in each cross. For each trait, determine whether the mutant phenotype appears in the heterozygous condition (i.e., when crossed with wild-type) or only in homozygous individuals. If the mutant phenotype appears in heterozygotes, it suggests dominance; if only in homozygotes, it suggests recessiveness.

Step 3: For the curled wings mutation, identify crosses where the mutant phenotype appears in the progeny of a wild-type × mutant cross. If the offspring show the mutant phenotype despite having one wild-type parent, this indicates dominance. Otherwise, if the mutant phenotype only appears when both parents are mutant, it is recessive.

Step 4: Repeat the same analysis for the short bristles mutation. Look for crosses where the mutant phenotype appears in heterozygous offspring to determine dominance or recessiveness.

Step 5: Summarize your conclusions by listing each mutation as dominant or recessive and citing the specific crosses (by their numbers or descriptions) that provide evidence supporting your determination.

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Key Concepts

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

Dominant and Recessive Alleles

Dominant alleles express their trait even if only one copy is present, while recessive alleles require two copies to show the trait. Identifying dominance involves analyzing offspring phenotypes from specific crosses to see if the mutant trait appears in heterozygotes.

Mendelian Inheritance and Punnett Squares

Mendelian inheritance explains how alleles segregate and assort independently during gamete formation. Punnett squares help predict offspring genotypes and phenotypes from parental crosses, allowing determination of dominance relationships based on observed ratios.

Chromosomal Location and Independent Assortment

Genes on separate chromosomes assort independently, meaning the inheritance of one trait does not affect the other. This principle helps interpret crosses involving multiple traits and confirms that mutations on different chromosomes segregate independently.

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