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

6. Chromosomal Variation

Chromosomal Mutations: Aneuploidy

Genetics

6. Chromosomal Variation

Chromosomal Mutations: Aneuploidy

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Problem 17b

Textbook Question

Drosophila may be monosomic for chromosome 4, yet remain fertile. Contrast the F₁ and F₂ results of the following crosses involving the recessive chromosome 4 trait, bent bristles:
monosomic IV, normal bristles x diploid, bent bristles.

Verified step by step guidance

Step 1: Understand the genetic setup of the problem. Monosomic IV means the individual has only one copy of chromosome 4 instead of the usual two. The diploid individual has two copies of chromosome 4. The trait 'bent bristles' is recessive, meaning it is expressed only when both copies of the gene on chromosome 4 are the recessive allele.

Step 2: Assign symbols to the alleles. Let 'B' represent the dominant allele for normal bristles and 'b' represent the recessive allele for bent bristles. The monosomic individual will have only one allele for this trait (e.g., B or b), while the diploid individual will have two alleles (e.g., Bb or bb).

Step 3: Determine the genotypes of the parents. The monosomic individual could be either B (normal bristles) or b (bent bristles), while the diploid individual is bb (bent bristles) based on the problem description.

Step 4: Predict the F₁ generation. Perform a Punnett square or equivalent analysis to determine the possible genotypes and phenotypes of the offspring. Remember that the monosomic parent contributes only one allele, while the diploid parent contributes two alleles. For example, if the monosomic parent is B, the F₁ offspring will inherit either B or b from the diploid parent, resulting in genotypes Bb (normal bristles) or bb (bent bristles).

Step 5: Predict the F₂ generation. If the F₁ individuals are allowed to self-cross or interbreed, perform another Punnett square to determine the genotypic and phenotypic ratios in the F₂ generation. Consider the inheritance patterns of the recessive trait and the monosomic condition when analyzing the results.

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Key Concepts

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

Monosomy

Monosomy refers to the condition in which an organism has only one copy of a particular chromosome instead of the usual two. In Drosophila, being monosomic for chromosome 4 means that there is a single copy of this chromosome, which can lead to specific phenotypic expressions, such as the presence of recessive traits. Despite this chromosomal deficiency, organisms can still be fertile, indicating that certain genetic functions can be compensated by other mechanisms.

Recessive Traits

Recessive traits are characteristics that are expressed only when an individual has two copies of the recessive allele. In the context of the bent bristles trait in Drosophila, this means that a fly must inherit the bent bristles allele from both parents to exhibit the phenotype. If one parent is monosomic for chromosome 4 and carries the normal bristles allele, the offspring may show a mix of phenotypes depending on the genetic contributions from both parents.

F₁ and F₂ Generations

The F₁ generation is the first filial generation resulting from a cross between two parental lines, while the F₂ generation is produced by interbreeding the F₁ individuals. In genetic crosses, analyzing the phenotypic ratios in these generations helps to understand inheritance patterns. In this case, the F₁ generation will reveal the dominance of the normal bristles trait, while the F₂ generation will provide insights into the segregation of the recessive bent bristles trait, allowing for predictions about offspring phenotypes.

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