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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1:39 minutes

Problem 17a

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, bent bristles x diploid, normal bristles

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Determine the genetic makeup of the parents: The monosomic IV, bent bristles parent has one copy of chromosome 4 with the recessive allele (b) for bent bristles. The diploid, normal bristles parent has two copies of chromosome 4, both carrying the dominant allele (B) for normal bristles.

Set up the F₁ cross: The monosomic parent can only contribute one chromosome 4 with the recessive allele (b). The diploid parent can contribute either of its two dominant alleles (B). Thus, the F₁ offspring will inherit one chromosome 4 from the monosomic parent and one from the diploid parent, resulting in a heterozygous genotype (Bb) for all F₁ individuals.

Predict the phenotype of the F₁ generation: Since the dominant allele (B) masks the effect of the recessive allele (b), all F₁ individuals will exhibit the normal bristles phenotype.

Set up the F₂ cross: The F₁ individuals (Bb) are crossed with each other. This involves a typical Mendelian dihybrid cross where each parent can contribute either the dominant allele (B) or the recessive allele (b).

Determine the F₂ genotypic and phenotypic ratios: Use a Punnett square to calculate the possible combinations of alleles in the F₂ generation. The expected genotypic ratio will be 1 BB : 2 Bb : 1 bb, and the phenotypic ratio will be 3 normal bristles : 1 bent bristles, as the recessive phenotype (bent bristles) only appears in individuals with the bb genotype.

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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 where 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 only one copy of this chromosome present, which can affect gene expression and phenotypic traits. Despite this, some organisms can still be fertile, as seen in the case of Drosophila, where certain traits may not be lethal even in a monosomic state.

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 recessive allele from both parents to exhibit bent bristles. If the fly has at least one dominant allele for normal bristles, the normal phenotype will be expressed instead.

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 individuals from the F₁ generation. In genetic crosses, analyzing the phenotypic ratios in these generations helps to understand inheritance patterns. For the given crosses, observing the F₁ and F₂ results will reveal how the monosomic condition affects the expression of the bent bristles trait compared to the diploid normal bristles.

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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.

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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, bent bristles x diploid, normal bristles

Key Concepts

Monosomy

Recessive Traits

F₁ and F₂ Generations

Watch next

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, bent bristles x diploid, normal bristles