An insect species is discovered in which the heterogametic sex is unknown. An X-linked recessive mutation for reduced wing (rw) is discovered. Contrast the F 1 and F 2 generations from a cross between a female with reduced wings and a male with normal-sized wings when the male is the heterogametic sex.

Everyone. Let's take a look at this question together in the absence of any knowledge of hetero gammy, dick sex, what would be the expected sex ratio in the offspring of a cross between a male and female insect? So we know that the sex chromosomes determine the sex of the progeny, and we know that these sex chromosomes differ among species, meaning that depending on the species, the male or female can be the hetero comedic sex, for example, in fish and birds, it is the female, but in other species it could be the male. And since we have the absence of any knowledge of hetero comedic sects, and we do not know what the insect is, there's no way to determine what the expected sex ratio in the offspring of a cross between a male and a female insect would be. So, answer choice D. Cannot be determined is the correct answer, because the sex ratio cannot be predicted without knowledge of the specific insect species that is used in this cross. And so the expected sex ratio of their offspring cannot be determined. So answer choice D. Is the correct answer. I hope you found this video to be helpful. Thank you and goodbye.

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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

Sex Chromosome

Genetics

3. Extensions to Mendelian Inheritance

Sex Chromosome

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Problem 10b

Textbook Question

An insect species is discovered in which the heterogametic sex is unknown. An X-linked recessive mutation for reduced wing (rw) is discovered. Contrast the F₁ and F₂ generations from a cross between a female with reduced wings and a male with normal-sized wings when the male is the heterogametic sex.

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Understand the problem: The goal is to determine the inheritance pattern of an X-linked recessive mutation (reduced wing, rw) in an insect species where the male is the heterogametic sex (XY). This means females are homogametic (XX). The cross involves a female with reduced wings (homozygous recessive, XrwXrw) and a male with normal wings (hemizygous dominant, XRWY).

Step 1: Determine the genotypes of the parents. The female with reduced wings is XrwXrw, and the male with normal wings is XRWY. Since the mutation is X-linked, the Y chromosome does not carry the allele for wing size.

Step 2: Predict the F₁ generation. Perform a Punnett square for the cross XrwXrw (female) × XRWY (male). The possible offspring genotypes are: XrwXRW (female, heterozygous with normal wings) and XrwY (male, hemizygous with reduced wings).

Step 3: Analyze the F₁ phenotypes. All F₁ females (XrwXRW) will have normal wings because the dominant allele (XRW) masks the recessive allele (Xrw). All F₁ males (XrwY) will have reduced wings because they inherit the Xrw allele from their mother and lack a second X chromosome to mask it.

Step 4: Predict the F₂ generation. Cross an F₁ female (XrwXRW) with an F₁ male (XrwY). Perform a Punnett square to determine the genotypes and phenotypes of the F₂ offspring. The possible genotypes are: XRWXrw (female, normal wings), XrwXrw (female, reduced wings), XRWY (male, normal wings), and XrwY (male, reduced wings). Analyze the phenotypic ratios based on these genotypes.

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Key Concepts

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

X-linked Inheritance

X-linked inheritance refers to the pattern of inheritance for genes located on the X chromosome. In this case, the reduced wing mutation (rw) is recessive and linked to the X chromosome. Males, having one X and one Y chromosome, will express the trait if they inherit the X chromosome carrying the mutation, while females, with two X chromosomes, must inherit two copies of the mutation to express the trait.

Heterogametic Sex

The heterogametic sex is the sex that produces two different types of gametes regarding sex chromosomes. In many species, including insects, males are heterogametic (XY), while females are homogametic (XX). This distinction is crucial for understanding inheritance patterns, especially for X-linked traits, as the male's single X chromosome will determine the expression of any X-linked traits.

F₁ and F₂ Generations

The F₁ generation is the first filial generation resulting from a cross between two parental organisms, while the F₂ generation is produced by interbreeding individuals from the F₁ generation. In this scenario, analyzing the phenotypes of the F₁ and F₂ generations will reveal how the X-linked recessive trait for reduced wings is inherited, particularly how it manifests differently in males and females based on their sex chromosomes.

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