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.

Verified step by step guidance

1. 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).
2. 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.
3. 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).
4. 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.
5. 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.

Key Concepts

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.