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. Identify the sex determination system given that the male is heterogametic. In this case, males have XY sex chromosomes and females have XX.
2. Determine the genotypes of the parents: the female with reduced wings must be homozygous recessive (X\_rwX\_rw) because the mutation is X-linked recessive, and the male with normal wings must have the genotype X\_RY (where X\_R is the normal allele).
3. Predict the F\_1 generation genotypes by crossing X\_rwX\_rw (female) with X\_RY (male). Write out the possible gametes and combine them to find the offspring genotypes and phenotypes.
4. Analyze the phenotypes of the F\_1 generation, noting which individuals show reduced wings and which show normal wings, considering the X-linked recessive inheritance pattern and the heterogametic male.
5. For the F\_2 generation, perform a cross between F\_1 individuals (usually F\_1 heterozygous females and F\_1 normal males) and determine the expected genotypic and phenotypic ratios, again considering the X-linked recessive inheritance and male heterogamety.

Key Concepts

Heterogametic Sex and Sex Chromosomes

The heterogametic sex produces two different types of sex chromosomes (e.g., XY in males), while the homogametic sex produces identical sex chromosomes (e.g., XX in females). Identifying which sex is heterogametic is crucial for predicting inheritance patterns of X-linked traits, as males typically have only one X chromosome, affecting how recessive mutations are expressed.

X-linked Recessive Inheritance

X-linked recessive traits are carried on the X chromosome and usually manifest in males who have only one X chromosome, making them hemizygous. Females must inherit two copies of the recessive allele to express the trait. This inheritance pattern influences the phenotypic ratios observed in offspring, especially when crossing heterozygous females with normal or affected males.

Mendelian Crosses and Generational Analysis (F1 and F2)

Mendelian genetics involves analyzing offspring (F1 and F2 generations) from specific parental crosses to predict genotype and phenotype ratios. The F1 generation results from the initial cross, while the F2 generation comes from crossing F1 individuals. Understanding these generations helps contrast expected phenotypic outcomes when considering sex-linked traits and heterogametic sex.