In a species of fish, a black spot on the dorsal fin is ...

Question

In a species of fish, a black spot on the dorsal fin is observed in males and females. A fish breeder carries out a pair of reciprocal crosses and observes the following results.

Cross I Parents: black-spot male x nonspotted female
Progeny: 22 black-spot male
24 black-spot females
25 nonspotted males
21 nonspotted females
Cross II Parents: nonspotted male x black-spot female
Progeny: 45 black-spot males
53 nonspotted females

Why does this evidence support the hypothesis that a black spot is sex linked?

Accepted Answer

Hi, everyone. Let's take a look at this practice problem together in sex influenced traits. The expression of the trait is influenced by the answer. Options are a, the presence of two copies of the same A little B, the presence of 2 different ails c, the presence of hormones and D the presence of an extra sex chromosome. So, recall that sex influenced traits are autosomal or they are non sex characteristics in an individual that are influenced by the sex of that individual. Option. A describes a homozygous genotype. Option B describes a heterozygous genotype. Both option A and B are incorrect because it is the individual's sex that influences the trait, not the genotype. Option D, the presence of an extra sex chromosome is also an incorrect answer. The correct answer is option C hormones influence sex influenced traits. For example, male pattern, baldness is a genotype that can occur in both males and females. However, it's only expressed in males due to the presence of a hormone testosterone and so testosterone in males leads to the male pattern baldness. So it is the hormone produced due to the individual sex that influences the trait. Therefore, the correct answer is option c the presence of hormones. All right. Everyone. I hope you found this helpful and I'll see you soon for the next practice problem.

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