Question

A phenotypic trait is considered sex-linked when

		a trait occurs only in males
		the genes for the phenotype occur on X or Y chromosomes
		the phenotype is expressed only after sexual intercourse
		the phenotype occurs only in females
		the phenotype is polygenic for both sexes

An individual that has two different alleles for the same trait is said to be

		polygenic.
		recessive.
		homozygotic.
		heterozygotic.
		pleiotropic.

Answer 1

Answer 1:

Sex linked traits are those whose phenotype is dependent on the individual's sex. These traits can be carried by either X or Y chromosome. Males have a single copy of X chromosome, thus all genes carried by their X chromosome gets expressed. On the other hand, females have two copies of X chromosome, and a situation of dominance-recessiveness is present. Also, only males can express Y linked genes, as females do not have Y chromosome.

Thus, the correct choice should be:

A phenotypic trait is considered sex-linked when: the genes for the phenotype occur on X or Y chromosomes.

Answer 2:

A trait is a character whose expression depends on the alleles present in an organism. For each trait there are two alleles in an organism, which can be the same (eg TT, tt) or different (eg.Tt).

When both the alleles are same, the condition is called homozygous, whereas when the alleles are different, the condition is called heterozygous.

Thus, the correct choice should be:

An individual that has two different alleles for the same trait is said to be: heterozygotic.

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