Question

1. Which one of the following is the best explanation for Haldane’s rule?

   	A.	Deleterious recessive alleles on the sex chromosomes that cause incompatibility between two species will not be masked in the heterogametic sex, but will be masked in the homogametic sex.
   	B.	New, deleterious combinations of alleles at two or more autosomal loci are present in hybrids, and those deleterious combinations of alleles do not occur in the species that gave rise to those hybrids.
   	C.	Random fluctuation of allele frequencies is more prevalent in populations with smaller, compared to larger effective population sizes.
   	D.	Deleterious recessive alleles occur more commonly on sex chromosomes than on autosomes.

2.

Which of the following is NOT a likely cause of linkage disequilibrium?

	A.	Free recombination between loci.
	B.	Beneficial mutations arising on a certain haplotype.
	C.	Selection acting against certain combinations of alleles.
	D.	Migration carrying certain haplotypes across populations.

3.

1. Sexual reproduction most likely originated:

   	A.	In the ancestor of both eukaryotes and prokaryotes.
   	B.	In the ancestor of all eukaryotes.
   	C.	In the ancestor of animals.
   	D.	Independently in the ancestor of plants and animals.

4.

1. Females are defined by:

   	A.	Having the same sex chromosomes (such as XX).
   	B.	The sex that gives birth.
   	C.	The sex that takes care of young.
   	D.	The sex that produces large, rather than small, gametes.

Answer 1

1. Answer: Option A is correct
Explanation:
Haldane's rule = The heterogametic sex is more likely to be inviable/sterile in a species hybrid if only one sex is to be inviable/sterile

For example, color-blindness is an X-linked recesive disorder in humans.
Males will be affected if they inherit a single mutant allele.
However, females have to inherit mutant alleles from both her parents to exhibit the mutant phenotype.
i.e. the recessive mutant allele is more likely to be masked by the presence of another allele in a homogametic sex.