Question

1.

In humans, there are several mutations that can cause hereditary deafness. Most of these mutations are recessive, yet two deaf people can marry and produce children with normal hearing. This is explained by the fact that deafness shows _________.

		The "Threshold Effect"
		Conditional mutations
		Genetic heterogeneity
		Genetic anticipation

2.

An individual with classic symptoms of Down syndrome is found to have 46 chromosomes. How can this be?

		It is possible if she or he carries a chromosome translocation, such as 14/21.
		This is possible if the individual has an extra chromosome 21 but has only one copy of chromosome 1.
		This is not possible.
		It is possible if she or he carries a chromosome inversion.

3.

In snapdragons, tall plants are dominant to dwarf plants, and red and white flower color is codominant, producing pink flower color in heterozygous individuals. A dwarf, red snapdragon is crossed with a plant homozygous for tallness and white flowers. What are the genotype and phenotype of the F1 individuals?

		TTRR - tall and red
		ttRr - dwarf and pink
		ttrr - dwarf and white
		TtRr - tall and red
		TtRr - tall and pink

The spines of cacti may be sharp or dull. Gene S controls the sharpness of spines in a type of cactus. Cactuses with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cactuses have dull spines. At the same time, a second gene, N, determines whether cactuses have spines or not. Homozygous recessive nn cactuses lack any spines at all. A cross between a true-breeding sharp-spined cactus and a spineless cactus would produce

		It is impossible to determine the phenotypes of the progeny.
		50% sharp-spined, 50% dull-spined progeny.
		25% sharp-spined, 50% dull-spined, 25% spineless progeny.
		all sharp-spined progeny.
		all spineless progeny.

Answer 1