Question

Questions 1-3?

1. 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.

2.

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

3.

Transfer of plasmid DNA from a donor F+ strain to a recipient F- strain is called

		Transduction
		Conjugation
		Transformation
		Translocation

Answer 1

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

The correct answer is

(1) It is possible if he or she carries a chromosome translocation, such as 14/21.

This a Translocation type of Down syndrome.In translocation, part of chromosome 21 breaks off during cell division and attaches to another chromosome, typically chromosome 14. While the total number of chromosomes in the cells remain 46, the presence of an extra part of chromosome 21 causes the characteristics of Down syndrome.

2) 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 correct answer is

(2) Conditional mutations

conditional mutation is one that produces a wild type phenotype under one environmental condition and a mutant phenotype under a different condition. A wild type phenotype means a phenotype found in a normal population, and in this scenario wild type phenotype is a hearing child and therefore deafness shows conditional mutation.

3.Transfer of plasmid DNA from a donor F+ strain to a recipient F- strain is called

The correct answer is

(2) Conjugation

conjugation is the bacterial equivalent of sexual reproduction or mating. To perform conjugation, one bacterium has to carry a transferable plasmid (referred to as F+), while the other must not. The transfer of plasmid DNA occurs from the F-positive bacterial cell to the F-negative bacterium