Question

QUESTION 21

Which of the following is a form of aneuploidy in which two members of the same homologous pair are absent?

A. disomy

B. monosomy

C. trisomy

D. tetrasomy

E. nullisomy

QUESTION 22

1. In performing a dihybrid cross, you expect to see a 9:3:3:1 ratio. What is a good explanation if you do not see a 9:3:3:1 ratio in a dihybrid cross?

   		The two genes are not linked.
   		The two genes are linked.
   		One of the genes is dominant over the other.
   		The two genes assort independently.
   		This proves that Mendel s laws are incorrect.

QUESTION 25

1. The _____ theory states that the ancestors of mitochondria and chloroplasts were free-living bacteria.

   	A.	cytoplasmic inheritance
   	B.	endosymbiotic
   	C.	old world
   	D.	cell
   	E.	phylogenetic

Answer 1

21.E. Nullisomy

Nullisomy is a genome mutation where a pair of homologous chromosomes that would normally be present is missing. Thus, in nullisomy, two chromosomes are missing, and the chromosomal composition is represented by 2N-2.

22. The two genes are linked

Linkage is one of the most important reasons for distortion of the ratios expected from independent assortment. Linked genes are located close together on the same chromosome. This close proximity alters the frequency of allele combinations in the gametes.

25. B. endosymbiont

The endosymbiotic theory states that some of the organelles in today's eukaryotic cells were once prokaryotic microbes. The ancestral eukaryote consumed aerobic bacteria that evolved into mitochondria. In a second endosymbiotic event, the early eukaryote consumed photosynthetic bacteria that evolved into chloroplasts. The eukaryotic host cell were benefitted as the organelles provided them with ATP