Question

1. A single-gene fruit color train in eggplant displays incomplete dominance. The purple and which fruit colors are true breeding phenotypes associated with being homozygous at the gene. Violet color results from heterozygosity at the gene. Which of the following ratios would you predict if you crossed a violet-fruit eggplant to purple-fruit plant and looked at their progeny?
   1. 3:1 purple:white
   2. 1:2:1 purple:violet:white
   3. 3:1 violet:white
   4. All violet
   5. 1:1 purple violet
2. Which of the following statements about replication origins is incorrect?
   1. Replication proceeds in both directions from each origin, so two replication forks going opposite directions are formed
   2. In eukaryotes, each linear chromosome contains a single replication origin sequence, which is activated during the G2 phase of the cell cycle
   3. The two strands of DNA at the origin are separated, allowing the formation of a replication bubble
   4. They are DNA sequences, not RNA or protein sequences
3. In humans, the sexual phenotype of male in an individual is caused by
   1. The absence of a Y chromosome, which carries the female determining SRY gene
   2. The presence of two copies of the Z gene
   3. The presence of a diploid chromosome number in the egg
   4. The presence of one X chromosome, which always causes male development in any eukaryotic organism
   5. The presence of a Y chromosome, which carries the male determining SRY gene
4. Vermillion eyes (an orange-red color) is an X-linked recessive trait in Drosophila (fruit flies). If a male fly with normal eyes is crossed to a female fly that has vermillion eyes, what percentage of the F1 females will have vermillion eyes?
   1. 25%
   2. 50%
   3. 0%
   4. 100%

Answer 1

1) let the alleles be P-purple, W- white

PP- purple

PW- violet

WW- white

purple * violet

PP * PW

	P	W
P	PP ( purple)	PW( violet)
P	PP ( purple)	PW ( violet)

the phenotypic ratio is purple: violet=1:1

so the answer is e) 1:1 purple violet

2) DNA replication starts at origin of replication, DNA melts at the origin of replication, from a single origin of replication, DNA replication proceeds in both directions, the bacterial chromosome has only one origin of replication, but eukaryotic linear chromosomes has multiple origins of replications.

DNA replication occurs during S phase of the cell cycle.

so the answer is b) In eukaryotes, each linear chromosome contains a single replication origin sequence, which is activated during the G2 phase of the cell cycle.

3) The genotype of males is XY and females is XX, the SRY gene located on the Y chromosome is responsible for the development of male sex organs.

e) The presence of a Y chromosome, which carries the male determining SRY gene

4) let the alleles be Xv- vermillion, XV- wildtype.

the genotype of a male fly with normal eyes is XVY and genotype of a female fly that has vermillion eyes is XvXv.

XvXv * XVY

	XV	Y
Xv	XVXv ( female with normal eyes)	XvY ( male with vermillion eyes)
Xv	XVXv ( female with normal eyes)	XvY( male with vermillion eyes)

none of the female progenies have vermillion eyes.

percentage of the F1 females will have vermillion eyes is c) 0%.