What Happens During the G1 Phase and How Does Genotype Affect It?

[jenc305]

G1 Phase and Genotype

I need help with two questions. I am unable to find the first answer from my book. I have an idea of what the answer is but I'm not positive.
Thank you.

At the G1 phase of the cell cycle, a eukaryotic chromosome consists of

a)one long linear DNA molecule stretching the length of the chromosomes
b)two linear DNA molecules joined together end to end at the centromere
c)many genes adjacent to each other in a linear organization
d)both a and c are correct
e)both b and c are correct

I think it's d.

I've got another questions I'm stuck on.

Two genes, X and Y, are located on the same chromosome. X is dominant over x and Y is dominant over y. These two genes are located so close together that, within the limits of this experiment, no recombination is seen between them. An individual whose genotype is XXYY is crossed to an individual whose genotype is xxyy. The F1 generation progeny is crossed to produce an F2 generation. Among the F2 generation what fraction of individuals would be expected to have the phenotype XY?
a)0
b)3/16
c)1/4
d)1/2
e)9/16

My guess would be e. F1 generation would create a progeny of XxYy. So if crossed with another individual with genotype XxYy then they would create a F2 progeny of 9:3:3:1 ratio.

 

[jenc305]

I think I figured out question 2. Since the question states that there is no recombination than the F1 progeny would have to come out 1/2 XXYY and the other 1/2 xxyy. Same goes for the F2 generation. So the answer must be d, right?

 

[oswaler]

For the first question, your answer of d is correct. The G1 phase of the cell cycle is when the cell grows and prepares for DNA replication. At this stage, the chromosome consists of one long linear DNA molecule with many genes adjacent to each other in a linear organization.

For the second question, your answer of e is also correct. The F2 generation would have a 9/16 chance of having the phenotype XY, as this combination would result from the crossing over of the X and Y chromosomes during meiosis. The other possible combinations (Xy, xY, and xy) would result in different phenotypes. The 9/16 ratio comes from the 3/4 chance of having the dominant X allele and the 3/4 chance of having the dominant Y allele.