Genetic questions help...

[Roger]

So I got this study guide and I am stuck on three questions. I have been trying to answer these for the past hour and my textbook really doesn't state much and I can't find any helpful info on the internet so I found this forum and hopefully you guys can help a little.

1. Classical albinism is NOT SEX-LINKED and results from a recessive allele. Which of the following is the expected offspring from a normally pigmented male [whose father was an albino] that has children with an albino woman?

A. 75% albino, 25% normal
B. 75% normal, 25% albino
C. all albino
D. all normal
E. 50% normal, 50% albino

I think this is B but to tell the truth its really an educated guess.

2. Why would you predict that half of the human babies born will be males and half will be females (think about this)?

A. because of the segregation of the X and Y chromosomes during male meiosis
B. because of the segregation of the X chromosomes during female meiosis
C. because all eggs contain an X chromosome
D. a and c

This question I don't have a clue

3. Colorblindness is sex-linked. A colorblind boy has a non colorblind mother and a colorblind father. From which parent did he get the colorblind gene?

A. father
B. mother
C. either parent could have given him the gene
D. none of the above

From what I read I think its father but again I am not sure and I want to be.

Any help would be great. Genetics always causes me to lose my mind. Its tough for me to understand.

Thanks!

[Anon]

1. So, if N is the normal pigment trait allele and n is the albino pigment, then the question is telling us that the man is Nn (he must have an N to be normally pigmented, his father must have given him a n because that's all his father had.)

We know that the woman is nn because she shows the recessive phenotype i.e. she's an albino.

The question is then a case of crossing Nn x nn.

Nn x nn = Nn (normal) or nn (albino)

Therefore, you'd expect 50% of each type, e.g. the answer is E.

2.I am not entirely sure but I think it is A.

3. It's his mother.

Colour blindness is on the X chromosome.

Since this is a little boy, he must have an X and a Y.

His mother doesn't have a Y chromosome to give therefore he got his Y chromosome from his father.

If he had XX, he'd be a she.

But since he's a boy, it has to be a faulty allele on his mother's X chromosome (which happened to be the one he got) that's the problem.

So B.

[Marshall Taylor]

I had a few questions that kind of stumped me on my homework assignment for Genetics.

1. T or F, For a given species, sex influenced traits are expressed in only one sex and have zero penetrance in the other sex.

2. T or F, Genomic imprinting and genetic anticipation both involve the inhibition of specific genes, or chromosomes, based on parental origin.
-I believe this one is true but Im not sure

3. In order to determine if mutations from different organisms that exhibit the same phenotype are allelic, which test would you perform?
a. test cross, b. epistasis cross, c. complementary test, d. allelic series test, e. biochemical test.
I have not a clue on this one

4. If the maternal phenotype always determines the phenotype of the offspring regardless of paternal input in the same and previous generations, it is not ...
a. sex-linked, b. genetic maternal effect, c. imprinted, d. cytoplasmic inheritance

I have not a clue on this last one

[Dana Mursa from Romania]

Unlaborator work in the genetics, and I amniocenteze some problems: why some doctors of the cells is not attached? I can help with examples of areas, a technique I'd be helpful ... thank you!