BIO: Topic- Genotype's , gametes and scenarios?

Question

**HELP ME PLEASE!!!!**

- Assume that a gene on the number 6 chromosome has the alleles A and a, and that a second gene on the number 8 chromosome has the alleles Band b.

a) what kinds of gametes could be produced by a person, genotype Aa Bb?

b) A person produces gametes of one type on ab. What is the probable genotype of this person?

-A man has the genotype RT/rt and these two gene loci are linked. Would he produce more Rt gametes than RT gametes?

- Two unaffected parents have a child affected by an inherited disorder. suggest two likely mode of inheritance?

- A man showing a dominant trait has a daughter who doesnt show the trait. could this be an x linked dominant trait. explain?

Answer 1

During meiosis, when alleles independently assort, you can get any combination of alleles so long as you have one from each gene.  So, a person who is AaBb can produce all combinations of A's and B's:  AB, Ab, aB, and ab.  If a person only ever produces ab gametes, then they very likely only have copies of those recessive alleles and would therefore be aabb.

If genes are linked, then the two alleles that are on the same chromosome will be carried together more frequently into gametes.  So, a person who is RT/rt would make more RT and rt gametes than they would Rt and rT gametes.

If two parents do not have the disorder and their child does, then the most likely explanation is that the disorder is caused by a recessive allele and both parents are heterozygous carriers.  Another possibility is that there was a mutation that occurred in the germ line of one of the parents so while the body cells of that parent are not affected, the mutated copy was passed on to the child.

If the man has the trait, and it is X-linked, then his only X chromosome (because men are XY) has to be carrying the dominant allele.  If he has a daughter, who has to be XX, then his one X chromosome (that is carrying the dominant allele) has to be passed on to her.  But, in this case she doesn't show the trait.  So, there are two possibilities:  

1.  The trait is not carried on the X chromosome.

2.  This guy isn't her real dad.

Answer 2

Assume that a gene on the number 6 chromosome has the alleles A and a, and that a second gene on the number 8 chromosome has the alleles Band b.

a) what kinds of gametes could be produced by a person, genotype Aa Bb?

ANSWER

Since they are not linked: AB , Ab , aB, ab

b) A person produces gametes of one type on ab. What is the probable genotype of this person?

ANSWER

If they only produced gametes containing ab then their only possible genotype would be  aabb.

-A man has the genotype RT/rt and these two gene loci are linked. Would he produce more Rt gametes than RT gametes?

ANSWER

There should be an equal probability of both gametes.

- Two unaffected parents have a child affected by an inherited disorder. suggest two likely mode of inheritance?

ANSWER

1. The disorder is caused by a recessive allele and the child received the recessive allele from both parents. The parents would be unaffected if they were both heterozygous ie possess one dominant (normal) allele and one recessive (defective) allele.

2. A Mutation has occured in one or more of  the child's chromosomes causing the disorder.

- A man showing a dominant trait has a daughter who doesnt show the trait. could this be an x linked dominant trait. explain?

ANSWER

No it could not be X linked. The males spem contains an X or a Y chromosome. If an X sperm fertilises an egg it will prodce a female child. This means a daughter always inherits an X chromosome from her father.

If it was X linked he would have passed the dominant trait to his daughter.

Hope this helps!