Biology (Genetics)

hi i have a couple of exam questions to ask to anyone who may know the answers.

In humans, cystic fibrosis is caused by a recessive allele, f.
(a) What is an allele?
......................................................................................................................................................
......................................................................................................................................................
(1 mark)

(b) A man and woman are both heterozygous for the cystic fibrosis allele. They have one
healthy son but would like to have another child. What is the probability that they will
produce a girl who has cystic fibrosis? Show your working.
Probability = .............................................
(2 marks)

(c) Sperms are produced by meiosis. Give two ways in which differences in sperms are a
result of meiosis.
1. ..................................................................................................................................................
......................................................................................................................................................
2. ..................................................................................................................................................
......................................................................................................................................................
(2 marks)

thanks hope some one can answer these.
kind regards
kubra

Reply 1

laurcor

Every person has two copies of every gene, each copy is called an allele,

B) Aa (mother) Aa (father) - has one gene thats dominant A and a
recessive one a

aa (1st child - recessive) Aa (heterozygous) Aa (recessive) AA (dominant)

so every child has one in four chance (25%) of inheriting two altered alleles and developing the disorder (- thats your answerer), a one in four chance of inheriting two normal alleles, and two in four chances(50%) of inheriting one dominant and one recessive allele and being a carrier like both parents.

the fact its a girl doesnt matter cos the gene isnt on the X or Y chromosomes.
to work it out you just make combinations of the parents letters (A and a)

C) .1 sperm is haploid (only has one copy of the genome)
2. prob that the cell divides ot give four cells meiosis and in mitosis you get 2. could be that after meiosis you get four sperm but in the egg the other three die. or you get anyway in meiosis a cell divides twice by mitosis to give two cell that each have two copies of the genome and then each of the two cell divides (gives half the chromosomes to each cell) to give four cell in total, each only has one copy of the genome.