Answer
A)
What is meant by sex-linked gene?
Sex-linked gene are genes
located on the sex chromosomes but are not involved in determining of sex of an
individual. Most of this gene are located on the X chromosomes. The allele
located on the same sex chromosomes are not separated during meiosis and is
inherited.
B)
What is the probability that their second child will be 1) a
haemophiliac boy, 2) a daughter who is a carrier for haemophilia?
Both of
the probability is 25%.
C)
Draw a simple pedigree diagram to show that the genotypes of the three
individual ( the parents and the haemophiliac son). Explain how the pedigree is
obtained.
The son is a haemophiliac. He inherit the X
chromosome from the mother and the Y chromosomes from the father. The X
chromosome carries the recessive alleles for haemophilia. The mother is
phenotypically normal but is a heterozygous carrier. The son inherits the
haemophlia recessive allele.
D) Explain why a human
population will contain more colour-blind individuals than haemophiliacs?
Under natural conditions, the selection pressure
against haemophilia is greater than that against colour-blindness.
Haemophiliacs are weaker than colour-blindness and maynot reach sexual
maturiry. Some of the haemophiliac gene are therefore lost from population.
However, haemophilia can now be treated by gene therapy and many of them live a
normal life.
Assignment submitted by L.Y., Kong, S. H., Lim, S. C., Soo, C. W. Tan and C.C.,Teh 2011/2012 (IBM)
No comments:
Post a Comment