Genetics

Question 1

the chromosomal theory

Answer 1

proposed by Sutton: hereditary traits are carried on chromosomes. Morgan showed that the trait for white eyes in Drosophila, cosegregated with sex chromosomes, indicating that traits are associated with chromosomes (sex-linked).

Question 2

which genetic disorders are sex-linked

Answer 2

colour blindness and hemophilia

Question 3

what happens when two genes are linked

Answer 3

when two genes are linked, they both occur on a chromosome , and their inheritance behaviour differ if the genes were on separate chromosomes

Question 4

non-disjunction

Answer 4

the failure of homologues or sister chromatids to seperate during meiosis, results in a condition called aneuploidy

Question 5

X inactivation

Answer 5

in mammalian females one of the X chromosomes is randomly inactivated during development. this inactivated condensed chromosome (or Barr body) is an example of dosage compensation, which balances levels of gene expression in males and females.

Question 6

barr bodies example

Answer 6

the calico cat is heterozygous for alleles of a coat color gene that produces either black fur or orange fur. this gene is on the X chromosome, so the different coloured fur is due to the inactivation of one X chromosome.

Question 7

amniocentesis

Answer 7

procedure that permits the prenatal diagnosis of many genetic disorders, a needle is inserted into the expanded uterus, removing a small sample of the amniotic fluid that bathes the fetus.

Question 8

chronic villi sampling

Answer 8

removes cells from the chorion (a membranous part of the placenta that nourishes the fetus), and yields results much more rapidly.

Question 9

why is there an increased risk of chromosomal abnormality in gametes from older women and men

Answer 9

errors in meiosis may be more likely to happen as a result of the aging process.