3.3.3 - Genes & Linkage

Question 1

What Does A Chromosome Consist Of?

Answer 1

A long DNA molecule that contains several hundred or thousands of different genes, coding for different proteins.

Question 2

What Is The Locus (Plural: Loci)?

Answer 2

The position of a gene on a chromosome.

Question 3

What Is A Gene?

Answer 3

A length of DNA that codes for a single polypeptide or protein.

Question 4

What Does Each Gene Occupy?
(3 Points)

Answer 4

~ A specific locus, so that the gene for a particular characteristic is always found on the same position on a particular chromosomes.

~ Each gene can exist in two or more forms called alleles.

~ Different alleles of a gene have slightly different nucleotide sequences but they still occupy the same position on the chromosome.

Question 5

Describe Autosomal Linkage
(4 Points)

Answer 5

~ Only occurs on the autosomes (Any chromosome that isn’t a sex chromosome).

~ Two or more genes on the same autosome do not assort independently during meiosis.

~ Instead these genes are linked and they stay together in the original parental combination.

~ These linked genes are passed on to offspring all together (Through the gametes).

Question 6

Describe Sex Linkage
(6 Points)

Answer 6

~ Sex-linked, when the locus of the allele that codes for it is on a sex chromosome.

~ Females -> XX, Males -> XY.

~ Some genes are only present on one sex chromosome and not the other.

~ If the gene is on the X chromosome, males will only have 1 copies whereas females will have 2 copies.

~ Males -> More likely to show sex-linked recessive conditions.

~ Females -> More likely to inherit one dominant allele that mask the effect of the recessive allele.