P2 Inheritance

Question 1

What is intraspecific variation, and what are it’s two types?

Answer 1

• Different characteristics of organisms of the same species.
• The two types of intraspecific variation are genetic variation and phenotypic variation.

Question 2

What is genetic variation?

Answer 2

Differences in DNA between organisms of the same species - due to genetic factors (different alleles and mutations).

Question 3

When can genetic variation occur?

Answer 3

1. During meiosis, different combinations of gamete alleles are produced (due to crossing over in prophase I, and independent assortment in metaphase I)
2. During sexual reproduction, as the two gametes randomly fuse at fertilisation.

Question 4

What is phenotypic variation?

Answer 4

• Differences in phenotypes between organisms of the same species, caused by genetic factors (such as differences in alleles) and environmental factors (different conditions in the environment, eg. diet).

Question 5

What is monogenic inheritance?

Answer 5

The inheritance of one gene.
eg. parental genotypes: Gg x Gg
parental gametes: G x G x g x g

Question 6

What is dihybrid inheritance?

Answer 6

The inheritance of two genes.
eg. parental genotypes: RrYy x RrYy
parental gametes: (RY x Ry x rY x ry) x (RY x Ry x rY x ry)

Question 7

What is codominance?

Answer 7

• When both alleles are expressed.
• Eg. blood type I^A and I^B are codominant, whereas i^O is recessive.

Question 8

What are autosomes?

Answer 8

• Any chromosome that isn’t a sex chromosome, they are arranged in homologous pairs.
• Before each cell division, DNA in each autosome undergoes replication, and the strands are called chromatids.
• Each chromosome in a homologous pair therefore has two identical sister chromatids connected at the centromere.

Question 9

What is autosomal linkage?

Answer 9

When two or more genes (linked genes) appear on the same autosome (both members of the homologous pair carry the same gene, but they may have a different allele).

Question 10

Difference between dihybrid inheritance of two heterozygous individuals and between gametes with autosomal linkage?

Answer 10

• Dihybrid inheritance of two heterozygous individuals produces 4 types of genotypes (possible gametes are B B b b)
• Whereas autosomal linkage of two heterozygous genes shows two types of genotype (possible gametes = AB ab, as genes don’t separate). This gives a ratio of 3:1.
• However if crossing over occurs on genes with autosomal linkage, then 4 types of genotype are produced (the further apart linked genes are, the more likely they are to be separated during crossing over). This gives a 9:3:3:1 ratio.

Question 11

What are sex-linked genes?

Answer 11

Genes that are located on a sex chromosome, so allele expression depends on the sex of the individual.
- sex linkage can be dominant, recessive or codominant alleles

Question 12

What is epistasis?

Answer 12

When one gene affects the expression of another gene to determine some of the phenotype. eg. fur colour in mice