Inheritance

Question 1

What is a dominant allele?

Answer 1

An allele that is always expressed in the phenotype even when there’s only one copy of it

Question 2

What is a recessive allele?

Answer 2

Alleles that are only expressed in the phenotype if two copies are present (homozygous)

Question 3

What are codominant alleles?

Answer 3

Both alleles are expressed in the phenotype as neither one is recessive (phenotype is intermediate)

Question 4

What do monohybrid crosses show?

Answer 4

The likelihood of the different alleles of a single gene being inherited by the offspring

Question 5

What do dihybrid crosses show?

Answer 5

The likelihood of the offspring inheriting certain combinations of the two characteristics controlled by separate genes

Question 6

What is sex linkage?

Answer 6

Where the expression of alleles located on sex chromosomes depends on the sex of the individual. Males are more likely to show recessive phenotypes for sex linked genes as they only have one X chromosome

Question 7

What is autosomal linkage?

Answer 7

Genes on non-sex chromosomes that stay together during independent segregation, therefore they will be inherited together, meaning more offspring will have the same genotype and phenotype as their parents. The closer the loci of genes on an autosome, the more closely linked they are

Question 8

Why may autosomal linkage not occur?

Answer 8

The alleles are separated during crossing over, meaning some offspring will have different genotypes and phenotypes to their parents

Question 9

What is epistasis?

Answer 9

The expression of one gene suppresses the expression of another. Occurs when a phenotype is controlled by more than one gene (eg. Boldness genes are epistatic to widows peak gene)

Question 10

Monohybrid cross phenotypic ratios

Answer 10

F1 = 100% heterozygous
F2 = 3:1 dominant:recessive

Question 11

Dihybrid cross phenotypic ratios

Answer 11

F1 = 100% heterozygous
F2 = 9:3:3:1 dominant-dominant:dominant-recessive:recessive-dominant:recessive-recessive

Question 12

Codominant phenotypic ratios

Answer 12

F1 = 100% heterozygous
F2 = 1:2:1 homozygous1:heterozygous:homozygous2

Question 13

Recessive episatic alleles phenotypic ratio

Answer 13

F1 = 100% heterozygous
F2 = 9:3:4

Question 14

Dominant episatic alleles phenotypic ratio

Answer 14

F1 = 100% heterozygous
F2 = 12:3:1