7.1 Inheritance

Question 1

Define genotype

Answer 1

The genetic constitution of an organism

Question 2

Define phenotype

Answer 2

The expression of an organism’s genetic constitution, combined with its interaction with the environment

Question 3

What is an allele?

Answer 3

• Different forms of a particular gene, found at the same locus on a chromosome.
• A single gene could have many alleles

Question 4

How many alleles per gene do diploid organisms carry?

Answer 4

2

Question 5

What is meant by a dominant allele?

Answer 5

An allele whose characteristic will always appear in the phenotype, whether one or two are present

Question 6

What is meant by codominant alleles?

Answer 6

Two dominant alleles that both contribute to the phenotype, either by showing a blend of both characteristics, or the characteristic appearing together

Question 7

What is meant by homozygous and heterozygous?

Answer 7

• Homozygous: both alleles are dominant, or both alleles are recessive
• Heterozygous: one allele is dominant, the other is recessive

Question 8

Define monohybrid inheritance

Answer 8

Where one phenotypic characteristic is controlled by a single gene

Question 9

Punnett square to show a monohybrid cross with parental genotypes of GG and gg

Answer 9

Question 10

What percentage of the offspring of the monohybrid cross with parental genotypes of GG and gg will express the characteristic determined by the allele G?

Answer 10

100% - all potential offspring genotypes are Gg, meaning none of them will express the recessive allele

Question 11

Punnett square to show a monohybrid cross with parental genotypes of Gg and Gg

Answer 11

Question 12

What percentage of the offspring of the monohybrid cross with parental genotypes of Gg and Gg should express the characteristic determined by allele G?

Answer 12

75% - only one of the combinations results in expression of the recessive allele

Question 13

Example of genetic diagram

Answer 13

Question 14

Define dihybrid inheritance

Answer 14

Where two phenotypic characteristics are determined by two different genes present on two different chromosomes at the same time

Question 14

Punnett square to show a dihybrid cross with parental genotypes of RrGg and RrGg

Answer 14

Question 15

How many of the offspring with a dihybrid cross with parental genotypes of RrGg and RrGg should have the same phenotype as their parents?

Answer 15

• 9 (out of 16)
• 6 will match their parents on one characteristic, but differ on the other
• 1 will differ on both characteristics

Question 16

What is meant by sex-linkage?

Answer 16

Where an allele is located on one of the sex chromosomes, meaning its expression depends on the sex of the individual

Question 17

Which parents do males inherit sex-linked characteristics from?

Answer 17

• Their mother, since their Y chromosome can only come from their father.
• Therefore if the mother is heterozygous for sex-linked alleles, she is a carrier and may pass on the trait

Question 18

Punnett square to show a sex-linked cross with parental genotypes of X^H X^h and X^H Y

Answer 18

Question 19

Describe the four possible phenotypes of the offspring with parental genotypes of X^H X^h and X^H Y

Answer 19

• Normal female
• Carrier female
• Normal male
• Affected male

Question 19

What is meant by autosomal linkage?

Answer 19

• Where two or more genes are located on the same (non-sex) chromosome
• In this case, only one homologous pair is needed for all four alleles to be present
• For genes that aren’t linked, two homologous pairs are needed

Question 20

Punnet square to show multiple alleles cross with parental genotypes of I^A I^O and I^B I^O

Answer 20

Question 21

If I^A and I^B are codominant and I^O is recessive, which alleles could the offspring express?

Answer 21

AB, A, B, O

Question 22

What is meant by epistasis?

Answer 22

Where two non-linked genes interact, with one gene either masking or suppressing the other gene

Question 23

Define two types of epistasis

Answer 23

- Recessive epistasis: where two homozygous recessive alleles mask expression of another allele - Dominant epistasis: where one dominant alleles masks expression of multiple other alleles

Question 24

Punnett square to show an epistasis cross with parental genotypes of AABB and aabb

Answer 24

Question 25

Genotypes BB or Bb allow expression of gene A with genotype bb masks gene A. With this in mind, what % of the offspring will have gene A masked?

Answer 25

25%

Question 26

What is the chi-squared test?

Answer 26

A statistical test to find out whether the difference between observed and expected data is due to chance or a real effect

Question 27

Criteria for chi-squared test

Answer 27

- Data placed in discrete categories (nominal) - Large sample size - Only raw data count allowed i.e. not percentages