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

Two

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 a recessive allele?

Answer 6

An allele whose characteristic only appears in the phenotype if no dominant allele is present, meaning two must be present

Question 7

What is meant by codominant alleles?

Answer 7

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

Question 8

What is meant by homozygous and heterozygous?

Answer 8

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

Question 9

Define monohybrid inheritance

Answer 9

Where one phenotypic characteristic is controlled by a single gene

Question 10

What percentage of offspring between homozygous dominant and recessive will express the characteristic determined by allele Gg?

Answer 10

100% ; all potential offspring genotypes are Gg

Question 11

What percentage of offspring between heterozygous alleles should express the characteristic determined by allele G?

Answer 11

75% ; only one combination results in expression of the recessive allele

Question 12

Define dihybrid inheritance

Answer 12

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

Question 13

How many of the offspring between parental genotypes of RrGg and RrGg should have the same phenotype as their parents?

Answer 13

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

Question 14

What is meant by sex-linkage?

Answer 14

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

Question 15

Why are males more likely to express a recessive sex-linked allele?

Answer 15

Most sex-linked alleles are located on the X chromosome. Therefore males only get one copy of the allele, so will express this characteristic even if it’s recessive. Since females get two alleles, this is less likely

Question 16

Which parent do males inherit sex-linked characteristics from?

Answer 16

Their mother, since the 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 17

Describe the four possible phenotypes of these offspring between X^H X^h and X^H Y

Answer 17

Normal female, carrier female, normal male, affected male

Question 18

What is meant by autosomal linkage?

Answer 18

Where two or more genes are located on the same 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 19

What is meant by epistasis?

Answer 19

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

Question 20

Define the two types of epistasis

Answer 20

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

Question 21

What is the chi-squared test?

Answer 21

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

Question 22

What are criteria for the chi-squared test?

Answer 22

• Data placed in discrete categories
• Large sample size
• Only raw count data allowed
• No data values equal zero

Question 23

How is a chi-squared test performed?

Answer 23

The formula results in a number which is then compared to a critical value. If the number is greater than or equal to the critical value, we conclude there is a significant difference between the observed and expected data and that the results did not occur due to chance

Question 24

How can we use a chi-squared test in relation to the content of this topic?

Answer 24

We can compare expected phenotypic ratios with observed ratios to test our understanding of how different genes and alleles are inherited