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 organisms 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 (position) 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 characteristics only appear 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 characteristics is controlled by a single gene

Question 10

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

Question 11

What % of these offspring will express the characteristic determined by allele G

Answer 11

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

Question 12

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

Question 13

What % of these offspring should express the characteristics determined by allele G

Answer 13

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

Question 14

Draw an example of a genetic diagram

Question 15

Define dihybrid inheritance

Answer 15

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

Question 16

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

Question 17

How many of these offspring should have the same phenotype as their parents?

Answer 17

9 (out of 16)

6 will match their parents on one characteristic, but differ on the other

1 will differ on both characteristics

Question 18

What is meant by sex-linkage?

Answer 18

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

Question 19

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

Answer 19

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 20

Which parent do males inherit sex-linked characteristics from?

Answer 20

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 21

Draw a Punnett square to show a sex-linked cross with parental genotypes of XHXh and XHY

Question 22

Describe the four possible phenotypes of these offspring

Answer 22

Normal female, carrier female, normal male, affected male

Question 23

What is meant by autosomal linkage

Answer 23

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 24

Draw a Punnett square to show a multiple alleles cross with parental genotypes of IAIO and IBIO

Question 25

If IA and IB are codominant and IO is recessive, which alleles could the offspring express?

Answer 25

AB,A,B,O

Question 26

What is meant by epistasis

Answer 26

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

Question 27

Define the two types of epistatsis

Answer 27

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 28

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

Question 29

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

Answer 29

25%

Question 30

What is the chi-square test?

Answer 30

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

Question 31

What are the criteria for the chi-squared test?

Answer 31

• data placed in discrete categories
  -large sample size
  -only raw count data allowed
  -No data values equal zero

Question 32

How is a chi square test performed

Answer 32

The formula results in a number, which is then compared to a critical value (for the corresponding degrees of freedom). 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 33

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

Answer 33

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