inheritence

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 an 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 characteristic only appears in the phenotype if no dominant allele is present, meaning two most 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

When one phenotypic characteristic is controlled by a single gene.

Question 10

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

Answer 10

G G
g Gg Gg
g Gg 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.

Answer 12

G g
G GG Gg
g Gg gg

Question 13

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

Answer 13

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

Question 14

Define dihybrid inheritence.

Answer 14

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

Question 15

What is meant by sex-linkage?

Answer 15

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

Question 16

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

Answer 16

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 its recessive. Since females get two alleles, this is less likely.

Question 17

Which parent do males inherit sex-linked characteristics from?

Answer 17

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 18

What is meant by autosomal linkage?

Answer 18

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 19

Where 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 asks 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 the criteria for the chi-squared test?

Answer 22

Data placed in discrete categories.
Large sample size.
Only raw count data allowed i.e. not percentages.
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 (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 the 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 inheritance?

Answer 24

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