Chapter 17 - Inherited Change

Question 1

Genotype def.

Answer 1

The genetic constitution of an organism

Question 2

Phenotype def.

Answer 2

The expression of the genes and its interaction with the environment

Question 3

Homozygous def.

Answer 3

A pair of chromosomes carrying the same the same alleles for a single gene

Question 4

Heterozygous def.

Answer 4

A lair of homologous chromosomes carrying two different alleles for a single gene

Question 5

Recessive allele def.

Answer 5

An allele only expressed if no dominant allele is present

Question 6

Dominant allele def.

Answer 6

An allele that will always be expressed in the phenotype

Question 7

Codominant def.

Answer 7

Both alleles are equally dominant and expressed in the phenotype

Question 8

Multiple alleles def.

Answer 8

More than two alleles for a single gene

Question 9

Sex linkage def.

Answer 9

A gene who’s locus is in the X chromosome

Question 10

Autosomal linkage def.

Answer 10

Genes that are located on the same chromosome

Question 11

Epistasis def.

Answer 11

When one gene masks or modifies the expression of a different gene on a different locus

Question 12

Monohybrid def.

Answer 12

Genetic inheritance cross if characteristics determined by one gene

Question 13

Dihybrid def.

Answer 13

Genetic inheritance cross for a characteristic determined by two genes

Question 14

Why do the actual phenotype observations differ from the predicted phenotypic ratios from tue dihybrid cross

Answer 14

• Gamete fusion
• Small sample sizes can lead to skewed ratios whilst larger samples minimise these random effects
• crossing over can change the allele combinations by separating the linked genes

Question 15

How many alleles of a specific gene can an individual hold

Answer 15

2

Question 16

Suggest one reason why the expected phenotype ratio may differ from the actual ratio

Answer 16

• crossing over during meiosis’s as a new combination of gametes will produce

Question 17

What are the effects of crossing over on autosomal linkage

Answer 17

• Crossing over seperates linked genes.
• fewer recombinant offspring tend to be produced (offspring that have a different combination of alleles from their parents due to crossing over) so less genetic variation being introduced from crossing over when genes are linked.
• The probability of linked genes being separated during crossing over is inversely proportional to how close they are on a chromosome i.e., the closer the genes, the more likely they will be inherited together.

Question 18

What is a hypostatic gene

Answer 18

The gene whose expression is blocked by another gene

Question 19

What is an epistatic gene

Answer 19

The gene whose allele affects the expression of the hypostatic gene

Question 20

Two types of epistatic interactions and what occurs during them

Answer 20

• recessive epistasis - occurs when the epistatic gene must be homozygous recessive to block the expression of the hypostatic gene
• dominant epistasis - Occurs when the epistatic gene is dominant and actively modifies or blocks the expression of the hypostatic gene.

Question 21

Two types of epistatic interactions and what occurs during them

Answer 21

• recessive epistasis - occurs when the epistatic gene must be homozygous recessive to block the expression of the hypostatic gene
• dominant epistasis - Occurs when the epistatic gene is dominant and actively modifies or blocks the expression of the hypostatic gene.

Question 22

Know how to do chi squared