Topic 3.4: Inheritance

Question 1

Define law of segregation

Answer 1

Law of Segregation: When gametes form, alleles are separated so that each gamete carries only one allele for each gene

Question 2

Define law of independent assortment

Answer 2

Law of Independent Assortment: The segregation of alleles for one gene occurs independently to that of any other gene*

Question 3

Define principle of dominance

Answer 3

Principle of Dominance: Recessive alleles will be masked by dominant alleles†

Question 4

Define gametes

Answer 4

Gametes are haploid sex cells formed by the process of meiosis – males produce sperm and females produce ova

Question 5

Define genotype

Answer 5

The gene composition (i.e. allele combination) for a specific trait is referred to as the genotype

Question 6

Define phenotype

Answer 6

The observable characteristics of a specific trait (i.e. the physical expression) is referred to as the phenotype

Question 7

Define co-dominance

Answer 7

Co-dominance occurs when pairs of alleles are both expressed equally in the phenotype of a heterozygous individual

Question 8

How to determine if a disease is autosomal dominant?

Answer 8

If both parents are affected and an offspring is unaffected, the trait must be dominant (parents are both heterozygous)
All affected individuals must have at least one affected parent
If both parents are unaffected, all offspring must be unaffected (homozygous recessive)

Question 9

How to determine if a disease is autosomal recessive?

Answer 9

If both parents are unaffected and an offspring is affected, the trait must be recessive (parents are heterozygous carriers)
If both parents show a trait, all offspring must also exhibit the trait (homozygous recessive)

Question 10

How to determine if a disease is X-linked dominant?

Answer 10

If a male shows a trait, so too must all daughters as well as his mother
An unaffected mother cannot have affected sons (or an affected father)
X-linked dominant traits tend to be more common in females (this is not sufficient evidence though)

Question 11

How to determine if a disease is X-linked recessive?

Answer 11

If a female shows a trait, so too must all sons as well as her father
An unaffected mother can have affected sons if she is a carrier (heterozygous)
X-linked recessive traits tend to be more common in males (this is not sufficient evidence though)

Question 12

Define epistasis

Answer 12

Epistasis describes a condition whereby one gene controls the expression of another gene