Genotype, Phenotype and Inheritance

Question 1

Define genotype.

Answer 1

The entire genetic makeup of an individual.

Question 2

Define phenotype.

Answer 2

The physical characteristics that are expressed.

Question 3

Define homozygous.

Answer 3

When an individual have two alleles of a gene that are the same.

Question 4

Define heterozygous.

Answer 4

When an individual have two alleles of a gene that are different.

Question 5

Define hemizygous.

Answer 5

Only one allele of a gene. This is usually on the X chromosome (Males only!)

Question 6

Define dominant.

Answer 6

A dominant allele determines the phenotype. This means that in a heterozygote the dominant allele determines the phenotype.

Question 7

Define recessive.

Answer 7

A recessive allele doesn’t usually determine the phenotype. In a heterozygote the recessive allele does not determine the phenotype.

Question 8

Explain the difference between gene, genotype and alleles.

Answer 8

If a gene is ‘A’ the genotype will A1A2 or AA. The alleles will be A1 and A2.

Question 9

Explain co-dominance.

Answer 9

For example in blood type which is determined by gene I there are three alleles: A, B and O or: IA, IB, and I0.
Both A and B are dominant over 0. However neither allele A or B are dominant over each other. This means they are co-dominant. This produces a produce a new phenotype.

Question 10

What is the genotype and phenotype of blood group A?

Answer 10

Genotype: IAIA or IAI0
Phenotype: A

Question 11

What is the genotype and phenotype of blood group B?

Answer 11

Genotype: IBIB or IBI0
Phenotype: B

Question 12

What is the genotype and phenotype of blood group AB?

Answer 12

Genotype: IAIB
Phenotype: AB

Question 13

What is the genotype and phenotype of blood group 0?

Answer 13

Genotype: I0I0
Phenotype: 0

Question 14

What is a autosomal recessive disease?

Answer 14

A disease that is only expressed when the recessive allele can be expressed.

Question 15

Will a heterozygote be affected by an autosomal recessive disease?

Answer 15

No heterozygotes are unaffected.

Question 16

Are males and females equally affected?

Answer 16

Yes they are.

Question 17

What is the chance of two heterozygote autosomal recessive to have affected offspring?

Answer 17

25%.

Question 18

Give an example of an autosomal recessive disease.

Answer 18

Cystic fibrosis.

Question 19

Can an autosomal recessive disease skip a generation?

Answer 19

Yes it can. It can seems to come out of no where.

Question 20

What is autosomal dominant.

Answer 20

When heterozygotes are affected. The dominant allele determine the phenotype.

Question 21

Can homozygotes have an autosomal dominant disease?

Answer 21

Yes in case they have both the dominant alleles that means. This is however very rare because diseases in a homozygote are usually very severe so it is not usually suitable for life.

Question 22

Give an example of an autosomal dominant disease?

Answer 22

Huntington’s Disease.

Question 23

Can an autosomal dominant disease skip a generation?

Answer 23

No it can’t. This is because it can’t be carried without being expressed.

Question 24

What is an X-linked recessive disease?

Answer 24

A disease where the allele is locate on the X chromosome.

Question 25

Give some features of x-linked recessive.

Answer 25

Disease is more common in males. This is because males only have one X chromosome whereas females have two. This mean that males cannot have a dominant allele to ‘overthrow’ the recessive allele.

Question 26

What is the chance of a female carrier to have an affected son?

Answer 26

50%

Question 27

What is the chance of an affected male to have an affected son?

Answer 27

0% the X-chromosome from a father to a son can’t give X-chromosome to son, only Y-chromosome.

Question 28

How does mitochondrial inheritance work?

Answer 28

Al individuals will inherit the disease from their mother, never from father.

Question 29

What does polygenic inheritance entail?

Answer 29

That more than one gene can be involved in producing a phenotype.

Question 30

What are linked genes? (regarding polygenic inheritance)

Answer 30

Genes on the same chromosome.

Question 31

What are non-linked genes? (regarding polygenic inheritance)

Answer 31

Genes that are on different chromosomes.

Question 32

How do non-linked and linked genes differ more?

Answer 32

Linked genes do not show independent assortment at meiosis since they are on the same chromosome. However recombination can occur.

Question 33

What is recombination frequency in linked genes dependent on?

Answer 33

The distance between the genes. Tightly linked genes are less likely to undergo recombination.