Genotype, Phenotype and Inheritance

Question 1

What is the difference between Genotype and Phenotype?

Answer 1

Genotype - Genetic make-up (genes on chromosomes in the nucleus)
Phenotype - Physical characteristics (proteins in the cytoplasm)

Question 2

What is the relationship between alleles and genes?

Answer 2

• There is one maternal and one paternal copy of each gene
• Each individual has two alleles of a gene
• There are many alleles of a gene within a population

Question 3

Define homozygous, heterozygous and hemizygous?

Answer 3

Homozygous - two alleles of a gene are the same
Heterozygous - two alleles of a gene are different
Hemizygous - one allele is a gene on the X chromosome (males only)

Question 4

What is the difference between dominant and recessive alleles?

Answer 4

• Dominant allele in a heterozygote determines the phenotype

Recessive - non-dominant allele in a heterozygote

Question 5

What is co-dominance and which phenotype demonstrates this?

Answer 5

• Alleles that are not dominant over each other

- Shown by A and B blood groups

Question 6

State the phenotype and genotype of blood groups

Answer 6

Phenotype - A, B, O

Genotype - Ia, Ib, Io

Question 7

What are unaffected and affected males and females represented by in pedigree analysis?

Answer 7

Male - unfilled square
Female - unfilled circle
Affected - black filled shape

Question 8

What is the pedigree analysis symbol for a carrier and a deceased individual?

Answer 8

Carrier - half black, half white

Deceased - diagonal line from bottom left to top right

Question 9

How are offspring organised in pedigree analysis?

Answer 9

Oldest on the left, youngest on the right

Question 10

Who is unaffected by autosomal recessive inheritance? Give an example of a disease

Answer 10

• Heterozygotes unaffected

- Cystic fibrosis

Question 11

What are both parents who have offspring with autosomal recessive disorder?

Answer 11

• Heterozygous carriers

- Disease can skip generations

Question 12

Describe 2 characteristics of an incidence of autosomal dominant inheritance

Answer 12

• Heterozygotes affected
• At least one parent is affected
• Disease cannot skip a generation

Question 13

Give an example of an autosomal dominant inheritance disorder

Answer 13

Huntingdon’s Disease

Question 14

Who can be affected by an X-linked recessive disease?

Answer 14

• Hemizygous males

- Homozygous females

Question 15

Give 2 characteristics of an X-linked recessive disease

Answer 15

• Disease is more common in males

- Males cannot pass disease to male offspring

Question 16

Give an example of an X-linked recessive disease

Answer 16

Haemophilia A

Question 17

Who is affected by an X-linked dominant disorder?

Answer 17

• Hemizygous males

- Heterozygous females

Question 18

Who can be passed down an X-linked dominant disease from a man?

Answer 18

Only to their daughters

Question 19

Give an example of an X-linked dominant disease

Answer 19

Fragile X Syndrome

Question 20

What type of genetic disease can only be inherited from a mother and why?

Answer 20

• Mitochondrial disease

- Only ova contain mitochondria

Question 21

What is polygenic inheritance? Give an example of this

Answer 21

• More than one gene produces the phenotype

- Albinism

Question 22

State 3 characteristics of polygenic inheritance?

Answer 22

• Genes close together on the same chromosome are linked
• Linked genes do not show independent assortment at meiosis
• Genes that are far apart on a chromosome behave as they are unlinked

Question 23

What is recombination frequency dependent on between linked genes?

Answer 23

It is dependent on the distance between genes

Question 24

Why are Y-linked diseases rare? Give an example of a disease

Answer 24

• Only males are affected

- Infertility