Genotype, Phenotype And Inheritance

Question 1

What is a genotype related to?

Answer 1

Genes on chromosomes in nucleus

Question 2

What is a phenotype related to?

Answer 2

Proteins in cytoplasm

Question 3

What environmental factors can change both the phenotype and genotype?

Answer 3

Radiation
Lifestyle
Mutagens
Diet
Chemicals

Question 4

Name a disease only due to genotypes?

Answer 4

Cystic fibrosis

Question 5

Name 3 diseases that can be both from genotype and environment

Answer 5

Diabetes
Cancer
Heart disease

Question 6

What does homozygous mean?

Answer 6

Two alleles of a gene are the same

Individual is a homozygote

Question 7

What does heterozygous mean?

Answer 7

Two alleles of a gene are different

Individual is a heterozygote

Question 8

What does hemizygous mean?

Answer 8

Only one allele of a gene on X chromosome

Only males

Question 9

What does dominant mean?

Answer 9

Dominant allele in a heterozygote determines the phenotype

Question 10

What does recessive mean?

Answer 10

Non-dominant allele in a heterozygote

Question 11

What is codominance?

Answer 11

When neither allele is dominant over the other

E.g. blood groups A and B

Question 12

How are the following shown in a pedigree:

• male
• affected male
• female
• affected female
• carrier male (x2)
• unknown sex
• deceased

Answer 12

Male: square
Affected male: shaded in square
Female: circle
Affected female: shaded in circle
Carrier male: half shaded square or square with shaded circle
Unknown sex: diamond
Deceased: square/circle with line diagonal through

Question 13

What happens in autosomal recessive inheritance?

Answer 13

Heterozygotes unaffected
Males and females equally affected
2 heterozygotes have 25% chance of having affected offspring
2 homozygous individuals will have affected offspring only
Disease can skip generations
Both parents of affected individual are heterozygous carriers
E.g. cystic fibrosis

Question 14

What happens in autosomal dominant inheritance?

Answer 14

Heterozygotes affected
Males and females equally affected
Disease rarely found in homozygous state as it is not viable for life
Every affected individual has 50% chance of having affected offspring
Every affected individual will have at least one affected parent
Cannot skip a generation
E.g. Huntington’s disease

Question 15

What is X-linked recessive inheritance?

Answer 15

Hemizygous males and homozygous females affected
Disease more common in males
Heterozygous female carrier has 50% chance of having affected sons
Affected males cannot give trait to sons
E.g. haemophilia A

Question 16

What happens in X-linked dominant inheritance?

Answer 16

Hemizygous males and heterozygous females affected
Heterozygous affected female has 50% chance of having affected offspring
Affected males cannot give trait to sons but will give it to all daughters
E.g. Rett syndrome

Question 17

What is mitochondrial inheritance?

Answer 17

All individuals inherit from their mother

Mitochondria of sperm either do not enter the egg or it is destroyed

Question 18

Polygenic inheritance

Answer 18

Genes on the same chromosomes are linked
Genes on different chromosomes are said to be not linked
Linked genes do not show independent assortment at Meiosis
Ratio will not be 1:1:1:1, depends on crossing over in Meiosis
Crossing over frequency between two linked genes is dependent on distance between 2 genes
Genes close together are tightly linked