Single genes and disorders

Question 1

Define:
Allele
Genotype
Phenotype

Answer 1

Allele: one of two or more alternative forms of a gene

Genotype: genetic constitution of an organism

Phenotype: Observable properties of an organism produced by a combination of genotype and environment

Question 2

What is a mutation?

Nonsense? Missense? Synonymous? Point?

Answer 2

Alteration in DNA or chromosome sequence or structure. The sources of alleles and genetic variation.

Nonsense - change in sequence coding for a stop codon
Missense - change to amino acid sequence of protein
Synonymous - base substitution but no change to amino acid
Point - single base substitution

Question 3

What can an insertion or deletion lead to?

Answer 3

Can lead to a frameshift mutation which throws off all the codons for the amino acids.

Question 4

How can a mutation in an intron have an effect?

Answer 4

A gene being transcribed has regulatory points where proteins bind and if these change, the proteins will not bind and this affects transcription.

Question 5

What is a homozygote?

A heterozygote?

Answer 5

Homozygote = a diploid organism having the same alleles at one or more genes

Heterozygote = a diploid organism having different alleles at one or more genes

Question 6

What is a haploinsufficent gene?

Answer 6

The heterozygote makes 50% of normal level gene product but this is not enough for normal function.

Question 7

What are the two types of autosomal inheritance?

Answer 7

Dominant and recessive

Question 8

Give some rules on inheritance patterns in autosomal dominant inheritance

Answer 8

• Males and females affected equally

- Probability of an affected child is 50% is one parent is homozygous recessive and the other is heterozygous dominant

Question 9

Give some rules on Sex (X) linked recessive inheritance

Answer 9

• More frequent in males as they have only one X chromosome
• Cannot be passed from father to son as Y chromosome comes from father
• All daughters of affected fathers are carriers
• By probability, half the sons of a carrier will be affected and half their daughters will be carriers.

Question 10

Give a point on multifactorial inheritance

Answer 10

Most common traits are multifactorial: arising from the action of two or more genes and interaction between genes and the environment.