Modes of inheritance

Question 1

How many genes and chromosomes are there in humans?

Answer 1

25000 genes, 23 pairs of chromosomes. 22 autosomal pairs with one pair of sex chromosomes.

Question 2

What are the 3 types of genetic disorders?

Answer 2

1. Single gene disorders
2. Chromosomal disorders
3. Complex disorders

Question 3

What is a dominant autosomal disorder?

Answer 3

A characteristic is dominant if it manifests in a heterozygote.

Question 4

What are the 3 types of dominant autosomal disorders?

Answer 4

1. Gain of function - gene makes a protein with a new function
2. Dominant negative effect - Mutated form interferes with the activity of proteins e.g. dimers or multimers that reduce activity.
3. Insufficient - mutation in one gene results in 1/2 the amount of protein produced which is not enough for normal function.

Question 5

What is an autosomal recessive disorder?

Answer 5

A disorder that requires two copies of the abnormal gene for the disease to develop. Tend to be loss of function disorders.

Question 6

Give an example of an autosomal recessive and dominant disorder

Answer 6

Recessive - cystic fibrosis

Dominant - Huntingdons

Question 7

Example of an X-linked disorder

Answer 7

Haemophilia

Question 8

How are mitochondrial disorders inherited and why?

Answer 8

Always maternally inherited, This is because mitochondria come from egg cell which is from mother. Mutations in mDNA can affect mitochondria function.

Question 9

Why are mitochondrial disorders variable even within a family?

Answer 9

There are many mitochondria within each cell. Random segregation causes changes in the ratio between wildtype and mutated mitochondria which affects severity.

The severity of the mutation also affects the severity of the disorder.