L20 Genetic Variation

Question 1

What is the difference between genetic mutation and genetic variation?

Answer 1

If the altered base sequence occurs in less than 1% of the population, it is a mutation.

If the altered base sequence occurs in more than 1%, it is genetic variation. These probably began as a mutation but aided survival.

Question 2

Which of the following (if any) are correct?

a) Mutation changes the DNA sequence whereas genetic variation changes the RNA sequence.
b) Both genetic variation and mutation change DNA and protein sequences.
c) Both genetic variation and mutation are harmful and may cause disease.
d) There is basically no difference between mutation and genetic variation.

Answer 2

b and d are correct.

Why is d correct?
Basically no difference. The only difference is in the size of the affected population. A mutation occurs in individuals, genetic variation is a distinct trait of a population.

Question 3

True or false: Cancer susceptibility, progeria (accelerated aging), neurological defects, and immunodeficiency are all potential consequences when genetic damage isn’t properly repaired.

Answer 3

True

Question 4

A mutation is a __?__ change in DNA sequence or chromosome number, form or structure.

Answer 4

hereditable

Question 5

What is recombination?

Answer 5

Genetic crossover that occurs during meiosis

Question 6

What is a missense mutation?

Answer 6

A change in the amino acid sequence that doesn’t affect the overall length of the chain.

Caused by point mutations and frameshifts.

May or may not affect protein and function.

If function is affected, this could be a loss or a gain of function.

Examples include haemophilia and achondroplasia.

Question 7

What is non-sense mutation?

Answer 7

A change in the nucleotide sequence that results in a premature stop codon.

Caused by point mutations and frameshifts.

Usually results in a non-functional protein as protein synthesis is terminated too early to form a good protein.

Question 8

What are insertion/deletion mutations?

Answer 8

Removal of 1 to several million nucleotides.

Small deletions often cause frame shifts that result in missense or nonsense mutations.

Question 9

What are expanding trinucleotide repeats?

Answer 9

Simple bits of sequence (with three nucleotides) repeated lots of times, one after the other.

e.g.
…AG-CAG-CAG-CAG-GT…

Question 10

Huntington’s disease is caused by which type of genetic mutation?

Answer 10

Expanding trinucleotide repeats

CAG repeats encode a polyglutamine region in a number of protein. In the IT15 gene, the coding region contains 6-35 glutamine repeats.

36 or above causes Huntington’s disease.

Question 11

Fragile X syndrome is caused by which type of genetic mutation?

Answer 11

Expanding trinucleotide repeats

Question 12

Kennedy disease is caused by which type of genetic mutation?

Answer 12

Expanding trinucleotide repeats

Question 13

Myotonic Dystrophy is caused by which type of genetic mutation?

Answer 13

Expanding trinucleotide repeats

Question 14

What are transposons?

Answer 14

A type of genetic mutation in which sequences of DNA can ‘jump’ around the genome.

Often repeated regularly throughout the genome and act as recombination hotspots.

Can be retrotransposons, DNA transposons, or Alu repeats.

Question 15

What is a retrotransposon?

Answer 15

A type of transposon mutation (mobile genetic element).

Similar to ‘copy and paste’.

The sequence exhibits an RNA phase prior to insertion into the genome.

Question 16

What is a DNA transposon?

Answer 16

A type of transposon mutation (mobile genetic element).

Similar to ‘cut and paste’.

Remove the transposon and move it elsewhere in the genome.

Question 17

What are Alu repeats?

Answer 17

The most abundant type of transposon mutation (mobile genetic element).

LDL receptor has a large number of Alu repeats, which may be responsible for the large number of pathogenic deletions in this 45 kb gene

LDL receptor removes ‘bad’ cholesterol from the body (FH, atherosclerosis)

Question 18

What is the relationship between genes Hb A and Hb S?

Answer 18

Hb A is the normal haemoglobin gene. Those with 2 Hb A genes are susceptible to malaria.

Hb S is the sickle cell gene. Those with 2 Hb S genes will likely die from sickle cell disease.

Carriers of 1 Hb A (normal) and 1 Hb S (sickle cell) gene are more likely to be immune to malaria, and they do not suffer from sickle cell disease.

This is an example of selective pressure.

Question 19

What is selective pressure?

Answer 19

Selective pressure relates to natural selection. It describes any cause that reduces reproductive success in a portion of a population.

E.g. malaria and sickle cell. Only those with one normal gene and one sickle cell gene survive. Therefore Malaria and sickle cell disease are causes of selective pressure.

Question 20

What is haploinsufficiency?

Answer 20

We should all get 2 copies of a gene - 1 from mum, 1 from dad.

Haploinsufficiency is when one copy is deleted, or inactivated
by a mutation, so you only have one copy functioning!

Haploinsuffiency means one functional gene on its own is not enough.

Question 21

What causes alpha-thalassemia?

Answer 21

Haploinsufficiency: Alpha-globin chain is affected by mutation that means haemoglobin cannot be made properly. This results in alpha-thalassemia.

If the beta-globin chain is affected, it results in beta-thalassemia.