Mutations

Question 1

What is a the definition of a mutation?

Answer 1

a heritable alteration in a gene or chromosome (a change in the sequence of nucleotides)

the process that produces the mutation

Question 2

What are transposable elements?

Answer 2

Specific DNA sequences (>1 gene)
Supernumerary (many copies)
• Always contained within other DNA molecule; never in a free form
• Move (transpose) as a discrete unit to random sites and insertionally inactivate target gene or activate transcription in wrong cells

“jumping genes”
-small genes less easily affected

Question 3

List some types of micromutations

Answer 3

deletions, duplications, inversions, substitutions- can cause frame shifts

Question 4

List some types of macromutations

Answer 4

deletion, duplication, inversions, substitutions, translocation- affects chromosomes

Question 5

What is a transition?

Answer 5

purine to purine or pyrimidine to pyrimidine mutation

Question 6

What is a transversion?

Answer 6

purine to pyrimidine or vice versa mutation

Question 7

What is a missense mutation?

Answer 7

amino acid changes

Question 8

What is a nonsense mutation?

Answer 8

stop codon inserted

Question 9

What is a silent mutation?

Answer 9

no change in amino acid sequence

Question 10

What is a synonymous mutation?

Answer 10

no effect but within the coding region

Question 11

How can a mutation change the amount of gene product?

Answer 11

mutation affects transcription or translation (Promotor regions, splicing, reducing mRNA stability)

Question 12

What is the difference between a germ line and somatic mutation?

Answer 12

germ line mutations occur in eggs or sperm, passed on to offspring and have bodywide consequences. somatic mutations occur in a body cell and are localised.

Question 13

Why are mutations to RNA less dangerous than mutations to DNA?

Answer 13

The long-term effects on the organism whose cell has made a transcription/translation error will not be the as bad as if the mistake was in the genome itself

The cell will be making multiple copies of this RNA, and it is unlikely that it will make the same mistake again in exactly the same place

RNAs are quickly degraded, so the ‘bad’ copy of the RNA will be quickly removed

RNAs are not inherited molecules passed down from generation to generation. Therefore, making an incorrect copy of an RNA molecule is not going to be as consequential as making a change in the genome,
which is lasting and permanent

Question 14

How can mutations affect mitochondria?

Answer 14

Mitochondrial DNA can suffer germ line and somatic mutations

Mitochondria are ‘energy producers’. Conditions caused by germ line mutations in mitochondrial DNA often involve multiple organ systems. The effects of these conditions are most pronounced in
organs and tissues that require a lot of energy (such as the heart, brain, and muscles

Mitochondrial DNA is also prone to somatic mutations, which are not inherited. Because mitochondrial DNA has a limited ability to repair itself when it is damaged, these mutations tend to build up over time

Question 15

Why are spontaneous mutations giving rise to autosomal recessive diseases unlikely?

Answer 15

mutations must be in the same place on two separate chromosomes, which is very unlikely

Question 16

How can errors in mitosis lead to chromosomal mutation?

Answer 16

If the duplicate chromosomes do not pair properly at the metaphase plate, the pair will not move properly to each pole during anaphase (anaphase lag). This results in one cell having two copies of the chromosome, while
the other cell has none

This type of error is normally fatal to the daughter cell lacking a copy of a chromosome

Cells receiving two copies of a chromosome will have an increase in expression of the genes contained on the extra chromosome. If the genes function to slow growth, the extra copy may be fatal to the cell. However, if
the genes promote growth, the cell may grow uncontrollably, leading to cancer. Other effects will depend on the nature of the additional gene

Question 17

In females, where do primordial germ cells arrest meiosis?

Answer 17

Once PGCs arrive in the fetal female gonad they differentiate into oogonia and undergo further mitosis. The majority continue in mitosis but some enter prophase of meiosis 1 and arrest their cell division –
these are now primary oocytes.

By birth all surviving primary oocytes have entered prophase of meiosis 1. A primary oocyte surrounded by
flattened epithelial cells is called a Primordial Follicle

At birth there are approx 800,000 Primary oocytes, many degenerate so that at puberty about 40,000 are left and less than 500 will be ovulated.

Note, meiosis is only complete on fertilisation as primary oocytes arrest in metaphase 2.

Question 18

In males, what happens once PGC’s arrive in the male gonad?

Answer 18

They rain until puberty. At this point spermatogenesis begins.

Question 19

Why is the mutation rate higher in spermatogenesis?

Answer 19

mutation rate vastly higher as spermatogenesis involves a lot more mutations, and spermatogonial germ cells are continuously active in adult men

Question 20

What features would allow a germ cell mutation to be inheritable?

Answer 20

It would not be lethal to the gamete
– It would not impair gamete function
– It would not be lethal at fertilisation
– It would allow the production of a viable adult with normal reproductive capacity