Topic 14: DNA and Chromosomal Mutations

Question 1

What is the definition of mutation?

Answer 1

Change in the nucleotide sequence in DNA

Question 2

What is the definition of mutagenesis?

Answer 2

Process of mutation generation

Question 3

What are 2 types of single nucleotide changes?

Answer 3

1. Transition

2. Transversion

Question 4

What is transition?

Answer 4

Change to same type of base

purine to purine - A/G
pyrimidine to pyrimidine - C/T

Question 5

What is transversion?

Answer 5

Change to different types of base

Purine (A/G) to pyrimidine (C/T)

Question 6

What are 4 possible consequences of single nucleotide changes?

Answer 6

Change gene product (polypeptide or RNA)
Change amount of gene product
Change polypeptide length
No effect

Question 7

What is missense mutation?

Answer 7

Single nucleotide change resulting in change of amino acid

Question 8

What is an example of a missense mutation?

Answer 8

Sickle cell disease

Mutation in codon 7 of HBB: GAG>GTG = Glu>Val

Question 9

What is a neutral or silent mutation?

Answer 9

Single nucleotide change resulting in no phenotypic change

Question 10

What is an example of a silent mutation?

Answer 10

Mutation in codon 7 of HBB

GAG>GAA = Glu>Glu

Question 11

What is synonymous mutation?

Answer 11

Single nucleotide change results in no effect as it codes for same amino acid

Question 12

What is non synonymous mutation?

Answer 12

Single nucleotide change that results in change in amino acid

Question 13

What is frameshift mutation?

Answer 13

Deletion or insertion leads to change in reading frame

Question 14

What is mutation of stop codon?

Answer 14

Single nucleotide change in stop codon making it another amino acid

Question 15

What is the result of frame shift mutations or mutations of the stop codon?

Answer 15

Change in polypeptide length

Question 16

What is nonsense mutation?

Answer 16

Single nucleotide change leading to creation of stop codon

Question 17

What is the result of nonsense mutation?

Answer 17

Change in polypeptide length

Question 18

What is the effect of mutations affecting regulatory sequences?

Answer 18

Amount of gene product

Question 19

What is the effect of multi nucleotide deletion/insertion?

Answer 19

Deletion/insertion of nucleotides other than multiples of 3bp lead to frame shifts

Question 20

How does fork slippage cause mutations?

Answer 20

Fork slippage can lead to backward slippage causing trinucleotide expansions

Question 21

What is an example of trinucleotide repeat disorders?

Answer 21

CAG repeats in HTT gene leads to polyglutamine repeats in Huntington protein

> 35 repeats = disease

Question 22

What are transposable elements?

Answer 22

Specific repetitive DNA sequences that move

Question 23

How do transposable elements cause mutations?

Answer 23

1. No effect
2. Inactivate - disrupt gene sequence
3. Reactivate - move out after disruption
4. Alter gene expression

Question 24

What are 2 types of chromosomal abnormalities?

Answer 24

Numerical and structural

Question 25

What are 3 types of numerical abnormalities in chromosomes?

Answer 25

Polyploidy Aneuploidy Mosaicism

Question 26

What is polyploidy?

Answer 26

Gaining haploid set of chromosomes = triploidy 69 chromosomes Eg polyspermy when 2 sperms fertilize one egg

Question 27

What is aneuploidy?

Answer 27

Loss or gain of whole chromosomes causing trisomies and mono somites

Question 28

What is aneuploidy caused by?

Answer 28

Meiotic non disjunction

Question 29

What are 4 examples of trisomies?

Answer 29

``` Down syndrome (21) Patau syndrome (13) Edwards syndrome (18) Klinefelter syndrome (XXY) ```

Question 30

What is an example of a monosomy?

Answer 30

Turner syndrome (X)

Question 31

What is mosaicism?

Answer 31

Presence of 2 or more cell lines in an individual throughout the body or tissue specific

Question 32

What is mosaicism caused by?

Answer 32

Mitotic non disjunction

Question 33

What are 5 structural abnormalities of chromosomes?

Answer 33

``` Deletion Duplication Inversion Substitution Translocation Isochromosomes Ring chromosomes Marker chromosomes ```

Question 34

What is reciprocal translocation?

Answer 34

Part of a chromosome changed places with part of another chromosome

Question 35

What is the meiotic consequence of reciprocal translocation?

Answer 35

Quadrivalent forms - 6 possible outcomes leading to 2 balanced and 4 unbalanced gametes

Question 36

What is Robertsonian translocation?

Answer 36

2 acrocentric chromosomes fuse, leading to no p arms, only q arm, total only 45 chromosomes

Question 37

What is the meiotic consequence of Robertsonian translocation?

Answer 37

Trivalent will form, segregation has 6 outcomes, risk of trisomy is 2/6 monosomy is 2/6, normal 1/6 and balanced carrier is 1/6

Question 38

What is cytogenetic analysis?

Answer 38

Study of chromosomes and their structure

Question 39

What are the 4 reasons why we do cytogenetic testing?

Answer 39

Accurate diagnosis and prognosis of clinical problems Better clinical management Assess future reproductive risks Prenatal diagnosis