Topic 9: Mutations

Question 1

Define mutation and mutagenesis

Answer 1

Mutation: heritable altertion in a gene or chromosome, change in sequence of nucleotides that make up a gene
Mutagenesis: process of creating mutations

Question 2

Explain and describe consequences of single nucleotide, and other small mutations

Answer 2

1. Insertion, deletion, duplication, inversion
2. synonymous/neutral mutations: have no effect: diff base pair that codes for same protein substituted
3. Missense: amino acid code is changed due to bp substitution
4. Nonsense mutations: form trunchated proteins as stop codon is substitued instead of bp
5. Single bp deletion/addition: leads to frameshift, if mutiples of 3 bp indel- no frameshift. Frameshift- AAcid mutation occurs, otherwise mostly not affected

Question 3

Describe how fork slippage and transposable elements cause mutations

Answer 3

Fork slippage: sequence of repetitive nucleotides at site of replication
Transposable elements: change in position of DNA sequence

Question 4

Describe potential consequences of mutations at gene level

Answer 4

addition/loss of protein function

Question 5

Desribe numerical and structural chromosomal abnormalities

Answer 5

Single: deletion, duplication, inversion( stretch on chromosome is inverted on same chromosome)
Insertion: deleted part of one chromosome inserted into another chromosome.
Reciprocal translocation: stretch on chromosome is swapped with another chromosome

Question 6

Describe consequences of chromosomal mutations

Answer 6

1. Cri du chat syndrome: deletino of short arm on chr 5. Low weight, growth retardation, small head, widely spaced eyes, cardiac defects, cat crying sound
2. Robertsonian tranlocation: chromosome breaks at centromere 13, 14,15,21,22 bfeore re-fusing. Affects acrocentric chromosome. May cause chromosomal addition/deletion: trisomy etc

Question 7

Desribe what numerical abnormalities are

Answer 7

1. Polyploidy: gains haploid set of chromosomes( total 69), due to polyspermy( egg fertilised by more than 1 sperm), causes many miscarriages. Extra copies of all genes.
2. Aneuploidy: loss and gain of single chromosome due to non disjunction in meiosis( incorrect separation of chromosomes to opposite sides). Leads to trisomy( down sydrome, patau, edwards, klinefelter) or monsomy(turner, only 1 X chromosome).

Question 8

Give and describe an example each of diseases caused by trisomy and monosomy

Answer 8

1. Trisomy: Patau syndrome, trisomy chr 13. Intellectual disability and motor changes. Changed face shape, cleft palate, extra fingers, deformed feet with prominent heel, kidney and heart defect.
2. Monosomy: Turner syndrome, female with short neck and webbed appearances, swollen hands and feet, soft nails that turn upwards, low hairline at back of neck.

Question 9

Describe reciprocal and robertsonian translocation, and their potential conseuences in cells?

Answer 9

Reciprocal translocation: stretch on chromosome is swapped with another chromosome
Robertosonian translocation: breaks off at centromere and attaches to another chromosome, forms very long or very short chromosomes.
Potential consequences: can be balanced( no genetic information is lost and no phenotypic changes present), or unbalanced( genetic information lost)

Question 10

Describe cytogenetic testing

Answer 10

Analysing cells and DNA to look for chromosomal abnormalities for diagnosis of sydrome or pregnancy loss, assess future reproductive risks
Reasons to refer: recurrent foetal loss, birth defect, abnormal sexual development, infertility etc