Week 2

Question 0

List 5 types of chromosome mutations?

Answer 0

Aneuploidy (number)
Duplications (structure)
Deletions (structure)
Translocations (structure)
Inversions (structure)

Question 1

What causes a DNA mutation to occur?

Answer 1

Unrepaired damage to DNA caused by radiation or chemical mutagens

Errors in replication or recombination

Insertion or deletion of segments of DNA by mobile genetic elements

Question 2

Explain meiosis in the context of aneuploidy

Answer 2

Meiosis involves doubling up of genetic information. “Cross over” of genetic material between maternal and paternal chromosomes of the same type. And then the division of genetic material into haploid cells containing half genetic information of a diploid cell and a mix of maternal and paternal DNA.

During meiosis there can be a malfunction in splitting of genetic material, instead of a haploid cell having one copy of the chromosome it can have 0 or 2

Question 3

Give an example aneuploidy

Answer 3

Down’s syndrome (3 copies of chromosome 21, characterised by low iq, folds over the eye, short and broad hands and below average height)

Or 
Klinfelters syndrome (gain of an extra X chromosome, characterised by underdeveloped testes, some breasts, taller than average, low iq)

Or 
Turners syndrome (loss of an X chromosome in females)

Question 4

Discuss structural mutations (duplications, deletions, translocation and aversions)

Overview

Answer 4

All begin with one of more breaks in the chromosome

Whe nether the break occurs, broken ends remain exposed and vulnerable to degradation

Broken ends of a chromosome are “sticky” and can adhere to other broken chromosome ends.
Or information can be deleted

Question 5

Explain chromosome deletion (segment)

Answer 5

It’s deletion of a segment of chromosome

Deletion covering centromere (the spindle fiber which the chromosome is attached to during cell division) leads to loss of a chromosome during meiosis - non-viable offspring
I
Cri-du-chat syndrome: 5p deletion. Prader-Willi syndrome: 15q deletion

Question 6

How does chromosome duplications occur and what is a syndrome that is the result of this?

Answer 6

Doubling of a segment of DNA caused by unequal crossing over

Important role in evolution of multiple genes with related functions

Pallister killian syndrome: 12p duplication

Question 7

Explain chromosome inversions

Answer 7

Segment of a chromosome is cut and then reintegrated in an orientation of 180 degrees from the original orientation

Genetic material is not lost but may be phenotypic consequences when the break points occur within genesis

Question 8

Explain chromosome translocation a

Answer 8

Change in position of chromosome segments to a different location in the genome

Rearrangement of parts between nonhomologous chromosomes (e.g. Part of chr. 17 moves to chr. 20)

Typically affects the gametesi

A lot of illnesses are linked with translocation a including schizophrenia

Question 9

What is a point mutation?

Answer 9

Single base pair substitution

Question 10

What are the two types of point mutation?

Answer 10

Transition mutation ( AT and GC becomes TA and CG) -common

Transversion (AT and TA becomes GC and CG)

Question 11

There are four effects of point mutations what are they?

Answer 11

Missense
Nonsense
Neutral
Silent

Question 12

What is a frameshift mutation?

Answer 12

(Insertions add one or more nucleotide to the DNA - deletions remove one of more nucleotide from the DNA)

If the number of nucleotides inserted or deleted is not divisible by 3 this can cause a frameshift mutation

Normally results in a non-functioning protein

Incorrect amino acids added to the polypeptide chain after the mutation site

Can generate new stop codons = shortened polypeptide

Or read through of the normal stop codon = lengthened polypeptide

Question 13

What is the one gene one polypeptide hypothesis and what is an example of this?

Answer 13

A single gene mutation that alters the function of an enzyme

Phenylketonuria (PKU)

Question 14

Discuss PKU

Answer 14

Recessive mutation in gene for phenylalanine hydroxylase (what breaks down phenylalanine)

PKU has pleiotropic effects as its phenylalanin affects the gene for tyrosine and tyrosine effects levels of dopa and therefore the amount of melanin produced.

Screening for PKU is done with bacterial inhibitions assay (Guthrie test)

Question 15

What is an example of a mongenic disease?

Answer 15

Sickle-cell anaemia

Or

Cystic fibrosis

Question 16

What is sickle cell anaemia?

Answer 16

It’s a mutation in the chemical structure of haemoglobin

Question 17

What are three types of common DNA variation?

Answer 17

SNP: single nucleotide polymorphism
VNTR: variable number tandem repeat
CNV: copy number variants (1000bp+)

Question 18

SNPs can result in three types of change, what are these?

Answer 18

Synonymous (doesn’t result in amino acid change)

Non-synonymous (results in amino acid chance

Non-sense (results in stop codon)

Question 19

VNTPs are subcategorised into 2 families, what are these and how are that defined?

Answer 19

Microsatellite (2-10bp)

Minisatellite (10-60bp)

Question 20

What type of DNA variation is often used in forensics and DNA fingerprinting?

Answer 20

Short nucleotide sequence of tandem repeats (VNTRs)

Question 21

What are CNVs?

Answer 21

Copy number variants = duplications or deletions between 1kb - 5MB

• major cause of structural variation in the genome and account for more between-individual variation than any other form of mutation

Important in terms of evolution as CNVs account got more differences between humans and other organisms than other mutations

They are also a significant contribution to differences in gene expression between individuals.

Question 22

Why are some disease alleles more common than others?

Answer 22

Sequence variants that are directly and overtly cause human diseases are generally rare in the population because they reduce fitness.

However a rare disease allele in one population can become a polymorphism in another if it confers an advantage and therefore increases in frequency

Example: sickle cell anaemia, in Caucasian population is rare and causes a severely debilitating blood disorder, in certain parts of Africa however the same allele is
Polymorphic because it confers resistance to the blood-borne parasite that causes malaria (co-dominance)

Question 23

What is epistasis?

Answer 23

A form a G xG interaction in which one gene masks the phenotypic expression of another

No new phenotypes are produced by this type of gene interaction

Question 24

What does epistatic mean?

Answer 24

A gene which masks another’s gene expression

Question 25

What does hypostatic mean?

Answer 25

A gene whose expression is masked by another

Question 26

What do quantitative traits mean?

Answer 26

Refers to phenotypes that vary in degree and can be attributed to polygenic effects, I.e. Product of two or more genes and their environment.

E.g. Skin colour affected by additive effects of multiple alleles and exposure to the sun

Question 27

Give an example of how environments may influence the expression of genes

Answer 27

Fur colour in Himalayan rabbits

White rabbits that develop dark spots on the coldest parts of their bodies (ears and nose)

All body cells have the same genotype,
Maybe this is a product of environmental influences

Reared rabbits in various heats (hot were all white and colder got darker)