genetics

Question 1

When does DNA replication occur?

Answer 1

During S phase

Question 2

Define polymorphism

Answer 2

Any variation in the human genome that has a population frequency of greater than 1% or any variation in the human genome that doesn’t cause a disease in its own right but may predispose to a common disease

Question 3

How is a chromosome recognised?

Answer 3

• banding pattern with specific stains
• position of centromere
• length

Question 4

Describe balanced chromosome rearrangement

Answer 4

All the chromosomal material is present but in a rearranged order

Question 5

Describe unbalanced chromosome rearrangement

Answer 5

Extra or missing chromosomal material, usually 1 or 3 copies of some of the genome

Question 6

What is aneuploidy?

Answer 6

Whole extra or missing chromosome

Question 7

Describe translocation

Answer 7

Rearrangement of chromosomes

Question 8

Describe robertsonian translocation

Answer 8

Two acrocentric chromosomes stuck end to end, increased risk of trisomy in a pregnancy

Question 9

What occurs in trisomy 14?

Answer 9

Miscarriage

Question 10

What occurs in trisomy 21?

Answer 10

Down syndrome

Question 11

What occurs in trisomy 19?

Answer 11

Edwards syndrome 47XY +18

Question 12

Why is x chromosome aneuploidy better tolerated by woman?

Answer 12

Due to X inactivation

Question 13

What does array CGH detect?

Answer 13

Any size of imbalance

Question 14

Where do new mutations occur?

Answer 14

In gametogenesis

Question 15

What occurs if the mutation is post-zygotic?

Answer 15

The child would be mosaic

Question 16

Describe mosaicism

Answer 16

Different cells have different genetic constitution, this could be a mosaic chromosome abnormality or mosaicism for a point mutation

Question 17

What could chromosome changes cause?

Answer 17

• activate an oncogene

- delete a tumour suppressor

Question 18

Only 2-3% of the genome is exons, what are the rest involved with?

Answer 18

• regulation of genes
• space genes out
• insulates genes from promotors
• provides substrate to expand genome/ add genes

Question 19

What occurs as a result of a promotor mutation?

Answer 19

No or reduced transcription

No or reduced protein

Question 20

Define penetrance

Answer 20

The likelihood of having a disease if you have a mutation. 100% penetrance means you will always get the disease if you have the mutation

Question 21

What are mendelian disorders?

Answer 21

Disease that segregate in families in the manner predicted by mendels law. A disease that is predominantly caused by a change in a single gene, high penetrance

Question 22

Describe autosomal dominant

Answer 22

One faulty copy of the gene causes the disease. Disease is seen in all generations

Question 23

Describe autosomal recessive

Answer 23

Two faulty copies of the gene to cause disease, 1 in 4 chance of inheriting the faulty gene

Question 24

Describe the genetics of Huntington’s disease

Answer 24

• 100% penetrance

- autosomal dominant

Question 25

Describe x-linked inheritance

Answer 25

Gene fault lies on the x chromosome. A female carries a mutation but will not show major features of the disease

Question 26

Describe x-inactivation

Answer 26

In female cells only on x chromosome is active, so in some cells the affected x chromosome is expressed and then in other cells the normal x chromosome is expressed

Question 27

What are single nucleotide polymorphisms?

Answer 27

Alterations in DNA sequence, snps must exert effects that are not in themselves a disease. Most snps have no effect

Question 28

Describe copy number variations

Answer 28

Extra or missing stretches of DNA, highly prevalent in the genome, deletions or duplications