Genetics

Question 1

In which direction is DNA always replicated?

Answer 1

5’ to 3’ carbon

Question 2

How is DNA packaged?

Answer 2

It is wrapped around positively charged histone proteins

Amongst other proteins, DNA is then wound into chromosomes

Question 3

How many genes are available to be coded in the body?

Answer 3

30,000

Question 4

What are the 5 phases of the cell cycle?

Answer 4

1. G1 - Cell growth
2. G0 - Cell functions normally and does not replicate
3. S - DNA synthesis and replication
4. G2 - DNA replication is checked
5. M - Mitosis occurs

Question 5

Which protein can detect and attempt repair of DNA damage?

Answer 5

p53

Question 6

Under which circumstances may p53 halt G2?

Answer 6

Low oxygen concentrations

Question 7

What is Li-Fraumeni syndrome?

Answer 7

A condition characterised by a mutation in the tp53 gene resulting in defective p53 protein

Question 8

What are the 5 different phases of meiosis I?

Answer 8

1. Interphase
2. Prophase
3. Metaphase
4. Anaphase
5. Telephase (and cytokinesis)

Question 9

What are the three differences between RNA and DNA?

Answer 9

1. RNA is single stranded
2. RNA uses ribose rather than deoxyribose sugar in DNA
3. Uracil is used in RNA rather than thymine

Question 10

After transcription what is produced?

Answer 10

Pre-mRNA

Question 11

How is mature mRNA obtained?

Answer 11

Splicing of introns to leave only exons which contain coding DNA

Question 12

In terms of the cell cycle, which stage will the cell remain in most of its life?

Answer 12

G0

Question 13

Which enzyme is responsible for unzipping DNA?

Answer 13

DNA helicase

Question 14

Which enzyme copies the 5’-3’ strand?

Answer 14

DNA polymerase

Question 15

Okazaki fragments are utilised to copy the 3’-5’ strand, these are joined with the aid of which enzyme?

Answer 15

DNA ligase

Question 16

How is variation obtained in meiosis?

Answer 16

• Crossing over
• Independent assortment

Question 17

What is a polymorphism?

Answer 17

DNA variant which has a population frequency of greater than 1%

Question 18

What is a mutation?

Answer 18

A DNA variant which causes or predisposes to a specific disease?

Question 19

How do polymorphisms and mutations differ?

Answer 19

• Polymorphisms are functioning versions of genes
• Mutations can be harmful

Question 20

What is a missense mutation?

Answer 20

A wrong base is used in one of the codons

Question 21

What is karyotyping?

Answer 21

It looks at chromosomes as a whole

Can see deletions of >5 million base pairings

Question 22

What is a balanced translocation?

Answer 22

There is an even exchange of material between chromosomes

There is no missing or extra genetic information

Usually such chromosomes will still function

Question 23

What is an unbalanced translocation?

Answer 23

There is an unequal exchange of genetic material between chromosomes

This results in extra or missing information

Usually these chromsomes do not function correctly

Question 24

What are acrocentric chromosomes?

Answer 24

A chromosome in which the centromere is located very near the end of the chromosome

Two acrocentric chromosomes may stick together is very bad

Question 25

What is fluorescent in-situ hybridisation?

Answer 25

FISH Chromosomes can be labelled by fluorescent probes This can aid in identifying aneuploidy (too many chromosomes in a cell) or translocations etc

Question 26

What is the risk of a carrier mother passing on a sex-linked genetic condition to her son?

Answer 26

25%

Question 27

What does the term penetrance mean?

Answer 27

The extent to which a particular gene is expressed in the phenotype of the individual carrying it

Question 28

In females how is it decided which X chromosome undergoes X inactivation?

Answer 28

It is a random process

Question 29

What is multifactorial disease?

Answer 29

Disease in which mutations in multiple genes combine with environmental factors to cause disease

Question 30

Genes involved in multifactorial disease will have what level of penetrance?

Answer 30

Low

Question 31

What do DNA methylation and acetylation affect about the DNA and histone binding?

Answer 31

They increase the strength of binding This may slow the rate of transcription when excessive and may cause disease

Question 32

Describe the meaning of imprinting

Answer 32

Differences in gene expression depending on whether a gene is maternally or paternally inherited

Question 33

Mitochondrial DNA is inherited from where?

Answer 33

Almost entirely the mother

Question 34

What is mosaicism?

Answer 34

The presence of two or more populations of cells with different genotypes in one individual

Question 35

What are the two types of mosaicism?

Answer 35

1. Somatic - derived from a post-zygotic mutation 2. Gonadal - a person has two populations of cells in the gonads, one with a DNA mutation or chrmosome anomaly

Question 36

BRCA1/2 mutations are associated with what?

Answer 36

Increased lifetime risk of breast or ovarian cancer (BRCA1/2 are associated with DNA repair)

Question 37

What is the normal function of the CFTR gene?

Answer 37

It functions as a channel across the membrane that produces mucus, sweat, saliva, tears and digestive enzymes It transports cholride ions out of the cell which indirectly controls the water movement allowing for thin free flowing mucus

Question 38

Mutations in CFTR cause what?

Answer 38

Sodium is not pumped out the cell and into the lumen or digestive or respiratory passages so mucus is thick as water does not enter these areas