Genetics

Question 0

What are chromosomes?

Answer 0

The basic packages of DNA in the nucleus of a cell

Question 1

What does DNA consist of?

Answer 1

Deoxyribose sugar
Phosphate backbone
Covalently bonded bases

Question 2

How many chromosomes are in a human cell?

Answer 2

22 pairs of autosomal

2 sex chromosomes

Question 3

What are the telomeres?

Answer 3

Regions at the end of each chromosome

Question 4

What are DNA strands wound around to be packaged into chromosomes?

Answer 4

Histones

Question 5

At which stage in the cell cycle does DNA replication occur?

Answer 5

S phase

Question 6

What is mitosis?

Answer 6

A cell divides to produce two daughter cells

Question 7

What are the stages of mitosis?

Answer 7

Interphase, prophase, metaphase, anaphase, telophase

Question 8

When does meiosis occur?

Answer 8

Gamete formation

Question 9

How many daughter cells are produced from one diploid parent cell in meiosis?

Answer 9

Four haploid daughter cells

Question 10

What is mosaicism?

Answer 10

When there are two or more populations of cells with different genetic constitutions within the same individual

Question 11

What is chromosomal aneuploidy?

Answer 11

The presence or absence of a whole extra chromosome

Question 12

What is the most common aneuploidy?w

Answer 12

Trisomy 21 (Down’s syndrome)

Question 13

What kind of aneuploidy is generally tolerated better by a fetus?

Answer 13

Sex chromosome aneuploidy e.g. Individuals with 47, XXX or 47, XYY show no obvious phenotypic features

Question 14

What happens to the majority of conceptions with aneuploidy?

Answer 14

Miscarriage

Question 15

What are chromosome translocation a?

Answer 15

Exchanges of chromosomal material between two or more chromosomes

Question 16

What is a balanced chromosomal translocation?

Answer 16

A translocation in which there is no net loss or gain of chromosomal material

Question 17

Which phenotypic effects can be expected in a child with an unbalanced chromosome translocation that is carried to term?

Answer 17

Renal, gastrointestinal and cardiac malformations

Developmental delay

Question 18

What determines the likelihood of chromosomal imbalance leading to miscarriage?

Answer 18

The size of the imbalance

Question 19

What is a Robertsonian translocation?

Answer 19

The long arms of two chromosomes become joined together, with the loss of the short arms

Question 20

Why does loss of short arms of acrocentric chromosomes not result in clinical phenotype?

Answer 20

Short arms contain highly repetitive DNA sequences and ribosome RNA genes

Question 21

What is reciprocal translocation?

Answer 21

Exchange of material between two, usually non-homologous chromosomes e.g. tip of chromosome 9 may translocate to chromosome 8

Question 22

What may a patient with a balanced reciprocal translocation present with?

Answer 22

Infertility
Multiple miscarriages
A child with multiple malformations

Question 23

At what size might deletion of a segment of a chromosome become visible microscopically?

Answer 23

If it is bigger than approx. 5 megabases

Question 24

What can fluorescence in-situ hybridisation be used to detect?

Answer 24

Microdeletions
Subtelomere deletions
Gross alterations in chromosome number

Question 25

What is the procedure in FISH?

Answer 25

A fluorescent dye is attached to a probe DNA that attaches to the chromosomal region of interest

Question 26

What happens in FISH if the region under investigation is present?

Answer 26

The dye fluoresces and can be visualised microscopically

Question 27

What is the drawback of FISH?

Answer 27

It can only be used when the chromosomal region for analysis is known

Question 28

What does the use of microarray comparative genomic hybridization allow for?

Answer 28

Analysis of the entire genome for small loses or gains

Question 29

What is Mendelian inheritance?

Answer 29

Single gene inheritance

Question 30

What is an autosomal gene?

Answer 30

A gene that is carried on one of the autosomes (chromosomes 1 to 22)

Question 31

What is an allele?

Answer 31

A specific version of a gene in an individual

Question 32

What is autosomal dominant inheritance?

Answer 32

A pattern of inheritance where an affected individual possesses one copy of a mutant allele and one copy of a normal allele

Question 33

What is the chance, in individuals with an autosomal dominant disease, of passing the mutation on to offspring?

Answer 33

50%

Question 34

What is autosomal recessive inheritance?

Answer 34

Both copies of a gene must harbour mutations for the disease to arise

Question 35

What is the chance of passing an autosomal recessive disease on to a child if both parents are carriers?

Answer 35

25%