Revision

Question 1

During which stage of Meiosis does recombination occur?

Answer 1

Prophase of Meiosis I

Recombination is the process in which homologous chromosomes are broken at the same place and rejoined to give new combinations of alleles..

Question 2

During which stage of meiosis does chromosomal cross-over occur?

Answer 2

Prophase I

This is when homologous chromosomes are paired and exchange genetic material. This acts to increase the genetic variation of the gametes produced. Genetic variation also arises by the independent assortment of chromosomes.

Question 3

Cells enter the G0 phase irreversibly.

Answer 3

FALSE! Cells that enter the G0 phase are in a resting state and do not divide, but continue to perform their normal functions. Although some cells will stay in this quiescent state, carrying out their function until cell death without dividing again, some cells can re-enter the cell cycle under certain conditions.

Question 4

What is meant by ‘Polymorphism’?

Answer 4

A variant present in the population at a frequency of MORE than 1%

Question 5

A genetic marker is a ‘flag’ in a genome. It enables us to study inheritance. Which of these is NOT a characteristic of an ideal marker?

Answer 5

Easy to view using a microscope

Question 6

what are idea markers to study inheritance?

Answer 6

All others are characteristics of an ideal marker. A possible pneumonic is ‘HiRES’: Highly polymorphic, Randomly distributed, Easily assayable, Stable.

Question 7

Concerning mutations:

Answer 7

ageing is thought to be due to accumulation of somatic mutations

Question 8

what is a translocation mutation?

Answer 8

Translocation is interchange of genetic material between nonhomologous chromosomes.

Question 9

examples of point mutations

Answer 9

Stop mutations
Frame shift mutations
Splicing mutations
Promoter mutations

Question 10

Responsible for about 2% of all Down’s Syndrome cases

Answer 10

Mosaicism

Most cases (more than 90%) of Down’s Syndrome are caused by Trisomy 21. A much smaller proportion is caused by mosaicism. Mosaicism is a condition in which an individual has two genetically different populations of cells. It occurs due to errors in mitosis during the very early stages of embryogenesis. In the affected individual, the chromosomal defect is usually not fully expressed.

Question 11

Serum testing in the Combined Test detects:

Answer 11

Beta-Human Choronic Gonadotrophin

Question 12

Low level of Alpha-Fetoprotein indicates:

Answer 12

Down’s Syndrome.

The level of Alpha-fetoprotein is ELEVATED by neural tube defects (e.g. Spina bifida), open abdominal wall defects, fetal death and multiple pregnancies.

Question 13

Klinefelter’s Syndrome is a condition which affects 1 in 1,000 male births and presents with infertility, reduced verbal IQ and some level of gynaecomastia (enlargement of breast tissue in males). What is the karyotype for this condition?

Answer 13

Presence of an additional X chromosome.

47, XXY

Question 14

What is the main metabolic defect causing Phenylketonuria?

Answer 14

Deficiency of Phenlyalanine Hydroxylase

Question 15

Which term refers to an agent that interferes with normal embryonic or foetal development?

Answer 15

Teratogen

Question 16

Which of the following is an example of an Autosomal Dominant disease?

Answer 16

Osteogenesis Imperfecta

Question 17

Which of the following is a difference between Duchenne Muscular Dystrophy and Becker Muscular Dystrophy?

Answer 17

BMD sufferers have a much longer survival.

BMD is a more benign allelic disease. Age of onset is about 12 years, and there is a much longer survival than Duchenne’s.

Question 18

Acts as an ATP-dependent chloride channel.

Answer 18

The CFTR protein (Cystic Fibrosis Transmembrane conductance Regulator) functions as an ATP-dependent chloride channel in the cell membrane. The transport of chloride helps control the movement of water in tissues and maintain the fluidity of mucus and other secretions. Mutations in this gene can lead to Cystic Fibrosis.

Question 19

The gene responsible for cystic fibrosis maps to?

Answer 19

chromosome 7q31

The CFTR gene is found in region q31 on the long (q) arm of human chromosome 7.

Question 20

What is the incidence of cystic fibrosis?

Answer 20

1 in 2,000

Question 21

What is the primary treatment given for cystic fibrosis?

Answer 21

Physiotherapy

Question 22

complex diseases

Answer 22

obesity and haemophilia A

Complex disorders included above are: obesity, type 2 diabetes and Parkinson’s disease. All the others are monogenic disorders.

Question 23

Di George syndrome is the commonest microdeletion disorder

Answer 23

Cri du Chat is characterised by MICROcephaly and Di George by thymic HYPOplasia.

Question 24

Which of the following is NOT a characteristic of the genetic phenomenon of dominant anticipation?

Answer 24

The transmissibility of the genetic mutation increases

The inheritance of the mutation itself is not altered due to anticipation, but the penetrance and severity of the disease is.

Question 25

Angelman’s syndrome

Answer 25

can be caused by uniparental isodisomy and translocation

Question 26

Which of the following statements about invasive pre-natal testing is most accurate?

Answer 26

Chorionic villus sampling is always carried out at a tertiary referral unit

Amniocentesis is carried out at >15 weeks, chorionic villus sampling has a 1% miscarriage rate and fetal blood sampling is primarily used to assess fetal anaemia

Question 27

Which condition is managed using diet restriction and growth hormone treatment?

Answer 27

Prader-Willi syndrome

Question 28

Which condition is transmitted exclusively from mother to child?

Answer 28

MELAS

Question 29

Which condition is characterised by above average height and an increased susceptibility to breast carcinoma?

Answer 29

Klinefelter’s syndrome