2.5 - Human genetics

Question 1

aneuploidy

Answer 1

numerical chromosome imbalance

Question 2

human syndromes caused by aneuploidy (5)

Answer 2

1. Klinefelter syndrome
2. Turner syndrome
3. Down syndrome
4. Edwards syndrome
5. Patau syndrome

Question 3

effects of Klinefelter syndrome (5)

Answer 3

1. XXY sex chromosome
2. male development but small testes/ infertility
3. Gynaecomastia
4. tall stature
5. learning difficulties

Question 4

How many people are affected by Klinefelter syndrome?

Answer 4

1-2/1000

Question 5

Turner syndrome symptoms (5)

Answer 5

1. Monosomy X sex chromosome
2. female development, no puberty
3. small stature
4. ovaries degenerate before birth
5. kidney/heart benefits

Question 6

How many people are affected by Turner syndrome?

Answer 6

1/2500 - 1/3000

Question 7

Down syndrome symptoms (6)

Answer 7

1. trisomy 21
2. typical facial characteristics
3. small stature
4. congenital heart defects
5. intellectual disability
6. higher incidence of leukaemia/ early onset Alzheimer disease

Question 8

How many people are affected by down syndrome?

Answer 8

1/1000

Question 9

Edwards syndrome symptoms (7)

Answer 9

1. Trisomy 18
2. abnormalities affecting many organs
3. congenital heart defects
4. small head
   5.clenched fists
5. severe intellectual disability
6. most babies die before 1st birthday

Question 10

how many people are affected by Edwards syndrome?

Answer 10

1/5000

Question 11

Patau syndrome symptoms (7)

Answer 11

1. Trisomy 13
2. abnormalities affecting multiple organs
3. congenital heart defects
4. severe intellectual disability
5. microphthalmia (abnormally small eyes)
6. deafness
7. 5-10% of children live past 1st birthday

Question 12

How many people are affected by Patau syndrome?

Answer 12

1/16,000

Question 13

What aneuploidies are live births possible with? (5)

Answer 13

1. trisomy 13
2. trisomy 18
3. trisomy 21
4. XXY
5. monosomy X

Question 14

what is the leading cause of miscarriage?

Answer 14

aneuploidies

Question 15

maternal age effect

Answer 15

aneuploidy increases exponentially with maternal age (fairly unique to humans)

Question 16

IVF pre-implantation genetic screening (3)

Answer 16

1. blastocyst biopsy
2. few cells analysed at genetics lab
3. allows embryologist to select chromosomally normal embryos for transfer

Question 17

what does the Y chromosome contain? (2)

Answer 17

1. many repetitive palindromic sequences
2. SRY

Question 18

SRY

Answer 18

sex determining region of Y chromosome

Question 19

SRY function (2)

Answer 19

1. encodes a transcription factor
2. switches on many genes required for teste development

Question 20

how was the sex-determining role of Y chromosome proved?

Answer 20

experiments in transgenic mice

Question 21

% of population born with intersex traits (abnormal sex chromosome paterns)

Answer 21

1.7%

Question 22

X-linked recessive pedigree (3)

Answer 22

1. more common in males
2. no father-son transmission
3. son of female carrier has 50% chance of having disease

Question 23

X-linked dominant pedigree (3)

Answer 23

1. male/female equally at risk
2. affected mother has 50% chance of passing disease containing X chromosome to offspring
3. affected father will pass X onto all daughters (no father-son transmission)

Question 24

pre-implantation genetic diagnosis (2)

Answer 24

1. parents without underlying fertility issues offered IVF with PGD
2. HFEA licensed to screen for over 600 genetic disorders

Question 25

polygenic diseases (2)

Answer 25

1. controlled by many genes
2. disease onset influenced by environment

Question 26

polygenic disease examples (3)

Answer 26

1. diabetes
2. heart disease
3. breast cancer