X&Y Chromosomes + Genetic Screening

Question 1

Abortion

(1 mark)


Answer 1

The medical process of ending a pregnancy so it doesn’t result in the birth of a baby.

Question 2

Carrier

2 marks

Answer 2

Someone who does not suffer from a condition but carries the allele + can pass it to his or her offspring.

Question 3

Clot

2 marks

Answer 3

A clump of platelets + blood cells that forms when a blood vessel is damaged.

Question 4

Dominant

(1 mark)


Answer 4

An allele that will override a recessive allele.

Question 5

Fertilisation

(1 mark)


Answer 5

When a sperm nucleus + an egg nucleus fuse together.

Question 6

Gender

2 marks

Answer 6

In Biology, often used to describe someone’s assigned sex at birth.

A person’s biological sex + gender identity are not always the same.

Question 7

Heterozygous

(1 mark)


Answer 7

When the 2 alleles are different (e.g. Bb)

Question 8

Homozygous

(1 mark)


Answer 8

When the 2 alleles are the same (e.g. BB)

Question 9

Sex-linked genes

2 marks

Answer 9

Genes found in the Sex Chromosomes- that code for a number of body functions.

Question 10

22 pairs of chromosomes apart from the Sex Chromosomes

2 marks

Answer 10

Have the same genes in the same position on both chromosomes.

Question 11

The difference in size between the X chromosome + the shorter Y chromosome

(2 marks)

Answer 11

Means some genes appear only on the X chromosome.

Question 12

The Effect of Sex-linked Genes is more obvious in Males because

(2 marks)

Answer 12

The X chromosome can contain genes the Y does not.

Question 13

A Recessive Allele on the X chromosome

2 marks

Answer 13

Will show in the phenotype as there is no dominant allele present to override it.

Question 14

A female will have another Allele on her other X chromosome which (if dominant) would

(1 mark)

Answer 14

Mask the effect of a recessive allele.

Question 15

Some genetic conditions are inherited meaning they are

1 mark

Answer 15

Passed from parent to child.

Question 16

Cause of Genetic conditions

1 mark

Answer 16

Mutations

Question 17

Mutations

2 marks

Answer 17

Random changes in the structure of a gene or in the number of chromosomes.

Question 18

Haemophilia

2 marks

Answer 18

Sufferers are unable to clot their blood resulting in excessive bleeding, even from small cuts or bruises.

Question 19

What kind of condition is Haemophilia?

2 marks

Answer 19

Sex-linked, inherited condition caused by a recessive allele on the X chromosome.

Question 20

Haemophilia Sufferers

2 marks

Answer 20

Almost exclusively males because they only need 1 recessive allele.

• if his X chromosome carries the dominant normal allele, the condition will not show.

Question 21

Females with 2 normal alleles.

1 mark

Answer 21

Will not show the condition (Haemophilia).

Question 22

In the (rare case) of a female having 2 recessive alleles

1 mark

Answer 22

Haemophilia will show.

Question 23

Women with 1 normal + 1 recessive allele

2 marks

Answer 23

Are carriers - Although they themselves are normal, they can pass the recessive allele to half of their children.

Question 24

Cystic fibrosis

3 marks

Answer 24

Mainly affects the lungs + digestive system

• which become clogged with mucus leading to frequent infections.

Question 25

Cystic Fibrosis Cause

2 marks

Answer 25

A recessive allele - means only homozygous recessive individuals (cc) will be affected.

Question 26

Huntington’s Disease

2 marks

Answer 26

Affects nerve cells in the brain, leading to brain damage.

Question 27

When does Huntington’s Disease usually become apparent?

1 mark

Answer 27

In middle age.

Question 28

Huntington’s Disease Cure

2 marks

Answer 28

There is no cure + it is eventually fatal.

Question 29

Huntington’s Disease Cause

1 mark

Answer 29

The presence of 1 dominant allele.

Question 30

Down Syndrome Effects

2 marks

Answer 30

Individuals have reduced muscle tone + cognitive development.

Question 31

Down Syndrome Cause

7 marks

Answer 31

Presence of an extra chromosome;
a sperm cell - 23 chromosomes fertilises an egg cell - 24 chromosomes.

• Individual also has 3 copies of the 21st chromosome rather than 2.

Question 32

Normal number of Chromosomes in the Human Body

1 mark

Answer 32

46

Question 33

Genetic screening

3 marks

Answer 33

Involves testing people or groups of people for the presence of a particular allele or other genetic abnormality.

Question 34

Amniocentesis

4 marks

Answer 34

Type of genetic screening - where foetal cells are extracted from the amniotic fluid to check for the presence of genetic abnormalities.

Question 35

Process of Amniocentesis

5 marks

Answer 35

Needle is inserted into the amniotic fluid surrounding the foetus + fluid is withdrawn

• Foetal cells in the fluid are then examined for the presence of genetic abnormalities such as Down Syndrome + Cystic Fibrosis.

Question 36

Who is usually offered Amniocentesis + why?

2 marks

Answer 36

It carries a 1% risk of miscarried

• so is usually only offered to pregnant women who are at higher risk of having a child with a genetic abnormality.

Question 37

Mothers with a greater risk of a giving birth to a child with a Genetic Abnormality

(5 marks)

Answer 37

Those who;

• previously carried a foetus with a genetic abnormality.
• have a family history of a genetic condition.
• older mothers.
• where possible problems have been identified in an earlier medical examination, e.g blood test.

Question 38

When screening for Down syndrome, pregnant mothers are offered

(3 marks)

Answer 38

Blood test between 10–14 weeks of pregnancy - determines if the possibility of having a Down Syndrome child is raised.

Question 39

While not as accurate as amniocentesis, the blood test carries no risk to the foetus or the mother; it simply

(1 mark)

Answer 39

Identifies women who may wish to take the riskier amniocentesis procedure.

Question 40

Arguments for the abortion of a foetus who are believed to have a genetic abnormality

(3 marks)

Answer 40

• Prevents child having poor quality of life.

- Child will need extra care meaning less time spent with other children.

Question 41

Arguments against the abortion of a foetus who are believed to have a genetic abnormality

(2 marks)

Answer 41

• Not morally right to kill a foetus.

- Banned due to religious beliefs.

Question 42

Other issues arising from genetic screening:

4 marks

Answer 42

• Who decides who should be screened?
• Is there an acceptable risk associated with genetic screening?
• The cost of screening compared to the cost of treating individuals with a genetic condition.
• Should genetic screening be extended to more than just serious genetic conditions?

Question 43

It is possible to genetically screen people in childhood + adulthood, providing us with

(1 mark)

Answer 43

An individual genetic profile.

Question 44

Arguments for Genetic Screening

1 mark

Answer 44

If made public the info could help with medical research.

Question 45

Arguments against Genetic Screening

2 marks

Answer 45

• Insurance companies may not insure certain individuals.

- Insurance companies could make these individual pay higher premiums.