X&Y Chromosomes + Genetic Screening Flashcards
Abortion
(1 mark)
The medical process of ending a pregnancy so it doesn’t result in the birth of a baby.
Carrier
2 marks
Someone who does not suffer from a condition but carries the allele + can pass it to his or her offspring.
Clot
2 marks
A clump of platelets + blood cells that forms when a blood vessel is damaged.
Dominant
(1 mark)
An allele that will override a recessive allele.
Fertilisation
(1 mark)
When a sperm nucleus + an egg nucleus fuse together.
Gender
2 marks
In Biology, often used to describe someone’s assigned sex at birth.
A person’s biological sex + gender identity are not always the same.
Heterozygous
(1 mark)
When the 2 alleles are different (e.g. Bb)
Homozygous
(1 mark)
When the 2 alleles are the same (e.g. BB)
Sex-linked genes
2 marks
Genes found in the Sex Chromosomes- that code for a number of body functions.
22 pairs of chromosomes apart from the Sex Chromosomes
2 marks
Have the same genes in the same position on both chromosomes.
The difference in size between the X chromosome + the shorter Y chromosome
(2 marks)
Means some genes appear only on the X chromosome.
The Effect of Sex-linked Genes is more obvious in Males because
(2 marks)
The X chromosome can contain genes the Y does not.
A Recessive Allele on the X chromosome
2 marks
Will show in the phenotype as there is no dominant allele present to override it.
A female will have another Allele on her other X chromosome which (if dominant) would
(1 mark)
Mask the effect of a recessive allele.
Some genetic conditions are inherited meaning they are
1 mark
Passed from parent to child.
Cause of Genetic conditions
1 mark
Mutations
Mutations
2 marks
Random changes in the structure of a gene or in the number of chromosomes.
Haemophilia
2 marks
Sufferers are unable to clot their blood resulting in excessive bleeding, even from small cuts or bruises.
What kind of condition is Haemophilia?
2 marks
Sex-linked, inherited condition caused by a recessive allele on the X chromosome.
Haemophilia Sufferers
2 marks
Almost exclusively males because they only need 1 recessive allele.
- if his X chromosome carries the dominant normal allele, the condition will not show.
Females with 2 normal alleles.
1 mark
Will not show the condition (Haemophilia).
In the (rare case) of a female having 2 recessive alleles
1 mark
Haemophilia will show.
Women with 1 normal + 1 recessive allele
2 marks
Are carriers - Although they themselves are normal, they can pass the recessive allele to half of their children.
Cystic fibrosis
3 marks
Mainly affects the lungs + digestive system
- which become clogged with mucus leading to frequent infections.
Cystic Fibrosis Cause
2 marks
A recessive allele - means only homozygous recessive individuals (cc) will be affected.
Huntington’s Disease
2 marks
Affects nerve cells in the brain, leading to brain damage.
When does Huntington’s Disease usually become apparent?
1 mark
In middle age.
Huntington’s Disease Cure
2 marks
There is no cure + it is eventually fatal.
Huntington’s Disease Cause
1 mark
The presence of 1 dominant allele.
Down Syndrome Effects
2 marks
Individuals have reduced muscle tone + cognitive development.
Down Syndrome Cause
7 marks
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.
Normal number of Chromosomes in the Human Body
1 mark
46
Genetic screening
3 marks
Involves testing people or groups of people for the presence of a particular allele or other genetic abnormality.
Amniocentesis
4 marks
Type of genetic screening - where foetal cells are extracted from the amniotic fluid to check for the presence of genetic abnormalities.
Process of Amniocentesis
5 marks
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.
Who is usually offered Amniocentesis + why?
2 marks
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.
Mothers with a greater risk of a giving birth to a child with a Genetic Abnormality
(5 marks)
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.
When screening for Down syndrome, pregnant mothers are offered
(3 marks)
Blood test between 10–14 weeks of pregnancy - determines if the possibility of having a Down Syndrome child is raised.
While not as accurate as amniocentesis, the blood test carries no risk to the foetus or the mother; it simply
(1 mark)
Identifies women who may wish to take the riskier amniocentesis procedure.
Arguments for the abortion of a foetus who are believed to have a genetic abnormality
(3 marks)
- Prevents child having poor quality of life.
- Child will need extra care meaning less time spent with other children.
Arguments against the abortion of a foetus who are believed to have a genetic abnormality
(2 marks)
- Not morally right to kill a foetus.
- Banned due to religious beliefs.
Other issues arising from genetic screening:
4 marks
- 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?
It is possible to genetically screen people in childhood + adulthood, providing us with
(1 mark)
An individual genetic profile.
Arguments for Genetic Screening
1 mark
If made public the info could help with medical research.
Arguments against Genetic Screening
2 marks
- Insurance companies may not insure certain individuals.
- Insurance companies could make these individual pay higher premiums.
