genetics

Question 1

what are human genetics?

Answer 1

a term referring to heredditary features and tries to predict characteristics of children from production.

Question 2

what is a dominant allele?

Answer 2

it is always expressed, even if one copy is present. Dominant alleles are represented by a capital letter

Question 3

what is a recessive allele?

Answer 3

it is only expressed if the individual has two copies and does not have the dominant allele of that gene. Recessive alleles are represented by a lower case letter

Question 4

what does homozygous mean?

Answer 4

means that the genotype could be the same. e.g the mum and dad likely have the same genotypes.

Question 5

what does heterozygous mean?

Answer 5

means that the genotype could be different. e.g. the mum and dad have different genotypes.

Question 6

what is a genotype?

Answer 6

is the inherited genetic information responsible for a particular trait

Question 7

what is a phenotype?

Answer 7

is the resulting physical characteristic / appearance, depending on what genes were inherited

Question 8

what happens when there’s a new mutation in a body cell

Answer 8

the effect will be minimal and only cause harmful effects in the new cells that divide from that cell

Question 9

what happens if there’s a new mutation in the sperm/ ovum

Answer 9

If it becomes a zygote- it will divide multiple times to form a human. every cell with therefore carry the mutation.

Question 10

what causes Down syndrome?

Answer 10

those who inherit an unbalanced translocation involving chromosome 21 may have extra genetic material from chromosome 21, this causes down syndrome.

Question 11

what causes mosaic down syndrome?

Answer 11

it is not inherited. it occurs as a random event during call division early in foetal development.

Question 12

how many chromosomes does someone with Down syndrome have?

Answer 12

a total of 47. usually an extra chromosome 21

Question 13

what is Huntington’s disease

Answer 13

an inherited disease that results in the death of brain cells. medication cannot cure it, however it can help to slow down the symptoms.

Question 14

what is cystic fibrosis causes by?

Answer 14

it’s caused by a recessive allele, so both parents must posses this faulty allele. the individual will have needed to inherit two copies of the faulty allele to be born with CF.

Question 15

what is sickle cell caused by?

Answer 15

it is caused by a defective allele that interfere with the normal production of red blood cells, which carry oxygen in the blood.

Question 16

what is PKU

Answer 16

it is where the body cannot break down the amino acid- phenylalanine, which then builds up in the blood and brain. this can lead to brain damage. it is caused by a recessive allele

Question 17

how is cystic fibrosis diagnosed?

Answer 17

by a sweat test, looking at if the persons sweat is abnormally salty

Question 18

how is PKU diagnosed?

Answer 18

can be diagnosed shortly after birth using a heel prick test to look for high levels of phenylalanine.

Question 19

how is Down syndrome diagnosed?

Answer 19

can be aided by the persons external features

Question 20

how is sickle cell diagnosed?

Answer 20

by a blood test that identifies red blood cells that show sickling

Question 21

how is Huntington’s diagnosed?

Answer 21

can be confirmed through chorionic villus sampling

Question 22

chorionic villus sampling: where is the sample taken from and at what week of pregnancy?

Answer 22

taken from the placenta after the 10th week of pregnancy

Question 23

what is found in the membranes surrounding the foetus?

Answer 23

the chorion and amnion

Question 24

how is the sample of the chorion found before being taken?

Answer 24

the placenta is located by ultrasound or endoscopy and a small sample of the villi is removed

Question 25

why can CVS not detect issues on the X chromosome? what can this lead to?

Answer 25

they are inactive in the foetal placental cells, meaning they sometimes give back false negatives.

Question 26

once CVS is sampled, what is created?

Answer 26

karyotype ( a chromosomal picture)

Question 27

what’s the results of the CVS have been told to the parents- what are their choices?

Answer 27

genetic counselling, or be offered a termination to avoid disorders.

Question 28

what are the risks of CVS?

Answer 28

miscarriage (1-2% chance) and increased infection chances.

Question 29

what is the process of amniocentesis?

Answer 29

involves taking a sample of amniotic fluid through the abdominal and uterine wall using a hollow needle.

Question 30

why are bilirubin and alpha-fetoprotein analysed?

Answer 30

to exclude other congenital disorders

Question 31

a woman may choose to have amniocentesis over CVS due to what? how does this reduce the risk?

Answer 31

due to the reducing the risk of miscarriage because its taken at a later stage (15 weeks)

Question 32

the amniocentesis test can only be performed between 15 and 20 weeks of pregnancy- why is this an issue for some?

Answer 32

it can become difficult to choose termination as its in the later stages. also likely to be more distressing.

Question 33

exam Q: describe two tests for genetic disorders in pregnancy (4 marks)

Answer 33

one test used for genetic disorders in pregnancy is amniocentesis, which tests fluid from the amniotic sac.

another test used is CVS. this tests tissues from the placenta.