2C Inheritance

Question 1

How does DNA replicate

Answer 1

semi-conservative replication

Question 2

semi-conservative replication

Answer 2

1. DNA helicase breaks hydrogen bonds between bases making the DNA unwind
2. Free floating DNA nucleotides line up using complementary base pairing to the exposed bases on the template strands
3. DNA polymerase catalyses condensation reactions joining the mononucleotides together.
4. Hydrogen bonds form between the bases of the original and new strands

Question 3

Evidence for semi-conservative replication

Answer 3

1. bacteria grown in heavy or light nitrogen broth
2. a sample of DNA from each was centrifuged, the heavy one settled lower than the light one.
3. bacteria were moved from heavy to light broth
4. if replication was conservative the original heavy DNA would sit at the bottom and new light would sit at the top
5. if semi-conservative, each of the new molecules would contain one strand of heavy and one of light, so the DNA would settle in the middle

Question 4

Errors during DNA replication

Answer 4

Substitution- one base substituted for another
Deletion- a base id deleted
Insertion- a base is added
Duplication- bases are repeated
Inversion- a sequence is reversed

Question 5

Gene

Answer 5

a sequence of bases on a DNA molecule which code for a protein

Question 6

Allele

Answer 6

A version of a gene

Question 7

Genotype

Answer 7

The alleles an organism has

Question 8

Phenotype

Answer 8

the characteristics displayed by an organism

Question 9

Incomplete dominance

Answer 9

When both alleles influence the phenotype

Question 10

Cystic fibrosis cause

Answer 10

a condition caused by a mutation in the gene coding for CFTR
CFTR is a channel protein which transports chloride ions into mucus, which makes water move into the mucus by osmosis
mutation makes it less effective and mucus is abnormally thick and sticky

Question 11

Cystic fibrosis in the respiratory system

Answer 11

cilia are unable to move thick mucus
mucus builds up
blocks airways reducing surface area, breathing difficulties
microorganisms in mucus aren’t removed, causing infection

Question 12

Cystic fibrosis and the digestive system

Answer 12

the tube connecting the pancreas to the intestine can be blocked preventing digestive enzymes from reaching it. fewer nutrients can be absorbed
can cause cysts in the pancreas which inhibit enzyme production
mucus lining small intestine is thick and inhibits absorption of nutrients

Question 13

Cystic fibrosis and the reproductive system

Answer 13

Mucus blocks tubes from the testes which prevents sperm from reaching the penis
Thick cervical mucus can prevent sperm from reaching the egg through reducing its motility

Question 14

3 main uses of genetic screening

Answer 14

Identification of carriers
Preimplantation genetic diagnosis
Prenatal testing

Question 15

Genetic screening- carrier testing

Answer 15

Offered to people with family history of genetic disorders, showing if they carry an allele for the condition.

This allows people to make informed decisions about whether to have children
this knowledge my cause stress and false results are possible
employers or insurance companies may use it to genetically discriminate.

Question 16

PGD preimplantation genetic diagnosis

Answer 16

Carried out on embryos produced by IVF before they are implanted into the womb
Avoids the issue of abortion and reduces chances of having babies with genetic disorders.

may lead to production of designer babies as it can be used to find out characteristics such as eye colour

Question 17

Prenatal testing

Answer 17

CVS Chorionic Villus sampling:
11-14 weeks so earlier, abortion is less traumatic physically
Sample of cells taken from the chorionic villi to analyse fetal DNA
1-2% miscarriage rate

Amniocentesis
15-20 weeks
amniotic fluid containing fetal cells is obtained
1% miscarriage rate

Allows parents to decide to abort the fetus or begin preparing for future care of the baby
It may be unethical to abort the fetus because it has a genetic disorder