Inheritance

Question 1

Describe the process of semi-conservative DNA replication.

Answer 1

1. DNA Helicase breaks H bonds between the bases
2. Each strand acts as a template for a new strand: free DNA nucleotides pair up with the exposed originals.
3. Condensation reactions join the nucleotides of the new strands together - catalysed by DNA polymerase - new H bonds form
4. Each new DNA molecule contains one new and one old strand

Question 2

Describe Meselson and Stahl’s experiment

Answer 2

1. Two bacteria samples were grown: one in a heavy nitrogen and another in a light nitrogen broth. The nitrogen became part of the bacteria’s DNA (bases).
2. DNA samples were taken and centrifuged: DNA from the heavy N group settled lower than the other groups’s DNA as it was denser.
3. Bacteria from the heavy H broth were left to replicate in the light N broth, then DNA samples were centrifuged
4. DNA settled in the middle of the centrifuge as it contained a mixture of light N and heavy N (semi-cons).

Question 3

Mutations are changes to the base sequence of DNA. What are the different types?

Answer 3

Substitution - one base is substitued with another
Deletion - a base is deleted
Insertion - an extra base is added
Duplication - one or more bases are repeated
Inversion - a base sequence is reversed

Question 4

How can mutations cause problems?

Answer 4

They change the primary structure of a protein and thus change the final 3D shape, affecting a proteins function.

Question 5

What does monohybrid inheritance refer to?

Answer 5

The inheritance of a single characteristic that’s controlled by different alleles.

Question 6

What are the effects of CF on the respiratory, digestive and reproductive system?

Answer 6

Respiratory - thick consistency of mucus stops expulsion by cilia, some airways become blocked - SA reduced for GE
Digestive - pathway from the pancreas to the small intestine blocked - digestive enzymes can’t access food, fewer nutrients absorbed
Reproductive - blockage of the vas deferens and thicker cervical mucus can prevent the sperm from reaching the egg

Question 7

What are the three types of genetic screening?

Answer 7

1. Carrier identification - couples can have their genes analysed to find out whether they carry an allele that could cause a disorder - allows for informed decisions
2. Preimplantation Genetic Diagnosis - IVF embryos are screened for genetic disorders
3. Prenatal testing - fetuses are screened for genetic disorders in amniocentesis and chorionic villus sampling

Question 8

Describe amniocentesis and CVS

Answer 8

Amniocentesis: carried out at 15-20 weeks of pregnancy, amniotic fluid obtained with a needle, fetal cells screened. 1% risk of miscarriage, results take 2-3 weeks or 3-4 days (rapid test for common disorders only).
Chorionic villus sampling: carried out at 11-20 weeks of pregnancy, fetal cells obtained from the chorionic villi using a fine needle. 1-2% miscarriage risk. Results available in 2+ weeks or a few days.

Question 9

What are some ethical and social issues with genetic screening?

Answer 9

• False results could provide incorrect info, and people will base their decisions on this.
• PGD can be used to find out other characteristics - fear of ‘designer babies’.
• Abortion is considered morally wrong for utilitarian and religious reasons.