Session 4

Question 0

Describe the process and role of the cell cycle

Answer 0

M - cell division
G1 - cell content replication (mainly growth)
S - DNA replication
G2 - double check and repair 
Checkpoints

Question 1

Describe the process and role of DNA replication

Answer 1

Semi-conservative replication
Catalysed by DNA polymerase (can only extend a 3’ end)
Recognition of origin of replication - sequence dependent
Needs primers
Primase - makes small amount of RNA which acts as a primer
DNA helicase unzips strands

1. Helicase unwinds double helix
2. DNA polymerase acts in 3’–>5’ direction to complementary bind nucleotides to free parent strands
3. Leading strand copied in 5’–>3’ direction and is continuous
4. Lagging strand produces Okazaki fragments
5. Ligated together to form continuous sugar phosphate backbone
6. As replication continues, replication forks enlarge and eventually merge
7. Two identical DNA molecules produced

Question 2

Describe the process and role of mitosis and meiosis, and compare and contrast the two processes

Answer 2

Mitosis - cell division for somatic cells, produces two genetically identical diploid daughter cells, one stage
Meiosis - cell division for germ line cells, produces four genetically different haploid daughter cells (egg and sperm), two stages

Question 3

Distinguish clearly between genotype and phenotype

Answer 3

Genotype - genes on chromosomes in nucleus

Phenotype - outward characteristic

Question 4

Explain how environmental factors have an influence on both phenotype and genotype

Answer 4

Phenotype - infection, getting fat
Genotype - skin cancer (UV)
Factors - radiation, mutagens, diet, lifestyle, chemicals that affect cell growth

Question 5

Distinguish clearly between a gene and allele

Answer 5

Gene - found on a chromosome, codes for something

Allele - different versions of the same gene

Question 6

Describe the different patterns of inheritance and be familiar with examples

Answer 6

Homozygous - two alleles that are the same
Heterozygous - two alleles are different
Hemizygous - only one allele on X chromosome (males only)

Question 7

Explain dominance, recessiveness, co dominance and complementation

Answer 7

Dominance - only requires one dominant allele for phenotype to be expressed (e.g. Huntington’s)
Recessive - requires two recessive allele for phenotype to be expressed, one allele = carrier (e.g. Cystic Fibrosis)
Co dominance - both alleles are expressed (e.g. Blood groups)
Complementation - more than one gene is involved in producing a phenotype (e.g. Albinism)

Question 8

Describe the basis of the co-inheritance of certain traits

Answer 8

Genes on the same chromosome are said to be ‘linked’
Genes on different chromosomes are said to be ‘non-linked’
Linked genes do not show independent assortment at meiosis
Recombination frequency between two linked genes depends on the distance
Genes close together are ‘tightly linked’
Genes far apart on the same chromosome also behave as unlinked genes

Question 9

Use genetic data to calculate probability of inheritance and recombination frequency

Answer 9

Recombination frequency - number of recombined individuals/total number of progeny

The smaller the frequency, the closer the genes
50 = genes are not close (not linked)