Section 2&3

Question 0

What happens in interphase before meiosis1?

Answer 0

DNA replicates so each chromosome has two identical sister chromatids joined at a centromere

Question 1

What is apoptosis

Answer 1

Very quick programmes cell death

1) enzymes break down cell cytoskeleton
2) cytoplasm becomes dense with organelles tightly packed
3) cell surface membrane breaks down into small bits called blebs
4) chromatin condenses, the nuclear envelope breaks and DNA becomes fragmented
5) cell breaks into vesicles that are taken up by phagocytosis
6) cellular debris is exposed of and does not damage any other cells or tissues.

Question 2

What happens at prophase 1?

Answer 2

• chromatin condenses and undergoes supercoiling so that chromosomes shorten and thicken, and can be seen with a light microscope.
• chromosomes come together and form homologous pairs to form a bivalent (1 maternal 1 paternal)
• non-sister chromatids wrap around each other and at points called chiasmata
• They swap sections in a process called crossing over
• nucleolus disappears and nuclear envelope disintegrates
• a spindle forms

Question 3

What is formed in telophase 2

Answer 3

4 haploid cells

Question 4

How is variation achieved through meiosis?

Answer 4

• crossing over
• reassortment of chromosomes - random distribution of maternal and paternal chromosomes at metaphase 1
• reassortment of chromatids - random distribution of sister chromatids at metaphase 2
• fertilisation - there are millions of different sperm all genetically different

Question 5

What does the chi-squared test find out

Answer 5

Whether the difference between observed and expected results is small enough to be down to chance alone

Question 6

What is continuous variation?

Answer 6

• quantitative
• polygenic(many genes involved)
• different alleles at each gene locus have a small effect on the phenotype
• large environmental effect

Question 7

What is discontinuous variation?

Answer 7

• qualitative
• monogenic (often 1 gene)
• different alleles at a single gene locus have large effects on the phenotype
• small or non-existent environmental effect

Question 8

Why is variety within a population necessary?

Answer 8

Increase biodiversity (greater variety of alleles in a gene pool)
When an environment changes the best adapted survive
Variation allows better chance of survival of a species

Question 9

What is used to measure allele frequencies in a population

Answer 9

Hardy-Weinberg principle

Question 10

Which type of epistasis has a ratio of 9:3:4

Answer 10

Recessive antagonistic

• need both dominan
• recessive (aa) is epistatic to both alleles to B (B/b)

Question 11

What so the ratio of Dominant Antagonistic epistasis

Answer 11

12: 3:1

- need dominant A jut dominant B gives different colour.

Question 12

What is the ratio of recessive complementary epistasis?

Answer 12

9: 7

- need both dominant to move through second precursor.

Question 13

What type of epistasis has the ration 15:1

Answer 13

Dominant complementary

-both enzymes work to get some product som dominant of either will get colour

Question 14

How do prokaryotes divide

Answer 14

Binary fission - DNA replicates and the cell divides into 2 genetically identical cells