T 4

Question 1

Genetic variation in meiosis

Answer 1

Prophase 1
crossing over between homologous chromosomes
exchange of alleles between them
forms different sequences of ( maternal and paternal) alleles on each chromosome

Metaphase 1
Homologous pairs align @ equator in a random order, independent
making it random as to which homologous chromosome from each pair will end up in the daughter cell
Producing different combinations of alleles in each daughter cell

Question 2

What are the key events of Meiosis 1?

Answer 2

Separation of homologous pairs

first chromosomes form homologous pairs
crossing over
independent segregation
both introduce genetic variation

2n-n, daughter cells are haploid

Question 3

Key events of meiosis 2

Answer 3

separation of chromatids

n-n
produces haploid, genetically different gametes 4 of them

Question 4

Importance of meiosis

Answer 4

produces haploid gametes
diploid post fertilisation
so chromosome number remains constant from one gen to next

introduces genetic variation ind seg and cross ov

Question 5

chromosome non-disjunction

Answer 5

homologous chromosomes fail to separate in A1 or chromatids in A2
one gamete with 1 extra 1 with 1 less
1 less- dies
1 more- survives but infertile

occurs spontaneously
case of some genetic diseases

Question 6

number of possible different combinations of chromosomes in daughter cells after meiosis

Answer 6

2^n

Question 7

number of different possible combinations of homologous chromosomes following fertilisation

Answer 7

(2^n)^2

Question 8

Life cycles in n

Answer 8

n-2n fertilisation
2n-2n mitosis
2n-n meiosis

Question 9

Prokaryotic vs eukaryotic DNA

Answer 9

Eu (us)
long, linear, assorted with histone proteins, tightly coiled into chromosomes

Pro
short, circular, not associated with histone proteins

Question 10

Define a homologous pair of chromosomes

Answer 10

pair of chromosomes exactly the same size and carrying the same genes but having different alleles

Question 11

Role of courtship behaviour

Answer 11

INCREASE CHANCE OF SUCCESSFUL MATING

allows recognition of members of the same species, as behaviour is species specific

attraction of a mate

sign of sexual maturity

stimulates the realise of gametes

Question 12

Measuring genetic diversity

Answer 12

compare:
amino acid base sequences of common proteins as coded by mRNA-DNA
base sequence of DNA
frequency of observed characteristics, as different characteristics are coded for by different alleles

Question 13

limitations of observable characteristics as a measure of genetic diversity

Answer 13

characteristics can be polygenetic, coded for by more than one gene
characteristics can be altered by the environment, not reflect genetic differences

Question 14

Conservation techniques applied to farming

Answer 14

crop rotation using nitrogen fixing crops
maintenance of hedge rows
reduce use of pesticides/ herbicides
use of natural rather than artificial fertilisers

Question 15

How to take a representative sample

Answer 15

use random sapling techniques to eliminate bias

divide area you wish to sample up into a grid, give each grid square co-ordinates
generate numbers randomly to generate a set of coordinates
sample at the intersection of each coronate using quadrants

Question 16

Comparing the base sequence of genes provides more evolutionary information than comparing the structure of proteins
Explain why.

Answer 16

Reference to base triplets / triplet code / more bases than amino acids / longer base sequence than amino acid sequence;

Different (base) triplets code for same amino acids = 2 marks;
Degeneracy of triplet code = 2 marks

Introns / non-coding DNA / degeneracy of code / more than one code for each amino acid;