B9 - Genetic diversity

Question 1

Define ‘gene mutation’ and explain how a gene mutation can have:
- no effect on an individual
- a positive effect on an individual

Answer 1

1. Change in base/nucleotide sequence of chromosomes/ DNA
2. Results in the formation of a new allele
3. Genetic code is degenerate (so amino acid sequence may not change) OR mutation occurs on intron
4. Does change amino acid but no effect on tertiary structure
5. New allele is recessive so does not influence phenotypes
6. Results in change in polypeptide that positively changes a named protein
7. May result in increased reproductive success OR many result in increased survival

Question 2

Describe the chemical reactions involved in the conversion of polymers to monomers and monomers to polymers. Give two named examples or polymers and their associated monomers to illustrate your answer.

Answer 2

1. A condensation reaction joins monomers together and forms a bond and releases water
2. A hydrolysis reaction breaks a bond between monomers and requires water to do so
3. A suitable example of polymers and monomers from which they are made;
   - amino acid and polypeptide, protein, enzyme, antibody or hormone
   - nucleotide and polynucleotide, DNA or RNA
   - alpha glucose and starch/glycogen
   - beta glucose and cellulose
   - monosaccharide and polysaccharide
4. A second suitable example of polymers and monomers
5. reference to correct bond within named polymer

Question 3

Describe and explain the processes that occur during meiosis that increase genetic variation.

Answer 3

1. Homologous chromosomes pair up
2. Independent segregation
3. Maternal and paternal chromosomes are re-shuffled in any combination
4. Crossing over leads to exchange of parts of sister chromatids/ alleles between homologous chromosomes
5. Both create new combinations of alleles

Question 4

Describe what happens to chromosomes in meiosis.

Answer 4

1. Chromosomes shorten/ thicken/ condense
2. Chromosomes associate in homologous pairs
3. Crossing over/ chiasma forms
4. Join to spindle fibres
5. Join via centromere
6. Homologous chromosomes move to opposite poles
7. pairs of chromatids separated in 2nd division

Question 5

Meiosis results in genetic variation in the gametes which leads to variation in the offspring formed by sexual reproduction. Describe how meiosis causes this variation and explain the advantage of variation to the species.

Answer 5

1. Crossing over
2. Independent/ random assortment/ segregation of homologous chromosomes in meiosis I
3. Independent/ random assortment/ segregation of homologous chromosomes in meiosis II

Any 3 from:
4. Different adaptations/ some better adapted
5. Some survive
6. Reproduce
7. Pass on gene/ allele
8. Allows for changing environment/ different environment/ example described