Diversity + adaptation

Question 1

Cause of spontaneous mutation

Answer 1

DNA polymerase makes a mistake during replication

Question 2

Deletion/addition of bases

Answer 2

Nucleotide added or removed from sequence -> frame shift mutation, so a.acid sequence will be read entirely differently

Question 3

Substitution of bases

Answer 3

One or more bases replaced
- can code for same a.acid (degenerate code)
- code for diff. a.acid creating abnormal but functional
protein (mis-sense mutation)
- premature stop codon coded (nonsense mutation)

Question 4

Process of meiosis

Answer 4

• Parent cell showing single pair of homologous chrom’s
• homologous chrom’s separated in meiosis 1 into 2 different cells
• chromosomes separated into 4 gamete cells each w/ a single chromatid (haploid) + all are genetically different

Question 5

How does meiosis bring about genetic variation?

Answer 5

• independent segregation of homologous chrom’s creates a random mix of paternal and maternal origins (1 and 2)
• new combinations of alleles by crossing over (1)

Question 6

Calculating possible chromosome combinations

Answer 6

n = no. of homologous chromosomes
2^n => one gamete
(2^n)^2 => two gametes

Question 7

Crossing over

Answer 7

• chromatids of each pair twist round each other
• creating tension breaking some portions off
• equivalent portions are exchanged as they rejoin
• new combinations of paternal + maternal alleles produced

Question 8

Independent segregation

Answer 8

• chromosomes line up w homologous partner randomly
• one of each pair passes to daughter cell according to arrangement
• combination of maternal/paternal origin is random

Question 9

Benefit of genetic diversity

Answer 9

More likely that individuals of population will survive environmental change (natural selection)

Question 10

Features of normal distribution

Answer 10

• mean, mode and median all the same
• 68% falls within one S.D

Question 11

Anatomical adaptation

Answer 11

Physical attributes eg. short ears + thick fur for arctic foxes

Question 12

Physiological adaptation

Answer 12

Chemical processes eg. oxidising of fat in a kangaroo

Question 13

Behavioural adaptation

Answer 13

Migration patterns / behaviour eg. Autumn migration of swallows UK -> Africa for food

Question 14

What do mutagenic agents do?

Answer 14

increase the rate of gene mutation (can be chemical or radiation)

Question 15

What is meant by chromosome non-disjunction during meiosis?

Answer 15

when chromosomes fail to split into separate daughter cells, resulting in a lower or higher number of chromosomes in those cells

Question 16

What are the four stages of natural selection?

Answer 16

1. random mutation can result in new alleles of a gene, increasing genetic variation
2. many mutations are harmful but, in certain environments, the new allele of a gene might benefit its possessor, leading to increased reproductive success
3. the advantageous allele is inherited by members of the next generation
4. as a result, over many generations, the new allele increases in frequency in the population

Question 17

What type of natural selection tends to keep variation around the mean?

Answer 17

stabilising natural selection

Question 18

Give one example of directional natural selection.

Answer 18

antibiotic resistance