3.4.4 natural selection

Question 1

what is genetic variation?

Answer 1

the small differences in DNA sequences between individual organisms within a species population.

Question 2

how is genetic variation related to genetic diversity?

Answer 2

genetic variations are transferred from one generation to the next > resulting in genetic diversity within a species population.

Question 3

what is genetic diversity?

Answer 3

the number of different alleles of genes in a population.

Question 4

mutations result in…

Answer 4

the generation of new alleles, contributing to genetic diversity// or the gene pool.

Question 5

what’s a gene pool?

Answer 5

all the different alleles in a species population.

Question 6

what is independent segregation and how does it contribute to genetic diversity?

Answer 6

• chromosomes are lined up into random formations.
• producing different gametes with different alleles.

Question 7

what is crossing over and how does it contribute to genetic diversity?

Answer 7

• crossing over is when homologous pairs of chromosomes associate and form a bivalent and chiasmata.
• lengths of non-sister chromatids are exchanged = genetic recombination.
• producing new combinations of alleles.

Question 8

what is random fertilisation and how does it contribute to genetic diversity?

Answer 8

• the fusing of an egg and sperm is random.
• producing new combinations of alleles in a population, which increase genetic diversity and gene pool.

Question 9

what is non-disjunction and how does it contribute to genetic diversity?

Answer 9

• when the chromosomes are incorrectly pulled apart in anaphase I/II.
• resulting in a changed structure and number of chromosomes.

Question 10

what is a mutation and what increases the likelihood of mutations?

Answer 10

• a change in the base sequence of DNA.
• mutagenic agents increase the likelihood of mutations: radiation, UV light, x-rays, chemicals viruses etc.

Question 11

mutations can be…

Answer 11

• harmful.
• neutral (do not impact survival).
• beneficial (the phenotype increases survival and reproductive success) = NATURAL SELECTION!!

Question 12

what is required for natural selection?

Answer 12

biodiversity as a wider range of phenotypes increases species chances of survival in a changing environment.

Question 13

what are the 6 steps of natural selection?

Answer 13

1) there is genetic diversity in the population.
2) new alleles arise due to a random mutation.
3) the population experiences a selection pressure (an environmental factor which reduces the organisms’ ability to survive).
4) the individuals with the advantageous allele (coding for the phenotypes which increases survival) survives and reproduces.
5) the advantageous allele is inherited by the offspring.
-> therefore, over many generations, the advantageous allele increases in frequency in the population.

Question 14

what does advantageous mean and what are advantageous adaptations?

Answer 14

the environment will determine what is advantageous.

• ANATOMICAL eg fur colour, neck length.
• PHYSIOLOGICAL eg rate of gas exchange, muscle contraction efficiency.
• BEHAVIOURAL eg courtship displays.

Question 15

what is stabilising selection?

Answer 15

• less genetic diversity.
• the intermediate/average phenotypes are best adapted to survive in the environment so these alleles are advantageous.
  > intermediate phenotypes are more common and extreme phenotypes may disappear.

Question 16

what is directional selection?

Answer 16

• one extreme is selected for: an extreme phenotype is best adapted to survive in the environment so a particular allele is advantageous.
  > extreme phenotype more common.