3.7.3 Speciation

Question 1

What are the 2 types of factor that cause phenotypic variation?

Answer 1

• genetic factors
• environmental factors

Question 2

How does meiosis result in cells that have the haploid number of chromosomes and show genetic variation?

Answer 2

• homologous chromosomes pair up
• crossing over
• produces new combination of alleles
• chromosomes separate
• at random (independent segregation)
• produces new combinations of chromosomes
• chromatids separated at meiosis II

Question 3

What are features of variation due to genetic factors? ***I’m not sure this is right

Answer 3

• monotonic characteristic - controlled for by 1 gene
• show discrete forms in the range of values
• no intermediate types found
• not affected by environment
• (frequency histogram has separate bars)
• eg ABO blood groups

Question 4

What are features of variation due to the environment *** I’m not sure this is right

Answer 4

• polygenic characteristic - controlled for by 1 gene
• show continuous forms in the range of values
• intermediate types found
• (frequency histogram is smooth curve)
• eg height

Question 5

What is evolution?

Answer 5

change in the allele frequency of a population over time

Question 6

What is sympatric speciation?

Answer 6

• formation of new species by reproductive isolation
• from a population living in the same area without geographical isolation

Question 7

What is allopatric isolation?

Answer 7

• formation of new species from different populations
• isolated in different areas

Question 8

What is speciation?

Answer 8

• variation exists due to mutation
• 2 populations of a species become separated (eg geographical isolation or another type of isolation)
• no gene flow between them so they are reproductively isolated
• each population may experience different environmental conditions (eg abiotic/biotic - selection pressures)
• change in allele frequency in each group due to selection pressures due to selection over a long time
• this is (allopatric/ sympatric) speciation
• (new species: eventually different species can’t breed to produce fertile offspring)

Question 9

How can sympatric speciation occur?

Answer 9

• temporal - different breeding seasons
• behavioural - different courtship displays
• mechanical - mismatch of reproductive parts
• gamete incompatibility - sperm killed in female reproductive tract/can’t enter egg
• hybrid inviability/infertility

Question 10

What is genetic drift?

Answer 10

• in small populations, changes in allele frequency have a large impact (alleles lost, new alleles selected for)

Question 11

How can genetic drift occur when isolated populations interbreed?

Answer 11

• smaller populations have fewer different alleles/smaller gene pool/less genetic variation
• migrants bring in new alleles and increase gene pool