Practise IB Biology HL D4.1 by explaining selection, calculating allele frequencies and comparing selection pressures with evolutionary evidence.
Explain how evolution may happen in response to environmental change with evidence from examples.
a. variation in population;
b. (variation is) due to mutation/sexual reproduction;
c. valid example of variation in a specific population;
d. more offspring are produced than can survive / populations over-populate;
e. competition / struggle for resources/survival;
f. example of competition/struggle for resources;
g. survival of fittest/best adapted (to the changed environment)/those with beneficial adaptations / converse;
h. example of changed environment and adaptation to it;
i. favourable genes/alleles passed on / best adapted reproduce (more) /converse;
j. example of reproduction of individuals better adapted to changed environment;
k. alleles for adaptations to the changed environment increase in the population;
I. example of genes/alleles for adaptations increasing in a population; m. evolution by natural selection;
n. evolution is (cumulative) change in population/species over time / change in allele frequency;
Suitable examples are antibiotic resistance and the peppered moth but any genuine evidence-based example of adaptation to environmental change can be credited.
Variation in genetically inherited characteristics is the basis for evolution.
Explain how genetic variation between the individuals in a species can be generated.
a. mutation (in genes/DNA generates variation)
b. base substitution / change to base sequence of gene / makes single nucleotide polymorphisms /SNPs
c. new alleles formed / different alleles of gene / multiple alleles
d. radiation/mutagenic chemicals/mutagens cause/increase the chance of mutation
e. meiosis (generates variation)
f. recombination/new combinations of genes/alleles produced by crossing over
g. independent assortment/random orientation of (pairs of homologous) chromosomes/bivalents
h. gametes/chromosomes/DNA/genes from two parents combined (in sexual reproduction)
i. random fertilization (increases genetic variation)
j. in reproductively/geographically isolated populations natural selection may differ
k. in small/isolated populations gene pools change/evolution occurs due to natural selection/genetic drift
I. disruptive selection can cause different varieties/variants/types/phenotypes to diverge transfer of genes (between bacteria) in plasmids
For mpf it is not enough just to state 'crossing over'.
Marking guidance:
Do not accept types of mutation other than substitution for mpb.
7 max
The Atlantic cod (Gadus callarias) is a fish which lays about 5000000 eggs in its lifetime. On average, only two of these eggs survive to become adult cod. How does this promote evolution?
All offspring are genetically identical, so become better adapted.
Laying many eggs provides food for other species to survive and become better adapted.
Some young cod change to become adapted to the environment and survive and pass on their genes.
Offspring with favourable variations survive and pass on their genes.
D