Question 21M.2.SL.TZ1.7b
| Date | May 2021 | Marks available | [Maximum mark: 7] | Reference code | 21M.2.SL.TZ1.7b |
| Level | SL | Paper | 2 | Time zone | TZ1 |
| Command term | Explain | Question number | b | Adapted from | N/A |
Explain how genetic variation between the individuals in a species can be generated.
[7]
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 ✔
l. 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’.
Do not accept types of mutation other than substitution for mpb.
More marks were scored here, with most candidates at least mentioning mutation and some of the events of meiosis. As this was an explain question it was not enough merely to name a process, such as crossing over, some indication of how it generates variation was expected. A common misunderstanding was to think that geographic isolation in itself generates variation.
