Question 18N.2.HL.TZ0.8c
| Date | November 2018 | Marks available | [Maximum mark: 7] | Reference code | 18N.2.HL.TZ0.8c |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Explain | Question number | c | Adapted from | N/A |
Research suggests that many living plant species are polyploid. Explain how polyploidy occurs and, using a named example, how polyploidy can lead to speciation.
[7]
a. polyploidy is having more than two sets of «homologous» chromosomes ✔
b. triploid has three sets/is 3n ✔
c. tetraploid has four sets/is 4n ✔
d. Allium/vizcacha rats/other named example» ✔
e. details of chromosome numbers in diploid and polyploid species in the example ✔
f. non-disjunction/failure of chromosome pairs to separate during meiosis ✔
g. diploid gamete «can lead to polyploidy» ✔
h. fusion of diploid and haploid gamete produces triploid cells ✔
i. DNA replication but no subsequent mitosis doubles the chromosome number/produces tetraploid «from diploid»
OR
fusion of two diploid gametes produces tetraploid/4n ✔
j. polyploid/tetraploid «crossed» with diploid/non-polyploid produces infertile offspring ✔
k. meiosis fails in triploids because «homologous» chromosomes cannot pair up ✔
l. polyploid individuals are reproductively isolated
OR
polyploidy causes instant/immediate speciation
OR
tetraploids can form a new species because they can cross with each other
OR
polyploids cannot cross/produce fertile offspring with diploids ✔
m. speciation by polyploidy is common in plants/commoner in plants than animals ✔
n. polyploid individuals tend to be larger ✔
