IB Biology HL A4.1.11 Polyploidy and speciation Question Bank
Practise IB Biology HL A4.1.11 by tracing chromosome doubling, hybrid fertility and abrupt reproductive isolation in plants.
- Syllabus
- First assessment 2025
- Course
- Biology HL
- Level
- HL
Exam points
- Trace how unreduced gametes or chromosome doubling create triploid and tetraploid plants.
- Explain how polyploid hybrids overcome sterility and become reproductively isolated new species.
A4.1.11 (HL)—Abrupt speciation in plants question 1
[Maximum number: 5]
Species are groups of organisms that can potentially interbreed to produce fertile offspring.
Explain how a new species can be formed abruptly by polyploidy.
a. polyploidy is having more than two sets of (homologous) chromosomes;
b. triploids have three sets of chromosomes/tetraploids have four sets of chromosomes;
c. polyploid/tetraploid cells generated from diploid cells by DNA replication without cytokinesis/non-disjunction (of all bivalents) during meiosis;
d. tetraploids produce diploid/2n gametes;
e. fusion of diploid and haploid gametes results in triploids;
f. triploids are sterile/no gametes produced because pairing of homologous chromosomes/meiosis fails;
g. diploids and tetraploids are reproductively isolated / tetraploids cannot interbreed with the diploid parent species / diploids and tetraploids only produce infertile offspring when they cross;
h. polyploids/tetraploids are therefore a different/new species (according to the biological species definition);
Marking guidance:
Reject polyspermy as the
origin of polyploid cells
5
max
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