Define polyploidy, explain how chromosome-number changes isolate new plant lineages, and connect hybrid chromosome doubling to restored fertility.
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