Meiosis is necessary for sexual reproduction, in which haploid gametes fuse to produce a diploid zygote. Sexual reproduction increases genetic diversity, the raw material of evolution by natural selection.
learning outcomes
You should be able to:
Compare and contrast asexual and sexual reproduction.
Differentiate between haploid and diploid cells.
Compare and contrast sexual life cycles in different organisms.
In terms of chromosomes, how does fertilization produce a diploid organism? How would you know the cell was diploid?
Take a dividing cell and examine the chromosomes. If each chromosome differs in size and centromere placement from the others, the plant sample is haploid. If there are two copies of each chromosome, the plant is diploid.
What general features do all sexual life cycles have in common?
Fertilization involves the union of two haploid gametes, each with one set of chromosomes, made from meiosis. So the fertilized cell is diploid.
You have a sample of a small green plant. How would you tell if it is haploid or diploid?
All sexual life cycles have some haploid and diploid cells, fertilization, and meiosis.
Diagram haplontic and diplontic life cycles, clearly showing haploid and diploid generations.
See Figure 11.14.