Diploid organisms contain pairs of homologous chromosomes.Homologous chromosomes:
- a pair of chromosomes in a diploid cell
- same structure, genes, loci
- pair together to form bivalent during the first division of meiosis
Haploid: possesses 1 complete set of chromosomes: n
Diploid: possesses 2 complete sets of chromosomes: 2n
Meiosis: reduction division
- number of chromosomes would double without meiosis
- introduces genetic variation à mutation
Gametogenesis in mammals
Gametogenesis in plants
Development of pollen grain
Development of embryo sac
16.1 Passage of information from parent to offspring Diploid organisms contain pairs of homologous chromosomes. The behaviour of maternal and paternal chromosomes during meiosis generates much variation amongst individuals of the next generation. a) explain what is meant by homologous pairs of chromosomes b) explain the meanings of the terms haploid and diploid and the need for a reduction division (meiosis) prior to fertilisation in sexual reproduction c) outline the role of meiosis in gametogenesis in humans and in the formation of pollen grains and embryo sacs in flowering plants d) describe, with the aid of photomicrographs and diagrams, the behaviour of chromosomes in plant and animal cells during meiosis, and the associated behaviour of the nuclear envelope, cell surface membrane and the spindle (names of the main stages are expected, but not the sub-divisions of prophase) e) explain how crossing over and random assortment of homologous chromosomes during meiosis and random fusion of gametes at fertilisation lead to genetic variation including the expression of rare, recessive alleles |
In the anther, diploid mother cells divide by meiosis to form four haploid cells. The nuclei of each cell divides by mitosis, but the cell itself does not divide, resulting in cells that each contain two haploid nuclei. These cells mature into pollen grains.
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