Senin, 20 Juni 2016

#129 Gametogenesis

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









  Syllabus 2016-2018

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