Sexual Reproduction (HL IB Biology)

• Meiosis is a form of nuclear division that results in the production of haploid cells from diploid cells
• It produces gametes in plants and animals that are used in sexual reproduction
• It takes place in two successive divisions: meiosis I and meiosis II
• More information about meiosis can be found here
• During meiosis, specific mechanisms occur to lead to genetic variation within the resulting gametes, this breaks up parental combinations of alleles derived from the mother and father chromosomes
  • Crossing over - the process by which non-sister chromatids exchange alleles during meiosis I
  • Independent assortment - the production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs of chromosomes during meiosis I
  • Random fertilisation - there are millions of combinations of sperm and egg cells and the fusion of these sperm and egg cell
• Within each division there are four stages; prophase, metaphase, anaphase and telophase
• Meiosis occurs:
  • In the testes of male animals and the ovaries of female animals
  • In the anthers and ovaries of flowering plants
• Meiosis leads to the production of the following haploid gametes:
  • Spermatozoa, or sperm cells, in male animals, ova (singular ovum) in female animals
  • Male plant gametes are carried in pollen grains and female plants gametes are held in the ovules within the plant ovary
• The fusion of gametes during fertilisation produces new combinations of alleles leading to genetic variation

• The process of meiosis in males and females is identical, however the resulting gametes are very different
• This leads to a number of difference in the reproductive strategies in males and females

Comparison of male & female gametes table

• The differences between male and female gametes, not just in humans, means that there are differences in the strategies developed for reproductive success
  • Human females release only one egg cell (per menstrual cycle) whereas a male will release many thousands of sperm cells per ejaculation, this is because the majority of which will not reach the egg cell (only one sperm cell can fertilise an egg cell)

• You should be able to draw and annotate diagrams of the female and male reproductive systems to identify the different structures
• You should also be able to recall the function of each of these structures

Female reproductive system diagrams

Front and side view of the female reproductive system

Female reproductive system table

Male reproductive system diagram

Front and side view of the male reproductive system

Male reproductive system table