Meiosis and sexual reproduction

• Diploid (2n) signifies a cell with a nucleus containing two full sets of chromosomes
• Haploid (n) signifies a cell with a nucleus containing one complete set of chromosomes
• A zygote is the cell formed when two haploid gametes fuse at fertilisation
• Fertilisation is the fusing of the haploid nuclei from two gametes to form a diploid zygote in sexual reproduction
• Polyploidy is when a cell or an organism has more than two sets of chromosomes
• Gonads are the sex organs in animals
• Anthers are the male sex organs in plants

  • Pollen, produced in the anthers, contains the haploid male gametes in plants
• Ovaries are the female sex organs in both animals and plants

  • Ovules, formed in the ovaries, contain the haploid female gametes in plants
• Testes are the male sex organs in animals

  • Spermatozoa (sperm) are the haploid male gametes in animals
• Ova are the haploid female gametes in animals
• Microspores are the result of meiosis in plants that produce the male gametes, pollen
• Megaspores are the result of meiosis in plants that produce the female gametes, ovules
• Homologous chromosomes:

  • A set of one maternal chromosome and one paternal chromosome that pair up during meiotic cell division
• Crossing over (recombination):

  • Process where large multi-enzyme complexes cut and rejoin parts of the maternal and paternal chromatids at the end of prophase 1
• Independent assortment (random assortment):

  • Process where chromosomes derived from the male and female parent are distributed into the gametes at random
• Chiasmata:

  • Points where the chromatids break during recombination
• Translocation is a mutation where part of one chromosome breaks off and joins a different chromosome
• Translocation may be balanced, where parts of two chromosomes swap, or unbalanced, where a piece breaks off one chromosome and joins another
• Sex chromosomes determine the sex of an individual
• Human females have two X chromosomes (XX)
• Males have an X and a Y chromosome (XY)
• Non-disjunction occurs when a pair of chromosomes fail to separate during meiosis, leading to gametes with abnormal chromosome numbers
• Monosomy is when only one member of a chromosome pair is present in a cell
• Polysomy is when a cell contains three or more chromosomes of a particular type
• Aneuploidy is when a cell has an abnormal number of chromosomes
• Mutation rate is the natural rate at which mutations occur
• Mutagens are chemicals that increase the rate of mutation
• Gametogenesis is the formation of gametes by meiosis in the sex organs
• Primordial germ cells divide by meiosis to ultimately form sperm and ova
• Spermatogenesis is the formation of sperm in the testes
• Oogenesis is the formation of ova in the ovaries
• Sporophyte generation is the diploid generation in plants that produces spores by meiosis
• Gametophyte generation is the haploid generation in plants that gives rise to gametes by mitosis
• Sporophyte is the diploid main body of the plant
• Pollen sacs are parts of anthers where pollen grains develop
• Tube nucleus is the male nucleus that controls the production of the pollen tube in fertilisation
• Generative nucleus is the male nucleus that fuses with the female nucleus
• Pollen tube is a tube that grows out of a pollen grain down the style, into the ovary and through the micropyle of the ovule to carry the two male nuclei to the ovule
• Placenta (plant) is the pad of special tissue that attaches the plant ovule to the ovary wall
• Pollination is the transfer of pollen from the anther to the stigma, often from one flower to another