6. inheritance variation and evolution
o asexual reproduction involves only 1 parent and no fusion of gametes which are sex cells
o so there is no mixing of genetic info
o there is a production of genetically identical offspring which are called clones
o mitosis is the process by which organisms can asexually reproduce
o many plants reproduce asexually and in different ways eg
o strawberry plants send out long shoots called runners which touch the ground to start growing
a new plant
o daffodils produce lots of smaller bulbs which can grow into new plants
o gardeners use asexual reproduction to produce large numbers of identical plants
o many fungi reproduce asexually by spores
o malarial Protists reproduce asexually when they are in the human host
o sexual reproduction and meiosis
o sexual reproduction involves the fusion aka joining of male and female gametes
o sperm and egg in animals
o pollen and egg in flowering plants
o this leads to the mix of genetic info which produces variation in offspring
o the formation of gametes involves meiosis
o meiosis:
o cells in reproductive organs like testes and ovaries have 23 pairs of chromosomes
o diploid cell
o replicates chromosomes
o divides into 2
o divided again into 4
o four haploid cells form each with different alleles and half the original number of chromosomes
o when a cell divides by meiosis
o copies of the genetic info are made
o the cell divides twice to form 4 gametes each with a single set of chromosomes
o all gametes are genetically different from each other
o meiosis is important as it halves the number of chromosomes in gametes
o this means that fertilisation can restore the full number of chromosomes
o once fertilised the resulting cell divides rapidly by mitosis and cells become specialised by
differentiation
o this is called an embryo now
o sperm cell has 23 chromosomes
o egg cell has 23
o fertilised egg cell has 23 pairs
o asexual vs sexual reproduction
o advantages of sexual reproduction:
o asexual reproduction involves only 1 parent and no fusion of gametes which are sex cells
o so there is no mixing of genetic info
o there is a production of genetically identical offspring which are called clones
o mitosis is the process by which organisms can asexually reproduce
o many plants reproduce asexually and in different ways eg
o strawberry plants send out long shoots called runners which touch the ground to start growing
a new plant
o daffodils produce lots of smaller bulbs which can grow into new plants
o gardeners use asexual reproduction to produce large numbers of identical plants
o many fungi reproduce asexually by spores
o malarial Protists reproduce asexually when they are in the human host
o sexual reproduction and meiosis
o sexual reproduction involves the fusion aka joining of male and female gametes
o sperm and egg in animals
o pollen and egg in flowering plants
o this leads to the mix of genetic info which produces variation in offspring
o the formation of gametes involves meiosis
o meiosis:
o cells in reproductive organs like testes and ovaries have 23 pairs of chromosomes
o diploid cell
o replicates chromosomes
o divides into 2
o divided again into 4
o four haploid cells form each with different alleles and half the original number of chromosomes
o when a cell divides by meiosis
o copies of the genetic info are made
o the cell divides twice to form 4 gametes each with a single set of chromosomes
o all gametes are genetically different from each other
o meiosis is important as it halves the number of chromosomes in gametes
o this means that fertilisation can restore the full number of chromosomes
o once fertilised the resulting cell divides rapidly by mitosis and cells become specialised by
differentiation
o this is called an embryo now
o sperm cell has 23 chromosomes
o egg cell has 23
o fertilised egg cell has 23 pairs
o asexual vs sexual reproduction
o advantages of sexual reproduction:
