Meiosis

• Where does differentiation happen in plants?

  Meristem- in the root tip
• What is the root tip made of?

  Meristem (zone of cell division)

  • Zone of elongation
  • Xylem and packing tissue (zone of differentiation)
• What happens at the meristem?

  Zone of cell division

  • Undifferentiated and unspecialised cells (stem cells) undergo mitosis and cell division
• What happens at the zone of elongation?

  Cells elongate
• What happens at the zone of differentiation?

  Cell specialization.
• What happens at the root tip?

  1. cells divide
  2. cells elongate
  3. cells become specialised
• What happens during chromosome replication?

  The duplicated homologous chromosomes are together- bound together
• What happens during Meiosis 1?

  It introduces genetic diversity by randomly dividing a cell's genes in two, leading to two haploid cells being produced.

  • the duplicated homologous chromosomes separate
• What happens during meiosis 2?

  Each duplicated chromosome is divided into two sister chromatids and each chromatic is placed in one daughter cell. This leads to four haploid gametes
• What is independent assortment?


  How the maternal and paternal chromosomes line up
• How does independent assortment lead to genetic variation?

  It is random how the maternal and paternal chromosomes from the homologous pairs line up and are arranged in each gamete, leading to genetic variation
• How does crossing over lead to genetic variation?

  The non-sister chromatids exchange corresponding alleles, giving rise to different combinations of alleles in gametes
• Why is meiosis important for gamete formation?

  1. During Meiosis I, the number of chromosomes is halved
  2. which forms a haploid nucleus
  3. the normal number of chromosomes/ diploid is restored during fertilisation
  4. genetic variation of gametes happens
  5. through independent assortment and crossing over
• Why are males more likely to have sex linked disorders?

  1. If it is a recessive condition, it is found on the X chromosome
  2. males only need to inherit one recessive allele to have the condition but females need to inherit two recessive alleles
• Why do some genes show linkage and others show sex-linkage?

  There are more genes than there are chromosomes.

  • Linkage relates to genes for different characteristics located on the same non-sex chromosome
  • Sex linkage relates to genes on the sex chromosomes