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Grade 12 IEB Life science/biology strand 3: (3.2) Chromosomes and meiosis summary CA$6.66   Add to cart
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Grade 12 IEB Life science/biology strand 3: (3.2) Chromosomes and meiosis summary

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  • Course
  • Life Sciences
  • Institution
  • 12th Grade

This aesthetic, in-depth, neatly typed document summarises 3.2 of strand 3 of the IEB grade 12 mind action series textbook: Chromosomes and meiosis. It includes the full 3.2 Chromosomes and meiosis syllabus as well as additional class notes, own research notes and all relevant diagrams

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Document information

  • January 4, 2023
  • 7
  • 2022/2023
  • Summary

Subjects

  • ieb
  • matric
  • grade 12
  • life science
  • biology
  • mind action series
  • typed
  • aesthetic
  • diagrams
  • strand 3
  • chromosomes and meiosis
  • notes
  • summary
  • 32

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  • 12th Grade
  • Life Sciences
  • 200
All documents for this subject (1085)

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Chromosomes and Meiosis:
Chromosomes:

• 46 chromosomes: 22 pairs = autosomes, X and Y chromosomes = gonosomes

• Long, thread-like structures form chromatin network in nuclei

• Made of strand of DNA wound around histones (proteins)

• Can only be seen during replication (form an x shape)



• In somatic cells of diploid organisms:

- Number of chromosomes in each cell is the same

- Chromosomes made up of 2 sets: maternal & paternal. Chromosome in each pair = diploid (2n)

- 1 paternal & 1 maternal = homologous pair

- DNA of each chromosome replicates to form 2 identical chromatids joined by centromere, in

interphase




Meiosis:

• Cell division taking place in reproductive organs to produce gametes and spores (plants)

• Number of chromosomes reduced from 2 sets (2n) in parent cell to 1 set (n) in each daughter cell

• Gametes formed = haploid (only 1 set of chromosomes: 1 chromosome from each homologous

pair)

• Haploid gametes fuse during fertilisation = diploid zygote

• Meiosis takes place in reproductive organs

- Formation of sperm: Spermatogenesis

, - Formation of eggs: Oogenesis



Process of meiosis:

• DNA of parent cells is replicated in interphase. Replication is followed by:

- Meiosis 1: Reduction devision resulting in 2 cells forming with half the number of chromosomes

of parent cell (n)

- Meiosis 2: Copying devision where 2 haploid cells divide again by mitosis and form 4 haploid

cells



Meiosis 1: A reduction devision:

• Early prophase 1:

- Chromosomes become short & fat (visible)



• Late prophase 1:

- Chromosomes of homologous pairs lie along one side (bivalent)

- Centrioles move to opposite poles

- Spindle (protein thread) develops

- Crossing over takes place (inner chromatids)



• Metaphase 1:

- Bivalents move to middle of cell

- Centromeres attach to spindle threads



• Anaphase 1:

- Centromeres don't split. Bivalents separate and chromosomes (not chromatids) are pulled away

from each other by contracting spindle threads

- Chromosomes move to opposite poles

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