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
• 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
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller Lindyprinsloo. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $4.50. You're not tied to anything after your purchase.
