Meiosis

Question 1

What is meiosis? Where does it occur? What does it produce?

Answer 1

• Meiosis is a succession of two specialised cell divisions that lead to the formation of gametes
• Occurs in all sexually producing eukaryotes.
• Produces 4 haploid gametes.
• It occurs in specialised cells within reproductive tissue. (testis/anther & ovary/gynaecium).

Question 2

What are the stages of prophase? What happens in each stage?

Answer 2

Prophase stages:
1. Leptotene:
o Chromosomes become visible as long, thin single threads that continue condensing.

2. Zygotene:
   o Telomeres of the chromosomes cluster & homologous chromosomes line up.
   o Recombination occurs between non-sister homologues and they start to synapse.
3. Pachytene:
   o Synapsis completed.
   o Synapsed chromosomes are held together by the proteins of the synptonemal complex.
   o Mature crossovers are formed.
4. Diplotene:
   o Homologues desynapse so two strands can be seen.

5.	Diakinesis:
o	Homologues move apart except for the crossover regions.
6.	Metaphase I
7.	Anaphase I
8.	Telophase I.

Question 3

What happens when meiosis goes wrong? What can this result in?

Answer 3

•	Failures can lead to aneuploidy (variation in chromosome number)
•	 Can result in:
o	miscarriage
o	liveborn with trisomy.
o	Reduced fertility in crops.