gametes and fertilisation

Question 1

process of producing gametes

Answer 1

gametogenesis

Question 2

gametogenesis mechanism

Answer 2

• meiosis

produces genetically variable gametes from gamete mother cell

Question 3

process of meiosis

Answer 3

1) gamete mother cell DNA replicates
2) homologous chromosomes - with same centromere position, size + genes at same loci
3) points of chiasmata form and recombination of alleles occurs
4) Independent assortment - chromosomes pulled apart independent of parental origin
5) 2 daughter cells with 1 double chromosome each
6) mitosis occurs without replication
7) 4 genetically different gametes

Question 4

features of sperm

Answer 4

• head - acromsome at top (contains acrosomal enzymes)
• flagellum for swimming
• middle contains many mitochondria

Question 5

features of ovum (oocyte)

Answer 5

• surrounded by follicle cells (corona radiata)

- outer membrane = zona pellucida - a protective glycoprotein layer

Question 6

process of fertilisation

Answer 6

1) Implanted sperm reach ampulla (where fertilisation usually occurs)
2) Sperm squeezes through corona radiata (follicle cells)
3) Sperm head binds with receptors on zona pellucida
- triggers release of acrosomal enzymes, digest zona pellucida allows sperm to be incorporated into ovum
4) Incorporation of sperm into egg membrane triggers release of cortical granules, digesting sperm receptors on zona pellucida, prevents polyspermy
5) DNA fuses and zygote is formed