3.6, 3.7 Gametes and Fertilisation (not done) Flashcards
3.6 Understand how mammalian gametes are specialised for their functions (including the acrosome in sperm and the zona pellucida in the egg). 3.7 Know the process of fertilisation in mammals, including the acrosome reaction, the cortical reaction and the fusion of nuclei.
1
Q
What are gametes?
A
the male and female sex cells found in all animals that reproduce sexually
2
Q
What are two gametes joined by fertilisation called?
A
a zygote
3
Q
What are the gametes in animals?
A
female = egg/ovum
male = sperm
4
Q
How many chromosomes do humans have? Where do these come from?
A
- 23 pairs
- half from the mother, half from the father
- 46 in total
5
Q
How many chromosomes do gametes have? How many chromosomes do body cells have?
A
gametes = half the number of chromomes (n) - haploid
body cells = full number of chromosomes (2n) - diploid
6
Q
What is fertilisation?
A
the exact moment when the nuclei of the male and female gametes fuse
7
Q
How is the egg specialised?
A
- zona pellucida: protective glycoprotein jelly like layer
- follicle cells from the ovary form protective coating around the egg
- contains protein and lipid food reserves for developing embryo
8
Q
How is the sperm specialised?
A
- flagellum: enables motility so the sperm can reach the egg
- mitochondria: provides energy for the flagellum to move
- acrosome: contains digestive enzymes that can break down the zona pellucida
9
Q
Describe the process of fertilisation:
A
- the sperm is attracted to chemicals released by the ovum
- the sperm reaches the egg and makes contact with the zona pellucida
- the acrosome reaction occurs:
- the acrosome swells, fusing with the sperms cell membrane
- the digestive enzymes are released
- these digest through the zona pellucida
- the sperm head fuses with the cell membrane of the egg
- the cortical reaction occurs:
- enzymes in vesicles called cortical granules are released
- this causes the zona pellucida to harden meaning it cannot be penetrated by other sperm cells
- this prevents polyspermy
- the sperm nucleus enters the egg cell and its tail is discarded
- the nucleus of the sperm then fuses with the nucleus of the egg and fertilisation occurs
