Reproduction and fertilisation Flashcards
What are the features of an egg cell?
Follicle cells are on the outside, they form a protective coating.
The zona pellucida is a protective glycoprotein layer that sperm must penetrate.
The plasma membrane and a nucleus.
What are the features of a sperm cell?
The acrosome contains digestive enzyme to allow the sperm to penetrate the zona pellucida.
A nucleus and plasma membrane.
A flagellum and loads of mitochondria to provide ATP for movement.
Where does fertilisation occur?
In the oviduct
What is the acrosome reaction?
Sperm touches the ZP - digestive enzymes form the acrosome are released, penetrating it. The sperm head fuses with the plasma membrane of the egg cell.
What is the cortical reaction?
Follows the acrosome reaction: egg cell releases cortical granules into the area between the plasma membrane and the zona pellucida. The chemicals from the granules thicken the ZP and prevent penetration by more sperm.
When does fertilisation occur?
Fertilisation occurs when the sperm nucleus fuses with the egg cell nucleus, forming a zygote with the full number of chroms.
Why is meiosis so important when it comes to producing gametes?
Meiosis ensures that the gamete (sperm or egg cell) only has half your number of chromosomes at fertilisation.
How does meiosis produce genetically different gametes?
- Independent assortment
2. Crossing over
Describe independent assortment
Independent assortment refers to the different combinations of parental and maternal chroms. that go into each cell, this begins in the first division of meiosis.
Describe the crossing over of chromatids
Crossing over: when two of the chromatids in each homologous pair twist around each other before the first division, the twisted sections break off their original chromatids and rejoin onto the other - recombining genetic material. The chromatids contain the same genes but now have a different combination of alleles. So the resulting four daughter cells will have chromatids with different alleles.
What are linked genes?
Linked genes are genes that have their loci on the same chromosome. Because of this, the genes will stay together during IA and their alleles will be passed on to offspring together, unless CO splits them up first. Genes are more linked the closer their loci on the same chromosome are because CO is less likely to split them up.
What are sex-linked genes?
Sex-linked genes: genes that have their loci on a sex chromosome.
Why are most genes on the sex chromosomes X-linked?
X chromosomes are larger than Y chromosomes.
Why are males more likely to express a recessive phenotype for sex-linked genes?
Males have only one X chromosome, so they have only one allele for many X-linked genes. Recessive phenotypes are therefore more likely to be expressed.
