Topic 3B : Reproduction & Inheritance Flashcards
How are mammalian eggs adapted for their function ?
The mammalian eggs have a zona pellucida which is a protective outer layer which the sperm has to penetrate in order for fertilisation to occurs and it also prevents polyspermy
The mammalian eggs have a haploid nucleus to restore a full set of chromosomes at fertilisation
The mammalian eggs also contain loads of nutrients which are essential for embryo development
The mammalian eggs have cortical granules which release substances which cause the zona pellucida to harden
The mammalian egg also has follicle cells which form a protective coating around the egg
How are mammalian sperm adapted for their function ?
The mammalian sperm contain many mitochondria to provide energy for the rotation of the flagellum which enables the cell to move
The mammalian sperm has acrosomes which contain digestive enzymes which break down the zona pellucida and allow the sperm to penetrate the egg
The mammalian sperm also contains a haploid nucleus to restore a full set of chromosomes at fertilisation
Describe the process of mammalian fertilisation
The sperm swim towards the egg
Once a sperm makes contact with the zona pellucida of the egg the acrosome reaction occurs where digestive enzymes are released from the acrosome of the sperm and digest the zona pellucida so that the sperm can move through it to the cell membrane of the egg cell
The sperm head fuses with cell membrane of the egg triggering cortical reaction where egg releases cortical granules in vesicles which contain chemicals that cause the zona pellucida to thicken making it impenetrable to other sperm (polyspermy)
Sperm nucleus enters the cell and the tail is discarded
The nucleus of sperm fuses with the nucleus of the egg
Where does fertilsation occur?
In the oviduct of the female reproductive system
In mammals, where is sperm deposited?
The sperm is deposited high up in the female vagina close to the entrance of the cervix meaning that in order for fertilisation to occur the sperm has to make its way up through the cervix and the uterus to the oviduct
What is the product of fertilisation?
Fertilisation between egg and sperm produces a diploid zygote which contains a full set of chromosomes
blastocyst
when a zygote becomes a blastocyst after a week of fertilisation/cell division
structure of blastocyst
fluid filled cavity forms
state the fate of the cells in a blastocyst
outer cells become placenta as they are totipotent
inner pluripotent cells become foetus
meiosis
cell division that happens in the reproductive organs and produces genetically different gametes
explain why it is important for gametes to be haploif
so when they join, the original diploid chromosome number will be restored
describe the outcome of meiosis and what happens to these cells in male and female organisms
four haploid cells and these in males become sperm and in females become eggs
state two ways in which meiosis can produce genetic variation
crossing over of chromatids
independent assortment of chromosomes
describe the process of crossing over
homologous pairs of chromosomes come together and pair up
two of the chromatids in each homologous pair twist around each other and twisted bits break off their original chromatid snd rejoin onto the other chromatid recombining their genetic material
how does crossing over of chromatids creates genetic variation
after they cross over, chromatids contain the dame genes but they now have a different combination of alleles
