3B Flashcards
How are mammalian eggs adapted for function
Protective zona pelucida, cortical granules to cause zona pellucida to harden, haploid nucleus
How are mammalian sperm adapted for their function
Contain many mitochondria for energy required for moving plus the flagellum.
Acrosome (head) contains digestive enzymes which break down the zona pellucida of the egg.
Outline the three main stages of mammalian fertilisation
Acrosome reaction, cortical reaction and nucleic fusion.
Escribe the acrosome reaction
Digestive enzymes are released from the head of the sperm that digest the zona pellucida.
Describe the cortical reaction
Eggs cell releases contents of cortical granules (exocytosis) into space between cell membrane and zona pellucida making it thicken.
What triggers the cortical reaction
Membrane of the sperm and egg fusing.
Describe nuclei fusion
Only the sperm nucleus enter the egg cell, the tail is discarded and the two haploid nuclei fuse
Define homologous pair of chromosomes
The pair of maternal and paternal chromosomes
Describe chromatids
When DNA condenses to form a double armed chromosome
Outline the main stages of meiosis
- DNA replicates and condenses to form chromatids
- The homologous pairs match up together
- 1st division- homolugous pairs separate
- Second division- sister chromatids separate
How many cells are formed in meiosis and how do they compare to each other?
4 and they are all genentically distinct
Give two reasons for meiosis leading to genetic variation
Crossing over and random assortment
Describe random assortment
When the four daughter cells are formed, different combinations of maternal and paternal chromosomes end up in each new daughter cell
What is a locus?
The fixed position on a chromosome occupied by a gene.
What is meant by autosomal linkage?
Where two or more genes are located on the same (non-sex) chromosome, so are inherited almost as if they were the same gene. The closer the loci, the closer the linkage, as the genes are less likely to be recombined.
