B - 3 Flashcards
What is the process involving the acrosome and cortical reactions?
The sperm head meets the protective jelly layer around the egg cell called the zona pellucida and the acrosome reaction occurs - enzymes digest the zona pellucida.
The sperm head fuses with the cell membrane of the egg cell thus allowing the sperm nucleus to enter the egg cell.
The cortical reaction occurs which causes the zona pellucida to harden.
The nuclei fuse and a full set of chromosomes is restored, forming a diploid zygote.
What is a locus?
The locus of a gene is its location on a chromosome.
What are sex linked disorders?
They occur on the x chromosome because the y chromosome is smaller than the x chromosome. Haemophilia is an example.
What are the stages in interphase?
G1 - the cell growths and DNA is replicated
S - chromosomes are replicated and begin to condense to form chromatin
G2 - the cell prepares to divide, replicating organelles
How is genetic variation achieved in Meiosis?
Crossing over - the exchange of sections of DNA between homologous chromosomes.
Independent assortment - there are various combinations of ways maternal and paternal chromosomes can be distributed between the two daughter cells.
What are multipotent, pluripotent and totipotent cells?
multipotent - can give rise to many differnet types of cells
pluripotent - give rise to many type of specialised cells but not placental cells
totipotent cells - can give rise to all types of specialised cells, inclusing placental cells.
How does differential gene expression occur and what is it?
It allows cells to become specialised.
- A stimulus acts on unspecialised cells
- Activator and repressor molecules can bind to promotor regions on the DNA sequence. Some genes can be switched on and are active. Some can be switched off by changing the structure of chromatin so it is less open to being freely transcribed.
- The active genes are then transcribed to produce RNA.
- mRNA is then translated on ribosomes and used to produce proteins.
- The protein has the ability to change the structure and function of the cell.
What is epigentics?
Modification to DNA which does not change the base. It modifies the activation of genes through DNA methylation and histone modification.
What is DNA methylation?
The proccess by which methyl groups are added to DNA. It modifies the function of DNA and supresses gene transcription. The change is permanent and prevents the cell from converting back into a stem cell or a different cell type.
What is histone modification?
Acetylation - addition of an acetyl group = activates chromatin and allows transciption.
Methylation - addition of a methyl group = causes activation/inactivation of chromatin.
What is the effect of the epigentic changes in relation to the lac operon?
This gene in bacteria is suppressed by repressor molecules in the absence of lactose, preventing energy expenditure. When lactose is present, it prevents the repressor molecule from binding to the operator region of the DNA, allowing the gene to be transcribed, thus its proteins produced.
What is meant by polygenetic inheritance?
Where a characteristic is determined by several different genes at different loci.
How are mammilian eggs adapted for function?
- Zona pellucida to prevent polyspermy
- Haploid nucleus to restore a full set of chromosomes at fertilisation.
What is meant by autosomal linkage?
Where two or more genes are found at the same non sex linked chromosme so are inherited almost as if they are the same gene.
In which way does meiosis ensure genetic variation?
1) Crossing over of alleles between chromatids
2) Independent assortment of chromosomes.
