What type of mutation can alter dna by the addition of a nucleotide base?
a.)crossing-over
b.)deletion
c.)insertion
d.)base-pair substitution

insertion

Crossing over is when homologous* chromosomes exchange genes, resulting in gene combinations.

Deletion is when a base pair is deleted from DNA. Insertion is when a base pair is added to DNA. Both insertion and deletion are serious because every amino acid beginning at the mutation will most likely be incorrect. This will lead to a nonfunctional protein.

Base-pair substitution is a substitution of one base pair for another in DNA. The effects of this may be a silent** point, missense*** point, or nonsense point.

*A pair of matching chromosomes. They have the same genes but can have different versions.

**A special case where no amino acids are affected.

***Affects one animo acid. The whole protein structure and function may or may not be disrupted.

Results in a stop codon that shortens the protein.

the menstrual cycle – higher tier. negative feedback mechanisms affect the production of hormones in the menstrual cycle. oestrogen also stimulates the release of lh (luteinising hormone) from the pituitary gland, which in turn controls the production of progesterone.