4.3 - Genetic Diversity Due To Mutations & During Meiosis Flashcards
What is a mutation?
An alteration to the DNA base sequence.
Often arise randomly during DNA replication.
Why might a mutation not lead to a change in the amino acid sequence?
Genetic code is degenerate - so mutation may end up coding for the same amino acid as the original triplet.
Mutation may occur in intron.
What is a substitution mutation?
When a nucleotide in the DNA sequence is replaced by another.
More likely to be a **”quiet mutation”* meaning no change occurs in the amino acid sequence.
What is a deletion mutation?
When a nucleotide in the DNA sequence is lost.
This is more likely to be harmful & significant, as it leads to a frame shift which means the entire amino acid sequence will be different.
What is a mutagenic agent?
Factors that increase the rate of gene mutation.
Give examples of mutagenic agents.
X-rays, UV light, gamma rays, certain chemicals
What is a polyploidy chromosome muation?
Where an individual has 3+ sets of chromosomes instead of 2.
What is chromosome non-disjunction?
When chromosomes fail to separate correctly in meiosis, resulting in gametes with one more or less chromosome than normal.
What is meiosis?
Form of cell division
Produces 4 genetically different haploid daughter cells
Which are known as gametes
How does meiosis differ from mitosis?
- meiosis produces 4 genetically different cells with half the number of chromosomes as the parent cells.
- mitosis produces 2 genetically identical cells with the same number of chromosomes as the parent cells.
What happens during meiosis 1?
- homologous chromosomes pair to form bivalents.
- crossing over (exchange of genetic material) occurs at chiasmata.
- cell divides into two, homologous chromosomes separate randomly
Each cell contains either maternal or paternal copy.
What happens during meiosis II?
- independent segregation of sister chromatids
- each cell divides again, producing 4 haploid cells.
In which 2 ways does meiosis produce genetic variation?
1) crossing over during meiosis I
2) independent segregation of homologous chromosomes & sister chromatids.
Results in new combinations of alleles.
