3.4.3 Genetic diversity due to mutations during meiosis Flashcards
what is a mutation?
An alteration to the DNA base sequence. Often arise spontaneously during DNA replication.
Why might a mutation not lead to change in amino acid sequence?
- degenerate code means that mutation may code for the same amino acid as original triplet
- mutation may occur in intron
what is a substitution mutation?
when a nucleotide in the DNA sequence is replaced by another. This is more likely to be a silent 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 and significant, as it leads to a frame shift which means the entire amino acid sequence will be different
what is a mutagenic agent? Give examples of this.
Factors that increase the rate of gene mutation. X-rays, UV light, gamma rays, certain chemicals e.g. in alcohol and tobacco
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 cells
with half the number of chromosomes 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 two genetically identical cells with the same number of chromosomes as the parent cells.
what happens during meiosis (I)?
- Homologous chromosomes pair to form bivalents.
- Crossing over (exchange of sections 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 two ways does meiosis produce genetic variation?
- Crossing over during meiosis (I)
- independent assortment (random segregation) of homologous chromosomes & sister chromatids
- result in new combinations of alleles