4.3 Genetic diversity can arise from mutation or 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 the amino acid sequence?
- Genetic code is degenerate so mutation may end up coding for 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
How does substitution mutation affect the amino acid sequence?
A substitution may not always be harmful as the as the substituted nucleotide may code in that triplet for the same amino acid
What is a deletion mutation?
When a nucleotide in the DNA sequence is lost
How does deletion mutation affect the amino acid sequence?
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?
Factors that increase the rate of gene mutations
Give examples for mutagenic agents?
- X-rays
- UV light
- Gamma rays
- Certain chemicals e.g. in alcohol and tobacco
What is a polyploidy chromosome mutation?
Where an individual has three or more sets of chromosomes instead of two
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?
A form of cell division that produces four non-identical haploid cells (cells with half the number of chromosomes found in the parent cell) known as gametes
How does meiosis differ from mitosis?
- Meiosis produces four 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
Describe independent assortment of chromosomes
There are various combinations of chromosome arrangement. During meiosis 1 homologous chromosomes line up in pairs, the arrangement of pairs is random, meaning that the division into the daughter cells is random
Describe crossing over of chromatids
When pairs of chromosomes line up they can exchange some of their genetic material. Crossing over occurs when one chromosome may swap places with the same part of its homologous pair leading to a different combination of alleles on the gene
What happens during meiosis I?
- Homologous chromosomes pair to form bivalents
- Crossing over occurs at chiasmata
- Cell divides into two. Homologous chromosomes separate randomly. Each cell contains either maternal or paternal copy
