Mutation And Meiosis Flashcards
Affect of mutation
Change in the base sequence of chromosomes may code for different amino acids. Change in sequence of amino acids affects hydrogen, ionic and sulfur bonds which changes the tertiary structure of proteins so a different polypeptide is formed
When is mutation most likely to occur
During DNA replication in interphase
What can cause frequency of mutations to increase (3)
X-rays
Carcinogens
UV light
Types of mutation (3)
Substitution
Deletion
Addition
Substitution
One base changed for another base so one amino acid may be changed
Deletion
A base has been removed causing frame shift do changes whole sequence of amino acids after the mutation
Addition
A base has been added causing frame shift so changes whole sequence of amino acids after the mutation
What does meiosis produce
4 genetically different daughter cells each containing half the number of chromosomes as the parent cell
Why must gametes have half the chromosomes
Haploid cell so when they fuse with another gamete at fertilisation, it restores the chromosome number
How does meiosis cause variation
Independent segregation of homologous chromosomes
Genetic recombination by crossing over
Independent segregation
… of homologous chromosomes
Random chromosomes from homologise pair go to either two of the new cells
Genetic recombination
… by crossing over
Forms new combinations of alleles when chromatids wrap around one another and share genetic information
Meiosis steps (4)
Homologous chromosomes pair up and crossing over occurs where the chromatids wrap around one another
Homologous pairs separate so one chromosome from each pair enters the daughter cell
Chromosomes line up along spindle equator and chromatids move apart by contracting spindle fibres attaching and pulling chromatids to opposite poles
Two cells split by cytokinesis to form four genetically different daughter cells
Allele
A different form of gene
Locus
The fixed position a gene occupies one a particular DNA molecule
