3.4.3 Genetic diversity can arise as a result of mutation or during meiosis Flashcards
Describe how crossing over introduces variation
Occurs during mitosis one
Homologous pair of chromosomes associate forming a bivalent
Chiasma forms
Equal tenths of the non sister chromatids are exchanged
Producing new combinations of alleles
Describe how independent segregation introduces variation
Homologous chromosomes align opposite at the equator
It random which side the parental and maternal chromosomes are
these separate into daughter cells and large combination of chromosome in daughter cells
What two factors can influence genetic diversity ?
Meiosis
Mutations
Homologous chromosomes carry the same genes but they are not genetically identical. Explain why
Homologous chromosomes carry different alleles
Explain the two ways in which the behaviours of chromosomes during meiosis produces genetic variation in gametes
Crossing over - different combinations of alleles
Independent segregation - different combination of maternal and parental chromosomes/ independent assortment of chromosomes
Give four differences between meiosis and mitosis
- Reduce number of chromosomes, maintains the same number of chromosomes as parent nucleus
- Homologous chromosomes associate in pairs, homologs chromosomes do not associate in pairs
- Crossing over, no crossing over
- Genetically different, genetically identical
What is the term used to describe a pair of homologous chromosomes
Bivalent
Give a process other than crossing over and independent segregation that results in genetic variation
Mutation - leads to different allele produced by different sequence of bases
What affects the rate of mutation
Environment
Why can different mutations not be passed onto different species
Different species do not interbreed as cannot produce fertile offspring
So mutations cannot be passed on from one species to another
Explain the appearance of homologous chromosomes
Two chromatids joined by a centromere, due to DNA replication
Define ‘gene mutation’ and explain how a gene mutation can have:
* no effect on an individual
* a positive effect on an individual.
- Change in the base sequence
- Genetic code is degenerate so amino acid sequence may not change
OR
Mutation is in an intron (so amino acid sequence may not change.
Has positive effect because results in change in polypeptide that positively changes the proteins
properties
For example may result in increased reproductive success OR result in increased survival
Genetic variation within a species is increased during meiosis by crossing over and the independent segregation of homologous chromosomes.
Apart from mutation, explain one other way genetic variation within a species is increased.
Random fusion of gametes
New allele combinations
