Meiosis And Mutation Flashcards
What is a gene mutation
A change in the DNA base sequence of chromosomes
How can mutations arise and what are the 2 ways this happens
-Spontaneously in DNA replication :
-base deletion
-base substitution
Describe base deletion
One base is deleted causing a frameshift
- this changes the subsequent codons result in amino acids being coded incorrectly
Describe base substitution
One base is substituted
- causing a change in the genetic code
Why might base substitution not cause a change in the sequence of encoded amino acids
The degenerate nature of genetic code
What is mutagenic agents
It can increase the rate of gene mutation
What are examples of mutagenic agents
UV light
Gamma rays
X-rays
Mustard gas
Mutations in the number of chromosomes can arise spontaneously by what
Chromosome non-disjunction during meiosis
What is chromosome non disjunction
When the chromosomes do not split equally during anaphase
Describe the process meiosis
DNA replicates in interphase
- 2 rounds of division
Meiosis I
-chromosomes in homologous pairs
-homologous chromosome pairs separate- independent segregation and crossing of homologous chromosomes happens
Meiosis II
-sister chromatid pairs separate
-produces 4 haploid cells that are genetically different
What are the 2 mechanisms in meiosis which introduce variation
Crossing over
Independent segregation which both occur in meiosis I
how does random fertilisation of haploid gametes further increases genetic variation within a species.
Fertilisation produces zygotes with different combinations of chromosomes to both parents
-mixing of genetic material in sexual reproduction results in genetic diversity in a species
genetically different daughter cells result from the independent segregation of homologous chromosomes explain how
- Homologous pairs of chromosomes lineup randomly on each side of the equator
-it’s random of which the homologous pair of the maternal or paternal chromosome ends up in which daughter cell once seperated
In each 4 daughter cells it has different combinations of Paternal and maternal chromosomes
-leads to genetically different daughter cells
crossing over between homologous chromosomes results in further genetic variation among daughter cells. Explain how
- Crossing over of chromatids in meiosis I
-parts of chromatids twist and break due to tension-broken part of chromatid recombine with another chromatid
-results in a different combination of alleles in 4 daughter cells
Independent segregation creates a large number of possible combinations of chromosomes in daughter cells
How can this be calculated
Using 2n
N= number of homologous pairs
