Genetics and Diversity - Meiosis and Mutations Flashcards
What is a mutation?
any change to the quantity or the base sequence of DNA
What is a gene mutation?
any change to the nucleotide bases
What are the 3 types of mutation?
- Substitution of bases
- Deletion of bases
- Chromosome mutation
What is substitution mutation?
When one nucleotide is replaced by another in the sequence/codon
What is the effect of substitution mutation?
may have an affect but not necessarily:
the triplet codon could still code for the amino acid but it could also now code for a different amino acid
What is deletion mutation?
When a base is deleted from the sequence/codon
What is the effect of deletion mutation?
All triplets in the sequence will be read differently as each will be shifted to the left, forming new triplets
Why is deletion of bases more likely to lead to a dysfunctional protein than subsitution of bases?
Because in substitution only one codon is affected, whereas in deletion all of the codons following the mutation are affected
What is a chromosome mutation?
When the structure or number of chromosomes change
What are the 2 types of chromosome mutation?
Polyploidy
Nondisjunction
What is a polyploid mutation?
When each pair has an extra chromosome
eg a human with polyploidy would have 69 chromosomes not 46
What is a nondisjunction mutation?
when a homologous pair fails to separate during meiosis, resulting in one of the pairs having one more or less chromosomes
How are nondisjunction and polyploid mutations linked?
If every pair of chromosomes was nondisjuncted, it would be the same as a polyploid mutation
What is an example of a nondisjunction mutation?
Down’s syndrome
In which type of organism is polyploid mutations more common?
plants
What is the link between polypeptide production and Alzhiemer’s disease?
Alzhiemer’s is caused by a failure in the splicing of pre-mRNA, so non-functional polypeptides are produced
What is meiosis?
a special form of cell division that produced gametes
What are the functions of meiosis?
- to form halpoid cells with 1/2 the chromosome number
- to re-arrange the chromosomes with a new combination of alleles
What is crossing over?
the exchange of genetic material between a pair of homologous chromosomes during meiosis
What is the process of crossing over?
piece of chromatid from one chromosome touches chromatid of the other
chromatids become twisted around each other, creating tension, causing portions to break off
broken portions rejoin chromatids of homologous partner (recombination)
results in different combination of alleles in each chromosome
What is recombination?
when the broken chromatids rejoin the chromosomes during crossing over
What part of crossing over ensures that there is no genetic information lost?
the material is exchanged between homologous chromosomes at the same gene loci
What are the ways that variation is introduced in meiosis?
crossing over
independent segregation
cross fertilisation
What is independent segregation?
the random order that the chromosomes align in at the equator of the cell
How does independent segregation introduce variation?
they way that one homologous pair randomly lines up will be different to how others line up, so the chances of each maternal or paternal chromosome entering a gamete is random
How can the number of possible chromosome combinations in a gamete be calculated?
2n
where n = haploid number
What is the number of chromosome combinations in humans?
223
How does cross-fertilisation introduce variation?
the fusion of male + female gametes is random
What is cross fertilisation?
the fusion of male and female gametes
What is independent assortment?
the random order that the chromosomes line up in the equator of the cell
