meiosis Flashcards
(8 cards)
how is genetic diversity caused during meiosis and explain them
this can happen by crossing over and recombination of alleles and random segregation. this produces unique gametes that are genetically different. crossing over occurs in prophase 1 and forms chiasmata
-homologous pairs of chromosomes associate and form a bivalent
-chiasmata forms
-equal lengths of non sister chromatids or alleles are exchanged
-producing new combination of alleles
in metaphase 1 , homoglous pairs line up either side of the equator
is it completely random which side of the equator is maternal and paternal
when they are seperated , one of each pair ends up in a daughter cell
this shuffling leads to different combos of maternal and paternal chromosomes in daughter cells
what are other sources of variation
fertilisation - random mating with random gametes - this results in random fusion of gemetes and produces new allele combinations of new maternal and parental chromosome combinations
what mutation occurs in meiosis
non disjunction mutation during meiosis can arise spontaneously and affect the number of chromosomes this is the failure to seperate chromosomes during meiosis
this results in different numbers of chromosomes
Why may offspring’s be sterile
Too many chromosomes
Chromosomes don’t separate
So meiosis doesn’t happen
Define gene mutation and explain how a gene can have no effect on an individual and a positive effect on an individual
Change in the base/nucleotide (sequence of chromosomes/DNA);
For 4 marks at least one mark must be scored in each section of the answer.
Accept named mutation for ‘change’.
2. Results in the formation of new allele;
(Has no effect because)
3. Genetic code is degenerate (so amino acid sequence may not change);
OR
Mutation is in an intron (so amino acid sequence may not change);
Accept description of ‘degenerate’, eg some amino acids have more than one triplet/codon.
4. Does change amino acid but no effect on tertiary structure;
5. (New allele) is recessive so does not influence phenotype;
(Has positive effect because)
6. Results in change in polypeptide that positively changes the
properties (of the protein) OR
Results in change in polypeptide that positively changes a named protein;
For ‘polypeptide’ accept ‘amino acid sequence’ or ‘protein’.
7. May result in increased reproductive success OR
May result in increased survival (chances);
Describe crossing over
- a bivalent forms where the chromosome pairs line up
- chiasma forms (point where chromatids cross over)
- equal amounts of dna are exchanged from each chromatid
- this produces a new combination of alleles
why do mutations not cause a change in protein
- mutation may result in a codon which codes for the same amino acid
- mutation may be in an intron
- mutation may be in a recessive allele
- mutation may cause amino acid with similar properties
why does a change in codon result in a change in protein structure
amino acid sequence changes
hydrogen bonds change
tertiary structure changes
mutagenic agents can increase rate of gene mutation for example uv radiation and chemicals
