3.4.3 meiosis and mutations Flashcards
what happens in meiosis 1?
PROPHASE 1 = homologous chromosomes appear make of two chromatids joined at the centromere.
METAPHASE 1 = spindle fires form and homologous pairs line up at the equator of the cell, by attaching to the spindle fibres using their centromere. crossing over occurs and a bivalent is formed, which is genetic recombination - increasing genetic variation.
ANAPHASE 1 = no centromere split, homologous pairs pulled to opposite poles of cells.
TELOPHASE 1 = nuclear membrane reforms around the 2 haploid nuclei.
what happens in meiosis 2?
PROPHASE 2 = nuclear membrane begins to break down again. chromatids are still joined by the centromere.
METAPHASE 2 = new spindle fibres form. chromosomes line up on the equator of the cell. chromatids attach to spindle fibres using their centromere.
ANAPHASE 2 = centromeres divide and chromatids are pulled to opposite poles of the cell.
TELOPHASE 2 = nuclear envelope reforms and chromosomes condense giving 4 haploid nuclei.
what is independent segregation?
- the chromosomes in a homologous pair are separated in meiosis 1 in a random formation = to produce two genetically varied daughter cells.
- the combination of chromosomes is random, independent segregation = increases genetic variation.
when does genetic recombination occur?
metaphase 1
what is genetic recombination?
crossing over.
what is chiasmata?
points where non-sister chromatids of homologous chromosomes are joined.
what are bivalents?
pairs of homologous chromosomes coiled around each other and joined at multiple points.
what is a genetic mutation?
a change in the DNA base sequence of chromosomes, which often happens randomly during DNA replication.
what increases the rate of mutation?
mutagenic agents like radiation, chemicals, viruses.
what is a substitution mutation?
a point mutation which changes a single base (or more) for a different one.
what is the effect of a substitution mutation?
- may have no effect due to degenerate genetic code = so same amino acid.
- change the amino acid as it will change the tertiary structure unless the chemical properties are the same.
- introduce a stop triplet and shorten the polypeptide chain.
what is an addition mutation?
add one or more bases.
what is a deletion mutation?
remove one or more bases.
what is the affect of a deletion mutation?
causes a frameshift as all base triplets after the mutation are changed, this cause a significant change in tertiary structure. as it changes number of nucleotides in the DNA sequence so its not divisible by 3. due to translation reading triplets = protein made is significantly different.
