3.4.3 | GENETIC DIVERSITY CAN ARISE AS A RESULT OF MUTATION OR DURING MEIOSIS Flashcards
what is a gene mutation
a change in the base sequence of DNA (that can arise spontaneously during DNA replication
what is a mutagenic agent
a factor that increases rate of gene mutation
explain how a mutation can lead to the production of a non-functional protein for enzyme
changes sequence in base sequence of DNA so changes sequence of codons on mRNA
so changes sequence of amino acids involved polypeptide
so changes position of hydrogen/ionic/disulphid bridges
so changes tertiary structure of protein
enzymes active site changes shape so substrate can’t bind, enzyme-substrate complexes can’t form
explain the possible effects of a substitution mutation
base/nucleotide in DNA replaced by a different base/nucleotide
this changes one triplet so changes one mRNA codon so one amino acid in polypeptide changes
- tertiary structure may change if position of hydrogen/ionic/disulphid bridges change
or amino acid doesn’t change
- as genetic code is degenerate or mutation is in an intron
explain the possible effects of a deletion mutation
one nucleotide/base removed from DNA base sequence
changes sequence of DNA triplets from point of mutation (frame shift)
changes sequence of mRNA codons after mutation
changes sequence of amino acids involved in primary structure of polypeptide
changes position of hydrogen/ionic/disulphide bridges in tertiary structure of protein
changes tertiary structure/shape of protein
describe features of homologous chromosomes
chromosomes that share the same structural features
what is the product of meiosis
four genetically different haploid cells
define loci
position of gene on chromosome
what happens in prophase I of meiosis I
chromatids condense and arrange themselves into homologous pairs
crossing over occurs
the nuclear envelope disintegrates
spindle fibres form
what happens in metaphase I of meiosis I
homologous pairs line up along the equator and attach to the spindle fibre by their centromeres
what happens in anaphase I of meiosis I
homologous chromosomes are separated
what happens in telophase I of meiosis I
chromosomes reach opposite poles of the cell
nuclear envelope disintegrates spindle reforms around the chromosomes
cytokines results in the formation of two daughter cells
what happens in prophase II of meiosis II
chromosomes condense
nuclear envelope disintegrates spindle disintergreates
spindle fibres form
what happens in metaphase II of meiosis II
chromosomes attach to the spindle fibres by their centromeres in the equator of cell
what happens in anaphase II of meiosis II
sister chromatids separated
what happens in telophase II of meiosis II
chromatids reach opposite poles of the cell
nuclear envelope reforms and cytokinesis takes place
four genetically unwise daughter cells produced
name two ways in which meiosis produces genetic variation
crossing over
independent assortment
explain how crossing over creates genetic variation
homologous pairs of chromosomes twist around eachother
chiasmata formed (point of contact between non-sister chromatids)
alleles exchanged between chromosomes creating new combinations of alleles on chromosomes
define allele
different versions of the same gene
explain how independent segregation creates genetic variation
homologous pairs randomly align at equation - so random chromosome from each pair goes into each daughter cell
creating different combinations of maternal + paternal chromosomes/alleles in daughter cells
