genetic diversity can arise as a result of mutation or during meiosis Flashcards
what is a gene mutation
change in base sequence of DNA
can arise spontaneously during DNA replication
involves bess deletion or substitution
what does a mutation cause
change in base sequence of DNA
changes squeeze of codons on mRNA
changes sequence of amino acids in primary structure of polypeptide
changes position of hydrogen ionic and disulphide bins in tertiary protein
changes shape of protein
substance can’t bind to active site and from e-s complexes
what is base deletion
one nucleotide removed from DNA sequence
changes triplet from point of mutation
changes sequence of codons on mRNA after point of mutation
changes sequence of amino acids in primary structure
changes hydrogen bonds in tertiary
non functional
what is base substitution
nucleotide in DNA replaces with another
changes one triplet
changes one mRNA codon and one amino acid - sequence of amino acids in primary changes
due to degenerate nature the new triplet may code for same amino acid so primary structure remains unchanged
what are mutagenic agents
increase rate of gene mutation
eg. uv, alpha particles
what is the process of meiosis
DNA replicates so there are two copies of each chromosome called sister chromatids joined by centromere
2x2n
meiosis I - separates homologous pairs
- chromosomes arrange in homologous pairs
- crossing over in prophase creates genetic variation
- independent segregation in metaphase I increases genetic variation in gametes
2n
meiosis II - separates chromatids
n
creates 4 haploid cells that are genetically varied
how does meiosis cause genetic variation
crossing over
- allows exchanges between chromosomes
- creates new combinations of maternal and paternal ales
independent segregation
- random alignment of homologous pairs at equator - fans which chromosome from each pair goes to each daughter cell
- creates different combinations of maternal and paternal chromosomes and alleles
random fertilisation when two games fuse to form zygote
what is the importance of meiosis
two divisions - creates haploid gametes
diploid number restore after fertilisation
maintains chromosome number from one generation to next
genetic diversity
what is chromosome non-disjunction during meiosis
mutations in number of chromosomes
homologous chromosomes fail to separate during meiosis I or sister chromatids fail to separate during meiosis II
one gamete has extra copy of this chromosome (survives) and the other has non (dies)
arises spontaneously
causes genetic disease eg. down’s syndrome
how to calibrate the number of possible different combinations in daughter cells following meiosis assuming no crossing over
2^n
n= number of pairs of homologous chromosomes
two gametes
(2^n)^2
what are the differences between meiosis and mitosis
mitosis produced diploid cells meiosis produced haploid cells
two divisions in meiosis one division in mitosis
genetically identical in mitosis genetically different in meiosis
mitosis produced 2 daughter cells meiosis produced 4
