[Unit 4.3] Genetic Diversity Through Mutation or Meiosis Flashcards
Genetic information, variation and relationships between organisms
define “meiosis”
cell division creates four haploid daughter cells
what is the purpose of meiosis 1
reduction division. halves the number of chromosomes
what are the two ways of creating variety in meiosis 1 and when do they happen
crossing over - prophase 1
independent segregation - metaphase 1
what is crossing over
homologous pairs twist around each other forming a chiasmata (point of cross over) creating a bivalent chromosome (with a cross over). The twisting causes tension which ultimately breaks. The broken end of chromatid arm re-joins onto the new chromatid forming a recombinant chromatid.
what is independent segregation
homologous chromosomes randomly arrange themselves on the equator next to each other.
what is the equation for “number of genetically different gametes”
2^n
where n is the number of homologous chromosomes.
what happens during anaphase 1
one copy of each pair of chromosomes go to the poles of the cell. Ergo genetic material has halved
what is the purpose of meiosis II
mitotic division. sister chromatids split into separate cells
what’s the difference between metaphase I and metaphase II
metaphase 1, chromosomes line up next to each other in homologous pairs.
metaphase 2, chromosomes line up down the equator of the cell
what happens during anaphase II
chromosomes are split and sister chromatids migrate to opposite poles of the cell
what results from telophase II
four haploid daughter cells
what are the three ways meiosis produces variation
independent segregation
crossing over
fertilisation
define “non disjunction”
chromosomes don’t split equally during anaphase.
meaning gametes don’t have correct number of chromosomes
define “polyploidy”
changes in whole sets of chromosomes
define “aneuploidy”
changes in number of individual chromosomes
what results from polyploidy non disjunction in meiosis 1
two cells that are 2n gamete diploid
and two gametes that have no chromosomes
what happens when a diploid gamete fertilises with a haploid gamete
diploid (2n) + haploid (n)
will produce a triploid (3n)
what results from aneuploidy non disjunction in meiosis 1
two cells that are n+1 haploid gamete
and two cells that are n-1 haploid gamete
what happens when a haploid n+1 fertilises with a haploid gamete
zygote with extra chromosome (down syndrome) 2n+1 diploid
what happens when a haploid n-1 gamete fertilises with a haploid gamete
zygote with a missing X chromosome (only in females) so they have turner syndrome.
2n-1 diploid
define mutation
change in DNA base sequence
what are the 6 types of mutation
insertion
deletion
substitution
inversion
duplication
translocation
define deletion
remove one or more base.
the frame shifts
affects every triplet after point of mutation
resulting protein is non-functional
define insertion
adding one or more base
the frame shifts
affects every triplet after point of mutation
resulting protein may be non-functional
define substitution
one base in triplet is changed
only changing that one amino acid
no frame shift
why may a substitution mutation have no effect. what is it called when this happens
genetic code is degenerate
may still code for same amino acid
having no affect
a “silent” mutation
define inversion
section of bases detaches from DNA
when it re-joins it is inverted
different amino acids coded
define duplication
one or more bases repeated.
the frame shifts
define translocation
section of bases on chromosomes detaches
attaches on to different chromosome
substantial alteration
causes significant impact on gene expression
define heredity mutation
gamete containing mutation (for type of cancer or genetic disorder) is fertilised.
mutation will be present in foetus.
