CELS 191 Lecture 16 Flashcards
the successful conclusion of meiosis requires the correct ____ of in anaphase 1 pairs of _________ and in anaphase 2 the pairs of _______.
disjunction - homologous chromosomes - sister chromatids
what is meiotic disjunction and what does this mean in meiosis 1 and meiosis 2
the failure of chromosomes to seperate (disjoin) properly. nondisjunction in meiosis 1 means homologous chromosomes do not seperate - in meiosis 2 this nondisjunction means sister chromatids do not seperate
can nondisjunction arise in mitosis
yes
when you get _______ in meiosis 2, the sister chromatids are identical except for recombination, they will be identical around the _____. therefore the chromosomes in the gamete that has 1 too many chromosomes will also be identical around the centromere. however if nondisjunction occurs in meiosis 1 it is the failure of ________ to seperate but the sister chromatids seperate just fine so the two daughter cells which have one too many chromosomes will not be identical around the centromere.
nondisjunction - centromere - homologous chromsomes
how many chromosomes will each daughter cell have if non-disjunction occurs at meiosis 1 e.g. (n+1)(n)(n-1)
(n+1)(n+1)(n-1)(n-1)
how many chromosomes will each daughter cell have if non-disjunction occurs at meiosis 2 e.g. (n+1)(n)(n-1)
(n+1)(n-1)(n)(n)
what is aneuploidy
this is a condition where meiotic nondisjunction results in some gametes receiving an abnormal number of a particular chromosome. when these gametes fuse with a normal gamete the resulting zygote will also have an abnormal number of a particular chromosome
what does monosomic mean
fertilisation that involves a gamete with no copy of a particular chromosome will result in a missing chromosome in the zygote (2n-1). this zygote in monosomic for that chromosome.
if a chromosome is present in a triplicate in the zygote the zygote is ____ for that chromosome
trisomic
what is the estimated occurrence rate for monosomy and trisomy (this is very hard to measure because many of these zygotes spontaneously abort)
10-25% of all human pregnancies
what is Down syndrome
an autosomal (because it doesn’t occurring the sex chromosomes) aneuploid condition in which there are three copies of chromosome 21 - karyotypes have 47chromosomes
what is the most common aneuploid condition in humans
down syndrome
what is Klinefelter syndrome
an aneuploid condition of a sex chromosome in which individuals have two X chromosomes and a Y. karyotypes have 47 chromosomes.
how do aneuploidy conditions affect fertility
they greatly reduce fertility
what is turner syndrome
an aneuploid condition of a sex chromosome in which individuals have only one X chromosome. karyotypes have 45 chromosomes. there are differences in the level of intellectual impairment depending on if the individual inherited an X chromosome from the mother or father
what is polyploidy and what causes it
the possession of more than two complete chromosome sets - this ay arise due to nondisjunction of all chromosomes in one gamete of the failure of a diploid zygote to divide after replicating its chromosomes in interphase.
where is polyploidy common
in the plant kingdom
which disrupts the genetic balance more - one extra or missing chromosome or an extra complete set of chromosome
one extra of missing chromosome has a much larger effect on phenotype
what are some other examples of chromosomal aberrations
deletion, duplication, inversion and translocation
when do deletion, duplication, inversion and translocation of chromosomes occur
during synapsis
what is deletion
when a chromosomes breaks in one of more places (usually due to crossing over) and a portion is lost, the missing piece is called a deletion. even small deletions can have severe effects and or be lethal. deletions usually result in a loss genes but do not change the order of the remaining genes
what is duplication
when a part of a chromosome is present more than once in the genome, it results in a duplication. this may arise when a broken fragment of one chromosome reattaches as an extra segment to a non-sister chromatid. this usually happens during crossing over. duplications usually change the number of some genes on a chromosome but do not change the order of remaining genes. duplications tend to have harmful effects.
what is an inversion
when a part of a chromosome in inverted within a chromosome, ir is referred to as an inversion. an inversion requires a break at two points along the length of the chromosomes and subsequent insertion of the inverted segment. inversion do not change the number of genes on a chromosomes but will change the linear order of the genes within the inverted segment
what are the impacts of inversions
inversions result in a change to the order of genes within the inverted segment. consequences on fertility may be more complex. inversion can cause problems in meiosis, as homologous chromosomes cannot align exactly. crossing over can then lead to deletions and duplications
