Lecture 16: Errors in Meiosis Flashcards
What is meiotic nondisjunction
Meiotic nondisjunction is the failure of chromosomes to separate (disjoin) properly during meiosis.
What is nondisjunction in Meiosis I
homologous chromosomes do not
separate.
What is nondisjunction in Meiosis II
sister chromatids do not separate.
What is aneuploidy
cell has abnormal number of chromosmes, meaning number is not a multiple of the haploid number
What is trisomy 21
Down syndrome, 3 copies of chromosome 21
Karyotypes have 47 chromosomes
What is Klinefelter Syndrome
Aneuploid condition of a sex chromosome.
Extra copy of chromosome X
47 chromosomes in karyotype
Turner Syndrome
Individuals have one X chromosome
XO
Karyotypes have 45 Chromosomes
What is polyploidy
Possession of more than two complete chromosome sets
How does polyploidy come about
May arise due to nondisjunction of all chromosomes in one gamete, or the failure of a diploid zygote to divide after replicating its chromosomes during interphase.
Polyploidy can also arise through hybridization
Why are many polyploids infertile?
due to possessing an odd number of chromosome sets.
What is deletion
When a chromosome breaks in
one or more places and a
portion is lost, the missing piece
is called a deletion.
What is duplication (error in meiosis)
When part of a chromosome is present more than once in the genome, it results in a duplication.
What do duplications change
Duplications usually change the number of some genes on a chromosome, but do not change the order of the remaining genes.
Duplications tend to have harmful effects
What is an inversion (error in meiosis)
When part of a
chromosome is inverted (i.e. turned around 180º) within a chromosome, it is referred to as an inversion
What do inversions change
Inversions do not change the number of genes on a chromosome but will change the linear order of genes within the inverted segment.
What do inversions cause
Inversions can cause problems in
meiosis, as homologous
chromosomes cannot align exactly
Consequences on fertility may be
more complex.
What are translocations (error in meiosis)
Translocation is where a segment of a chromosome attaches to a nonhomologous chromosome.
Dont usually do not change the overall number of genes,
but they can sometimes change gene expression
How do translocations cause Familial down syndrome
In familial Down syndrome, one parent is the carrier of a 14/21 translocation
21 attatches to 14
parent can be phenotypically normal even though they only have 45 chromosomes
