Variation in Chromosome Number Flashcards
What is a euploid cell?
A cell that contains multiple of one complete set of chromosomes.
A “normal” amount of chromosomes.
What does euploidy look like in humans?
In human cells, one complete set consists of one of each autosome and one sex chromosome, and two complete sets consist of two of each autosome and two sex chromosomes (either XY or XX).
How many pairs of chromosomes do humans need to be fully functional?
23 pairs
How many complete sets of chromosomes are in euploid and haploid cells?
One complete set
How many complete sets of chromosomes are in euploid and diploid cells?
Two complete sets
What is an aneuploid cell?
Any variation from a euploid cell.
An abnormal amount of chromosomes.
What are the most common types of aneuploidies?
Trisomy and monosomy
What is a monosomy?
Having one copy of one chromosome
What is a trisomy?
Having three copies of one chromosome
How does aneuploidy affect late-stage cancer cells?
Many late-stage cancer cells have numerous aneuploidies but do not die from these.
What happens if all of an individual’s cells are aneuploid?
This situation is detrimental to the individual
What do aneuploidies affect?
Aneuploidy does not affect the cell itself. It affects the surrounding cell and development.
Basically bad interaction with neighbors, but functions perfectly.
Aneuploidies involving which chromosomes are more severe?
Autosomes, not sex chromosomes
What percentage of aneuploidies are observed in live births?
0.3% of all live births
What are the most common autosomal aneuploidies?
Trisomy 13, 18, and 21
What syndrome is caused by trisomy 21? At what frequency?
Down syndrome; 1 in 800 live births
What syndrome is caused by trisomy 18? At what frequency?
Edwards syndrome; 1 in 6000 live births
What syndrome is caused by trisomy 13? At what frequency?
Patau syndrome; 1 in 15000
What is a stillbirth?
Death of a fetus after the 20th week, but before birth
What is a spontaneous abortion/miscarriage?
Death of a fetus after 6-8 weeks to the 20th week
Death prior to 6-8th week
Similar to stillbirth/miscarriages
Usually occurs before woman knows she is pregnant
Hard to study
What percentage of aneuploidies are observed in stillbirths?
4%
Seen in trisomy 13, 18, and 21
What percentage of aneuploidies are observed in spontaneous abortions?
35%
Seen in trisomy 16, 21, and 22
What is the reason that autosomal monosomies are rarely observed in spontaneous abortions, stillbirths, or live births?
Autosomes are necessary for the development of fetuses. Having a monosomy in an autosome means the dosage of that chromosome is insufficient to continue development (i think)
What are the three most common sex chromosome trisomies?
XXX
XXY
XYY
What syndrome is caused by XXX? At what frequency?
Triple X
1 in 1000 females
What syndrome is caused by XYY? At what frequency?
Jacob’s Syndrome
1 in 1000 males
What syndrome is caused by XXY? At what frequency?
Klinefelter syndrome
1 in 650 males
What is XO?
A sex chromosome monosomy
O refers to a missing sex chromosome
What syndrome is caused by XO? At what frequency?
Turner’s syndrome
1 in 2500 females
Which occurs more in spontaneous abortions/stillbirths: Sex chromosome trisomies or XO?
What is nondisjunction?
The failure of dyads or monads to segregate properly during meiosis I or meiosis II
When can nondisjunction occur?
Either meiosis I or meiosis II
What happens during meiosis I nondisjunction?
Two dyads within the same tetrad do not separate.
There will be aneuploid four gametes produced. Two gametes will have an extra chromosome and produce a trisomy. Two will be missing a chromosome a produce a monosomy.
What happens during meiosis II nondisjunction?
Two monads within the same dyad do not separate.
