chapter 8 lecture 10 Flashcards
Metacentric
Centromere located approx. in the middle
- Arms of equal length
submetacentric
○ Centromere displaced toward one end
○ Creating along arm and a short arm
○ In humans long arm = q
○ Short arm - p
Acrocentric
○ Centromere is near one end, producing a long arm and a knob, or satellite at the other end
telocentric
centromere is at or very near the end of the chromosome
karyotyping
- complete set of chromosomes possessed by an organism
- chromosomes prepared from actively dividing cells
e. g. WBCs or bone marrow - halted in metaphase (with Colchicine)
- chromosomes arranged according to size
G bands
Giemsa stain
distinguishes areas of DNA rich in A-T base pairs
Q bands
quinacrine stain
- viewed under UV
variation of brightness from differences in relative amounts of C-G and A-T base pairs
C bands
reveals centromeric heterochromatin
R bands
regions rich in C-G base pairs
reverse Giemsa stain
T- banding
telomeric banding after heat denaturation
Aneuploidy
the loss or gain of (individual) chromosomes
polyploidy
contain more than two complete paired (homologous) sets of chromosomes
4 types of chromosome rearrangements
duplication
inversion
deletion
translocation
chromosomes duplication
a segments of the chromosome is duplicated
- have an extra copy
chromosome inversion
a segments of the chromosome is turned 180 degrees
chromosome deletions
a segment of the chromosome is deleted
- loss of a segment
- large ones detected because during pairing normal chromosome loops out
translocation
a segments of a chromosome moves from one chromosome to a nonhomologous chromosome or to another place on the same chromosome
what are 3 effects of deletions
- imbalances of gene products
- pseudodominance
- haploinsifficiency
pseudodominance
expression of a normally recessive gene
haploinsufficiency
gene not sufficient to produce a wild-type phenotype
paracentric inversion
inversion in which the breakpoints are confined to one arm of a chromosome
- the inverted segment does not span the centromere
pericentric inversion
inversion in which the breakpoints occur on both arms of a chromosome. the inverted segment spans the centromere
dicentric chromatid
has two centromeres
acentric chromatid
lacks a centromere
a dicentric chromosome is produced when crossing over takes place in an individual heterozygous for which type of chromosome rearrangement? a. duplication b. deletion c. paracentric inversion pericentric inversion
a. paracentric inversion
nonreciprocal translocation
segment moves from the first chromosome to the second without any transfer from the second to the first
- results in a chromosome will less material than it is supposed to have
reciprocal translocation
a 2-way exchange of segments between the chromosomes
-
Robertsonian translocation
the short arm of one acrocentric chromosome is exchanged with the long arm of another
- creates a large metacentric chromosome and a fragment that often fails to segregate and is lost.
What is the outcome of a Robertsonian translocation?
a. two acrocentric chromosomes
b. one metacentric chromosome and one chromosome with 2 very sort arms
c. one metacentric chromosome and one acrocentric chromosome
d. two metacentric chromosomes
b. one metacentric chromosome and one chromosome with 2 very sort arms
causes of aneuploidy
- deletion of centromere during mitosis and meiosis
- robertsonian translocation
- nondisjunction during meiosis and mitosis
Nullisomy
type of aneuploidy
- loss of both members of a homologous pair of chromosomes
2n-2
monosomy
type of aneuploidy
- loss of a single chromosome
2n-1
trisomy
type of aneuploidy
gain of a single chromosome
2n+1
tetrasomy
gain of two homologous chromosomes
2n+2
a diploid organism has 2n=36 chromosomes, How many chromosomes will be found in a trisomic member of this species?
2n+1
36+1 = 37
Turner syndrome is ?
Klinefleter syndrome is ?
what’s another common example of a trisomy?
Turner XO
Klinefelter XXY
Down syndrome or trisomy 21
Briefly explain why in humans and mammals, sex chromosome aneuploids are more common than autosomal aneuploids
No mechanism of dosage compensation for autosomal chromatids. Autosomes carry more genes. Most autosomal aneuploids are spontaneously aborted
uniparental disomy
both chromosomes are inherited from the same parent
- mosaicism and nondisjunction in mitotic division
What factors in humans increase aneuploidy?
increases with maternal age
Autopolyploidy
all chromosome sets are from a single species
- can arise through nondisjunction in mitosis or meiosis
allopolyploidy
Chromosome sets are from two or more species
- arises from hybridization between two species
What is the link between polyploidy and cancer?
nondisjunction can happen and mitosis occurs so we get a tetraploid. it’s unstable and has a dosage problem;; if survives get cells with extra copies and when overcome checkpoints become overstable. If the cell survives it is stronger and grows more/faster than the rest to yield cancer
species A has 2n= 16 chromosomes and species B has 2n=14. How many chromosomes would be found in an allotriploid of these two species?
a. 21 or 24
b. 42 or 48
c. 22 or 23
d. 45
c 22 or 23
2A+B = 16+7=23
A+2B = 8+14=22
