Human Karyotypes and Chromosome Behavior
Chapter 6 (9
thEd) Chapter 8 (8th ed)
Karyotype
metaphase spread fluorescent probes
nocadozole: microtubule inhibitor
giemsa staining: G banding rich in G-C base pairs
chromosomes have same seq same pattern
G bands gene poor replicate late R bands gene rich replicate early
numerous ORİ on chromosome!
Chromosome arms:
p: petite short arm q: que long arm
numbered consecutively proceeding
from the centromere toward the telomere
1p34 indicates chromosome 1, short arm, division 34
Rh (Rhesus) blood-group locus, which is in the region between 1p34 and 1p36.2
ABO blood-group locus at 9q34
the red–green color blindness genes at Xq28 SRY (sex-determining region, Y) at Yp11.3
A chromosome that lacks a centromere is an acentric chromosome
two centromeres and is said to be dicentric. A dicentric chromosome is also genetically unstable
chimpanzee, human 46 chr
great apes 48 chr 2x acrocentric chr--> chr.2
doi: 10.1101/gr.337602
• Drosophila male X chromosome expressed more than female.
• C. elegans female X chr. exactly half of male! HOW?
• 64- to 128-cell stage, one and only one X chromosome in each cell, chosen at random, remains genetically active
• Any X chromosome that is inactivated in a particular
somatic cell remains inactive in all the descendants of that cell
Dosage compensation
Cytosines of DNA methylated
The active X chromosome does not transcribe its Xist gene.
Tisx gene encodes and RNAi that inactives the Xist gene on the active X chromosome.
Xist
Xist Tsix
Inactive
Active X from
mother
X from father
RNAi RNAi
RNAi Females have:
white patches are due to an allele of the W locus, ws
Calico cat
males are orange or black.
females who are heterozygous orange/black can be calico
W DOMİNANT
PAR Pseudo-autosomal region NOT INACTİVATED
PARp
PARq
crossing over between X and Y because Y also has PARp and PARq
Genetically looks like autosomal inheritance
Y chromosome shortening
Frequency of Down syndrome
Elvan Böke
doi: 10.1016/j.tibs.2017.11.005.
https://www.crg.eu/en/elvan-boke
trisomic refers to an otherwise diploid organism that has an extra copy of an individual chromosome
Triploids and tetraploids are examples of euploid conditions, because they have the same relative gene dosage as found in the diploid.
unbalanced chromosome complements are said to be aneuploid.
All chromosomes diploid but one individual chromosome, is missing (single copy): monosomy.
Trisomy 21 is Down syndrome
Meiotic pairing in a trisomic
(NONDİSJUNCTİON) trisomy because mother’s meiosis made 1 gamete that has 2x chr.21 (viable)
and 1 gamete
that has NO chr.21 (nonviable)
NORMAL GAMETE
47,XXX normal female (2x X-inactive) 47,XYY normal male
47,XXY male (Kleinfelter syndrome) 45,X monosomy (Turner syndrome)
DELETİON
ECTOPİC
RECOMBİNATİON
notch w+
notch w+ + w x + w
Large notch deletion causes w (white) deletion.
notch del + w
Drosophila Notch and White are linked Red eye White eye
White eye
Deletion mapping
Deletion “unmasks” mutant allele
physical mapping
X chromosome in
polytene salivary gland
tandem duplication
Unequal Crossing Over in Human Red– Green Color Blindness
different X chr
R and G genes are very similar arising from a gene duplication event X linked so mostly seen in males
chimeric gene
gene duplication
Evolution of the globin genes.
psudogenes protein family one copy continues function other copy evolves
Ectopic recombination between inverted repeats results in an inversion
no problems in mitosis but problems in meiosis
No XO in loop
Paracentric Inversion (Not Including the Centromere)
Pericentric Inversion (Including the Centromere)
Reciprocal Translocations
9:22
Robertsonian Translocations and Trisomy 21
a piece of chromosome gets moved into
heterochromatin
by translocation/inversion
phenotype goes from red to white X linked so in males.
Position effect variegation
Polyploidization
