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Chapter 8
Human
Karyotypes and
Chromosome
Behavior
The banding patterns of human chromosomes
The short arm of
a chromosome is
called “p” and
the long arm
“q”. A, B, C, etc.
refer to grouping
of chromosomes
by size.
The 3 shapes of chromosomes
based on the location of the centromere
The proposed mechanism for the creation of the
long human chromosome 2 by fusion of two
shorter chromosomes
In human females, one of the 2 X-chromosomes
is inactivated early in development
Proposed steps in the creation of the modern
Y-chromosome by rearrangement of segments
in an ancient Y-chromosome
Distribution of Y-chromosome haplotypes,
presumed to have descended from Genghis Khan
The probability of a child with Down’s
syndrome increases with Mother’s age
Pairing and segregation of 3 homologous
chromosomes in meiosis I
This kind of
chromosome
pairing occurs in
trisomics (2n+1) or
triploids (3n)
Mapping the deletion of part of a chromosome segment by
testcrosses and uncovering of recessive genes
Mapping of genes in Drosophila using overlapping
deletions and polytene chromosomes
Unequal crossing over of misaligned repeat
sequences leads to gain or loss of repeats
Unequal crossing over involving eye
pigment genes
Mechanism of creation of a chromosomes
with an inverted segment
Pairing of homologous chromosomes
in an inversion heterozygote
An inversion
which does not
involve the
centromere
is called a
paracentric
inversion
Absence of recombination within an inversion
loop does not create deletions or duplications
A crossover within an inversion loop of a
paracentric inversion creates dicentric and
acentric chromosomes
A crossover within an inversion loop of a
pericentric inversion creates chromosomes
with deletion and duplication
When an inversion
involves the
centromere, it is called
a pericentric inversion.
Crossing over in a
pericentric inversion
does not create
dicentric and acentric
chromosomes
Structure of chromosomes with a
reciprocal translocation
Pairing and segregation of chromosomes with a reciprocal
translocation during meiosis I
Mechanism of creation of a
Robertsonian translocation
Pairing and segregation with a Robertsonian translocation
involving human chromosomes 14 and 21
Such a
translocation
results in a high
probability of
having a child
with Down’s
syndrome.
Variegation (mottling) of eye color due to positioning of the eye
color gene near centromeric heterochromatin
When the
expression of a
gene is affected by
its location on a
chromosome (even
though the gene
itself is not
changed), such a
variation is called
“position effect”
Two kinds of polyploidy
Multiplication of the entire chromosome complement is called
polyploidy. When all the genomes are the same, it is called
autopolyploidy. When two (or more) different genomes
are duplicated, it is called allopolyploidy.
Formation of a tetraploid organism
Creation of a totally homozygous diploid cell by
doubling of chromosome number in a
monoploid cell by colchicine
Monoploid cells
can only be
grown in plants.
In humans, the
only viable
monoploid cells
are the egg and
the sperm.
Monoploidy in
somatic cells is
lethal.
Evolution of wheat genome through
allopolyploidy
Evolution of wheat genome