chapter 8 human karyotypes and chromosome behavior
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Chapter 8Chapter 8
Human Human Karyotypes Karyotypes
and and Chromosome Chromosome
BehaviorBehavior
The banding patterns of human chromosomesThe 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 The 3 shapes of chromosomes based on the location of the centromerebased on the location of the centromere
The proposed mechanism for the creation of the The proposed mechanism for the creation of the long human chromosome 2 by fusion of two long human chromosome 2 by fusion of two
shorter chromosomesshorter chromosomes
In human females, one of the 2 X-chromosomes In human females, one of the 2 X-chromosomes is inactivated early in developmentis inactivated early in development
Proposed steps in the creation of the modern Proposed steps in the creation of the modern Y-chromosome by rearrangement of segments Y-chromosome by rearrangement of segments
in an ancient Y-chromosomein an ancient Y-chromosome
Distribution of Y-chromosome haplotypes, Distribution of Y-chromosome haplotypes, presumed to have descended from Genghis Khanpresumed to have descended from Genghis Khan
The probability of a child with Down’s The probability of a child with Down’s syndrome increases with Mother’s agesyndrome increases with Mother’s age
Pairing and segregation of 3 homologous Pairing and segregation of 3 homologous chromosomes in meiosis Ichromosomes 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 Mapping the deletion of part of a chromosome segment by testcrosses and uncovering of recessive genestestcrosses and uncovering of recessive genes
Mapping of genes in Drosophila using overlapping Mapping of genes in Drosophila using overlapping deletions and polytene chromosomesdeletions and polytene chromosomes
Unequal crossing over of misaligned repeat Unequal crossing over of misaligned repeat sequences leads to gain or loss of repeatssequences leads to gain or loss of repeats
Unequal crossing over involving eye Unequal crossing over involving eye
pigment genespigment genes
Mechanism of creation of a chromosomes Mechanism of creation of a chromosomes with an inverted segmentwith an inverted segment
Pairing of homologous chromosomes Pairing of homologous chromosomes
in an inversion heterozygotein an inversion heterozygote
An inversion which does not
involve the centromere is called a
paracentric inversion
Absence of recombination within an inversion Absence of recombination within an inversion
loop does not create deletions or duplicationsloop does not create deletions or duplications
A crossover within an inversion loop of a A crossover within an inversion loop of a paracentric inversion creates dicentric and paracentric inversion creates dicentric and
acentric chromosomesacentric chromosomes
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
A crossover within an inversion loop of a A crossover within an inversion loop of a pericentric inversion creates chromosomes pericentric inversion creates chromosomes
with deletion and duplicationwith deletion and duplication
Structure of chromosomes with a Structure of chromosomes with a reciprocal translocationreciprocal translocation
Pairing and segregation of chromosomes with a reciprocal Pairing and segregation of chromosomes with a reciprocal translocation during meiosis Itranslocation during meiosis I
Mechanism of creation of a Mechanism of creation of a Robertsonian translocationRobertsonian translocation
Pairing and segregation with a Robertsonian translocation Pairing and segregation with a Robertsonian translocation involving human chromosomes 14 and 21involving 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 Variegation (mottling) of eye color due to positioning of the eye color gene near centromeric heterochromatincolor 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 polyploidyTwo 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 organismFormation of a tetraploid organism
Creation of a totally homozygous diploid cell by Creation of a totally homozygous diploid cell by doubling of chromosome number in a doubling of chromosome number in a
monoploid cell by colchicinemonoploid 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 Evolution of wheat genome through allopolyploidyallopolyploidy
Evolution of wheat genomeEvolution of wheat genome