Variations in Chromosome Number and Arrangement

Variations in Chromosome Number and Arrangement

* Chromosomal mutations or aberrations
o Abnormal chromosomal number
o Gene deletion or duplication
o Chromosome rearrangements
* Aberrant chromosomes passed on in a Mendelian fashion

Terminology
* Euploid – chromosomes present in complete haploid units
o Haploid
o Diploid
o Triploid
o Tetraploid
* Aneuploid – loss or gain of one or more chromosomes
* Alloploid – multiples of different genomes

Aneuploidy
* Commonly results from nondisjunction during meiosis
o Monosomy, trisomy, tetrasomy, etc.
o Klinefelter and Turner syndromes are examples involving human sex chromosomes

Nondisjunction
Monosomy
Cri-du-Chat Syndrome
* Autosomal monosomy in humans not reported beyond birth (die quickly)
* Partial autosomal monosomy may survive
* “Cry of cat” syndrome

Trisomy
* Trisomy (2n + 1)
* Meiotic issues

Trisomy Meiosis
Down Syndrome
* Discovered in 1866 by John Langdon Down
* Now known to result from trisomy 21 (47 +21)
* One per 800 live births
* 75% due to nondisjunction in meiosis I
* Ovum is source of extra 21 in 95% of cases

Down Syndrome – Trisomy 21
Maternal Age and Down Syndrome
Patau Syndrome
Edwards Syndrome
Viability in Human Aneuploidy
More From the Carr Study
Polyploidy in Plants
Autopolyploidy
Experimentally Produced Tetraploids
Yeast Models
Allopolyploidy
Allotetraploid Formation
Allotetraploids
Wheat/Rye Cross
Somatic Cell Hybridization
Protoplast Fusions
Endopolyploidy
Chromosome Rearrangements
Consequences of Rearrangements
Deletions
Compensation Loop in a Polytene Chromosome
Duplications
Unequal Crossing Over
Position Effects
Gene Duplication and Evolution
Chromosomal Inversions
Inversions and Gametogenesis
Inversions and Recombination
Translocations
Familial Down Syndrome
Fragile Sites
Fragile X Syndrome
Fragile X Chromosomes

Variations in Chromosome Number and Arrangement.ppt