Chromosome MutationsVariation in Number and Arrangement

What are chromosome mutations?

These are chromosome mutations!

Variation in Chromosome Number

Variations in Chromosome Number

Aneuploidy› Gain or loss, one or more chromosomes› Monosomy, Trisomy

Euploidy› Complete haploid sets

Polyploidy › More than two sets are present

Variations in Chromosome Number

Monosomy X(Turner’s Syndrome)

Haploinsufficiency A single copy of a recessive gene (due

to monosomy) may be insufficient to provide life-sustaining functions

Trisomy 21 (Down’s Syndrome)

Nondisjunction

Klinefelter Syndrome

Prenatal Diagnoses

Prenatal Diagram

Amniocentesis Fetal cells obtained from amniotic fluid

Chorionic Villus Sampling Fetal cells obtained from the chorion of

the placenta

Noninvasive Prenatal Genetic Diagnosis

Fetal cells and DNA are derived directly from maternal circulation

Human Aneuploidy

Patau Syndrome (Trisomy 13)

Patau Syndrome

Edwards Syndrome (Trisomy 18)

Polyploidy

Polyploidy Originates in two ways: 1. the addition of one or more extra

sets of chromosomes, identical to the normal haploid complement of the same species, resulting in autopolyploidy

2. the combination of chromosome sets from different species occurring as a consequence of hybridization, resulting in allopolyploidy

Autopolyploidy

Autopolyploidy

Allopolyploidy

Allopolyploidy

Autopolyploidy vs. Allopolyploidy

Variation in the Composition and Arrangement of

Chromosomes

Deletions Also called a deficiency A chromosome breaks in one or more

places and a portion is lost

Deletions Terminal deletions

Intercalary deletions

Cri du Chat Syndrome Loss of a small part of the short arm of

chromosome 5

Duplications

A piece of the chromosome is present more than once in the genome

Duplications

Duplications 1. may result from

gene redundancy 2. may produce

phenotypic variation 3. have been an

important source of genetic variability during evolution

rDNA and Gene Amplification

rDNA codes for RNA segments Gene amplification occurs when

multiple copies of gene code for a specific product

The Bar Mutation in Drosophila

Fragile X Syndrome (Martin-Bell Syndrome)

Inversions A segment of the chromosome if

turned around 180 degrees within the same chromosome

Inversions

Chromosome 9 Inversion

Translocations

The movement of a chromosomal segment to a new location in the genome

Translocations

Acute Myeloid Leukemia

Fragile Sites

Fragile Sites Appear as gaps in some karyotypes Appear to be susceptible to breakage

in some situations

Fragile Sites and Cancer Chromosome 16, WWOX gene

› Lung, breast, ovary, prostate, bladder, esophagus, pancreas

Chromosome 3, FHIT gene› Esophagus, breast, cervix, liver, kidney,

pancreas, colon, stomach Increased susceptibility to mutations

and deletions