Structural Abnormalities - Brandeis Life Sci Powerpoints/chapter… · Mutation in one or many...

Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

Structural Abnormalities

Deletions

Translocations

Inversions

Duplications


Deletions

Small or large

Mutation in one or many genes

Homozygosity or heterozygosity for each

Consequences for gene function


Deletions

• Loss of chromosomal material• Large-scale deletions are lethal• Example: Cri du chat

–Deletion of short arm of chromosome 5–Affects motor and mental function– Infant cry resembles a meowing cat–Specific chromosomal break points are

associated with specific phenotypicchanges


Cri du chat Syndrome

Fig. 6.26

Variation in phenotypeassociated with regiondeleted has been observed

Researchers have identifiedregions with genes involvedin larynx and nervoussystem development


Cri-du chat syndromeDeletion in Chrom. 5

Prader-Willi SyndromeAngelman Syndrome

Deletions in Chromosome 15



Deletions

Translocations

Inversions

Duplications


Translocations

• Exchange of chromosomal segmentsbetween nonhomologous chromosomes

• Two major types–Reciprocal translocation

–Non-reciprocal translocation


Types of Translocations


Burkitt’s lymphoma

Ig- myc


Reciprocal Translocation: yields normal and defective gamets

ABCDEKLMN

ABMNKLCDE

ParentHas complete information

ABCDEABMN

ABMNKLMN

Deletion andDuplication gametes

ABCDEKLMN

ABMNKLCDE

Normal gametes


Types of Translocations

– Robertsonian Translocation• Centromeres from two nonhomologous

chromosomes fuse and chromosomal materialfrom the short arms is lost

• 5% of Down syndrome cases involve aRobertsonian translocation betweenchromosomes 21 and 14


Robertsonian Translocation

A translocation betweenchromosome 14 and 21 mayproduce

• Translocation carrier

• Normal phenotype

• Translocation Down syndrome

• Lethal monosomy 21

• Lethal trisomy 14

• Lethal monosomy 14

Fig. 6.27



Deletions

Translocations

Inversions

Duplications


New context Antennapedia

•Antp protein is made in antennal primordial cells, where the WT Antp does not express

•Legs grow out in Antp mutant in place of antenna

•Inversions reorganize DNA sequences


Wild-type head

Antp required for identity of T2 (Wings and legs)

Expression of Antp in head results in legs forming in place of antennae

Antp expressed in head



Deletions

Translocations

Inversions

Duplications


Evolution of genes/gene families

myoglobin

α familyß family

Hemoglobin family

gene duplicationdivergence

gene duplicationdivergence

(~ 700 million years ago)

(~ 450 million years ago)

Primordial geneEncodes O2 carrier protein


Other Chromosomal Abnormalities

• Uniparental disomy–Both copies of a chromosome are

inherited from a single parent–Due to error in cell division–Examples

• Females affected with rare X-linked disorders• Prader-Willi and Angelman syndromes

• Fragile sites–Over 100 have been identified


Fig. 6.29

Uniparental Disomy


Fragile Siteson the Human X Chromosome

Fig. 6.30

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