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Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Structural Abnormalities
Deletions
Translocations
Inversions
Duplications
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Deletions
Small or large
Mutation in one or many genes
Homozygosity or heterozygosity for each
Consequences for gene function
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
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
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
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
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Cri-du chat syndromeDeletion in Chrom. 5
Prader-Willi SyndromeAngelman Syndrome
Deletions in Chromosome 15
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Structural Abnormalities
Deletions
Translocations
Inversions
Duplications
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Translocations
• Exchange of chromosomal segmentsbetween nonhomologous chromosomes
• Two major types–Reciprocal translocation
–Non-reciprocal translocation
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Types of Translocations
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Burkitt’s lymphoma
Ig- myc
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Reciprocal Translocation: yields normal and defective gamets
ABCDEKLMN
ABMNKLCDE
ParentHas complete information
ABCDEABMN
ABMNKLMN
Deletion andDuplication gametes
ABCDEKLMN
ABMNKLCDE
Normal gametes
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
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
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
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
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Structural Abnormalities
Deletions
Translocations
Inversions
Duplications
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
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
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
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
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Structural Abnormalities
Deletions
Translocations
Inversions
Duplications
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
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
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
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
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fig. 6.29
Uniparental Disomy
Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning
Fragile Siteson the Human X Chromosome
Fig. 6.30
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