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Explore the various changes in chromosome structure due to mutations like duplications, deletions, inversions, and translocations, leading to genetic imbalances, new phenotypes, and potential evolutionary implications. Understand the mechanisms behind chromosome mutations and their consequences on gene products.
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Breakage and Rejoining Unequal crossing-over Mechanisms of Chromosome Mutation
Consequences of Duplications • Altered phenotypes as a result of imbalances in amounts of gene products
Consequences of Duplications • Duplication can lead to other genetic changes • Alleles with new functions
Consequences of Duplications • Duplication can lead to other genetic changes • Higher degrees of duplication
Consequences of Deletions • Chromosome is lost if centromere is deleted. • Chromosomes with deletions do not revert to the wild type state. • Recombination frequencies between genes flanking the deletion are reduced. • Deletions are lethal in the homozygous state.
Solid tumors can accumulate deletions Cri du chat syndrome results from a deletion in chromosome 5 Consequences of Deletions 5. Multiple defects occur in heterozygotes due to • imbalances in the amounts of gene products
Wild Type Wing Notch Wing Consequences of Deletions 5. Multiple defects occur in heterozygotes due to • pseudodominance = recessive alleles on the non-deleted homolog are expressed • haploinsufficiency = certain genes must be present in two copies for normal function
Consequences of Inversions • Generally viable since amount of genetic material is unchanged. • Leads to lethal mutation if breakpoint is within an essential gene.
Consequences of Inversions • Position Effect = Gene regulation can be altered by a difference in chromosome location • Recombination frequency is reduced due to inhibition of pairing and since crossover in heterozygotes yields additional structural mutations.
Anaphase II Crossing Over in a Pericentric Inversion Heterozygote
Robertsonian Translocation • Long arms of two acrocentric chromosomes are joined to the same centromere • Results in one large chromosome and one small chromosome • Smaller chromosome may be lost
Inheritance of Down Syndrome from the carrier of a Robertsonian translocation, joining the long arms of chromosomes 14 and 21.
Burkitt’s lymphoma is caused by a position effect. Consequences of Translocations • Behave as point mutationsif the breakpoint disrupts an essential gene. • Show new linkage arrangements. • Position Effect = Gene expression is altered as a result of the new environment for translocated material.
Consequences of Translocations Position-effect variegation of eye color in fruit flies due to translocation of w+ next to heterochromatin
Consequences of Translocations Meiotic Structures • Leads to semisterility, where approximately half of the gametes carry structural mutations.
