Genetics Exam 3 - Chromosome Variation

Small Scale Variation Types

Seen at the sequence level: SNP, INDEL, SSR/STR/Satellite, CNV

Large Scale Variation Types

Differences at chromosome level: Ploidy, Structure

CNV

Copy number variants, arise from unequal crossing over

PCR and Small Scale Differences

Aplification can reveal size/sequence of product, must know surrounding sequence, CODIS examines strs.

Huntingtons Disease

Triple repeats in HD coding (glutamine), more repeats → higher penetrance and expressivity + earlier onset.

Polyploidy

Change in number of complete sets of chromosomes (common in plants). Tolerated/beneficial in plants like wheat (hexaploid from 3 different species).

Aneuploidy Types

Change in number of individual chromosomes: Nullisomy (loss homologous chromosome pair), Monosomy, Trisomy, Tetrasomy.

Allopolploids

Chromosomes sets from 2 or more species (usua

Autopolyploids

Generated during nondisjunction of mitosis.

Autotriploids Sterility

Unbalanced segregation of gametes → not all necessary genetic material can be passed on.

Human Aneuploidy

Turner: XO, Klinefelter: XXY, Trisomy 21: Down syndrome (Primary: 75% random nondisjunction in egg, Familial: Translocation between portion of chromosome 21 and other chromosome).

4 Types of Large Rearrangements of Chromosomes

Duplication, Deletion, Inversion, Translocation. Last 3 caused by double stranded breaks. Visualized with fluorescent in situ hybridization.

Copnsequence of homozygous large deletion

Chromosome disappears if centromere is removed, loss of multiple coding sequences is deleterious

Heterozygous Large Deletion

Seen as loop when chromosomes pair up, imbalanced gene products, recessive mutations in remaining copy appear (pseudodominance).

Haploinsufficiency

Gene requires both alleles for wild type function (ex. dosage effect)

Crossing Over with Inversion

Forms inviable gametes, so inversion suppresses crossing over (forms dicentric and nullcentric chromosome).

Translocation

Movement of portion of chromosome to other chromosome, can be innocuous if no gene affected/reciprocal, if it breaks genes it can cause: new protein fusion, splicing, expression patterns, disease.

Philadelphia Chromosome

Translocation visible, causes CML leukemia, C9→C22. C-abl oncogene that increases cell growth but is regulated + Bcr which causes cell growth to be unregulated.

Burkitts Lymphoma

Translocation of myc gene and antibody-producing genes (Overgrowth/tumor formation in B cells).