Pedigree Analysis. Genetic disorders. Dominant inheritance. Recessive inheritance. Autosomal vs. sex-linked traits. X-linked recessive inheritance

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1 Genetic disorders 4.2 Errors During Meiosis 5.3 Following Patterns of Human nheritance Pedigree Analysis 2005 Lee Bardwell Autosomal vs. sex-linked traits Autosomal traits are caused by genes on autosomes (chrms #1- #22) e.g., we speak of autosomal recessive or autosomal dominant traits or diseases Sex-linked traits are caused by genes on the sex chrms (X or Y) e.g., we speak of X-linked recessive or X-linked dominant traits or diseases 2004 Lee Bardwell Dominant inheritance f D is the disease allele and d is normal, then only dd genotypes are disease free* Dominant trait/disease found in every generation* Affected kid never** born to unaffected parents *Assuming 100% penetrance **Assuming no new mutation Recessive inheritance f d is the disease allele and D is normal, then only dd genotypes are affected typically not seen in every generation Affected kid can be born to unaffected parents X-linked recessive inheritance Rules for recessive inheritance apply Males are more frequently affected Affected mothers pass trait too all her sons 1

2 X-linked dominant inheritance Rules for dominant inheritance apply Affected fathers pass disease to all of their daughters and none of their sons f two affected parents have an unaffected kid, recessiveness* can be ruled out (assuming 100% penetrance) *both autosomal and x-linked f unaffected parents have an affected kid, dominance* can be ruled out f unaffected parents have an affected daughter, dominance and x-linked recessive can be ruled out *both autosomal and x-linked 2000 Lee Bardwell f affected woman has unaffected son, or unaffected man has affected daughter, x-linked recessive can be ruled out f unaffected woman has affected son, or affected man has unaffected daughter, x-linked dominant can be ruled out NOT XR NOT XR XD XD 2

3 Pedigree showing X-linked recessive inheritance Could this be autosomal recessive? Could this be X-linked dominant? Could this be autosomal dominant? Could this be autosomal recessive? Errors During Meiosis How do genetic disorders arise? nheritance of dominant trait 3

4 Errors During Meiosis Cri du Chat Changes in chromosome structure Deletion Duplication nversion Translocation French for cry of a cat Caused by a deletion in chromosome 5 Children often exhibit a high-pitched, cat-like cry Also low birth weight, widely spaced eyes, recessed chin, and developmental and cognitive delays There is no cure for this disorder Cri du Chat Errors during Meiosis Changes in chromosome number Caused by non-dysjunction Failure of homologous chromosomes to segregate in meiosis Failure of sister chromatids to segregate in meiosis Produces gametes with either too many or too few chromosomes Non-dysjunction Trisomies and monosomies Many genetic disorders are the result of individuals having an incorrect number of Monosomy the condition that occurs when a chromosome is lost due to nondysjunction Trisomy the condition that occurs when a chromosome is gained due to non-dysjuntion 4

5 Down Syndrome Trisomy 21 extra chromosome or extra piece of chromosome 21 ncidence increases with maternal age No treatment or cure Down Syndrome Autosomal dominant disorder Causes brain deterioration over a period of about 15 years Symptoms include: Decline in mental abilities Personality changes Decreased muscle coordination Erratic body movements There is no cure for the lethal disease, but medication can lessen the symptoms Two forms: Adult onset symptoms in mid 30s-40s Early onset symptoms in childhood or adolescence (rare) Caused by a mutation called a trinucleotide repeat in a gene on chromosome 4 5

6 Cystic Fibrosis Cystic Fibrosis Most common disorder affecting young Canadians Autosomal recessive disorder Symptoms are caused by a defective protein that is involved in the movement of water in and out of cells Thickened mucus builds up in the body Cystic Fibrosis Causes breathing and digestive problems, and proneness to infections There is no cure but early treatment can increase life expectancy Often caused by deletion in the CFTR gene on chromosome 7 Genetic Testing Prenatal testing for genetic based abnormalities Past - only high risk (older age, family history) Present - any woman referred by a doctor in Ontario Blood tests, ultrasounds and possibly invasive testing on the fetus Genetic Testing Amniocentesis Chorionic villus testing Karyotyping FSH (fluorescence in situ hybridization) Gene Testing Biochemical Testing 6