Genetic Disorders and Pedigrees

Overview So far, we’ve investigated errors that can occur during meiosis Crossing over mistakes Deletion, duplication, translocation, inversion Non-disjunction Monosomy, polysomy

Overview Mutations is another problem: any change in the functioning of the gene Very harmful, fortunately DNA is very stable Mutations in somatic cells usually unnoticed Mutations in gametes are passed to offspring and can be detrimental Caused by: teratogens, viruses, alcohol

Now let’s consider the consequences of these problems

Diseases Associated with DNA Errors Autosomal Recessive: people must be homozygous for this gene Sickle Cell Anemia: abnormal oxygen carrying pigment in RBC Cystic Fibrosis: excessive mucus production SCA: single a.a. change due to single nucleotide change in a 146 a.a. chain

Diseases Associated with DNA Errors Autosomal Dominant: only requiring one copy of the gene Huntington’s Disease: brain tissue degeneration, onset thirties and forties

Diseases Associated with DNA Errors Sex Linked Disorders: most often recessive, but can be dominant Red-green colour blind Hemophilia Duchene Muscular Dystrophy All listed above = recessive

Diseases Associated with DNA Errors Chromosomal abnormalities: monosomy, polysomy, partial deletion etc… Down syndrome (tri-21): 1 in 700 births Cri-du-chat syndrome: partial deletion of chromosome 5, mentally challenged See table 7.3 page 205 for further disorders Responsible for table

Diagnosis and Use of Karyotypes Eg: Cri-du-chat syndrome Prenatal Diagnosis: Amniocentesis: amniotic fluid withdrawn most common Cells grown then analyzed 95% women at risk, do not display genetic problem

Pedigrees and their use! Geneticists realized these undesirable traits run in family groups, so they developed a type of chart called a Pedigree

Pedigrees and their use! Common Symbols: Text page 142

Pedigrees and their use! Usually developed once undesirable trait appears in the family Data collected and chart produced

Pedigrees and their use! The pattern can be affected by many factors Autosomal vs X-linked Recessive vs Dominant Chance of transmission

Distinctive Features: Autosomal Recessive: May skip generations, males/females affected equally, parents may be affected or carriers Autosomal Dominant: parents must be affected Half the children affected, does not skip generation, male/female affected equally X-linked: Predominantly males affected, no father son transmission, may skip generations

Pedigrees and their use! Text page:170

Famous Royal Families of Europe Text page 170 fig 8

SUMMARY Pedigrees are a visual representation of the transmission of genetic disorders Autosomal Dominant/Recessive X-linked Designated Symbols Handout and p147 case study