1. Genetic Disorders and Pedigrees

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

3. 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

4. Now let’s consider the consequences of these problems

5. 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

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

7. 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

8. 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

9. 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Amniocentesis: amniotic fluid withdrawn most common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

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

11. Pedigrees and their use!
Common Symbols:
Text page 142

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

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

14. 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

15. Pedigrees and their use!
Text page:170

16. Famous Royal Families of Europe
Text page 170 fig 8

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