Lecture 18 - Autosomal Disorders

Lecture 18 - Autosomal Disorders - Lecture 18 Background...

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1 Autosomal Disorders Biology 1F25 for Biology Non-Majors Lecture 18 Background Reading Textbook, Chapters 18 and 20. The People Who Prepared This Lecture Harry Peery Alan Castle The Punnett Square enables you to calculate Autosomal Dominant Probability Father’s genetic contribution Mother’s genetic contribution Dn 50% of the children will be normal. 0% of the children will be carriers. 50% of the children will have the autosomal dominant disease. n n D n n n D n n n The Children 25% 25% 25% 25% D = Autosomal dominant Disease; n = normal recessive gene
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2 There are a number of Autosomal Dominant Traits that are not bad • Dimples on the cheeks • Unattached earlobes • Wet ear wax (cerumen) • Freckles • Widow’s peak • Rh factor on red blood cells Codominance • Some dominant alleles act together with other dominant alleles. • This is called codominance. • Blood groups A and B are codominant if an individual has both alleles. Their blood type is AB. Genetic Pedigree can Trace an Inherited Disorder Females are the round circle; males are the square. Each line represents a new generation. In this pedigree, there are offspring from brother and sister. This is incest and it will tend to enhance (but not always) the number of cases. Genotype and Phenotype • Genotype is the genetic makeup of an individual. – It would include dominant and recessive genes • Phenotype is what is expressed (that is, what can be observed or measured) – It would include only dominant genes – Or, two recessive genes
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3 DJ’s parents • Had the recessive Tay- Sachs genes in their genotypes. • Their phenotypes displayed the dominant normal genes Here holding DJ and his younger normal sister at Lake Michigan in 2001 Expression • Expression is the ability of a gene to produce a protein. • In defective genes, the expression is the ability to produce a defective protein and hence, a disease. Expressivity • Expressivity is the severity of the expression (the phenotype). • The severity of the same disease in people with the same genotype will differ. • DJ had a slightly milder form of Tay-Sachs because he developed seizures later than most children and lived almost 6 years (most Tay-Sachs children die two years earlier). • Therefore, DJ’s Tay-Sachs expressivity was slightly less than normal. Pleiotropic Expression • Sometimes a gene produces different effects in different individuals. • For example, in Marfan’s syndrome (which is coming up), some patients have eye defects, others do not. • This is called pleiotropic expression (from Greek pleion – meaning more – our word plural and plus comes from this Greek word). • In pleiotropic expression the gene is expressed in different ways in different individuals.
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4 Autosomal Dominant Diseases Marfan Syndrome Who was Marfan?
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This note was uploaded on 06/10/2008 for the course BIOL BIOL-1F25 taught by Professor Peery during the Spring '08 term at Brock University, Canada.

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Lecture 18 - Autosomal Disorders - Lecture 18 Background...

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