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Human Genetics

Human Genetics. Biology 40S Summer Session 2013. Outline. Human Traits – Focus on Disorders. Chromosome Theory Human Inheritance Patterns Pedigree Analysis. Why Focus on Disorders?. Humans have thousands of traits that are common to all individuals. List some examples

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Human Genetics

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  1. Human Genetics Biology 40S Summer Session 2013

  2. Outline • Human Traits – Focus on Disorders. • Chromosome Theory • Human Inheritance Patterns • Pedigree Analysis

  3. Why Focus on Disorders? • Humans have thousands of traits that are common to all individuals. • List some examples • There are more rare “traits” that show up in some individuals – genetic abnormalities that result in a genetic disorder. • Why would we want to understand the mechanism of inheritance of disorders?

  4. Chromosome Theory • Our traits are controlled by gene sequences of DNA that are located in various structures called chromosomes.

  5. Chromosome Number • Every species has a unique number of chromosomes. • Chromosomes are paired up in diploid organisms. • Chromosomes pair up according to similarities in size and structure. • Chromosome pairs are known as homologous pairs.

  6. Human Genome • Males andfemales contain 22 pairs of similar chromosomes – autosomes. • The 23rd pair is unique to males and females and are called the sex chromosomes.

  7. Human Inheritance Patterns

  8. Autosomal Dominant Pattern • The gene is on one of the autosomes and the trait is dominant. • Homozygotes and heterozygotes both express the trait. • Males and females affected equally. • Examples: Marfan syndrome, sickle cell anemia, achrondoplasia.

  9. Autosomal Recessive Pattern • The gene is on one of the autosomes and is in the recessive form to show the trait. • Heterozygous individuals never show the trait, but do carry the recessive allele. • The trait may skip a generation in a family. • Males and females affected equally. • Examples: cystic fibrosis, tay-sachs disease, albinism, phenylketonuria

  10. X-Linked Dominant Pattern • The gene is on the X chromosome. • Males always express the dominant gene if received, females express if heterozygous or homozygous. • Males affected more severely – usually lethal. • More common for females to be affected in a population. WHY?? • Rare disorders: Coffin-Lowry syndrome, incontentia pigmenti

  11. X-Linked Recessive Pattern • The gene is located on an X chromosome and is recessive to express the trait. • Males affected if the recessive allele is received. • Females affected only if both recessive alleles received. Heterozygous females are carriers. • Examples: colour blindness, muscular dystrophy, hemophilia, androgen insensitivity syndrome

  12. Pedigrees • A pedigree is a specialized chart used to track a specific trait within a family. • Pedigree analysis allows us to • Determine the pattern of inheritance • Predict the chance of passing on the trait http://www.ndsu.edu/pubweb/~mcclean/plsc431/mendel/mendel9.htm

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