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Introduction to Genetics and Genetic Disorders

This article provides an introduction to the study of genetics, including a discussion on karyotypes, genetic disorders, Punnett squares, dominant/recessive genes, genotype and phenotype, and the laws of genetics. It also explores topics such as co-dominance, incomplete dominance, multiple alleles, blood types, the laws of segregation and independent assortment, sex-linked disorders, gene chromosome theory, linked genes, pedigree charts, and mutations.

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Introduction to Genetics and Genetic Disorders

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  1. GENETICS The study of how hereditary information is passed from parent to offspring.

  2. KARYOTYPE • A karyotype is a picture of the chromosome pairs.

  3. GENETIC DISORDERS

  4. LIST OF GENETIC DISORDERS • Sickle Cell Anemia • PKU • Hemophilia • Down Syndrome • Tay Sachs • Fragile X • Color-blindness

  5. PUNNETT SQUARES • Cross Male and Female • (sex determination)

  6. DOMINANT/RECESSIVE • If a gene is dominant, it shows-it is more powerful. *T* • If a gene is recessive, it may show-it is weaker. *t*

  7. GENOTYPE AND PHENOTYPE • Genotype • What the genes (letters) say • Ex. TT or Tt or tt • Phenotype • How the genes appear (physically) • Ex. Tall or Short

  8. GENETICS • Gregor Mendel • “father of genetics” • Studied the inheritance of pea plants in the 1850’s • Crossed (mated) pea plants with different traits and helped develop the 3 laws of genetics • 1. Law of Dominance • 2. Law of Segregation and Recombination • 3. Law of Independent Assortment

  9. LAW OF DOMINANCE • Cross 2 pure/homozygous tall (TT) pea plants. • Ex. • Cross 2 pure/homozygous short (tt) pea plants. • Ex.

  10. LAW OF DOMINANCE • Cross two hybrid/heterozygous pea plants. • Ex.

  11. CO-DOMINANCE or INCOMPLETE DOMINANCE • For some traits, there are TWO dominant alleles (genes). • Two things can happen: • 1. Co-Dominance: Both alleles are expressed • 2. Incomplete Dominance: Alleles blend together

  12. CO-DOMINANCE • Punnet Square

  13. CO-DOMINANCE

  14. INCOMPLETE DOMINANCE • When neither allele dominates-the result is a new phenotype. • Ex. 4 o’clock flower

  15. INCOMPLETE DOMINANCE • Punnet Squares • Worksheet

  16. MULTIPLE ALLELES • Sometimes there are more than two possible alleles for a trait. • Ex. Blood types • Rules for blood typing (three alleles). • 1. Type A dominates Type O • 2. Type B dominates Type O • 3. Type O is recessive • 4. Type A is CO-DOMINANT to Type B

  17. BLOOD TYPES

  18. BLOOD TYPE PUNNET SQUARE • Cross a homozygous Type A mother with a homozygous Type O father. • Cross a homozygous Type A mother with a heterozygous Type B father.

  19. BLOOD TYPE PUNNET SQUARE • Cross two heterozygous Type A parents.

  20. BLOOD GENOTYPES • Type A- I I • Type B- I I • Type O- i i • Type AB- I I

  21. LAW OF SEGREGATION AND RECOMBINATION • During meiosis, the two genes responsible for each trait separate from each other. • Each gamete contains only one gene for each trait. • Ex. Hybrid Tall Pure Short Tt tt

  22. SEGREGATION AND RECOMBINATION

  23. LAW OF INDEPENDENT ASSORTMENT • If 2 traits are crossed at the same time (dihybrid cross), each trait is inherited randomly.

  24. SEX LINKED DISORDERS • The X chromosomes carry some genes that the Y chromosomes do not. • Ex. Hemophilia (a recessive disorder) • h is the gene for hemophilia • H is the gene for non-hemophilia (normal) • Genotypes X Y X Y X X X X X X • Cross a normal male with a hemophiliac female.

  25. SEX LINKED DISORDERS • Cross a hemophiliac male with a carrier female. • Cross a colorblind male with a normal female.

  26. GENE CHROMOSOME THEORY • Each gene is found in a specific place on a chromosome (locus/loci).

  27. LINKED GENES • Some traits are found on the same chromosome and are usually inherited together. • Ex. • Red hair and _____________

  28. PEDIGREE CHART • Hemophiliac Story

  29. PEDIGREE CHART

  30. MUTATIONS • Some mutations can occur during meiosis. • Ex. Non-disjunction causes Down Syndrome • Other mutations can be caused by environmental factors. • 1) Chemicals such as asbestos, pesticides and industrial pollutants can cause genetic changes (mutation). • 2) Radiation • 3) Natural conditions may influence which genes are expressed. Ex. Cold temperatures change fur color.

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