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Theoretical Genetics

Theoretical Genetics. Mrs. Ragsdale Bio SL. A Lil Vocab. Genotype – the actual genes (alleles) Each gene has two alleles Example: Aa, AA, aa Phenotype – the physical characteristic expressed Blue eyes vs green eyes Dominant – the allele that is always expressed if its present

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Theoretical Genetics

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  1. Theoretical Genetics Mrs. Ragsdale Bio SL

  2. A Lil Vocab • Genotype – the actual genes (alleles) • Each gene has two alleles • Example: Aa, AA, aa • Phenotype – the physical characteristic expressed • Blue eyes vs green eyes • Dominant – the allele that is always expressed if its present • Recessive – an allele that is only expressed when a dominant allele isn’t around

  3. Some More Vocab… • Homozygous – when both alleles are the same • AA or aa • Both dominant or both recessive • Heterozygous – when one allele is dominant, the other recessive • Aa • Locus – the location of a gene on a chromosome

  4. GREGOR MENDEL • “FATHER OF MODERN GENETICS” • STUDIED PEA PLANTS GENETICS – THE STUDY OF HUMAN HEREDITY • STUDIES HOW TRAITS ARE PASSED FROM PARENT TO OFFSPRING

  5. Law of Segregation • GAMETES – SEXUAL REPRODUCTIVE CELLS • EGG AND SPERM • LAW OF SEGREGATION – EACH PARENT PASSES ON ONE OF THEIR ALLELES FOR A GENE TO THEIR OFFSPRING

  6. LAW OF INDEPENDENT ASSORTMENT • GENES FOR DIFFERENT TRAITS CAN SEPARATE DURING GAMETE FORMATION • They separate and assort themselves independently of each other • ALL OF YOUR MOM’S DNA DOES NOT END UP IN ONE GAMETE AND ALL OF YOUR DAD’S IN A DIFFERENT GAMETE • EACH OF YOUR GAMETES WILL BE A MIXTURE OF YOUR MOM AND DAD’S GAMETES

  7. GENETIC PROBABILITY • PUNNETT SQUARES • DOMINANT ALLELES – CAPITAL LETTERS • RECESSIVE ALLELES – LOWER CASE

  8. Punnett Example Two heterozygous blue flowering pea plants are crossed. • Blue is dominant over white What is the probability of a white flowering pea plant being produced?

  9. Punnett Example 2 A heterozygous blue flower is crossed with a homozygous white flower. What are the possibilities of the offspring and to what predicted probability?

  10. Dihybrid Crosses • T=tall, t=short, R=red, r=white • Tall white x short red • Ttrr x ttRr • Phenotypes: Tall red, Tall white, short red, short white

  11. INCOMPLETE DOMINANCE • SOMETIMES ONE ALLELE IS NOT COMPLETELY DOMINATE OVER ANOTHER • INCOMPLETE DOMINANCE IS A BLEND OR A MIXTURE OF TWO ALLELES • ONLY CAPITAL LETTERS ARE USED

  12. Test Cross • Let’s say you have a flower that is dominant when red and recessive when white • If you have a red flower, how can you know if it is homozygous dominant or heterozygous? • Test cross – in order to test if something is AA or Aa, cross the unknown with a homozygous recessive aa. • If the subject was AA the offspring will all be Aa • If the subject was AA the offspring will be 50/50 Aa and aa

  13. INCOMPLETE DOMINANCE THE OFFSPRING OF A CROSS BETWEEN DOMINATE RED AND DOMINATE WHITE IS A BLENDED PINK

  14. CODOMINANCE • BOTH ALLELES ARE SHOWN IN A PHENOTYPE

  15. MULTIPLE ALLELES WHEN A GENE HAS MORE THAN 2 DIFFERENT ALLELES THAT CONTROL IT’S PHENOTYPE Ex: Rabbit color C = full color cch = gray ch = white with some brown c = albino

  16. Blood Groups: ABO • Human blood inheritance is a perfect example of both a multiple allele and codominance situation • Three alleles all based on the letter I • IA and IB are codominant to each other. Both these alleles are dominant to i • The Allele hierarchy is IA = IB and both are > i

  17. Punnett Squares Revisited IA IB IA i i i IA i

  18. POLYGENIC TRAITS • CHARACTERISTICS CONTROLLED BY MORE THAN ONE GENE • EXAMPLES: HUMAN SKIN AND EYE COLOR

  19. Polygenic Inheritance • -skin color

  20. Polygenic Inheritance Continuous variation • Height • Eye color • Continuous variation • Different amounts of melanin

  21. Two Main Types of Chromosomes: • Sex Chromosomes • Chromosomes that determine the sex of the individual • In humans – X and Y • Females have XX • Eggs always donates X • Males have XY • Sperm donates either X or Y • Autosomes • Every other chromosome is an autosome

  22. Human Sex Determination • Females XX • Males XY • Always a 50/50 chance of male or female at birth

  23. Karyotyping • Photographic display of human chromosomes arranged in homologous pairs • Paired based on size, centromere location and banding

  24. Sex Linkage • Sometimes, certain diseases and disorders only affect you based on your sex • These alleles are typically found on the sex chromosomes X or Y • For recessive alleles, women become carriers while men display the phenotype (the actual disease). • Examples: • Hemophilia • Color Blindness

  25. Hemophilia: Recessive Sex-Linked Disease • Carried by women, expressed by males • The hemophiliac allele (Xh)is recessive to the normal allele (XH) • Females can be either homozygous or heterozygous for sex linked diseases **Heterozygous females are called carriers because they have the allele but don’t express it

  26. Pedigree Charts • Modified family tree • Shows relationships within a family

  27. Example Pedigree

  28. Royal Pedigree • http://www.sciencecases.org/hemo/hemo.asp

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