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Mendelian Genetics

This article explores Mendelian genetics and how genes work to determine physical appearance. It covers topics such as genotype, alleles, Punnett squares, and the chromosomal basis of inheritance. The text is informative and easy to understand.

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Mendelian Genetics

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  1. Mendelian Genetics How Genes Work

  2. Phenotype How you look; PHysical appearance Genotype Your genetic makeup; GENEs Who Are You?

  3. Father of Genetics • Modern genetics began with Gregor Mendel’s quantitative experiments with pea plants Stamen Carpel Figure 9.2A, B

  4. Mendel crossed pea plants that differed in certain characteristics and traced the traits from generation to generation White 1 Removed stamensfrom purple flower Stamens Carpel 2 Transferred pollen from stamens of white flower to carpel of purple flower PARENTS(P) Purple 3 Pollinated carpel matured into pod • This illustration shows his technique for cross-fertilization 4 Planted seeds from pod OFF-SPRING(F1) Figure 9.2C

  5. Genetics Basics • Chromosomes occur in pairs, one from MOM, one from DAD (homologues) • Genes are carried on chromosomes • Genes code for a trait or characteristic (I.e. hair color) • Alternate forms of that trait are called ALLELES (ie. Blond, brown, redhead, etc)

  6. Alleles… • Alleles can be dominant or recessive • Heterozygous vs. homozygous • Only way to “see” a recessive trait?

  7. Mendel ‘s basic laws Law of Segregation Law of Independent Assortment

  8. The chromosomal basis of Mendel’s principles Figure 9.17

  9. Walter Sutton’s Theory of Chromosomal Inheritance(Mendel’s proof) • Gametes contribute to heredity via nuclear material (chromosomes) • Homologues segregate during meiosis • Homologues separate independently of other homologous pairs

  10. Probability • Mathmatical model of how often specific events will happen • # of occurances/# of attempts

  11. Punnett Square • Visual representation or model of • what alleles can be present in gametes • how those alleles can recombine in offspring • Used to determine the probability of offspring’s genetic makeup

  12. Monohybrid Cross • One gene • 2 alleles considered (one from mom, one from dad

  13. Dihybrid Cross • 2 genes • 4 alleles considered

  14. How can we determine Homo- vs. heterozygous individuals? • Test Cross • Must use homo recessive to conduct cross in order to “see” the questionable allele

  15. What Mendel Didn’t See • Multiple alleles • Codominance • Epistasis • Polygenic traits or Continuous Variation • Pleiotropy • Incomplete Dominance or “blended inheritance” • Environmental Effects • Sex linked and sex influenced traits

  16. CoDominance • Both alleles expressed at the same time; both dominant

  17. Incomplete dominance: neither allele is fully dominant (blended inheritance) Figure 9.12Ax

  18. Epistasis • Sequential action of genes • Product of one gene influences another (one gene gives “permission” for another allele to work • Gene action acts as a biochemical pathway & feedback inhibition • Ex: Indian corn coloration

  19. Pleiotropy • Where one allele may have multiple effects on phenotype

  20. Normal and sickle red blood cells Figure 9.14x1

  21. Individual homozygousfor sickle-cell allele Sickle-cell (abnormal) hemoglobin Abnormal hemoglobin crystallizes,causing red blood cells to become sickle-shaped Sickle cells Clumping of cells and clogging of small blood vessels Breakdown of red blood cells Accumulation ofsickled cells in spleen Physical weakness Heart failure Pain and fever Spleen damage Brain damage Damage to other organs Anemia Impaired mental function Pneumonia and other infections Rheumatism Kidney failure Paralysis

  22. Continuous Variationor Polygenic Traits • Multiple genes acting to influence a characteristic • Produces gradual changes, not distinct “borders” • Ie. Height, weight, nose length, skin pigment

  23. P GENERATION aabbcc(very light) AABBCC(very dark) F1 GENERATION AaBbCc AaBbCc Sperm Fraction of population Skin pigmentation F2 GENERATION Figure 9.16

  24. Environmental Influence • Example = color change of fur in arctic animals

  25. Same eyes, different lighting

  26. Multiple Alleles • More than one allele per gene

  27. 3 alleles (ABO) • 4 phenotypes (A, B, AB, O) • Uses concept of glycoproteins (sugar name tags or antigens) to mark cells • Non-recognition of the correct “name tag” for blood type can cause agglutination

  28. Landsteiner Blood Groups • Type A – galactosamine – AA (homo) or AO (hetero) • Type B – galactose – BB or BO • Type AB – galactosamine + galactose (codominant) • Type O – no sugar marker - OO

  29. Universal Donor Universal Recipient Blood Donor Facts

  30. Rh factor • Rh factor can be + or – • + is like a “seen” name tag or antigen • - is “invisible” • Rh- moms that have Rh+ babies are subject to spontaneous abortions • Erythroblastosis fetalis • Controlled with an injectionof RhoGam to “hide” babies cells

  31. Sex Linked • “Sex on the X” • Specific trait/disorder is found on sex chromosome, usually the X • Usually recessive traits • Seen more often in males than females • Ex: color blindness, hemophilia

  32. Barr Body inactivation • In females, both X chromosomes are not metabolically active • Random inactivation of one X chromosome may influence traits expressed

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