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Mendelian Genetics

Mendelian Genetics . The Basics. Gregor Mendel???. Known as the Father of Genetics: His experiments with Pea plants from 1856-1863 began our understanding of how traits, things like hair or eye color, height, weight, ect……., were passed down from generation to generation.

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Mendelian Genetics

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  1. Mendelian Genetics The Basics

  2. Gregor Mendel??? • Known as the Father of Genetics: His experiments with Pea plants from 1856-1863 began our understanding of how traits, things like hair or eye color, height, weight, ect……., were passed down from generation to generation. • He came up with the principles of heredity that still hold true today by studying 7 characteristics of peas in his garden. • His work started and formed the base of all genetics, a field we learn more about every day.

  3. How did He do it • Mendel would cross-pollinate (hybridize) two contrasting, true-breeding pea varieties. • He got true breeders by allowing self pollination. • The true-breeding parents are the P generation and their hybrid offspring are the F1 generation. • Mendel allowed the F1 hybrids to self-pollinate to produce an F2 generation. Here he came up with his 2 famous laws of segregation and independent assortment.

  4. Mendel reasoned that the heritable factor for white flowers was present in the F1 plants, but it did not affect flower color. • This is where dominant and recessive come in. Dominate genes always show and ‘dominate’. Recessive genes can hide, and only show when no dominate genes are present

  5. The Law of Segregation • 1. different version of genes (alleles) account for variations in inherited characters or traits • Ex Blue and Brown eyes, both eye color genes just different versions • 2. For each trait, organisms inherit 2 alleles, one from each parent.

  6. The Law of Segregation • 3. If two alleles differ, then one, the dominantallele, is fully expressed while the other, Recessive, is masked or only partially shown (ie if you get an allele for brown eyes from your mom and an allele of blue eyes from you dad, the dominate gene (Brown) is the colour of your eyes.

  7. Dominate alleles are capitalized, while recessive genes are non capitals • Ie • B- Brown eyes (dominate) • b – blue eyes (recessive) • E – attached earlobes (dominate) • e – unattached earlobes (recessive)

  8. Punnett Square Predictions http://www.youtube.com/watch?v=V_pl5lcSUFg

  9. Genetics Vocabulary • organism with two identical alleles for a trait is homozygous. ( TT or tt) Big letters= Dominant small or lower case = recessive. • Organisms with two different alleles for a character is heterozygous ( Tt or Pp) • http://en.wikipedia.org/wiki/List_of_Mendelian_traits_in_humans • http://faculty.southwest.tn.edu/jiwilliams/Human_Traits.htm

  10. Genetics Vocabulary • description of an organism’s traits is its phenotype Ex) What it looks like, tall, short ,white, black ect…. • description of its genetic makeup is its genotype. Ex) Homozygous brown eyes BB Genotype – BB Phenotype – Brown Eyes Heterozygous brown eyes Bb Genotype ___, Phenotype ___

  11. Test Cross Tales the Tale

  12. Sound Simple Right???? • The relationship of genotype to phenotype is rarely simple like in our examples because there are exceptions to all rules. • Mendel lucked out in picking peas plants because each trait is controlled by 1 gene, genetically simple. But this is rare…. • some alleles show incomplete dominance where heterozygotes show a distinct intermediate phenotype, not seen in homozygotes. • Snapdragons and roses are good examples

  13. Snapdragons

  14. Codominance • codominance 2 alleles affect the phenotype in separate, distinguishable ways • 2 dominant alleles expressed at the same time. • Ex. Is blood type. DRAW. This is also multiple allele gene have 3 alleles present. A,B,O • Fact: Just because an allele is dominant does not make it more prevalent in a population. • Ex. Polydactylis dominant to having the normal 5 fingers and toes but 399 out of 400 have the recessive genes, what we call normal 5 and 5

  15. Cont….. • most genes are pleiotropic, affecting more than one phenotypic trait • extensive symptoms of sickle-cell anemia are owed to a single gene. • epistasis, a gene at one locus, or location, alters the phenotypic expression of a gene at a second locus • Ex. Mice and other mammals 1 gene determines if there is pigment in the hair C, there is, c, is not, and another determine color B,black or b, brown. Cc is albino

  16. Punnett Squares of Test Crosses Homozygous recessive Homozygous recessive a a a a A A Aa Aa Aa Aa A a aa Aa aa Aa Two phenotypes All dominant phenotype

  17. Dominant Traits Recessive Traits Freckles No freckles Widow’s peak Straight hairline Free earlobe Attached earlobe Genetic traits in humans can be tracked through family pedigrees • The inheritance of many human traits • Follows Mendel’s laws Figure 9.8 A

  18. D ? John Eddy Dd Abigail Linnell D ? Hepzibah Daggett Dd Joshua Lambert dd Jonathan Lambert Dd Elizabeth Eddy D ? Abigail Lambert Dd Dd dd Dd Dd Dd dd Female Male Deaf Hearing • Family pedigrees • Can be used to determine individual genotypes Figure 9.8 B

  19. Parents Normal Dd Normal Dd  Sperm Dd Dd Normal (carrier) DD Normal D Offspring Eggs Dd Normal (carrier) dd Deaf d • Recessive Disorders • Most human genetic disorders are recessive Figure 9.9 A

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