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Genetics the study of heredity

Genetics the study of heredity. Gregor Mendel “Father of Genetics”. Heredity -the transfer of characteristics from parents to offspring through their genes Gregor Mendel -used garden peas to study heredity. Mendel’s Experiments.

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Genetics the study of heredity

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  1. Geneticsthe study of heredity

  2. Gregor Mendel“Father of Genetics” • Heredity -the transfer of characteristics from parents to offspring through their genes • Gregor Mendel -used garden peas to study heredity

  3. Mendel’s Experiments • cross fertilization: Mendel crossed two parent plants with opposite traits (purple x white). This was the Parental generation (P). The First generation (F1) were identical (purple). • self fertilization: Mendel allowed the purple flowers from the First generation (F1) to self-pollinate. Self pollination produced the Second generation (F2). Muskopf, Shannan

  4. Mendel’s Conclusions • The F1 generation all showed the purple trait (called the dominant trait) • In the F2 generation the (white) trait reappears in ¼ of the flowers (called the recessive trait) • Each flower has two alleles that determine the appearance • The alleles are represented by letters (uppercase letter represents the dominant allele; lowercase letter represents the recessive allele) • P is dominant and represents purple • p is recessive and represents white • The Dominant Is Expressed No Matter What • Need 2 Copies Of The Recessive Allele In Order To Be Expressed • PP = purple flower Pp = purple flower pp = white flower

  5. Alleles • homozygous: organisms that have 2 identical alleles for a trait (could be two capital or two lowercase letters) • PP • pp • heterozygous: organisms that have 2 different alleles for a trait • ex: Pp (the dominant allele P is expressed so this flower would be purple)

  6. Genotype: letters used for the alleles • ex: PP, Pp, pp • Phenotype: what an organisms looks like • ex: purple, white

  7. Punnett square • A Punnett squareis used to show the possible allele combinations in the offspring of 2 parents. • Monohybrid cross = cross involving only 1 trait The four boxes represent the four possible offspring

  8. Example of a Monohybrid Cross A plant heterozygous with green peas (Gg) is crossed with a plant that has yellow peas (g). • Step 1: Choose a letter for the alleles (green is dominant; yellow is recessive) • G : green pea g: yellow pea • Step 2: Write the genotypes of the parents • heterozygous plant with green peas : Gg • plant with yellow peas: gg • parents: Gg x gg

  9. G g G g G g G g g g g g g g g g gg Gg gg gg Gg gg Gg gg Gg gg G g g g Step 3: Set up the punnett square with one parent on each side Step 4: Fill out the punnett square middle

  10. Step 5: Look at the four boxes from Step 5 and determine the genotypes of the four offspring • Genotypic ratio: 2 Gg: 2 gg • Step 6: Look at the genotypes in Step 6 and determine the phenotypes; • Green (G) is dominant over yellow (g), plants that have G in their offspring have green peas • Phenotypic ratio: 2 green: 2 yellow

  11. Practice-Monohybrid Crosses Cross an individual with blue eyes with an individual with homozygous brown eyes. Brown eyes (B) is dominant to blue eyes (b). Phenotypes: Genotypes: B B b b

  12. Cross an individual with blue eyes with an individual with homozygous brown eyes. Brown eyes (B) is dominant to blue eyes (b). Phenotypes: All Brown Eyes Genotypes: All Bb B B b Bb Bb b Bb Bb

  13. Practice-Monohybrid Crosses A child is diagnosed with a recessive genetic disease. Neither parent has the disease. What are the genotypes of the parents? Phenotypes: Genotypes: N ? N ? nn

  14. A child is diagnosed with a recessive genetic disease. Neither parent has the disease. What are the genotypes of the parents? Genotypes of the parents are Nn N n N NN nn n Nn nn

  15. Incomplete Dominance = Blending In snapdragons, there is not a dominant allele. The flower color can be red, pink, or white. A heterozygous flower (Rr) will a blending of red and white (pink). • Muskopf, Shannan. Online Images. The Biology Corner. 20 April 2007. http://www.biologycorner.com/bio1/celldivision-chromosomes.html

  16. Codominance: the recessive & dominant traits appear together (both are dominant, no recessive allele) • Ex: Cross a red cow with a white cow. What will the offspring be? R R W W

  17. phenotype: all red and white speckled • genotype: all RW R R W RW RW • Muskopf, Shannan. Online Images. The Biology Corner. 20 April 2007. http://www.biologycorner.com/bio1/celldivision-chromosomes.html W RW RW

  18. Polygenic Traits: “many genes” act together resulting in a range of phenotypes • Ex: skin, hair, eye color Skin color is a polygenic trait because it shows a range of colors. There is not a dominant and recessive color. Farabee, M.J. “Skin Pigmentation.” 2001. Online Image. Online Biology Book. 5 May 2007. http://www.emc.maricopa.edu/faculty/farabee/biobk/BioBookgeninteract.html

  19. Multiple Alleles: genes that have more than two alleles • There are four blood types (phenotypes): A, B, AB, and O • Blood type is controlled by three alleles: A, B, and O • Each individual only inherits two alleles (one from each parent). • A and B are codominant • O is recessive, two O alleles result in type O Blood • Blood Types Possible Genotypes • Dominant A AA or AO • Dominant B BB or BO • Codominant AB AB • Recessive O OO

  20. Practice: Cross a Type AB with a Type O. AB x OO 1. Set up punnett square with one parent on each side A B O AO BO 2. Fill out the punnett square middle O AO BO What are the possible blood types of the four offspring? Genotype Blood Type 2 AO 2 Type A 2 BO 2 Type B

  21. Practice A woman heterozygous for Type A blood marries and a man with Type AB blood. Show the cross and the possible offspring. 1. Write the genotypes of the parents: • woman heterozygous for Type A: AO • man with Type AB: AB 2. Set up punnett square with one parent on each side and fill in the middle. A O Blood types of possible offspring: AA: Type A blood AO: Type A blood AB: Type AB blood BO: Type B blood A AA AO B AB BO

  22. Practice If a Type O individual marries a Type B individual can they have offspring with Type O blood? What type of blood can the offspring have? B ? Blood types of possible offspring: AA: Type A blood AO: Type A blood AB: Type AB blood BO: Type B blood O O

  23. If a Type O individual marries a Type B individual can they have offspring with Type O blood? What type of blood can the offspring have? B O Yes, they can have a child with type O or type B blood. O BO OO O BO OO

  24. Practice If 2 individuals with Type AB blood marry, what percentage of their offspring will have Type AB blood? A B A B

  25. If 2 individuals with Type AB blood marry, what percentage of their offspring will have Type AB blood? 50% of their offspring could be Type AB A B A AA AB B AB BB

  26. Review of Terms • Allele A form of a gene • Homozygous Both Alleles are the Same • Heterozygous Alleles are Different • Homozygous Dominant AA • Homozygous Recessive aa • Heterozygous Aa • Genotypic Ratio 2 PP : 2 pp • Phenotypic Ratio 2 Purple : 2 White

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