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To Mendel and BEYOND!!

To Mendel and BEYOND!!. Mendel was fortunate to use pea plants because each trait that he observed was not only controlled by one set of genes , but there were also two alleles – dominant vs. recessive . Many traits are not that simple!! Other patterns of inheritance include:

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To Mendel and BEYOND!!

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  1. To Mendel and BEYOND!! • Mendel was fortunate to use pea plants because each trait that he observed was not only controlled by one set of genes, but there were also two alleles – dominant vs. recessive. • Many traits are not that simple!! • Other patterns of inheritance include: • Incomplete dominance • Codominance • Multiple Alleles • Polygenic traits

  2. Incomplete Dominance • Pattern of inheritance where the dominant trait does not completely “mask” the recessive trait resulting in a blending of the two traits • Example: Snapdragons and Four O’Clock flowers • Red x White  Pink

  3. Snapdragons & Four O’Clocks

  4. Incomplete Dominance in Snapdragons Alleles: - Red = R - White = W Genotypes: - RR - WW Phenotypes: - Red - White RR WW Genotypes: - RW Phenotypes: - Pink RW RW RR RW RW WW

  5. Why did the F1 generation only have pink flowers? What happened to the red flowers and the white flowers? RR X WW R R RW RW W RW RW W 100% RW Therefore, 100% PINK!

  6. Heterozygous Crosses • What would be the results if the crosses made were between two heterozygous plants? RW x RW • The results are as follows: • Genotype: 1 RR: 2 RW: 1 WW • Phenotype: 1 red: 2 pink: 1 white R W R RR RW W RW WW

  7. Codominance • Pattern of inheritance where both alleles are dominant and both are expressed independently. • Example: Cows • NOT PINK CATTLE . . . Both red and white fur are present . . . known as roan. • White cow x red bull  roan

  8. Working with Codominance • Red Allele: FR • White Allele: FW • Red Bull’s Genotype: FRFR • White Cow’s Genotype: FWFW The Cross: FRFRxFWFW • Roan Genotype: FRFW FR FR FW FR FW FR FW FR FW FR FW FW

  9. Working with Codominance • If the cross were between two roan cows: FRFW x FRFW • Show a Punnett Square: FR FW • Genotypic ratio: • 1 FRFR:2FRFW:1FWFW • Phenotypic ratio: • 1 red:2roan:1white FR FR FR FR FW FW FR FW FW FW

  10. X

  11. Multiple Alleles • Mendel worked with traits that had only two alleles: • Pea Flower Color: Purple (P) vs. white (p) • Pea Plant Height: Tall (T) vs. short (t) • Pea Color: Yellow (Y) vs. green (y) • Many traits are controlled by more than just two alleles; therefore they are called multiple alleles.

  12. Examples of Multiple Alleles • Rabbit fur: In rabbits, coat color is controlled by multiple alleles. Full color (C), white (c), light-gray or chinchilla (cch) and white with black points or a Himalayan (ch). Full color is dominant to all the other alleles. Chinchilla is dominant to Himalayan and white.

  13. ABO Blood Typing • ABO blood grouping in people is classic example of multiple alleles in a SINGLE gene • Four Blood Types: • A • B • AB • O

  14. Why is it Multiple Alleles? • IF it was just simple, there would be only be three genotypes: II (homozygous dominant), Ii (heterozygous), or ii (homozygous recessive). • Blood typing is an example of multiple alleles because it has more than two alleles • There’s more than just dominant (I) and recessive (i) • However, there are three different alleles: • IA (dominant) • IB (dominant) • i (recessive) Two forms of the dominant allele!

  15. Genotypes of Blood Types • Type A • IAIA or IAi • Type B • IBIB or IBi • Type O • ii • Type AB • IAIB

  16. Each allele codes for a specific ANTIGEN that’s found on the surface of the red blood cells: IA = antigen A (protein A) IB = antigen B (protein B) i= no antigen The antibodies in the blood “attack” the antigens making mixed red blood cells to clump.

  17. Summary of Blood Types

  18. Blood Type Patterns • Type A can receive A or O • Type B can receive B or O • Type O can only receive type O • Type AB can receive from any blood type (universal recipient) • Type O can give blood to any blood type (universal donor) • Type AB can only give to other AB

  19. Polygenic Traits • Traits that are controlled by two or more genes • Not to be confused with genes with multiple alleles!! (One set vs. many sets) • In humans: skin color, eye color, height • Ex: gene A; gene B; gene D; gene E • Each gene would have two alleles: dominant and recessive (A & a; B & b . . . Etc)

  20. Interpreting Polygenic Genotypes • Skin Color: • Dominant allele = pigment • Recessive allele = no pigment • A, B, D, E = pigment • a, b, d, e = no pigment • AABBDDEE = 8 dominant: 0 recessive • aabbddee = 0 dominant: 8 recessive • Which is darkest? Which is lightest?

  21. Interpreting Polygenic Genotypes • How many variations are there for AABBDDEE or aabbddee? • Only one way to get 8 dominant or 8 recessive alleles • Consider genotype: AaBbDdEe • How many dominant alleles? How many recessive? • What can you infer about the skin color?

  22. Interpreting Polygenic Genotypes • Is there another way to get 4 dominant alleles and 4 recessive alleles within the genotype? • Examples: AAbbDdEe and aaBBDdEe • Each example above have 4 dominant alleles and 4 recessive; therefore, their phenotypes are the same as AaBbDdEe!

  23. Interpreting Polygenic Genotypes • The intermediate combination occurs most frequently; therefore, most in a population show that particular phenotype and the two extremes show up the least • This pattern is also seen in height!

  24. Polygenic Traits – Skin Color

  25. Polygenic Traits in Humans

  26. Heterochromia

  27. Famous People with Heterochromia Mila Kunis Kate Bosworth Max Scherzer

  28. Heterochromia in Pets

  29. Albinism

  30. Albino Animals

  31. X-linked Disorders (also known as sex-linked)

  32. X-linked • Genes located on the X-chromosome • Women = two X chromosomes • Men = only one X chromosome • Disorder occurs more often in males than females • Examples: Color blindness, hemophilia, muscular dystrophy

  33. Test for Color Blindness Ishihara Test

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