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Gregor Mendel

Gregor Mendel. Gregor Mendel: Austrian monk lived from 1822-1884 Mendel developed principles of heredity without any knowledge of genes or chromosomes His principles were established through experiments with pea plants. Why was Mendel successful with the pea?.

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Gregor Mendel

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  1. Gregor Mendel • Gregor Mendel: • Austrian monk lived from 1822-1884 • Mendel developed principles of heredity without any knowledge of genes or chromosomes • His principles were established through experiments with pea plants

  2. Why was Mendel successful with the pea? • Used pure breeding, 7 contrasting traits • Studied characteristics one at a time for many generations • Used mathematics in analyzing his results • Obtained large numbers of offspring • Chose pea plants which normally self-fertilize • Inexpensive • Used scientific method • Easy to pollinate (transfer of male pollen to egg)

  3. Mendel’s 7 contrasting traits

  4. Genetics Terms • Define genes: factors that control organism’s traits. the part of chromosome that contains the genetic code. • Every organism requires a set of coded instructions for specifying its traits • For offspring to resemble their parents, their must be a reliable way to transfer hereditary information from one generation to the next

  5. Genetics Terms • homozygous (pure): the alleles on homologous chromosomes are the same • heterozygous: (hybrid): the alleles on homologous chromosomes are different • parental generation (P): the two original organisms being crossed - usually pure • first filial generation (F1) :the first generation of offspring from the parents • second filial generation (F2) :generation of offspring arising from the first filial generation

  6. Genetics Terms • Genotype: the genetic makeup of an organism • Homozygous Dominant: TT • Homozygous Recessive: tt • Heterozygous: Tt • Phenotype: the appearance of an organism • Describes what it looks like TT - Tall tt - short Tt - Tall

  7. Punnett Squares • a model used to predict the results of a genetic cross • BB X bb B B b B b B b b B b B b

  8. Three Laws by Mendel 1. Law of Dominance: a pattern of heredity in which one allele of a gene may express itself by masking the presence of the other allele Dominant Trait: the trait or allele that is expressed (capital letter) R Recessive Trait:the trait or allele that is present but that is not expressed (lowercase letter) r

  9. Three Laws by Mendel 1. Law of Dominance: Example: red flower (RR) X white flower (rr)  red flower (Rr) X 

  10. Example of Dominance Problem:Cross homozygous dominant with homozygous recessive R R • R = red • r = white • RR x rr Rr Rr r r Results:Phenotype: Genotype: Rr Rr 100% red 100% heterozygous

  11. 2. Law of Segregation Mendel’s second law • When gametes are formed during meiosis: • There is a random segregation of homologous chromosomes • Random segregation of sister chromatids & alleles • The result: new gene combinations are likely to be produced • Segregation means separation and can lead to genetic recombination.

  12. Example of Segregation Problem:Cross two offspring from 1st cross (2 heterozygous parents) • R = red • r = white • Rr x Rr R r RR Rr R r Phenotype: ____% red, ____% white ___ red : ___ white Genotype: ___% homozygous dominant, ___% homozygous recessive, ___% heterozygous 75 25 Rr rr 3 1 25 25 50

  13. 3. Law of Independent AssortmentMendel’s third Law • Scenario: Two different traits located on two different chromosomes • They segregate randomly during meiosis • May be inherited independently of each other • The cross of two organisms heterozygous for a trait is known as a dihybrid cross

  14. Law of Independent Assortment

  15. Dihybrid Cross Problem:Cross homozygous tall and homozygous wrinkled seeds with homozygous short and homozygous smooth seeds What are the genotypes for these plants? TTQQ x ttqq T = tallt = short Q = wrinkledq = smooth

  16. TTQQ x ttqq TQ TQ TQ TQ tq TtQq TtQq TtQq TtQq TtQq tq TtQq TtQq TtQq tq TtQq TtQq TtQq TtQq tq TtQq TtQq TtQq TtQq Phenotype: 100% Tall & Wrinkled

  17. Dihybrid Cross • What is the phenotype from this cross? • 100% Tall and Wrinkled • What is the genotype from this cross? • We don’t worry about genotype for dihybrid crosses

  18. Complete the following Dihybrid cross Step 1 - set up gamettes(sex cells) (1 3, 1 4, 2 3, 2 4) TtQq x TtQq

  19. Complete the following Dihybrid crossTtQq x TtQqT-Tall t-shortQ-Wrinkled q-smooth tq TQ Tq tQ TTQq TtQQ TtQq TQ TTQQ TTQq TtQq TTqq Ttqq Tq TtQQ TtQq ttQQ ttQq tQ tq TtQq Ttqq ttQq ttqq

  20. What are the phenotypes for the above cross??? • - Tall & Wrinkled • - Tall & smooth • - Short & wrinkled • - Short & smooth 9 3 3 1

  21. Incomplete Inheritance • Two examples of Incomplete Inheritance: • Incomplete Dominance & Codominance • Incomplete Dominance: • A case where one allele is partially dominant over the other • Examples of Incomplete Dominance: red snapdragons X white snapdragons  pink snapdragons cross between black and white Andulusian fowl gives blue (gray) fowl

  22. Example of Incomplete Dominance Pink Snapdragons  X

  23. Example of Incomplete Dominance Problem:Cross offspring from 1st cross (2 heterozygous parents) R r Rr RR • R = red • r = white • Rr x Rr R r rr Rr Results:Phenotype:___% red, ___% pink, ___% white Genotype: ___% homozygous dominant ___% heterozygous ___% homozygous recessive 25 50 25 1 2 1 Ratio ___ : ___ : ___ 25 50 1 2 1 Ratio ___ : ___ : ___ 25

  24. Intermediate Inheritance • Codominance: a case in which neither allele is dominant over the other • Alleles have equal power • Examples: • Cross between red and white short horned cattle gives roan cattle • Checkered black & white chicken • Sickle-cell Anemia - a blood disease where RBCs are sickle shaped or half moon. Most common African. • Heterozygous - half normal half sickle shape

  25. Roan Cattle Red Cattle  X Roan Cattle White Cattle

  26. Example of Codominance Problem:Cross offspring from 1st cross (2 heterozygous parents) R r Rr RR • R = red • r = white • Rr x Rr R r rr Rr Results:Phenotype:___% red, ___% red & white, ___% white Genotype: ___% homozygous dominant ___% heterozygous ___% homozygous recessive 25 50 25 1 2 1 Ratio ___ : ___ : ___ 25 50 1 2 1 Ratio ___ : ___ : ___ 25

  27. Problem 1 Phenotype of tt ------------------------- Genotype of tt--------------------------- Phenotype of TT ----------------------- Genotype of TT------------------------- Phenotype of pure dominant-------- Genotype of pure dominant--------- Phenotype of pure recessive--------Genotype of pure recessive--------- Short Homozygous recessive Tall Homozygousdominant Tall TT Short tt

  28. Problem 2:A married couple want to know their chances of having girl X Y XX XY X X __ __ x __ __ X Y X X XY XX Results: Phenotype: 50% male, 50% female Phenotype ratio: 2 male : 2 female

  29. Problem 3:Cross two heterozygous parents R r RR Rr • R = red • r = white • __ __ x __ __ R r Rr rr R r R r Phenotype: ___% red, white___% Phenotypic Ratio: __ : ___ Genotype: ___% heterozygous ___% homozygous dominant ____% homozygous recessive 75 25 1 white 3 red 25 50 25 25

  30. R R Problem 4: Pure dominant crossed with hybrid RR RR • R = red • r = white • __ __ x __ __ R r Rr Rr R R R r Results: Phenotype: ___% red, white___% Phenotype Ratio: __ : _ _ __ Genotype: ___% heterozygous ___% homozygous dominant ___% homozygous recessive 100 0 4 red 0 white 50 50 0

  31. Problem 5:The male’s genotype is homozygous recessive. The female is phenotypically dominant but does carry the recessive allele. r r Rr Rr • R = red • r = white • __ __ x __ __ R r rr rr r r R r 50 50 Phenotype: ___% red, white___% Phenotypic Ratio: __ : ___ Genotype: ___% heterozygous ___% homozygous dominant ___ % homozygous recessive 2 red 2 white 50 0 50

  32. Problem 6: Law of Codominance R r Cross two heterozygous parents Rr RR • R = red • r = white • __ __ x __ __ R r Rr rr R r R r Results: Phenotype: ___% red, ___ % red and white, white___% Phenotypic Ratio: __ red : __ red and white : ___ white Genotype: ___% heterozygous ___% homozygous dominant ___ % homozygous recessive 25 50 25 1 2 1 50 25 25

  33. Problem 7: Law of Incomplete Dom R r RR Rr Cross two heterozygous parents • R = red • r = white • __ __ x __ __ R r Rr rr R r R r Results: Phenotype: ___% red, ___ % pink, white___% Phenotype Ratio: __ red : __ pink : ___ white Genotype: ___% heterozygous ___% homozygous dominant ___ % homozygous recessive 25 50 25 1 2 1 50 25 25

  34. Test Cross: It will determine if a horse/dog in question is pure or carrying a recessive gene.

  35. Problem 8:A test cross uses an individual that is homozygous recessive. It will determine if the dog in question is pure or carrying a recessive gene. B B Bb Bb b b Bb Bb • B = brown • b = white • __ __ x __ __ • or • __ __ x __ __ B B b b B b Bb bb b b B b b b Bb bb

  36. Multiple alleles • Traits that are controlled by more than 2 alleles • Results in multiple phenotypes • Examples: • Pigeons BA dominant over B BA and B are dominant over b • Blood groups in humans Four blood types A B AB & O

  37. X-linked InheritanceExamples:Hemophilia, Color Blindness, Loss of Hearing & Muscular Dystrophy

  38. X-linked Recessive Inheritance XDXd XDY XD Xd ___% NORMAL HEARING of TOTAL OFFSPRINGS, ___ % HEARING LOSS of TOTAL OFFSPRINGS ___% NORMAL HEARING OF FEMALES ___ % HEARING LOSS OF MALES XD XDXD XDXd XDXD XDY XDXd XdY Y XDY XdY 75 25 100 50

  39. Polygenic Inheritance A pattern of a trait that is controlled by 2 or more genes. Phenotype express a range of variability. • Examples: • Stem length, human height, eye color & skin color Stem length for a totally recessive plant is____ cm. aabbcc = 4 cm AABBcc = cm Aabbcc = cm AABBCc = cm AAbbcc = cm AABBCC = cm AABbcc = cm

  40. Gene Expression • Influence of External Environment: • Examples: Temp., nutrition, light, chemicals • Color of rabbit in the summertime: brown • Color of rabbit in the winter: white • The temperature effects what color fur (or what proteins) are expressed • Temp also determines the sex of a gator • Light determines color of bacteria

  41. Gene Expression • Influence of Internal Environment: • Examples: Hormonal influences • Horn size in mountain sheep • Male pattern baldness • Peacock feathers

  42. Gene Expression • Influence of Internal Environment: • Examples: Hormonal influences • Horn size in mountain sheep • Male pattern baldness • Peacock feathers

  43. Nature vs. Nurture • In many cases it is not only the genes that we have that determine what we look like • Scenario: If identical twins (same DNA) were separated at birth and lived in 2 different environments and then brought together 25 years later would they look the same? Why or why not?

  44. Nature vs. Nurture • Answer: The identical twins would have similar features (eye color, size of nose, etc.) but may look very different. What they did throughout their lives effects what they look like • For example: sun exposure, diet, hygiene, injuries, etc.

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