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Genetics and Heredity

Genetics and Heredity. Probability. The likelihood that a specific event will occur Probability = # of 1 times event occurs number of possible outcomes. Example: What is the probability that a tossed coin will be heads? ½ or 50%. Probability.

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Genetics and Heredity

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  1. Genetics and Heredity

  2. Probability

  3. The likelihood that a specific event will occur Probability = # of 1 times event occurs number of possible outcomes Example: What is the probability that a tossed coin will be heads? ½ or 50% Probability

  4. The First Law of Probability: the results of the first trial of a chance event do not affect the results of later trials of the same event. In other words, no matter how many times a flipped coin lands on tails, every flip still has a ½ chance of tails. Probability

  5. Second Law of Probability: The probability of two or more independent events occurring together is the product of their separate probabilities. What is the probability that a couple will have four boys? 50% (1/2 probability each time) ½ x ½ x ½ x ½ = 1/16 Probability

  6. Inherited Traits

  7. Are these inherited traits? Your eye color Your hair color and texture Your height

  8. Are these inherited traits? Your personality Your musical, athletic, and artistic abilities

  9. Think about this…. • “My parents have brown eyes, why are mine blue?” • “My brother is tall. Why am I short?” • “Why does my sister have blonde hair while mine is brown?”

  10. These are questions that Gregor Mendel tried to answer.. Born in 1822 in Austria 1843 – Studied Theology 1846-Studied Science at the University of Vienna Gregor Mendel Father of Genetics

  11. Johann Mendel was born in 1822 in Heinzendorf, Austria, to a peasant farming family. Austria Poland Italy Germany Czech Republic Austria

  12. During his early years, Do I LOOK like a farmer? Johann did NOT like agriculture very much. He lay around in his bed “sick” for weeks, possibly to avoid farm chores.

  13. When Johann was 16, his father had a debilitating farming accident and Johann was forced to provide for himself.

  14. When Johann was 18, he borrowed money from his younger sister’s dowry to pay for his education at the university for two years.

  15. When he was 21, one of Johann’s teachers took note of his exceptionally bright mind and persuaded him to join the Augustinian monks. St.Thomas Church, (now Brno, Czechoslovakia)

  16. After he arrived at St. Thomas, Johann Mendel changed his name to Brother Gregory. The monastery was a center of learning for young men who wanted to study theology and natural science.

  17. Report Card F- Brother Gregory also spent time teaching mathematics at a nearby school. After one year, in order to become a teacher, he took the teacher’s examinations at the University of Vienna . . . and failed.

  18. During his early years at the monastery, Mendel began studying and breeding mice. The bishop was not pleased.

  19. Brother Gregor settled on bees . . .

  20. and peas.

  21. University of Vienna While at the monastery, Gregor continued his studies at the University of Vienna for several years. He became a “reserve” teacher for an ailing professor, teaching science at a local college while studying physics at the University of Vienna.

  22. Report Card F- - - After many years at the university, Gregor retook the teacher’s exam, and failed for the second time.

  23. In spite of these failures, Mendel continued to conduct numerous experiments on plants. Mendel narrowed his focus to one particular garden pea, Pisum sativm. For 8 years, Mendel experimented with over 28,000 peas in the large gardens attached to the monastery.

  24. Rather than study every characteristic of the garden pea, Mendel narrowed his observations to 7 traits.

  25. Garden Pea Traits Observed

  26. Seed shape smooth wrinkled Seed color yellow green inflated constricted Pod shape green yellow Pod color purple white Flower color Flower location axial terminal tall short Plant size

  27. In 1866 when Mendel was 44, his experimental results were published . . . and ignored long after he died.

  28. In 1900, 3 scientists - Carl Correns, Hugo de Vries, and Erich von Tschermak - all independently rediscovered and verified Mendel's principles, marking the beginning of modern genetics. He is now considered the father of genetics.

  29. Dominant (H) Homozygous (HH or hh) Genotype (HH, Hh or hh) Purebred (HH or hh) Recessive (h) Heterozygous (Hh) Phenotype (blonde, brown, red) Hybrid (Hh) Mendel’s studies led to: Concepts in Inheritance

  30. Theory of Heredity Inherited allele for purple P Inherited allele for purple P HOMOZYGOUSpurple flower PP

  31. Theory of Heredity Inherited allele for purple flower (P) Inherited allele for pink flower (p) HETEROZYGOUS purple flower (Pp)

  32. Theory of Heredity Inherited for pink flower (p) Inherited for pink flower (p) HOMOZYGOUS pink flower (pp)

  33. PREDICTING HEREDITY

  34. PUNNETT SQUARES • A Punnett square is a tool used to help predict the probability of offspring of a couple. • 1. Decide the genes that could be passed on to the offspring in the gametes from each parent. • 2. Cross the different gene/gamete possibilities for each possible offspring combination.

  35. Monohybrid Cross: a cross that shows the possible offspring for one trait Aa x Aa A: White fur a: Brown fur Monohybrid Cross Parent Aa has what gentotype? Parent Aa can produce a gamete with either an “A” or with an “a”

  36. Monohybrid Cross: a cross that shows the possible offspring for one trait Aa x Aa A: White fur a: Brown fur Aa produces gamete “A” or “a” Monohybrid Cross a A A a • Separate the two genes (as though they were separating into different gametes) and place one outside the first row on the left and the other under it outside the second row. • Separate the other parent genes and place at the top, one above each column.

  37. Monohybrid Cross: a cross that shows the possible offspring for one trait Aa x Aa A: White fur a: Brown fur A a AA A Aa a Aa aa Monohybrid Cross • Cross over the genes to fill in the boxes of the square.

  38. Genotypic Ratios compare the possible genotypes (gene combinations in the offspring. Genotypic ratio: Number of offspring with homozygous dominant genes AA Number of offspring with heterozygous/hybrid genes Aa Number of offspring with homozygous recessive genes aa A a AA Aa A a Aa aa Genotypic Ratios • Aa x Aa • A: White fur • a: Brown fur • Sometimes abbreviated as: • GR = #hom dom (AA) : #hyb (Aa) : hom rec (aa) GR = 1 : 2 : 1

  39. Phenotypic Ratios compare the possible phenotypes (appearance of the offspring); how many show the dominant trait or recessive trait. Phenotypic ratio: Number of offspring showing the dominant trait (AA & Aa) Number of offspring showing the recessive trait (aa) A a AA Aa A a Aa aa Phenotypic Ratios • Aa x Aa • A: White fur • a: Brown fur • Sometimes abbreviated as: • PR = #show dom (AA & Aa) : #show rec (aa) PR = 3 : 1

  40. A A A a Practice! Cross a HOMOZYGOUS dominant female with a HETEROZYGOUS male using the same trait. What is the genotypic ratio? AA AA 2:2 or 50% What is the phenotypic ratio? 4 white fur Aa Aa

  41. Dihybrid Cross: shows the possible offspring for two traits This shows a cross between parents hybrid for two traits: BbRr x BbRr BR Br bR br BR BBRR BBRr BbRR BbRr Br BBRr BBrr BbRr Bbrr bR BbRR BbRr bbRR bbRr br BbRr Bbrr bbRr bbrr Dihybrid Cross BbRr x BbRr Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

  42. BR Br bR br BR BBRR BBRr BbRR BbRr Br BBRr BBrr BbRr Bbrr bR BbRR BbRr bbRR bbRr br BbRr Bbrr bbRr bbrr Dihybrid Crosses Phenotypic Ratio: # dom/dom : # dom/rec : # rec/dom : # rec/rec • How many of the offspring would have a black, rough coat? (#dom/dom) • How many would have a black, smooth coat? (#dom/rec) • How many would have a white, rough coat? (#rec/dom) • How many would have a white, smooth coat? (#rec/rec) 16 Phenotypic Ratio: 9:3:3:1

  43. #1 x #16 BBRR x bbrr If mouse #1 were crossed with mouse #16, what would their offspring look like? BR Br bR br BR BBRR BBRr BbRR BbRr Br BBRr BBrr BbRr Bbrr bR BbRR BbRr bbRR bbRr br BbRr Bbrr bbRr bbrr Dihybrid Crosses 1 Coat Texture: R: Rough r: Smooth Fur Color: B: Black b: White • #6 x #10 • BBrr x BbRr 16 • #14 x #16 • Bbrr x bbrr

  44. More Complex Patterns of Heredity • Incomplete Dominance • Codominance • Multiple Alleles • Sex-Linked Traits

  45. Incomplete Dominance R R R’ Red (RR) X white (R’R’) make pink (RR’) RR’ RR’ R’ RR’ RR’

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