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10.1 Genetics developed from curiosity about inheritance

10.1 Genetics developed from curiosity about inheritance. I. The Blending Hypothesis of Inheritance. A trait is a variation of a particular characteristic such as for red flowers or yellow flowers

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10.1 Genetics developed from curiosity about inheritance

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  1. 10.1 Genetics developed from curiosity about inheritance

  2. I. The Blending Hypothesis of Inheritance • A trait is a variation of a particular characteristic such as for red flowers or yellow flowers • In the early 1800’s many biologists believed in the blendinghypothesis, which stated that offspring would be a blend of their parents traits. A red and yellow flower would produce and orange flower

  3. II. Mendel’s Plant Breeding Experiments • Mendel’s work gave rise to the branch of Biology called genetics, the study of heredity • Mendel developed the particulate hypothesis which states that parents pass on separate and distinct factors, or genes

  4. Mendel’s Plant Breeding Experiments • To test this hypothesis, Mendel crossed true-breeding plants that had distinct and contrasting traits such as purple and white flowers • Mendel cross-fertilized all his pea plants by hand to control which traits he wanted to control

  5. Mendel methods

  6. 10.2 Mendel’s Principle of Segregation

  7. I. Mendel’s Principle of Segregation • The offspring of two different true-breeding varieties are called hybrids B. When Mendel crossed plants that differed in only one-trait it was called a mono-hybrid cross

  8. C. From these results Mendel developed the following hypothesis • There are alternative forms of a gene called alleles. • For each inherited trait, an organism has two alleles for the gene controlling that character, one from each parent. If both alleles are the same the individual is homozygous, and if the alleles are different the individual is heterozygous.

  9. Mendel developed the following hypothesis 3. When only one of the alleles in a heterozygous individual appears to affect the trait, that allele is called the dominant trait. The allele that does not appear to have an affect on the individual is called the recessive trait

  10. Mendel’s Observation

  11. Mendel’s Observations

  12. Mendel developed the following hypothesis 4. The two alleles for a character separate during the formation of gametes, so each gamete carries only one allele for each character. This is known as Mendel’s Principle of Segregation

  13. II. Probability and Punnett Squares • The inheritance of alleles follows the laws of probability • If you were to flip two pennies the probability of flipping a head or a tail on one does not affect the probability of the other one • A diagram that shows all the possible outcomes of a genetic cross is the Punnett Square

  14. Probability and Punnett

  15. Punnett Square Eye color Homozygous Brown male X Homozygous Blue female

  16. III. Genotypes and Phenotypes • The way an organism looks is not the same as its genetic make-up • An observable trait is called a phenotype while the genetic make-up of alleles is called the genotype

  17. IV. The Testcross • A testcross breeds individuals of unknown genotypes, but the dominant phenotype with a homozygous recessive individual • Depending on the ratios of the offspring, the genotype of the unknown can be determined

  18. Testcross

  19. V. Mendel’s Principle of Independent Assortment • Mendel also did crosses between plants that differed in two traits called a dihybrid cross • From this he developed his Law of Independent Assortment which states that during gamete formation the way in which one allele is inherited does not affect the way another is inherited if they are on separate chromosomes

  20. Independent Assortment

  21. Problem: Monohybrid 1 • 1. An allele for brown eyes B is dominant over that for blue eyes b. A blue-eyed man, both of whose parents were brown-eyed, marries a woman. They have one child who is blue-eyed. What are the genotypes of all the individuals mentioned?

  22. Problem 1 Man’s parents: Bb Dad: bb Mom: Bb Kids: Bb or bb

  23. Problem: Monohybrid 2 2. The ability to taste the chemical PTC is determined by a single gene in humans with the ability to taste given by the dominant allele T and inability to taste by the recessive allele t.  Suppose two heterozygous tasters (Tt) have a large family. 

  24. Problem: Monohybrid 2 • Predict the proportion of their children who will be tasters and nontasters.  Use a Punnett square to illustrate how you make these predictions. • What is the likelihood that their first child will be a taster?  What is the likelihood that their fourth child will be a taster? • What is the likelihood that the first three children of this couple will be nontasters?

  25. Problem 2 • 3:1 b. 3/4, 3/4 c. 1/64

  26. Dihybrid Cross

  27. Dihybrid Cross- FOIL First Outside Inside Last RrYy x RrYy

  28. Problem 3: Dihybrid 3. In pepper plants, green (G) fruit color is dominant to red (g) and round (R) fruit shape is dominant to square (r) fruit shape.  These two genes are located on different chromosomes.

  29. 3. Dihybrid a.   What gamete types will be produced by a heterozygous green, round plant? b. If two such heterozygous plants are crossed, what genotypes and phenotypes will be seen in the offspring and in what proportions?

  30. #3 Types of gametes FOIL First- GR Outside- Gr Inside- gR Last- gr

  31. Dihybrid: Pepper Plants

  32. Pepper Plants 9 Green, round 3 Green, square 3 Red, round 1 Red, square

  33. 10.3 There are many variations of inheritance patterns

  34. I. Intermediate Inheritance • When an organism has two alleles and neither is dominant the phenotype is intermediate between the two alleles • This pattern of inheritance is called intermediate inheritance

  35. Intermediate Example

  36. Problem: Intermediate Inheritance 4. A hybrid pink CRCW snapdragon was crossed with a pure white one CWCW. Red flower color is incompletely dominant. • Make a diagram and list the genotypic and phenotypic ratios of the F1 generation

  37. Problem 4 1:1 CR CW :CW CW Pink:White

  38. II. Multiple Alleles • Many genes have several alleles for each trait which expands the number of genotypes and phenotypes • Codominance is when a heterozygous individual expresses both traits equally.

  39. Multiple Allele Example

  40. Problem: Multiple Alleles 5. Paul is blood type O. His father was blood type A and his mother was blood type B. What were the genotypes of his parents and what are the possible blood types and ratios expected for crosses involving these parental genotypes?

  41. Problem 5 IAi and IBi 1:1:1:1 AB:A:B:O

  42. III. Polygenic Inheritance • When multiple genes affect a character the variation in phenotypes can become even greater. • When two or more genes affect a single character, it is called polygenic inheritance • Examples of polygenic inheritance would include skin color, and height

  43. Problem: Polygenic • 6. Melanin is coded for when the gene L, M, or N is present. The more of these genes are present, then the darker the skin the individual. Number the following genotypes in order of the darkest to lightest skin color phenotypes.

  44. Problem 6 1= Darkest 6=Lightest

  45. IV. The Importance of Environment • An individuals phenotype depends on environment as well as on gene • In humans, nutrition influences height, exercise affects build, and exposure to sunlight darkens the skin

  46. 10.4 Meiosis Explains Mendel’s principles

  47. I. Chromosome Theory of Inheritance A. Biologists worked out the processes of mitosis and meiosis in the late 1800s and observed the parallels between the behavior of chromosomes and the behavior of Mendel’s heritable factors

  48. Chromosome Theory B. The chromosome theory of inheritance states that genes are located on chromosomes, and the behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns C. The alleles for a gene reside at the same location or gene locus

  49. Pea Plant

  50. II. Genetic Linkage and Crossing Over • Mendel’s principles only work when for genes that are located on separate chromosomes • The tendency for the alleles on one chromosome to be inherited together is called genetic linkage C. The closer the two genes are on a chromosome, the greater the genetic linkage

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