1. Fundamentals of Genetics

2. Genetics
The field of Biology devoted to understanding how characteristics are transmitted from parents to offspring.

3. Gene
A segment of DNA that contains coding for a polypeptide or protein
A unit of hereditary information.

4. Heredity
The transmission of characteristics from parents to offspring.

5. Pollination
Self -Pollination
Cross-Pollination
Web Link

6. Discussion How are traits inherited?
Where does a person get their eye color, hair color, and so on?
What if one parent has brown hair and the other one is blond? What hair color will their children have?

7. Gregor Mendel Austrian monk who experimented with garden peas
Used knowledge of statistics and studied heredity

9. Mendel Video

10. Mendel’s First (P1 to F1)
In the first set of experiments, Mendel conducted cross-pollination between a pure breeding tall plant and a pure breeding dwarf plant. He collected the seeds from this cross pollination and allowed them to germinate. All the resulting plants were found to be tall.
P1 to F1
generation

11. Next he…
In a similar pollination between a pure breeding plant with axial flowers and a pure breeding plant with terminal flowers, all the resulting plants of the next generation produced only axial flowers.
F1 generation

12. Principle of Dominance
Based on these results, Mendel came to the conclusion that in a cross-involving two contrasting characters, only one character expresses itself in the next generation.
Mendel called the character, which expressed as dominant character and the character, which failed to express, as recessive character. This idea came to be known as the principle of dominance (first law).

13. F2 Generation
At this stage, Mendel wanted to know whether the tall plants resulting from a cross between tall and dwarf plants, were similar to the tall plants of the P1 generation. Hence, he allowed the tall plants of the F1 generation to undergo self- pollination. In the next generation, Mendel found both tall plants and dwarf plants, approximately in the ratio 3:1. The results were most surprising since the recessive character dwarfness had reappeared in the next generation. (F2 generation)

14. Mendel’s Garden Peas
Observed 7 characteristics of pea plants. Each characteristic occurred in 2 contrasting traits.
Characteristic Trait
Plant height long or short stems
Flower position axial or terminal
Pod color green or yellow

15. P= Parent
F1=first Filial cross
F2 =second Filial Cross
Mendel’s monohybrid

17. Mendel’s Garden Peas
Observed that seeds grown from purple flowered plants produce plants with purple flowers and plants with white flowers.
Tall seeds produced tall plants and short plants.
Wanted explanations.

18. Mendel’s Methods
Able to document the traits of each generation’s parents by carefully controlling how plants were pollinated.
Pollination: occurs when pollen grains produced in the male reproductive parts of a flower (anthers) are transferred to the female reproductive parts (stigma).

19. Self-pollination: occurs when pollen is transferred from the anthers of a flower to the stigma of either the same flower or a flower of the same plant.
Cross pollination: involves flowers of two separate plants.
Mendel was able to control pollination by transferring pollen manually and removing the anthers from the flower.

21. Mendel’s Experiments
Studied each characteristic and its contrasting traits individually.
Began by growing plants that were pure for each trait.
Strain: plants that are pure for a specific trait.
Eventually produced strains for each of 14 characteristics.
Called each strain a parental generation or P1 generation.

22. Mendel’s Experiments
Cross-pollinated pure strains (P1) for contrasting traits, planted seeds and recorded the number of each type of offspring produced. Called the F1 generation (first filial generation)
Allowed F1 generation to self-pollinate and collected seeds. Grew the plants F2 generation (second filial) and recorded the number of each type produced.
Performed and documented the results of hundreds of crosses.

23. Mendel’s Results and Conclusions
Crossed green pods with yellow pods (P1)
All green pods produced (F1)
¾ green pods and ¼ yellow pods (F2)

24. Mendel’s Results and Conclusions
Hypothesized that something within the pea plants controlled the characteristics he observed – called these “factors”
Said that each trait was inherited by the means of a separate factor. Reasoned that there must be a pair of factors controlling each trait because the characteristics he studied had 2 alternative forms.

25. Recessive and Dominant Traits
When Mendel crossed strains, one of the P1 traits failed to appear in the F1 plants but reappeared in a 3:1 ratio in the F2 generation.
Mendel concluded that one factor in a pair may prevent the other from having an effect.

26. Dominant factor: masks the other factor for a specific characteristic
Recessive factor: has no observable effect on an organism’s appearance when paired with a dominant factor. The hidden factor.

28. The Law of Segregation
States that a pair of factors segregate or separate during formation of gametes (reproductive cells).
Each gamete receives only one factor of each pair
When two gametes combine during fertilization, the offspring have two factors controlling a specific trait

29. The Law of Independent Assortment
States that factors for different characteristics are distributed to gametes independently.

30. The Law of Independent Assortment
Mendel crossed plants that differed in two characteristics such as flower color and seed color.
Data showed that traits from dominant factors do not necessarily appear together.
Factors for different characteristics are not connected.

31. Most of Mendel’s findings agree with what biologists now know about molecular genetics.

32. Molecular Genetics
The study of the structure and function of chromosomes and genes

33. Chromosomes and Genes
Chromosome: a threadlike structure made up of DNA
Gene: the segment of DNA on a chromosome that controls a particular hereditary trait.
Chromosomes occur in pairs. Genes occur in pairs.
Allele: each of several alternative forms of a gene (Mendel’s factors)
Letters are used to represent alleles.
Dominant is capital ex. G = green pod color
Lowercase is recessive. Ex, g= yellow pod color

34. In meiosis, gametes receive 1 chromosome from each homologous pair
In meiosis, gametes receive 1 chromosome from each homologous pair. When gametes combine in fertilization, the offspring receives 1 allele for a given trait from each parent.
PTC Tasting Characteristic

35. Mendel’s Law of Independent Assortment is supported by the fact that chromosomes segregate independently to gametes during meiosis.
But it is observed only for genes located on separate chromosomes or located far apart on the same chromosome where crossing over can occur.

36. Modern Versions
Law of Segregation: states that pairs of alleles are separated during meiosis.
Law of Independent Assortment: states that alleles located on separate chromosomes or far apart on the same chromosome separate independently of one another.

37. Ted-Ed How Mendel’s pea-plants helped us understand genetics
Video

38. Genetic Crosses Genotype and Phenotype Probability
Predicting Results of Monohybrid Crosses
Predicting Results of Dihybrid Crosses

39. Genotype and Phenotype
Genotype: the genetic makeup of an organism. Consists of the alleles that the organism inherits from its parents
Purple flowered plants PP or Pp
White flowered plants pp

40. Phenotype: the appearance of an organism as a result of its genotype.
PP or Pp = purple flowers
pp = white flowers

41. Human phenotypes can appear to be altered: hair dye, colored contact lenses, surgery, etc but they do not alter the individual’s true phenotypes or genotype.
Colored Contact Lenses

42. Homozygous: when both alleles of a pair are alike.
PP= homozygous dominant
pp= homozygous recessive
Heterozygous: when the two alleles in the pair are different.
Pp= heterozygous for flower color.
Video (1.5 minutes)

43. Probability
Probability: the likelihood that a specific event will occur.
May be expressed as a decimal, %, fraction, or ratio
Probability= # of actual times
# of opportunities

44. Example: Mendel’s experiments – the dominant trait of yellow seed color in F2 generation occurred 6022 times, the recessive trait of green seed color appeared 2001 times. Total # of individuals = 8023
Probability of Dominant trait
6022 / 8023 = 0.75 or 75%, ¾, 3:4
Probability of Recessive trait
2001 / 8023 = 0.25 or 25%, ¼, 1:4

45. Predicting Results of Monohybrid Crosses
Monohybrid: a cross between individuals that involves one pair of contrasting traits.
Punnett Square: a diagram used to predict the probability that certain traits will be inherited by offspring

46. Examples

47. Homozygous x Homozygous
Predict the possible outcome of a monohybrid cross between a pea plant homozygous for purple flower color (PP) and a pea plant homozygous for white flower color (pp).
PP purple flower x pp white flower

48. Showing Results of Cross
Genotypic ratio: the ratio of the genotypes that appear in offspring.
Ex. 1BB:2Bb:1bb
Phenotypic ratio: the ratio of the offspring’s phenotype.
Ex. 4purple

49. Homozygous x Heterozygous
Cross a guinea pig that is homozygous dominant for the trait of black coat color (BB) and a guinea pig that is heterozygous for this trait (Bb).

50. Showing Results of Crosses
Genotypic ratio: the ratio of the genotypes that appear in offspring.
Ex. 2BB:2Bb
Phenotypic ratio: the ratio of the offspring’s phenotype.
Ex. 4black

51. Heterozygous x Heterozygous
Cross two rabbits that are both heterozygous (Bb) for coat color (B=black, b=brown)

52. Showing Results of Crosses
Genotypic ratio: the ratio of the genotypes that appear in offspring.
Ex. 1BB:2Bb:1bb
Phenotypic ratio: the ratio of the offspring’s phenotype.
Ex. 3black:1brown

53. Test Cross
An individual of unknown genotype is crossed with a homozygous recessive individual (bb).
Can be used to determine the genotype of any individual whose phenotype is dominant. If one of the offspring turns up with the recessive trait, then you know the unknown parent is heterozygous (Bb).

55. Complete, Incomplete and Co- Dominance
Video 8 minutes Amoeba Sisters

56. Complete Dominance
One allele is completely dominant over another (Mendel’s pea plant crosses)
Ex. Heterozygous plants and homozygous dominant plants are indistinguishable in phenotype. PP and Pp are both purple.

57. Incomplete Dominance
Occurs when 2 or more alleles influence the phenotype resulting in a phenotype intermediate between the dominant trait and the recessive trait.
Ex. 4 o’clock flowers RR=red, rr=white, Rr=pink

59. Codominance
Occurs when both alleles for a gene are expressed in a heterozygous offspring. Neither allele is dominant or recessive The alleles do not blend in the phenotype.
Ex. RR= red coat, R’R’ = white coat,
RR’= roan coat or both red and white

61. Predicting Results of Dihybrid Crosses
Dihybrid Cross: a cross between individuals that involves 2 pairs of contrasting traits. Considers how the four alleles from each parent can combine.

62. Examples

63. Homozygous x Homozygous
Predict the results of a cross between a pea plant that is homozygous for round, yellow seeds and one that is homozygous for wrinkled, green seeds.