1. Fundamentals of Genetics
CHAPTER 9
Fundamentals of Genetics

2. Objectives
Defend how Mendel was able to control how his pea plants were pollinated
Analyze the steps in Mendel’s experiments on true-breeding garden peas
Distinguish between dominant and recessive traits
Analyze the two laws of heredity that were developed from Mendel’s work
Describe how Mendel’s results can be explained by scientific knowledge of genes and chromosomes

3. Introduction: Breeding in plants and animals
Examples:
corn was developed from a wild grass in Mexico and Central America, probably about 5000 years ago
dogs were domesticated by 12,000 years ago; selective crossing has created many breeds we have today
some artificial pollination was done to increase yields in fruit
Chromosomes - seen in the 1800s, but their role in heredity was not understood until the early 1900s

4. Genetics
The science of heredity & the mechanisms by which traits are passed from parent to offspring

5. I. Gregor Mendel (1822-1884) History
Austrian Monk who taught high school & worked in the garden
1851-Entered University of Vienna to study science & math
He started breading pea plants (Pisum sativum) about 1855, studied heredity
Mendel formulated 2 fundamental laws of heredity in the early 1860's

6. The “Father of Modern Genetics”
Mendel’s experiments established the basic ideas & laws that predict the pattern of inheritance from generation to generation

7. Heredity Characteristic Trait (or strain)
the transmission of characteristics from parents to offspring
Characteristic
An inheritable feature (flower color, height)
Trait (or strain)
A genetically determined variant of a characteristic (white or red flower)

8. Work with Peas: Mendel used statistics to study 7 Characteristics, each occurred in 2 Contrasting Traits:
   
Flower Color – purple or white
Flower Position along Stem – axial or terminal
Seed or Pea Color - yellow or green
Seed Texture or Shape – round (smooth) or wrinkled
Pod Color – green or yellow
Pod Appearance or Shape – inflated or constricted
Plant Height - long or short stems

9. Seven pea plant characteristics studied:

10. Mendel’s Methods
Pollination: when pollen grains (from anther- male) are transferred to stigma (female)
Self-pollination- occurs when pollen is transferred from flower anthers to stigma of either same flower or flowers on the same plant
Cross-pollination- occurs between flowers of 2 plants

11. Pea plants usually reproduce through self-pollination

12. Pollination Methods
Mendel first collected seeds that were true breeding (always produce offspring with that trait) for many generations for 14 traits
Interrupted self-pollination & performed cross-pollination
Removed all the anthers from flowers on a plant
Manually pollinated the stigma of this plant with pollen from another plant

13. Cross section of a flower

14. Three Steps of Mendel’s Experiments
Produce a true-breeding or PURE P generation
By self-pollination for several generations
“P” is for parent
saw: 2 pure traits- 1 for each parent

15. Step Two Produce an F1 generation
By cross-pollination of parents pure for different traits
Example- purple flowers with white flowers
“F1” is for first filial generation
saw: only 1 trait (dominant - recessive trait disappeared)

16. Step Three Produce an F2 generation
By allowing F1 generation to self-pollinate
“F2” is for second filial generation
saw reappearance of recessive trait in 3: 1 ratio (3 purple to 1 white)

17. Results of F2 generation- showed a 3:1 ratio
Mendel’s Results & Conclusions Experiments were repeated carefully for hundreds of crosses
Results of F1 generation- showed all offspring of crossed true-breeding plants were of one trait.
Example: purple flowers x white flower parents
Offspring all purple
Results of F2 generation- showed a 3:1 ratio
Example: 705 purple and 224 white flowers

20. Dominant & Recessive Traits
When strains of plants pure for a trait were crossed, one trait always failed to appear in the F1 generation
The absent trait reappeared in ¼ of the F2 generation
Mendel concluded that each trait was inherited by means of a separate factor, so a pair of factors controlled each trait

21. Dominant- Term for a factor (allele) that masks the presence of another factor
Recessive - Term for a factor (allele) that is masked by the presence of another allele.

22. Law of Segregation
A pair of factors are separated during formation of gametes
Each reproductive cell, or gamete, receives one factor of each pair
Gametes combine during fertilization, offspring then have two factors for each characteristic

24. Law of Independent Assortment
Different pairs of factors are passed to offspring independently
New combinations of genes, present in neither parent, are possible. 
Example: flower color & plant height not connected
The genes controlling different traits are inherited independently of one another.

25. Independent assortment of these two homologous chromosomes (Pp and Yy) would result in gametes that contain these allele combinations

26. Mendel’s Conclusion
Molecular genetics – study of the structure and function of chromosomes and genes
Chromosomes made of DNA
Genes on DNA control traits
Chromosomes occur in pairs
Genes occur in pairs
Allele – each of two or more alternative forms of a gene

27. “alleles” represented by letters
Dominant are CAPITAL letters
Recessive are small letters
Example 1: Brown eyes dominant: Blue recessive
“B” for brown & “b” for blue
Example 2: Red flower dominant-White recessive
“R” for red and “r” for white
REMEMBER- USE ONLY 1 LETTER PER PAIR: Bb or Rr for example - don’t mix!!! Never: Rw!!!

28. Section 1 Review
Page 178 #1-5

29. Exit Slip
What are the P, F1, and F2 generations that Mendel studied? What is the difference between dominant and recessive?

30. Objectives
Differentiate between the genotype and the phenotype of an organism
Explain how probability is used to predict the results of genetic crosses
Use a Punnett square to predict the results of monohybrid and dihybrid genetic crosses
Explain how a testcross is used to show the genotype of an individual whose phenotype expresses the dominant trait
Differentiate a monohybrid cross from a dihybrid cross

31. Genetic Crosses Genotype - WHAT IS ON THE GENES
the genetic make- up of an organism for a trait
the alleles that the organism inherits from its parents
Not always observable
Example: white flower = pp ; purple flower = Pp or PP
Phenotype - WHAT YOU SEE
An organism’s appearance or observable characteristic
the detectable expression that results from the organism’s genotype
Example: pp = White ; PP or Pp = Purple

32. Homozygous & Heterozygous
Homozygous (2 OF THE SAME)
-When both alleles of a pair are alike
Example: PP (Both alleles purple color)
pp (both white color)
Heterozygous (2 DIFFERENT)
– When the alleles in the pair are different
Examples: Pp (one Purple & one white)
Or Tt (one tall & 1 short)
( REMEMBER not to use Ts or Rw !!!!!!!!)

33. Probability The likelihood that something will happen
Predicted results more likely for more trials
Example: flipping a coin
Q1- What is the chance that it will be head or tails?
Q2- Discuss what happens if you flip it 10 times? 100?
Q3- If you flip 2 coins- Does that result have anything to do with the other- why or why not?
REVIEW: Relate this back to the law of independent assortment.

34. Q1 What is your genotype for this trait?
PROBLEM:
Tongue Rolling is Dominant (R)
You can roll your tongue but your spouse cannot
Your first child also cannot roll his tongue
Q1 What is your genotype for this trait?
Q2 What is the probability of having a tongue roller child next time?

35. Predicting Monohybrid Cross Results
Monohybrid Cross - A cross in which only 1 trait is tracked
Punnett square – A graphic or diagram used to predict the results of a genetic cross.
Draw a Punnett square - 4 small squares in the shape of a window. Write the possible gene(s) of one parent across the top and the gene(s) of the other parent along the side of the Punnett square.                                 

36. Fill in each box of the Punnett square by transferring the letter above and in front of each box into each appropriate box
As a general rule, the capital letter goes first and a lowercase letter follows
The letters inside the
boxes indicate probable
genotypes
Predict the phenotype
of these offspring

37. Monohybrid Cross
Homozygous purple (PP) is crossed with homozygous white (pp) producing only heterozygous purple (Pp) offspring

38. Homozygous X Homozygous
Black- BB homozygous dominant
White- bb homozygous recessive
All (100% probability)
offspring are heterozygous (Bb) genotype & black phenotype

39. Homozygous X Heterozygous
BB - homozygous dominant genotype, black phenotype
Bb – heterozygous genotype, black phenotype
Offspring:
Genotype:
50% BB, 50% Bb
Phenotype:
100% Black, 0% white

40. Heterozygous X Heterozygous
Cross 2 heterozygous parents (Bb) x (Bb) (2 black rabbits)
Offspring:
Genotypic ratio:
1 BB: 2Bb: 1bb
25%BB, 50%Bb, 25% bb
Phenotypic ratio:
3 black: 1 white
75% black, 25% white

41. Testcross
Since you don’t know if a black rabbit might have a genotype of BB or Bb, you could perform a test cross
A test cross is when an individual of unknown genotype is crossed with a homozygous recessive (bb)
Try this to see what happens with BB, then Bb crosses

42. If a black rabbit is crossed with a brown rabbit and even one of the offspring is brown, the black rabbit is heterozygous

43. Monohybrid Practice Complete the following monohybrid crosses:
Tt X Tt (T is dominant for tall, t is recessive for short)
Dd X dd (D is dominant for dimples, d is recessive for no dimples)
bb X BB (B is dominant for Brown eyes, b is recessive for blue eyes)
What is the genotypic and phenotypic ratios for each cross?

44. Tt x Tt T t
Genotypic Ratio:
Phenotypic Ratio:

45. Dd x dd D d
Genotypic Ratio:
Phenotypic Ratio:

46. bb x BB B b
Genotypic Ratio:
Phenotypic Ratio:

47. Complete Dominance
One allele is completely dominant over another (one trait masks another)
Heterozygous & homozygous plants look alike
Pea plants PP & Pp both have purple flowers

48. Incomplete Dominance
Occurs when the trait of a heterozygote is intermediate between the phenotypes of the parents
The dominant allele is unable to express itself fully
Example: Japanese four o’clock flowers
RR is red
Rr is pink
rr is white

49. Cross between 2 Pink Genotypic ratio: 1 RR:2Rr:1rr
Phenotypic Ratio: 1 red: 2 pink:1 white

50. Codominance
Occurs when both alleles for a gene are expressed in heterozygous offspring
Neither allele is dominant or recessive
Alleles do not blend
Example: Human blood types A, B, AB, O
Type of trait expressed by Multiple Alleles

51. Dihybrid Crosses A cross in which 2 characters are tracked
More complicated, due to more possible combinations
Examples:
Peas can be round or wrinkled AND yellow or green
Cats can have short or long tails AND brown or white fur
Pea plants can be tall or short AND have purple or white flowers

52. Homozygous x Homozygous
Homozygous for round, yellow seeds crossed with Homozygous for wrinkled, green seeds
Round (R) is dominant over wrinkled (r)
Yellow (Y) is dominant over green (y)
Genotypic Ratio:
100% RrYy
Phenotypic Ratio:
100% Round & Yellow

53. Heterozygous x Heterozygous
Cross RrYy x RrYy results 9 genotypes and 4 phenotypes
9/16 have round, yellow seeds (RRYY, RRYy, RrYy, RrYY
3/16 have round, green seeds (RRyy, Rryy)
3/16 have wrinkled, yellow seeds (rrYY, rrYy)
1/16 have wrinkled, green seeds (rryy)

54. Heterozygous x Heterozygous

55. Extra Practice

56. What is the genotypic ratio in the F2 generation?
What is the phenotypic ratio in the F2 generation?

57. Fill in the table to complete the cross between 2 heterozygous parents
What is the genotypic ratio and phenotypic ratio?

59. Section 2 Review
Page 186 #1-5