1. Section 1: Mendel’s Work
What were the results of Mendel’s experiments, or crosses?
What controls the inheritance of traits in organisms?

2. What is Genetics? Genetics: the study of heredity
Heredity: the passing of physical characteristics from parents to offspring

3. The Father of Genetics
The field of Genetics was founded by Gregor Mendel, an Augustinian priest.
Between 1856 and 1863, Mendel cultivated and tested almost 30,000 pea plants.
The importance of Mendel's work was not discovered until almost 30 years after Mendel died.

4. Crossing Pea Plants
Gregor Mendel crossed pea plants that had different traits. The illustrations show how he did this.

5. Mendel’s Experiments
In all of Mendel’s crosses, only one form of the trait appeared in the F1 generation. However, in the F2 generation, the “lost” form of the trait always reappeared in about one fourth of the plants.

6. Dominant and Recessive Alleles
Mendel studied several traits in pea plants.

7. Dominant and Recessive Alleles
Today, scientists use the word “gene” to describe a piece of DNA that controls a trait.

8. Dominant and Recessive Alleles
The traits that Mendel studied in his pea plant experiments are controlled by different genes:
GENE
Seed Shape
Seed color
Seed coat color
Pod shape
Pod color
Flower position
Stem height

9. Dominant and Recessive Alleles
These genes usually have 2 or more alleles, or different forms of the gene:
GENE ALLELE ALLELE
Seed Shape round wrinkled
Seed color yellow green
Seed coat color gray white
Pod shape smooth pinched
Pod color green yellow
Flower position side end
Stem height tall short

10. Dominant and Recessive Alleles
Some of these alleles are known as dominant. Others are known as recessive:
DOMINANT RECESSIVE
GENE ALLELE ALLELE
Seed Shape round wrinkled
Seed color yellow green
Seed coat color gray white
Pod shape smooth pinched
Pod color green yellow
Flower position side end
Stem height tall short

11. Dominant and Recessive Alleles
In a dominant allele, the trait always shows up as long as there is at least one dominant allele.
Key
T = tall
t = short
T T
“pure tall”
T t
“hybrid tall”

12. Dominant and Recessive Alleles
In a recessive allele, the trait only shows up if both alleles are recessive.
Key
T = tall
t = short
t t
“pure short”

13. Dominant and Recessive Alleles
Dominant alleles are always symbolized with capital letters. Recessive alleles are always symbolized with lower-case letters.
Key for Height
T = tall
t = short
Key for Seed Color
Y = yellow seed color
y = green seed color
Key for Pod Color
G = green pod color
g = yellow pod color
Key for Coat Color
A = gray coat color
a = white coat color

14. End of Section: Mendel’s Work

15. Section 2: Probability and Heredity
What is probability and how does it help explain the results of genetic crosses?
What is meant by genotype and phenotype?
What is codominance?

16. A Punnett Square
The diagrams show how to make a Punnett square. In this cross, both parents are heterozygous for the trait of seed shape. R represents the dominant round allele, and r represents the recessive wrinkled allele.

17. Probability and Genetics
In a genetic cross, the allele that each parent will pass on to its offspring is based on probability.

18. Phenotypes and Genotypes
An organism’s phenotype is its physical appearance, or visible traits. An organism’s genotype is its genetic makeup, or allele combinations.

19. Practicing Punnett Squares
Key for Height
T = tall
t = short
T T x T T
t t x t t
T t x T t
Key for Seed Color
Y = yellow seed color
y = green seed color
Key for Pod Color
G = green pod color
g = yellow pod color

20. Practicing Punnett Squares
Key for Height
T = tall
t = short
Y y x y y
Y Y x y y
g g x G g
G g x G g
Key for Seed Color
Y = yellow seed color
y = green seed color
Key for Pod Color
G = green pod color
g = yellow pod color

21. Homozygous vs. Heterozygous
Homozygous = 2 identical alleles
also called “pure” or “purebred”
Examples: T T t t
Heterozygous = 2 different alleles
also called “hybrid”
Examples: T t

22. Codominance
In codominance, the alleles are neither dominant nor recessive. As a result, both phenotypes are expressed in the offspring.

23. Incomplete Dominance
In incomplete dominance, the contributions of both alleles are visible and do not overpower each other in the phenotype. As a result, both phenotypes look “mixed”.

24. Dihybrid Cross

25. Dihybrid Cross Key for Height T = tall t = short Key for Seed Color
Y = yellow seed color
y = green seed color
Key for Pod Color
G = green pod color
g = yellow pod color

26. Dihybrid Cross

27. End of Section: Probability and Heredity

28. Section 3: The Cell and Inheritance
What role do chromosomes play in inheritance?
What events occur during meiosis?
What is the relationship between chromosomes and genes?

29. Meiosis
During meiosis, the chromosome pairs separate and are distributed to two different cells. The resulting sex cells have only half as many chromosomes as the other cells in the organism.

30. Punnett Square
A Punnett square is actually a way to show the events that occur at meiosis.

31. A Lineup of Genes
Chromosomes are made up of many genes joined together like beads on a string. The chromosomes in a pair may have different alleles for some genes and the same allele for others.

32. Human Chromosomes Humans have 23 pairs of chromosomes:
23 from their mother, and 23 from their father.

33. Human Chromosomes
The first 22 pairs are organized and named according to their size:
Chromosomes #1 are the largest, #2 are the second largest, etc.

34. Human Chromosomes
The final pair of chromosomes (“X” and “Y”) are the sex chromosomes because they determine the gender of the person:
XX = girl
XY = boy

35. Sex Chromosomes Father Mother
The father is who determines the gender of the child since males need a “Y” chromosome, and only males have “Y” chromosomes.
The mother can only give out an “X”, and both boys and girls have at least 1 “X” chromosome.
Father
Mother

36. End of Section: The Cell and Inheritance

37. Section 4: Genes, DNA, and Proteins
What forms the genetic code?
How does a cell produce proteins?
How can mutations affect an organism?

38. The DNA Code
Chromosomes are made of DNA. Each chromosome contains thousands of genes. The sequence of bases in a gene forms a code that tells the cell what protein to produce.

39. How Cells Make Proteins
During protein synthesis, the cell uses information from a gene on a chromosome to produce a specific protein.

40. Mutations
Mutations can cause a cell to produce an incorrect protein during protein synthesis. As a result, the organism’s trait, or phenotype, may be different from what it normally would have been.

41. Damages Made by Mutation
THEBIGBADCATATETHEBIGREDRAT

42. End of Section: Genes, DNA, and Proteins