1. DO NOW Take our your vocab HW.
Talk to your table – which characteristics do people inherit from their parents?

2. Chapter 3:
“Heredity”

3. Heredity – the passing of traits from parent to offspring (children).
Vocabulary
Heredity – the passing of traits from parent to offspring (children).
Trait – a characteristic of an organism

4. Gregor Mendel (“Father of genetics”) was the first scientist to study genetics and how traits are passed from parents to offspring.

5. Pea Plants
Mendel bred pea plants and was able to see that some traits are passed down to offspring and some skip a generation.

6. Pollination
Pea plants are bred through pollination, which is the fertilization of plants that contains both male & female reproductive structures.
Fertilization occurs when a sperm from the pollen travels through the stigma and enters the egg in an ovule.

7. Pea Plants Create Offspring By…
Self-Pollination: pollen (male part) from one flower can fertilize the ovule (female part) of the SAME flower.

8. Pea Plants Create Offspring By…
2. Cross-Pollination: pollen (male parts) from one plant can fertilizes the ovule (female parts) of a flower on a DIFFERENT plant.

9. Why Mendel used pea plants:
Grow & reproduce quickly.
Easy self- pollination & cross-pollination
Many observable traits.
Traits are easily observed
Examples: seed shape,
flower color & plant height

10. T R A I S

11. Breeding Pea Plants Mendel bred one characteristic at a time.
He used true-breeding plants, in which all of the offspring will have the same trait as the parent.
Example: Purple flowers have purple offspring and white flowers have white offspring.

12. Mendel’s First Experiment
He used cross-pollination for two true-bred plants with different traits
He took a true-bred purple pea plant & cross-pollinated it with a true-bred white pea plant.

13. All pea plants came back purple!
RESULTS
All pea plants came back purple!

14. Mendel’s Conclusions
He found that one trait always showed up and the other trait disappeared.
He called them:
Dominant– The trait that always appears (purple). Shown as an upper case letter -“P”
Recessive - The trait that always disappears (white). Shown as a lower case letter “p” )

15. Pd 1, 3

16. Mendel’s Second Experiment
Mendel allowed each offspring plant from the first experiment cross to self-pollinate.
Results – Some came back dominant (purple) and some came back recessive (white).

17. Simple Dominance Mendel’s experiment was an example of
Simple Dominance – When one trait is completely dominant to the other.
Example: Red and white flowers that are crossed only produce either red or white flowers.
They will NEVER produce pink flowers.

18. Generations
The true-breeding cross is called the P or parental generation.
The offspring of a cross-pollination are called the F1 or first generation.
The offspring from a F1 cross is called the F2 or second generation.

19. Ratios
Mendel created a ratio of dominant to recessive traits to determine the reason for the results.
Each parent donates genes to their children, so each offspring has two forms of genes called alleles.
(Ex. “AA”, “Aa”, “aa”)
Genes Can Be:
Heterozygous (Hybrid)- One dominant & one recessive trait (Aa, Bb, Cc, Dd, etc.)
Homozygous – Both dominant or both recessive traits
Homozygous Dominant = AA
Homozygous Recessive = aa

20. True-Bred Short X True-Bred Long Resulted in 100% long offspring (F1)
“P (Parental) Cross”
True-Bred Short X True-Bred Long
Resulted in 100% long offspring (F1)

21. “F1 (First Generation) Cross”
Cross pollinated 2 of the long offspring produced in the “P” generation
F1 long X F1 long
Results:
75% long and 25% short

22. EXAMPLES R= dominant gene for red r= recessive gene that appears white
RR=homozygous dominant, red
rr=homozygous recessive, white
Rr=heterozygous, red

23. Genotype - the actual letters (alleles) that represent genes.
Example: GG, Gg, or gg
Phenotype - The physical appearance of those genes.
Ex: Green or Yellow Peas

24. PUNNETT SQUARES

25. Punnett Squares
Punnett Squares –a model used to represent crosses between organisms.
Example: What are the possible offspring of a cross between a homozygous dominant green plant and a homozygous recessive green plant?

26. Steps in doing a Punnett Square:
Step #1: Identify the alleles
Example: What are the possible offspring of a cross between a homozygous dominant green plant and a homozygous recessive green plant?
Homozygous dominant = GG parent
Homozygous recessive = gg parent

27. Steps in doing a Punnett Square:
Step #2: Draw a square with 4 boxes
Example: What are the possible offspring of a cross between a homozygous dominant green plant and a homozygous recessive green plant?

28. Steps in doing a Punnett Square:
Step # 3: Put the alleles from one parent on
the top of the box & the alleles from the
other parent on the side of the box
gg parent GG parent G G g g

29. Steps in doing a Punnett Square:
Step # 4: Cross multiply to find the genotypes of the children G G G g g g

30. Steps in doing a Punnett Square:
Step # 4: Cross multiply to find the genotypes of the children G G G g G g g G g G g g

31. Steps in doing a Punnett Square:
Step # 5: Write the phenotypes of each child in the boxes G G G g G g g
Green
Green G g G g g
Green
Green

32. Steps in doing a Punnett Square:
Step # 6: Calculate genotypic and phenotypic ratios of the offspring G G
List all Genotypes: GG Gg gg
List all Phenotypes:
green
yellow G g
Green G g
Green g G g
Green G g
Green g

33. Steps in doing a Punnett Square:
Step # 6: Calculate genotypic and phenotypic ratios of the offspring G G
Count how many of each:
Genotypes: GG Gg gg
Phenotypes:
green
yellow G g
Green G g
Green
= 0/4 = 0%
= 4/4 = 100% g G g
Green G g
Green g
= 4/4 = 100%
= 0/4 = 0%

34. Now try this one… G g G g g g G g g g
What are the possible offspring of a cross between a pea plant which is heterozygous for green peas and a pea plant which is homozygous recessive for green peas? G g
Count how many of each:
Genotypes: GG Gg gg
Phenotypes:
green
yellow G g
Green g
yellow
= 0/4 = 0%
= 2/4 = 50% g G g
Green g
yellow g
= 2/4 = 50%

35. Another example… G g G g G G G g g g
What are the possible offspring of a cross between 2 pea plants which are both heterozygous for green peas? G g
Count how many of each:
Genotypes: GG Gg gg
Phenotypes:
green
yellow G
Green g G
Green
= 1/4 = 25%
= 2/4 = 50% G G g
Green g
yellow g
= 3/4 = 75%
= 1/4 = 25%

36. INCOMPLETE DOMINANCE

37. Incomplete Dominance
Sometimes there are two dominant alleles and no recessive alleles.
This means that one trait is not completely dominant over the other. Both are dominant!
Ex: flower color

38. In some flowers, red & white are both dominant.
A red flower has the phenotype ______ and the genotype .
A white flower has the phenotype ______ and the genotype
RED RR
WHITE WW

39. What if you cross a RED (RR) flower with a WHITE (WW) flower?

40. What color are the offspring?
WHITE RW RW W +
RED RW RW W
PINK

41. What is the phenotype of this flower
What is the phenotype of this flower? What is the genotype of this flower?
PINK RW

42. What Are The Genotypes & Phenotypes?
RR =
WW =
RW =
Phenotypes
Red =
White =
Pink = R R 0% W RW RW 0%
100%
Pink
Pink W RW RW
Pink
Pink 0% 0%
100%

43. So, when a trait is inherited by incomplete dominance, there are ____ possible phenotypes and ____ possible genotypes. 3
Red
White
Pink 3 RR WW RW

44. Practice
Red and White flowers are incompletely dominant. Cross a pink flower and a white flower
Genotypes
RR =
WW =
RW =
Phenotypes
Red =
White =
Pink = 0% R W
50%
50% RW W WW
pink
white 0% RW
50% WW W
50%
pink
white

45. Practice
Red and White flowers are incompletely dominant. Cross a pink flower and a pink flower
Genotypes
Phenotypes

46. More Practice
Genotypes
Phenotypes

47. Multiple Alleles Sometimes, there are more than 2 possibilities.
There are any set of 3 or more alleles.
Examples:
hair color, eye color, skin color

48. Co dominance Co dominance - When 2 alleles are equally dominant. AA A
Example: Blood Type
2 Dominant alleles – A & B
1 recessive allele – O
Genotype
Phenotype AA A AO BB B BO AB OO O

49. HOMOGYGOUS VS. HETEROZYGOUS
HOMOZYGOUS
DOMINANT
RECESSIVE
HETEROZYGOUS
CO DOMINANT AA OO AO AB BB BO

50. What if you cross a AO parent with a BO parent?
Genotypes
AB =
BO =
AO =
OO =
Phenotypes
A =
B =
O =
25%
25% A O
25%
25% AB BO B
25% AO OO O
25%
25%
25%
You get all possible blood types in the offspring!

51. Practice What if you cross a AB parent with a O parent?

52. In your own words explain what incomplete dominance is…
Exit Slip
In your own words explain what incomplete dominance is…