1. 4A introduction to Genetics
Mendelian Genetics
4A introduction to Genetics

2. Mendel Austrian monk Father of modern genetics Law of Segregation
Law of Independent Assortment

3. Mendel’s Experiment Mendel performed experiments on garden pea plants
Looked at the features shown in each plant generation after generation

4. Mendel’s Experiment
Found that features of one generation may not show up in the next generation, but may reappear in the 3rd generation
Performed many experiments and came up with the basis for modern genetics
Why did he use pea plants?
Easy to grow, lots of offspring, simple traits that are easy to see and can control the pollination

5. Mendel’s Peas
When Mendel began his investigation, he cross-pollinated pea plants with purple flowers with a pea plants with white flowers
This was his P generation
The F1 generation then had ALL purple flowers

6. Mendel’s Peas Not only did the F1 generation have all purple flowers…
But when he allowed the F1 generation to self-pollinate, the F2 generation…
Had both purple and white!

7. Mendel’s Peas
Being confused by why this happened, Mendel recorded data on 6 other characters

8. Mendel’s Peas
After many, many generations and lots a data, Mendel found that…
For every character he observed, the ratio of one trait over another was 3:1
Three purple flowered plants to every 1 white flowered plant
How do we explain this?

9. More Vocabulary
GENE
Segment of DNA that codes for a protein and thus coded for a trait
Gene for eye color
Gene for height
We get one copy of DNA from mom and one copy of DNA from dad
Gene refers to all of the DNA needed for one trait (both mom and dad)

10. Genes There are alternate forms of every gene
Flower color – purple or white
Allele
One of the multiple forms of one gene
One allele from mom and one allele from dad together make one gene

11. Genes Meiosis Meiosis creates ___?___ cells
HAPLOID
Those haploid cells deliver the alleles from mom and alleles from dad to make up your genes

12. Alleles Dominant Allele Recessive Allele
Describes an allele that is fully expressed whenever it is present
Recessive Allele
Describes an allele that is expressed only when a dominant allele is not present

13. Dominant vs. Recessive Dominant Alleles = Capitol letters
Recessive Alleles = Lowercase letters
T = tall pea plant
t = short pea plant
NOTE: for plant height there is only one letter (T) capitol means tall, lowercase means short, but the letter is always T (not s for short)

14. Dominant vs. Recessive
Any time a dominant allele is present, that trait will be expressed
TT (tall)
Tt (tall)
If NO dominant allele is present, the recessive trait will be expressed
tt (short)

15. Review Meiosis
Diploid
Haploid TT TT T T T T

16. Review Meiosis
Diploid
Haploid tt TT t t T T

17. Review Meiosis
Diploid
Haploid Tt Tt T t T t

18. Review of Meiosis In meiosis, cells divide
Start with DIPLOID, end with HAPLOID
Homologous pairs separate
Sister chromatids separate

19. TWO copies of each gene.
Sexually reproducing organisms have two copies of each gene. One from a female parent, one from a male. (Homologous Pairs)

21. Mendel’s 1st Law Law of Segregation
Parent has two alleles
During meiosis, alleles separate into different gametes
Each gamete produced has the same chance of receiving any given allele
Alleles are separated randomly during meiosis

23. Law of Segregation If dad is Tt…
Any gamete produced, has the same chance as being T as it does being t.
Separately randomly
50-50 chance either way

24. Mendel’s 2nd Law Law of Independent Assortment
Alleles separate during meiosis
Different alleles for different traits do not affect how each other separate
The alleles for seed color will not affect the alleles for seed shape
Alleles can mix and match independently of each other

26. Mendel’s Laws Law of Segregation Law of Independent Assortment
Gametes have equal chances of receiving any given allele
(T or t)
Law of Independent Assortment
Different alleles do not affect how each other separates during meiosis
(T is not affected by R)

27. Vocabulary Once two gametes are joined, fertilization occurs
New organism now has one allele from each parent
The two alleles now together form the organisms GENOTYPE
Genotype is the specific alleles present
TT or Tt or tt

28. Vocabulary
The resulting visible feature of the organism as a result of the two alleles is the PHENOTYPE
Phenotype is what the organism looks like
Phenotype – Physical looks
Tall or short

29. Vocabulary A pea plant’s genotype is Tt
What the alleles are
The same plant’s phenotype is tall
What the plant looks like
Phenotype is the result of the Genotype

30. Practice 2. The pea plant is tall 1. A pea plant is TT
This is the plant’s (genotype or phenotype)?
2. The pea plant is tall

31. TT, Tt, tt Different genotypes have different terms to describe them
Hetero
means different
Homo
means same
Zygous
zygotic (fertilized)
Zygote = fertilized egg

32. TT, Tt, tt Heterozygous genotype - plant height
2 different alleles
Homozygous genotype – plant height
TT or tt
2 of the same alleles

33. TT, Tt, tt Homozygous = Differentiate between the two…
TT or tt
Differentiate between the two…
What is different?
TT = homozygous dominant
tt = homozygous recessive

34. TT, Tt, tt Homozygous Dominant Heterozygous Homozygous Recessive TT Tt

35. Punnett Squares
A model that predicts the likely outcomes of a genetic cross
The simplest is a monohybrid cross
One trait
Punnett square for one trait uses four boxes

36. Probability The likelihood of an event actually occurring
Probabilities can be expressed as fractions (1/2, 3/4) or as percentages (25%, 50%)

37. Practice Problems

38. Genotype vs. Phenotype Yellow (Y) vs. Green (y) Pea Plants
Genotype Phenotype
Homozygous dominant
Heterozygous
Homozygous recessive

39. Genotype vs. Phenotype Purple (P) vs White (p) Flowered Pea Plants
Genotype Phenotype
Homozygous dominant
Heterozygous
Homozygous recessive

40. Genotype vs. Phenotype Round (R) vs Wrinkled (r) Pea Plant Seed Shape
Genotype Phenotype
Homozygous dominant
Heterozygous
Homozygous recessive

41. Genotype vs. Phenotype Smooth (S) vs Wrinkled (s) Pea Plant Pod Shape
Genotype Phenotype
Homozygous dominant
Heterozygous
Homozygous recessive

42. Probability of Genotype for a Heterozygous Cross
Fraction % TT Tt tt
T t T t

43. Probability of Phenotype for a Heterozygous Cross
Fraction % TT Tt
Tall tt
Short
T t T t

44. Probability of Genotype & Phenotype for a Homozygous Cross
Fraction % TT Tt
Tall tt
Short
T T T

45. Spongebob & Friends
Scientists at Bikini Bottoms have been investigating the genetic makeup of the organisms in this community.
Use the following information to test your knowledge of genetics.

46. Spongebob Yellow body color is dominant to blue
What is Spongebob’s phenotype?
Yellow
What is Spongebob’s possible genotype?
YY or Yy

47. Patrick Tall head is dominant to short head.
What is Patrick’s phenotype?
Tall
What is Patrick’s possible genotype?
TT or Tt

48. Spongebob
Spongebob Squarepants recently met SpongeSusie Roundpants at a dance.
Spongebob is heterozygous for his squareshape, but Susie is round.
What are the possible genotypes if they had children?
Draw a Punnett Square

49. Spongebob What are the chances of a child with a square shape?
___ out of ___
___%
What are the chances of a child with a round shape?

50. Patrick Patrick recently met Patti at a dance.
Both of them are heterozygous for their pink skin color which is dominant over yellow.
What are the possible genotypes if they had children?
Draw a Punnett Square

51. Patrick What are the chances of a child with pink skin? ___ out of ___
___%
What are the chances of a child with yellow skin?

52. Squidward
Squidward’s family has light blue skin, which is the dominant trait for body color.
His family brags that they are a “purebred” line.
He recently married a nice girl with light green skin, which is a recessive trait.
What are the possible genotypes if they had children?
Draw a Punnett Square

53. Squidward What are the chances of a child with blue skin?
___ out of ___
___%
What are the chances of a child with green skin?

54. Mr Krabbs
Mr Krabbs and his wife recently had a Lil’ Krabby, but it has not been a happy occasion.
Mrs. Krabbs has been upset since she first saw her baby who had short eyeballs.
She claims that the hospital goofed and mixed up her baby with someone else’s baby.
Mr. Krabbs is homozygous for his tall eyeballs, while Mrs. Krabbs is heterozygous.
Draw a Punnett Square to figure out if the hospital made a mistake.