1. Mendelian Genetics

2. What is Heredity?
Female normal wing
The passing on of traits from one generation to the next X
P- generation
Male double wing
F1 – normal wing

3. Early Ideas about Heredity
Chapter 9, Section 1: Pre-Mendel
Early Ideas about Heredity
Blending Theory (19th century):
Each parent contributed “factors” that were blended in the offspring
What was the problem with this theory?
All individuals of a population would eventually look the same.
Once blended, traits would never separate and show up in later generations.

4. Gregor Mendel (1822 – 1884) Augustinian monk who studied pea plants
Chapter 9, Section 1: Mendel
Gregor Mendel (1822 – 1884)
Augustinian monk who studied pea plants
Established the particulate theory of heredity
Significance:
Developed pure lines
Counted results and kept statistical notes (data)
His work remained undiscovered until 1903.

5. Why did he research pea plants?
Character
Dominant Trait
Recessive Trait
Mendel’s Research
Flower Color
Why did he research pea plants?
Purple
White
They are normally self-pollinated, but can be cross-pollinated.
They have several qualitative traits that are easy to distinguish
i.e.,Tall vs. Short
Self Pollination
Flower Position
Side
Top
Seed Color
Yellow
Green
Seed Shape
Round
Wrinkled
Pod Shape
Inflated
Constricted
Pod Color
Green
Yellow
Cross Pollination
Stem Length
Tall
Dwarf

6. Watch this video clip, and see if you can explain why…
Mendel’s Research
Removed stamens from purple flower.
Transferred pollen from stamens of white flower to pistil of purple flower.
Pollinated flower matured into a pod.
Planted seeds from pod.
Examined offspring: All purple flowers…
Watch this video clip, and see if you can explain why…

7. Mendel’s Conclusions Law of Segregation
Factors (genes) for a particular trait occur in pairs
For each trait, an organism inherits two genes, one from each parent.
Dominant alleles mask recessive ones
Exception 1: Incomplete Dominance
Exception 2: Co-dominance
Two alleles for each trait segregate (separate) during gamete production

8. Genes: The “factors” that control traits.
Homologous pair of Chromosomes
Genes: The “factors” that control traits.
Law of Segregation:
Factors for a particular trait occur in pairs
Alleles: Different forms of a gene.
Locus for Flower Color Gene
Allele for White Flowers (p)
Allele for Purple Flowers (P)
Back to Mendel’s Conclusions

9. Each individual is diploid Each gamete is haploidW w or or w w
W = widow’s peak
w = no widow’s peak Ww ww
Each individual is diploid
Diploid: Containing a double-set of chromosomes (2n)
Each gamete is haploid
Gamete: Reproductive cell (egg or sperm)
Haploid: Containing a single-set of chromosomes (n)
Law of Segregation:
One version of each gene is inherited from each parent
Back to Mendel’s Conclusions

10. P (Parent) Generation True-breeding parents
Dominant alleles mask recessive ones
P (Parent) Generation True-breeding parents
(PP x pp)
F1 (1st Filial) Generation Hybrid Offspring (Pp)
What happened to the recessive traits?
705 plants had purple flowers
F2 (2nd Filial) Generation
224 plants had white flowers
What is the F2 ratio?
705:224  3:1

11. P Generation F1 Generation F2 Generation PP:Pp:pp  1:2:1 3: 1
Dominant alleles mask recessive ones
P Generation
Phenotype (Appearance)
Purple Flowers
White Flowers
Genotype (Genetic Makeup) PP pp
Gametes P p
F1 Generation
Phenotype (Appearance)
Purple Flowers
Genotype (Genetic Makeup) Pp
Gametes P p
Punnett Square
F2 Generation P P
What is the Genotypic Ratio of the F2 Generation? PP p p
PP:Pp:pp  1:2:1 Pp Pp pp
What is the Phenotypic Ratio of the F2 Generation? 3: 1

12. Genotype Phenotype PP Purple 1 (homozygous) Pp Purple 3 (heterozygous)
Dominant alleles mask recessive ones
Genotype
Phenotype PP
Homozygous: same alleles
Heterozygous: different alleles
Purple 1
(homozygous) Pp
Purple 3
(heterozygous) 2 Pp
Purple
(heterozygous) pp 1 1
(homozygous)
White
Ratio = 1:2:1
Ratio = 3:1

13. Vocabulary Practice
We will now play “Got Gametes?” in order to practice understanding the following new terms: alleles, genotype, phenotype, homozygous, heterozygous

14. Vocabulary Practice
Each of you are haploid gametes carrying single alleles – for a trait.
Your single letter can be combined with another single letter (i.e., Hh) to form a genotype in a diploid organism.
You will observe a series of faces. Come to the front of the classroom if you think you have the right genotype to match the phenotype shown. Make sure to find the corresponding allele for the trait you represent!

19. How do you set up a Punnett square?
Now you try!
Example 1:
Heterozygous short hair (____) X heterozygous short hair (____) Hh Hh Hh Hh H H HH h h Hh Hh
Genotypic Ratio HH:Hh:hh
1:2:1
Phenotypic Ratio Short hair:long hair
3:1 hh

20. If you have a dominant phenotype (like purple flowers) how would you determine if it was homozygous (PP) or heterozygous (Pp)? What experiment would you design?
Dominate alleles mask recessive ones
Dominant phenotype, unknown genotype: PP or Pp?
Recessive phenotype, known genotype: pp
What would your hypothesis be if the genotype was PP?
What would your hypothesis be if the genotype was Pp?
If PP, then all offspring purple:
If Pp, then ½ offspring purple and ½ offspring white: P p P p Pp Pp P p p p Pp Pp pp Pp Pp pp
This is called a test cross
Back to Mendel’s Conclusions

21. P Generation F1 Generation F2 Generation
Phenotype(s): Red and White
Genotype(s): CRCR and CWCW
Gamete of Red flower: CR Gamete of White flower: CW CR CW
F1 Generation
Phenotype: Pink
Genotype: CRCW
Gametes: CR and CW CR CW
F2 Generation
Exception to Dominant Alleles Masking Recessive Alleles
Incomplete Dominance: Pink Snapdragons
Use Root Letter “C” to designate incomplete dominance interaction CR CR
CRCR CW CW
CRCW
CRCW
CWCW
Back to Mendel’s Conclusions

22. Back to Mendel’s Conclusions
Exception to Dominant Alleles Masking Recessive Alleles: Co-dominance: Blood Types (video)
Use root letter “I” for dominant alleles of equal strength and “i” for recessive
Back to Mendel’s Conclusions

23. This occurs in a process called meiosis:
Back to Mendel’s Conclusions
Law of Segregation:
Two alleles for each trait segregate (separate) during gamete production
This occurs in a process called meiosis:
Specifically it is “crossing over,” which occurs very early during Prophase I of Meiosis and separation in Anaphase I and II

24. Mendel’s Conclusions
The law of segregation followed one single trait at a time, such as seed color.
What if two traits were followed, such as seed color and seed shape?
Are these genes somehow connected (linked) and inherited together?

25. Following two traits: Seed shape and seed color
Gametes YR yr
Hypothesis: If the genes for seed shape and color are connected in some way,
then the dominant R and Y alleles and the recessive r and y alleles will be matched sets in the gametes. F1
YyRr
Ova
Sperm YR YR yr yr F2
For the traits of seed shape and color, this hypothesis is NOT supported by experimental evidence

26. What did the data support instead?

27. YyRr Now try to do it on your own! What are the phenotypic ratios?
What are the genotypes of the P Generation?
YYRR
yyrr
Law of Independent Assortment
What does the P Generation pass on to F1? YR yr
Gametes
F1 Phenotype?
YyRr
F1 Genotype?
What does the F1 Generation pass on to F2?
Ova
Sperm YR YR Yr
Combine the sperm and ova to produce the offspring in F2 Yr
YYRR yR yR
YYRr
YYRr yr yr
What do you expect the phenotype will be when YR and YR are combined?
YyRR
YYrr
YyRR
Phenotypic Ratios
YyRr
YyRr
YyRr
YyRr
9/16
Yellow & Round
What will the Genotype be when YR and YR are combined?
Yyrr
yyRR
Yyrr
3/16
Green & Round
yyRr
yyRr
3/16
Yellow & Wrinkled
Now try to do it on your own!
yyrr
1/16
Green & Wrinkled
What are the phenotypic ratios?

28. Mendel’s Conclusion! FOIL Law of Independent Assortment:
If the genes are not connected, then they should segregate independently. The alleles are randomly packaged into different gametes during meiosis
(For example, genes for seed shape and color were not inherited together.)
YyRr 
FOIL YR Yr yR yr

29. Significance of Mendel’s Research
Punnett Square was introduced as a tool to predict or determine the probability of an event
Now, let’s practice dihybrid crosses!

30. White board exercises One-trait cross
The allele for the hairy trait is “H,” while the allele for the hairless trait is “h.”
Make a cross between two homozygotes for each of these traits.

31. Punnett Square Exercise
One-trait cross
In a population of Wisconsin fast plants, purple color is created by the pigment anthocyan. The gene that codes for this pigment is dominant (A), and without this pigment, the plant is green recessive (a).
Predict the offspring from the cross of a purple homozygous plant and a green plant.
What if the purple plant was heterozygous? How would the offspring be different?
Purple plant: AA
Green plant: aa
Purple plant: Aa
Green plant: aa A a A a a A Aa a a Aa Aa Aa
50% Purple
50% Green
100% Purple aa Aa Aa aa
Green Purple

32. Punnett Square Exercise
One-trait cross
In populations of hamsters, brown fur is dominant (B), and white fur is recessive (b).
Predict the offspring from the cross of a white hamster and a brown hamster if the brown hamster's mother was white.
Brown hampster: Bb
White hampster: bb B b
Offspring
50% brown mice
50% white mice b b Bb bb Bb bb

33. Punnett Square Exercise
One-trait cross
Henry VIII divorced six of his wives (two of whom were executed) for not bearing him any sons.
Use Mendelian Genetics to prove to King Henry that it wasn’t his wives’ fault.
Remember: Females are XX and Males are XY.
Go to Test Crosses

34. White-board exercises
Two-trait cross
Following two traits:
Kernel shape: Plump vs. withered (P and p) and Kernel color Red vs. yellow (R and r)
Predict the cross between a homozygous recessive corn plant and a homozygous dominant corn plant.

35. Punnett Square Exercise
Two-trait cross
Now take the offspring from that cross, and self-pollinate that plant.
What is the phenotypic ratio of this cross?

36. Punnett Square Exercise
Two-trait cross
My pet guinea pigs (Joni and Chachi) are going to have little guinea pigs.
What is the possibility that their offspring will have long hair, if I know that Joni and Chachi are heterozygous for the following traits?
Black fur (B) White fur (b)
Long hair (L) Short hair (l)