1. Objective 3.03 Interpret and Predict Patterns of Inheritance
Genetics Part 1
Objective 3.03
Interpret and Predict Patterns of Inheritance

2. How did genetics get its start?
Gregor Mendel: The Father of Genetics
Austrian Monk
Worked with Pea Plants
Raised on a farm
Member of the regional agricultural
society.
Won awards for developing improved
varieties of vegetables and fruits.

3. More about Gregor Mendel’s work
Studied the traits (characteristics) of the pea plants.
Did controlled experiments with the pea plants  He studied ONE trait at a time.

4. What Mendel knew about pea plants ...
Mendel knew that pea plants were…
Self fertilizing
Individual pea plants breed true for certain traits. Successive generations are JUST LIKE their parents.
Can be cross pollinated. Pollen from one plant is used to fertilize the eggs of another plant.

5. Vocabulary Alert!!! Heredity – the passing on of characteristics from
parents to offspring.
Genetics – The study of heredity
Trait - a characteristic you get from your
parents.
Gametes – sex cells; egg cells or sperm cells.
Fertilization - egg + sperm
Zygote – fertilized egg.

6. Mendel’s Experiment Flowers have both male and female parts.
Mendel removed the male part from a purple flower.
Transferred pollen (has the sperm cell) from a white flower to purple female parts.
All of the offspring were purple!! WHY???

7. Mendel’s Conclusions Rule of Factors
Each organism has two “factors” that control each trait.  Genes (You get 1 from Mom and 1 from Dad.)
Genes are represented with letters.
Genes exist in different forms called alleles.

8. Mendel’s Conclusions Rule of Dominance
One allele is dominant over the other allele….. This one is called dominant.
The other allele can be “hidden” by the dominant allele. This one is called recessive.
Sooo… If the dominant allele is present, it will be seen!!! It can hide the recessive allele!!!

9. Application of Mendel’s Conclusions
Let’s link this back to the experiment that Mendel did with the purple and white flowers.
Remember that Mendel crossed a purple flower with a white flower and all of the offspring were purple.
Which trait was seen? Purple or white
Purple
Does this make it the dominant or the recessive trait?
Dominant

10. Application of Mendel’s Conclusion
What does this mean as far as the white flowers are concerned?
White is recessive and can be hidden.

11. How do we represent these differences?
We use letters to represent the different alleles for each trait.
If a trait is dominant, we use a capital letter.
If a trait is recessive, we use a lower case letter.
P = purple (Dominant trait)
p = white (recessive trait)

12. Vocabulary Alert Gene – Segment of DNA on a chromosome
that codes for a trait.
Allele – Different versions of a gene.
Dominant – Trait that is seen if it is present ;
Represented with a capital letter
Recessive – Trait that can be hidden; Must
have two copies in order for it to
be expressed; Represented with
a lower case letter.

13. Mendel’s Conclusions Law of Segregation
Every individual has 2 alleles (letters) for each trait; 1 from mom and 1 from dad.
Gametes get only 1 of those alleles. (Think about meiosis!!!)

14. Example of Law of Segregation
Plants could be TT or Tt or tt as combinations for alleles, but it would only donate one to a gamete.
TT - T or T
Tt - T or t
tt - t or t T Tt t
Pre Sperm

15. Mendel’s Conclusions Law of Independent Assortment
Each gene is inherited independently of other genes.

16. Example of Law of Independent Assortment
Pea seed color and shape are inherited independently of each other, so you can have:
Smooth green peas OR wrinkled green peas
Smooth yellow peas OR wrinkled yellow peas
More genes = more combinations!!!!

17. What is a Genotype
Genotype = actual combination of alleles on chromosomes (TT, Tt or tt)  The Letters!!!
Example
Height (T= Tall, t = short)
- TT = Homozygous dominant
- tt = Homozygous recessive
- Tt = Heterozygous

18. What is a Phenotype? Phenotype = Physical appearance
This is determined by the genotype.

19. Eddie Munster…. What is Eddie’s Phenotype?
What are Eddie’s possible genotypes?

20. Practice!!!!! What’s the Genotype? What’s the Phenotype?
T = tall, t = short
Homozygous Tall?
Homozygous Short?
Heterozygous?
What’s the Phenotype?
G = green, g = blue
GG?
Gg?
gg?

22. Punnett Squares
A tool used for predicting the likelihood of genotypes and phenotypes of offspring using both parents genotypes.

23. How did you do that?!?! Determine the genotype of both parents.
Let’s say Tall is dominant to short.
T= _____ and t = ______
Mom is short _____
Dad is heterozygous tall  ___
Draw a box like this:

24. Punnett Square Continued…
Put 1 of each of mom’s letters across the top.
Put 1 of each of dad’s letters down the side.

25. Punnett Square Continued
Fill in one letter from each parent in each box.

26. ANALYZE that Punnett Square!!!
Genotypic Ratio: Compare the allele combinations of the offspring.
There are several ways to write it:
a. 2:2 (2 Tt, 2 tt)
b. ½ Tt, ½ tt
c. 50% Tt, 50% tt

27. MORE Analysis!!!! Phenotypic Ratio: Compare how the offspring LOOK.
There are several ways to write it:
a. 2:2 (2 tall: 2 short) (Dominant : Recessive)
b. ½ tall, ½ short
c. 50% tall, 50% short.

28. Punnett Squares and Probability
Punnett Squares show all possible outcomes.
Chance plays a role in genetics
Sometimes the outcome might not match the Punnett Square exactly.

29. Punnett Square Practice
A dog can have dark fur or light fur. D = dark fur, d = light fur Cross a homozygous dominant dog with a heterozygous dog. What are the parent dog’s phenotypes? What are the expected genotypes and phenotypes of their dog babies?