1. Before genetics, a quick review…
What cell organelle houses our genetic information?
Nucleus
What molecule is our genetic information found on?
Deoxyribonucleic Acid (DNA)
What process allows for organisms to be unique from their parents?
Meiosis

2. Do you look like your parents?
Most of us share some traits with our parents
Traits are distinguishing characteristics that are inherited, such as eye color or skin color.
Give some other examples of traits…
Most of us also differ from our parents in some ways.
This is because during meiosis, there are different actions taken to ensure a unique individual!
Do you remember these actions?

3. So, what’s responsible for all this?
Genetics is the study of biological inheritance patterns and variation in organisms.
Heredity is the passing of traits from one generation to the next

4. Who discovered all this stuff?
Gregor Mendel
Considered the “Father of Genetics”
Austrian Monk and Horticulturist
Studied the garden pea plant
1st to publish findings on heredity

5. Mendel’s Experiment
Mendel used pollen to fertilize selected pea plants.
Purebred first generation (P) crossed to produce second generation (F1)
interrupted the self-pollination process by removing male flower parts
Mendel controlled the
fertilization of his pea plants
by removing the male parts,
or stamens.
He then fertilized the female
part, or pistil, with pollen from
a different pea plant.

6. Mendel allowed the resulting plants to self-pollinate.
F1 generation, all plants had purple flowers
F1 plants are all heterozygous (different alleles)
Among the third (F2) generation, some plants had purple flowers and some had white

7. Mendel’s Results

8. Mendel’s Conclusions
Traits are inherited as separate discrete units. This is the Principle of Independent Assortment.
Today these are called genes.
Organisms inherit two copies of each gene, one from each parent
Organisms donate only one copy of each gene in their gametes
Then the two copies of each gene segregate, or separate, during gamete formation
One factor in a pair may mask the effect of the other. This is the Principle of Dominance and Recessiveness.
Together, these two make up
the Principle of Segregation

9. Mendel called them discrete units, we call them genes.
A gene is a piece of DNA that provides a set of instructions to a cell to make a certain protein
Every gene has a locus (a specific position on a pair of homologous chromosomes)
Think about how your house has a specific address. The locus is the gene’s address

10. Most genes exist in many forms
An allele is any of the alternative forms of a gene that may occur at a specific locus
Your cells have TWO alleles for each gene, one on each of the homologous chromosomes
Each parent gives ONE allele

11. Genes influence traits.
A genome is all of an organism’s genetic material
This genome determines ALL of your traits
A genotype refers to the genetic makeup of a specific set of genes
For example, eye color
What is it?
A phenotype refers to the physical characteristic or trait
For example, eye color of blue
How does it appear?

12. Remember the Principle of Dominance and Recessiveness?
Alleles will be dominant or recessive
A dominant allele is the allele that is expressed when two different allele are present
Represented by capital letters
A recessive allele is the allele that is masked, or only expressed when there are two recessive alleles present.
Represented by lowercase letters
Example: blue eyes are recessive and brown eyes are dominant

13. So, how do we figure all this stuff out?
Glad you asked!!! 
Shortly after Mendel’s experiments became widely known, a poultry geneticist named R.C. Punnett developed the Punnett square.

14. Punnett squares illustrate genetic crosses.
A cross is the mating of two organisms.
The Punnett square is a grid system for predicting all possible genotypes resulting from a cross.
The axes represent the possible gametes of each parent.
The boxes show the possible genotypes of the offspring.
The Punnett square yields the ratio of POSSIBLE genotypes and phenotypes.

15. A monohybrid cross involves one trait.
Monohybrid crosses examine the inheritance of only one specific trait.
For example: a cross between a homozygous dominant and a homozygous recessive yields all heterozygous, all dominant

16. And another example…
Cross between a heterozygous and a heterozygous yields a ratio of 1:2:1
1 homozygous dominant:
2 heterozygous:
1 homozygous recessive
OR a ratio of 3:1
3 dominant to 1 recessive

17. And, another…
A cross between a heterozygous and a homozygous recessive yield a ratio of 1:1
1 heterozygous
1 homozygous recessive
OR a ratio of 1:1
1 dominant to 1 recessive

18. A dihybrid cross involves two traits.
Mendel’s dihybrid crosses with heterozygous plants yielded a 9:3:3:1 phenotypic ratio.
Two Traits are represented by two different letters: Yy and Rr

19. Sometimes we use Punnett squares to find unknown genotypes
A testcross is a cross between an organism with an unknown genotype and an organism with the recessive phenotype.
The offspring will show whether the organism with the unknown genotype is heterozygous or homozygous dominant.

20. Let’s Practice!
If you are crossing a heterozygous purple parent with a homozygous dominant purple parent, what percent of offspring will have purple flowers? Represent purple with P and white with p.

21. PP Pp PP Pp Step 1: Decide the genotype for each parent.
Heterozygous purple = Pp
Homozygous dominant purple = PP
Step 2: Draw your Punnett square and label your axes.
Step 3: “Cross” your parents P p PP Pp P PP Pp P

22. So, What is the percentage of flowers with purple flowers?
100%
What is the ratio of purple flowers to white flowers?
4:0

23. Now, you try one.
You are crossing a heterozygous black dog and a homozygous recessive brown dog. What percentage of offspring will be black? What percentage will be brown?
Represent black with B and brown with b