1. Gregor Mendel
The basic laws of heredity were first formed during the mid-1800’s by an Austrian botanist monk named Gregor Mendel. Because his work laid the foundation to the study of heredity, Mendel is referred to as “The Father of Genetics.”

2. Mendel’ Pea Plants
Mendel based his laws on his studies of garden pea plants. Mendel was able to observe differences in multiple traits over many generations because pea plants reproduce rapidly, and have many visible traits such as:
Pod color
Seed Color
Plant Height
Green
Yellow
Green
Yellow
Seed Shape
Short
Pod Shape
Tall
Wrinkled
Round
Smooth
Pinched

3. Mendel’s Experiments
Mendel noticed that some plants always produced offspring that had a form of a trait exactly like the parent plant. He called these plants “purebred” plants. For instance, purebred short plants always produced short offspring and purebred tall plants always produced tall offspring. X
Short Offspring
Purebred Short Parents X
Purebred Tall Parents
Tall Offspring

4. Mendel’s First Experiment
Mendel crossed purebred plants with opposite forms of a trait. He called these plants the parental generation , or P generation. For instance, purebred tall plants were crossed with purebred short plants. X
Parent Short P generation
Parent Tall P generation
Offspring Tall F1 generation
Mendel observed that all of the offspring grew to be tall plants. None resembled the short short parent. He called this generation of offspring the first filial , or F1 generation, (The word filial means “son” in Latin.)

5. Mendel’s Second Experiment
Mendel then crossed two of the offspring tall plants produced from his first experiment.
Parent Plants
Offspring X
Tall F1 generation
3⁄4 Tall & 1⁄4 Short F2 generation
Mendel called this second generation of plants the second filial, F2, generation. To his surprise, Mendel observed that this generation had a mix of tall and short plants. This occurred even though none of the F1 parents were short.

6. Mendel’s Law of Segregation
Mendel’s first law, the Law of Segregation, has three parts. From his experiments, Mendel concluded that:
1. Plant traits are handed down through “hereditary factors” in the sperm and egg.
2. Because offspring obtain hereditary factors from both parents, each plant must contain two factors for every trait.
3. The factors in a pair segregate (separate) during the formation of sex cells, and each sperm or egg receives only one member of the pair.

7. Dominant and Recessive Genes
Mendel went on to reason that one factor (gene) in a pair may mask, or hide, the other factor. For instance, in his first experiment, when he crossed a purebred tall plant with a purebred short plant, all offspring were tall. Although the F1 offspring all had both tall and short factors, they only displayed the tall factor. He concluded that the tallness factor masked the shortness factor.
Today, scientists refer to the “factors” that control traits as genes. The different forms of a gene are called alleles.
Alleles that mask or hide other alleles, such as the “tall” allele, are said to be dominant.
A recessive allele, such as the short allele, is masked, or covered up, whenever the dominant allele is present.

8. Homozygous Genes
What Mendel refered to as a “purebred” plant we now know this to mean that the plant has two identical genes for a particular trait. For instance, a purebred tall plant has two tall genes and a purebred short plant has two short genes. The modern scientific term for “purebred” is homozygous.
short-short
short-short
short-short X
Short Offspring
Short Parents
According to Mendel’s Law of Segregation, each parent donates one height gene to the offspring. Since each parent had only short genes to donate, all offspring will also have two short genes (homozygous) and will therefore be short.

9. Hybrid Alleles
In Mendel’s first experiment, F1 offspring plants received one tall gene and one short gene from the parent plants. Therefore, all offspring contained both alleles, a short allele and a tall allele. When both alleles for a trait are present, the plant is said to be a hybrid for that trait. Today, we call hybrid alleles heterozygous.
tall-tall
short-tall
short-tall
short-short X
Parent Short P generation
Parent Tall P generation
Offspring Tall F1 generation
Although the offspring have both a tall and a short allele, only the tall allele is expressed and is therefore dominant over short.

10. Dominant Alleles
Mendel observed a variety of dominant alleles in pea plants other than the tall allele. For instance, hybrid plants for seed color always have yellow seeds.
Green & Yellow Allele
Yellow Seed
However, a plant that is a hybrid for pod color always displays the green allele.
Green Pod
Green & Yellow Allele
In addition, round seeds are dominant over wrinkled seeds, and smooth pods are dominant over wrinkled pods.

11. Law of Independent Assortment
Mendel’s second law, the Law of Independent Assortment, states that each pair of genes separate independently of each other in the production of sex cells. For instance, consider an example of the following gene pairs:
According to Mendels’ Law of Independent Assortment, the gene pairs will separate during the formation of egg or sperm cells. The plant will donate one allele from each pair. The plant will donate either a yellow or green seed allele, either a yellow or green pod allele, and a wrinkled or round seed allele. It will always donate a wrinkled pod shape. The donation of one allele from each pair is independent of any other pair. For example, if the plant donates the yellow seed allele it does not mean that it will also donate the yellow pod allele.

12. Genetics Terminology: Chromosomes & Genes
Genome - Complete complement of an organism’s DNA.
Cellular DNA is organized in chromosomes.
Genes have specific places on chromosomes.
Genome
Chromosomes
Genes
Image: Chromosome & gene, Graham Colm, National Human Genome Research Institute
From the Virtual Cell Biology Classroom on ScienceProfOnline.com

13. What is an ALLELe? Different form/version of a gene
You inherited ONE ALLELE from each parent for each trait.
For example –
Gene = eye color
Allele = blue, hazel, brown, and green

14. Dominant vs. Recessive Alleles
Dominant allele hides the recessive allele.
The Dominant allele always shows/is visible
For example – hair color – brown is dominant to all other hair colors
EX: mom gave you the allele (gene) for brown hair. Dad gave you the allele for blonde hair.You will have what color hair?
Answer: Brown hair

15. Dominant vs. Recessive Alleles (Cont.)
Recessive allele is always hidden if a dominant allele is present.
You must inherit 2 recessive alleles for the trait to show up/become visible.
EX:– hair color – blonde is recessive to all other hair colors
mom has to give you the allele (gene) for blonde hair and dad gave you the allele for blonde hair, you will have blonde hair!

16. Writing Alleles? All alleles are assigned letters
Dominant allele=CAPITAL letters
B=(Brown eyes)
Recessive allele – lower case
b= (blonde eyes)

17. Two letters pair for each trait – one passed on from mom and one from dad
Using the letter B tell me what a person with brown hair would look like
BB_____
Bb_____
bb_____
Is this trait dominant or recessive?
DOMINANT
What if the person had blonde hair (recessive trait)? bb

18. How you get your traits?
Dimples are a dominant trait. Non dimples are recessive. If both parents have have dimples would all the kids have dimples?

19. Genotype vs. Phenotype Phenotype- physical trait
can be seen
Brown or blonde
Genotype- genetic makeup
Alleles inherited
(not seen BB, Bb)

20. Genotype/Phenotype Practice
Are the following genotype or phenotype
Hazel Eyes.
Phenotype BB
Genotype
Long Toes Rr
genotype Tt
Ear Hair
Phenotype Ff
Freckles
phenotype

21. Homozygous vs Heterozygous
PREFIXES:
HOMO=SAME alleles for a specific trait ( TT or tt)
HETERO=DIFFERENT alleles for a specific trait (Tt or Bb)

22. Practice-
1.) If you inherited the 2 alleles for blue eyes (1 from each parent), your phenotype is __________, your genotype is _____, and you’re _____ zygous.
2.) If you inherit the dominant allele for dimples from your dad, and the recessive for no dimples from your mom, your phenotype is ______, your genotype is _______, and you’re ____ zygous.

23. Practice Problems
Will the following plants be tall or short? T=tall and t=short Tt TT tt
Are the following plants homozygous or heterozygous?

24. What is the phenotype of the following plants? Tt TT tt
Practice
What is the phenotype of the following plants? Tt TT tt

25. Genotype codes for Phenotype.
P = Purple and p= white
Y = Yellow and y = green
R = Round and r = wrinkled
Genotype is RR, the Phenotype is ______.
Genotype is YY, the Phenotype is ______.
Genotype is pp, the Phenotype is ______.
Genotype is Rr, the phenotype is ______.
Genotype is Yy, the phenotype is ______.
Phenotype is wrinkled, the genotype is ____.
Phenotype is green, the genotype is _____.

26. Genotype codes for Phenotype.
P = Purple and p= white
Y = Yellow and y = green
R = Round and r = wrinkled
Genotype is RR, the Phenotype is ______.
Genotype is YY, the Phenotype is ______.
Genotype is pp, the Phenotype is ______.
Genotype is Rr, the phenotype is ______.
Genotype is Yy, the phenotype is ______.
Phenotype is wrinkled, the genotype is ____.
Phenotype is green, the genotype is _____.

27. C ______ d _______ e _______ F _______ f ______ v ______ P ______
. Write dom. For dominant or rec. for recessive next the letter.
A ______
C ______
d _______
e _______
F _______
f ______
v ______
P ______
m ______
M ______
Q _______
n ________
b ________
X ________
Y _________

28. AA _____ Bb ____ Cc ____ DD _____ eE _____ Ff ____ Gg ____ Hh ____
. Write Ho. for homozygous or He. for heterozygous.
AA _____
Bb ____
Cc ____
DD _____
eE _____
Ff ____
Gg ____
Hh ____
Kk ____
Mm ____
Nn ____
RR ____
Ss ____
NN ____

29. Write Ho. Dom if it is homozygous dominant, Ho. Rec
. Write Ho. Dom if it is homozygous dominant, Ho. Rec. if it is homozygous recessive or He if it is Heterozygous.
AA ____
BB ____
Cc ____
dd ____
FF ____
qq ____
SS ____
TT ____
VV ____
Tt ____
uu ____
WW ____
ii ______
xx ____
bb ____