1. (And why was his work so important?)
Who was Gregor Mendel?
(And why was his work so important?)

2. Gregor Mendel
Gregor Mendel was a monk who lived in the 1800s

3. Mendel’s Mind Wandered…
Mendel wondered how the same species of plants could have different characteristics
Characteristic is a trait that makes the plant (and you) look a certain way

4. Mendel began to think…
Mendel wondered about the Characteristics that appeared with each generation
He wondered if they were “heritable features” – “Heritable” means they are inherited (passed down) from parents to children
Some traits appeared more often with the same parent plants
Mendel wondered why…

5. Pea Plants Mendel performed an experiment and chose pea plants to use
He chose pea plants because he could identify seven pairs of contrasting traits found among
 typical garden peas: 
Seed color (yellow or green)
Seed shape (smooth or wrinkled)
Pod color (yellow or green)
Pod shape (inflated or pinched)
Flower color (purple or white)
Flower position (middle or end)
Stem height (tall or short)

6. Either or….
One or the other…
Easy to see AND collect data!

7. Watching the plants grow…
For two years, Mendel grew different varieties of peas to make sure that their offspring were always the same
This meant that the 
plants he used were 
purebred
Purebred means an 
organism always 
produces the same 
traits in its offspring

8. Think about purebred dogs…
When you purchase a purebred dog, you receive a record of their family tree so you know who their parents and grandparents and great grandparents were!
Proof that the dog is purebred.

9. Patience is a virtue
After recording his observations over a couple 
of years, Mendel decided to breed different 
varieties together to make hybrids
Hybrid means it’s a “mix” - a “cross” - of different traits
(Think… Hybrid cars!)
He made these hybrids by cross-pollinating 
plants with different characteristics
Cross-pollinating means “mating” (crossing) two 
different plants of the same species
White flower x Purple flower
Smooth pea x Wrinkled pea

10. Cross-pollinating (making hybrids)
Mendel brushed the 
pollen off yellow pea 
plants and put it on 
green pea plants
He did the same for 
plants with each of the 
seven pairs of traits
He then grew 
generation after 
generation of hybrids 
and tracked the 
appearance of the 
different traits

11. Crossing Hybrids gives a 3 to 1 ratio of traits in offspring!
His Findings…
Crossing Hybrids gives a 3 to 1 ratio of traits in offspring!

12. Crossing Characteristics
Mendel crossed many different traits and 
 carefully recorded the traits of the offspring
He determined that each parent supplies one 
 “unit” or “factor” for each different trait…
Somehow…
Some traits seemed to disappear in the first generation but reappear later…

13. Recessive and Dominant
The traits that disappeared in the first 
generation of hybrids he called “Recessive.”
He called those that always appear,
“Dominant.”
In later generations the recessive traits reappeared in a predictable pattern.
For example, later generations of plants had 
 one green pea for every three yellow peas. 
  The same ratio appeared for all seven pairs of traits.

14. Pea Soup Anyone?
Mendel grew an estimated 28,000 pea plants 
over eight years.
He recorded the traits of parent generations 
 (P) as well as the traits of the first generation 
(F1)
(F1) is the “First Filial” generation: the first 
offspring to be born
Can you guess what the second generation 
was listed as? _____________

15. What Mendel Discovered
Mendel discovered that 
traits are inherited
And it occurs in a 
consistent pattern
Mendel used math to figure 
out what was going on in the cell and how the “factors” (traits) would be passed on. 
See????? Math IS useful!!!!

16. The “Father of Genetics”
He published his results, observations and 
conclusions
These are now known as Mendel’s Laws
Mendel's laws of heredity work with other 
organisms as well
They form the basis of modern genetics
Even though Mendel knew nothing about genes and DNA, we call him the
“Father of Genetics”

17. Now called “Genetics”
Mendel used the terms “unit”, “factor” and “element” to describe how traits are inherited (passed) from parents to offspring
Today, we call these “units” GENES (DNA)
Genes are found on our chromosomes (in the nucleus of our cells) and are made up of DNA (which is made of nucleotides!)

18. What are Genes, Anyway? Genes are the basic “unit” of heredity
They are a sequence of DNA that causes a 
 certain characteristic to appear in an organism
Genetics is the science of genes, traits and heredity
Genetics is the study of how traits are inherited (through genes) from one generation to another

19. The Punnett Square
Mendel found out that every trait is controlled by two “elements” (genes)
One from one parent and one from the other parent
Now, the “Punnett Square” is used to show how different traits are passed from one generation to the next
This is called Probability
The chance that a given event will occur

20. Predictable Ratios
Mendel repeated his experiments over and over and the F2 generation always had a 3:1 ratio of yellow to green or round to wrinkly
Mendel then crossed plants that differed in 
 more than one trait: round, yellow peas with wrinkled, green one, or tall, violet- flowered plants with short, white-flowered ones
These traits appeared in predictable ratios, too

21. Dominant & Recessive
Mendel determined that, in order to show-up, 
 a Dominant trait needs only one trait “unit” from one of the parents
A dominant trait can “cover up” (mask) a 
 recessive trait
Dominant is stronger, more powerful
The Recessive trait needs two “units”, from 
 both parents, in order to show up in the next generation
Recessive is “weak”, possessing little power/influence

22. Mendel’s Laws of Inheritance
Mendel came up with these important 
conclusions known as Mendel’s Laws:
The Law of Dominance states that some unit characters can mask the expression of others.
The Law of Segregation states that each unit character separates into a different sex cell.
The Law of Independent Assortment states that genes segregate (separate) according to chance.

23. The Vocabulary of Genetics
The genetic make-up of an organism is called 
its “genotype”
 It is the type of genes found in the cell
The appearance of the organism that is 
determined by its genotype is called its 
“phenotype”
 It is how the organism looks (appears) on 
 the outside

24. Homologous Pairs
When making a new organism, one gene 
from the mother matches up with a 
“similar” gene from the father
These genes are called “homologous” pairs
Homologous means similar (in length, 
size, genetic make up, etc…)
The homologous “genes” are found on 
chromosomes – so, if homologous genes 
pair up, they create homologous 
chromosomes!

25. Genes Vs. Alleles
A gene is a section of DNA which codes for a certain characteristic, such as height.
Genes, however, can have variations and this is 
where alleles come in…
 Height can be either tall or short
Alleles are different versions of a gene.
For example, a tall allele or a short allele.
They are the different sequences of DNA that 
determine a single characteristic (height).
They occur in pairs (one from one parent, one from the other) and can be classified as recessive or dominant.

26. More Vocab!
Homozygous means that the two alleles 
(genes) for an organism are exactly the same 
(TT or tt).
Also known as Purebred…
Heterozygous means that the two alleles for 
an organism are different (Tt).
Also known as Hybrid…

27. Heredity
Heredity is the passing of traits from one 
 generation to another”.
Inherited traits are passed (genetically), from the parent generation to the offspring

28. How do Geneticists figure it out?
Geneticists use letters to represent alleles.
The same letter is used to indicate both alleles.
A capital letter = a Dominant trait
A lowercase letter = a Recessive trait
Examples:
Flower color: P= purple, p= white
Seed color: Y= yellow, y = green
Seed shape: W = wrinkled, w = round

29. In humans…. Widow's peak: W = widow's peak, w = continuous hairline
Freckles: F = freckles, f = no freckles
Earlobes: E = unattached, e = attached
Thumbs: H = hitch-hiker, h = non-hitch-hiker
Cleft chin: C = cleft chin, c = no cleft chin
Hair on Fingers: F = hair, f = no hair
Spock Fingers: S = spock yes, s = spock no
Handedness: R = right handed, r = left handed

33. Genes & Mutations Each gene carries a separate piece of information
DNA codes for all genes
Changes in the sequence of the DNA molecule (and therefore the gene) are called mutations 
A mutation may change the manner in which a trait is expressed by an organism.
So, a mutation in the genotype, changes the phenotype
 Remember that not all mutations are bad!