1. Early Belief about Inheritance
Blending Theory
Children were a mixture of both parents
But, if this were true over time what would we see?
A reduction in variety of traits.

2. GREGOR MENDEL
The monk who worked with?

3. MENDEL’S GOAL
EXPLAIN the PATTERN of HEREDITY from PARENT to OFFSPRING

4. WHY PEA PLANTS? EASY TO GROW REPRODUCE IN A SHORT TIME
GET RESULTS QUICKLY
ONLY 7 TRAITS
EACH TRAIT ONLY HAS 2 FORMS
MALE & FEMALE PARTS on flowers allow for
SELF-FERTILIZATION OR MENDEL could CROSS FERTILIZE them

5. HOW MENDEL CROSS FERTILIZED

6. FLOWERS & THEIR PARTS

7. MENDEL’S FIRST TRAIT EXPERIMENT- Flower Color
We use a punnett square to show the results:
Two purebred parents are crossed
One parent has PP it has purple flowers
The other has pp white flowers
A dominant trait is a capital letter P
A recessive trait is a small letter p
The offspring are all purple. Because they have one dominant gene P. Even though they have a p gene.
White recessive
offspring
Purple Dominant

8. How to fill & label a punnett cross
The letters pp or PP are called ALLELES.
Each parent CONTRIBUTES one ALLELE to their offspring
Therefor there are 2 ALLELES for each TRAIT, one from each parent
The alleles are genes. So we call the combination of alleles, genotype, think Genes
When we look at the physical characteristics the genotype creates this is called a phenotype, think Physical. Purple, white flowers
Phenotype white flower
alleles
Phenotype Purple flower
Genotypes of 4 offspring are ?___
What is the phenotype of offspring?___

9. How to do a punnett square
How to do a punnett square

10. MENDEL’S OBSERVATIONS OF OF 1ST PURE-BRED CROSS
THE PARENT’s generation uses the code P.
They are PUREBRED plants. They had 2 genes that were both represented by the same letters, either PP for purple flowers or pp for white flower color.
We also call purebreds Homozygous for a trait. Two letters that are the same- PP or pp.
THE OFFSPRING generation uses the code F-1
In this example the offspring are Hybrids or Heterozygous, Pp. They have 2 genes, one dominant and one recessive. Because the offspring have one dominant gene P they have purple flowers.

11. If someone believed in the Blending Hypothesis they would have predicted that the offspring of a purple and white flower …
LIGHT PURPLE
But they were not. Mendel therefore called the purple color a Dominant trait.

12. MENDEL’S OBSERVATIONS OF 1ST PURE-BRED CROSS
ALL OFFSPRING had DOMINANT, purple flowers
None had the white flowers, or Recessive trait.

13. MENDEL’S 2ND EXPERIMENT SELF-FERTILIZATION CROSS
He bred the F-1GENERATION
Remember the F-1 were HYBRIDS, Pp
They had two genes, one dominant and one recessive.
But Mendel did not realize this. He only saw that they had purple flowers. So he expected to see?
All purple offspring when they were bred with each other

14. F-2 RESULTS
However, he had SOME PURPLE & also some White flowered plants appear
HOW WAS THIS POSSIBLE?!
THE RECESSIVE TRAIT was always there in the genes of the flowers.
To get a white flower two recessive genes had to come together in an offspring to show up. pp
The phenotype ratio of offspring he had by flower color was 3:1 Three purple to one white.
The genotype ratio he got was 1 PP, 2Pp, 1 pp
it is written at 1:2:1

15. Mendel’s 2nd Experiment
Ratios

16. Mendel’s 2nd experiment
Crosses purebreds
Mendel’s 1st exp.
Mendel’s 2nd experiment
Crosses hybrids

17. DI-HYBRID CROSSES

18. MENDEL’S HYPOTHESIS Mendel’s Theories
1. EACH TRAIT IS CONTROLLED BY A FACTOR…
2. MANY FACTORS HAVE 2 FORMS
3. ONE IS DOMINANT OVER ANOTHER
4. EACH PARENT CONTRIBUTES 1 FACTOR
5. FACTORS SEPARATE WHEN GAMETES FORM, & JOIN TO MAKE A PAIR for a ZYGOTE
6. SOME TRAITS DISAPPEAR IN A GENERATION, THEN REAPPEAR.
What we know About Genetics
A factor is a GENE
A gene has two copies (chromosomes)
DOMINANT/RECESSIVE
1 GENE
MEIOSIS and Fertilization
A PARENT can have a Recessive TRAIT & not EXPRESS it physically & can pass it onto their child

19. INDEPENDENT ASSORTMENT

20. ABILITY TO PREDICT FUTURE EVENT
PROBABILITY
ABILITY TO PREDICT FUTURE EVENT
PREDICT THE FREQUENCY OF OFFSPRING TRAITS
EXAMPLE A COIN TOSS
WHAT are the CHANCES of GETTING HEADS with 1 COIN?
½, one side is heads, the other is tails
WHAT are the CHANCES of getting HEADS with 2 COINS?
½ x ½ =? ¼!

21. TEST CROSS
When you are not sure what the GENOTYPE is for a dominant trait, example a black dog
It can be HOMOZYGOUS BB or HETEROZYGOUS Bb
You would breed the dominant trait organism with a HOMOZYGOUS RECESSIVE bb mate since they have no dominant genes
This mate can only give recessive genes to the offspring
This is what a breeder would do to determine if the dominant organism’s phenotype is homozygous or heterozygous

22. TEST CROSS Cross your dominant organism w/a recessive organism
HOMOZYGOUS genotype
HETEROZYGOUS genotype
Example 2
Example 1 t
All offspring are heterozygous then the unknown parent must be a purebred, or homozygous dominant
2 offspring are heterozygous, 2 are recessive. Therefore, the parent is not a purebred.