1. Lesson 6.1
Mendel’s Experiments

2. Mendel Is the Father of Modern Genetics
Modern genetics began with Gregor Mendel’s experiments with pea plants

3. Mendel Chose Chose Peas for Good Reason
Peas reproduce sexually
It is possible to control which plants are allowed to reproduce
Pea plants produce many offspring in a small amount of time
Peas have easily identified characteristics

4. Cross Pollination
A single pea flower can contain both male and female gametes
Anthers make pollen (male gametes)
Stamen contain ovules (female gametes)
Fertilization results from pollen being transferred to the stamen
When the pollen of one flower fertilizes the ovule of the same plant, this is self - fertilization
When the pollen of one plant fertilizes the ovule of another plant, this is cross - fertilization

5. 1
Removed stamens from purple flower
White
Stamens
Carpel
Purple
PARENTS (P)
OFF-SPRING (F1) 2
Transferred pollen from stamens of white flower to carpel of purple flower 3
Pollinated carpel matured into pod 4
Planted seeds from pod
How Mendel Controlled Cross - fertilization - He did this to thousands of plants and kept detailed notes

6. Monohybrid Crosses
Mendel chose parent plants from pea populations that had been tall for many generations
He bred these tall plants with other plants from populations that had been short for many generations
He called the parent plants the P generation
All the parent plants were true breeding
The true breeding tall plants cross - pollinated the true breeding short plants
What do you think the offspring looked like?

7. All of the offspring were as tall as the tall parent plant
The short trait seemed to disappear from the population
Was the short trait gone for good? How could Mendel find out?

8. Mendel allowed all of the offspring from his first cross to self - fertilize.
When the seeds sprouted he found that 3/4 were tall plants and 1/4 were short

9. Mendel’s Rules
Mendel did similar monohybrid crosses with a total of seven different pea plant traits, always studying one trait at a time
Every time, one version of the trait appeared to disappear in the F1 generation, but return in 1/4 of the F2 generation
Mendel summed up his conclusions from this experiment with two rules and one law
-The Rule of Unit Factors
-The Rule of Dominance
-The Law of Segregation

10. Some of the Traits Mendel Studied

11. The Rule of Unit Factors
Each organism has two factors that control each of its traits. There are two possible forms of each of these factors.
We now call these factors genes and the different forms of a gene are alleles
One allele is inherited from each parent
Example: All plants receive two alleles for the height gene. A plant could receive any of the following combinations
Two tall alleles
One tall allele and one short allele
Two short alleles

12. The Rule of Dominance
Of the two possible alleles for any gene, one allele is dominant and the other allele is recessive. The dominant allele is the one that is always expressed.
Example:
Short allele (t) and short allele (t) = short plant (tt)
Short allele (t) and tall allele (T) = tall plant (tT)
Tall allele (T) and short allele (t) = tall plant (Tt)
Tall allele (T) and tall allele (T) = tall plant (TT)

13. The Law of Segregation T or t gametes T or t gametes
During gamete formation, pairs of alleles segregate into separate gametes. During fertilization gametes pair up creating offspring with 2 alleles for each trait
Example:
Parent # Parent # 2
Tt Tt
Produces
T or t gametes
Produces
T or t gametes
Possible Offspring: TT or Tt or tT or tt

14. Genotype and Phenotype
Genotype is the combination of alleles an individual receives for a gene, it is the type of genes they have.
TT (homozygous dominant)
Tt (heterozygous)
tt (homozygous recessive)
Phenotype describes what version of a trait the individual will express
Tall
Short

15. Mendel’s Second Experiment
Next Mendel crossed pea plants that differed in two traits. This is called a Dihybrid cross.
From his results Mendel Formulated the Law of Independent Assortment

16. Mendel’s Law of Independent Assortment
Genes for different traits are inherited independently of each other.
In other words the gene for pea shape and the gene for pea color are inherited independently of each other.
A round, yellow parent and a wrinkled, green parent can produce any combination of round, wrinkled, yellow, or green pea offspring.
Round and yellow - Wrinkled and yellow
Round and green - Wrinkled and green