1. Activity 4 – Genes and Traits
Click the button to learn about the “father of genetics” (3:10)

2. Early Breeding Practices:
Heredity: The passing of genes or traits from one generation to the next
Early farmers knew that if they carefully chose which plants would reproduce, they could get offspring with favorable characteristics like better size color or taste!
Selective breeding by early farmers also led to the creation of many different varieties of crops like potatoes.

3. Gregor Mendel Mendel was a 19th century monk and scientist
He studied how traits were passed on in pea plants
Some of the traits that he studied included:
Seed color - Stem length
Seed shape - Flower color
Seed texture
These physical characteristics that he looked at are known as phenotypes

4. Gregor Mendel
Not present in next generation!
Mendel also noticed that when he crossed pure breeding plants for two versions of a trait something strange happened –
One of the versions was always missing from the next generation
Today we know that this “hidden” trait is the recessive version

5. Gregor Mendel
Mendel worked for years with his plants to develop three basic principles of heredity:
1. In the first generation of offspring (F1) which ever trait is expressed is the DOMINANT trait, whichever trait is hidden is the RECESSIVE trait
2. Every plant has 2 copies of a gene
(2 alleles)
3. Each parent can only pass on 1 of their alleles to the offspring

6. Gregor Mendel
Look at the table of Mendel’s Traits, which traits are Dominant, and which are Recessive?
How Can You Tell?
The dominant traits are the ones that are expressed in the F1 generation

7. Genetics Today We know that heredity is controlled by:
Genes – a segment of DNA that
produces a specific protein or trait
Genes are passed on to offspring through the:
Gametes – A sex cell such as sperm
or egg that contains half of the
parent’s genetic material
The combination of alleles in an organism is its GENOTYPE

8. Heterozygous (dominant)
Alleles
When looking at alleles, an organism can be either homozygous or heterozygous
Homozygous – having 2 of the SAME copies of an allele for a trait
i.e. PP or pp for flower color
Heterozygous – Having 2 DIFFERENT alleles for a trait
i.e. Pp for flower color
Homozygous Dominant PP
Homozygous Recessive pp
Heterozygous (dominant) Pp

9. Beyond Mendel!
Not all traits are passed on through simple dominance like Mendel studied!
Incomplete Dominance – When mixing 2 alleles creates a BLENDING of the traits
What would happen if you bred red snapdragons with white snapdragons?
You always get plants with PINK flowers!
(a mix of red and white)

10. Beyond Mendel! CR CW CW CRCW CWCW CRCW CWCW
If the pink flower is crossed with a white flower, what offspring would be produced?
CR CW CW
Could This cross ever produce a red snapdragon?
CRCW
CWCW
CRCW
CWCW

11. Beyond Mendel! CR CW CR CW CRCR CRCW CRCW CWCW
What if you cross 2 pink flowers?
All three colors can be produced!
CR CW CR CW
CRCR
CRCW
CRCW
CWCW

12. Beyond Mendel!
Codominance occurs when the two alleles are EQUALLY expressed in the offspring
i.e. Blood type in humans
Humans can have alleles IA , IB , or i for blood type:
Click for a tutorial on blood types!

13. Codominance Punnett Square
If the parent blood types are:
IAi and IBi
Show a Punnett square to represent all the possible offspring blood types
IA i
Crossing
Heterozygous A blood with Heterozygous B blood could produce offspring of any blood type!
IA IB IB i
IB i
IA i
i i

14. 3 Types of Dominance
Simple (Complete) Dominance: one allele is dominant over the other (which is recessive)
Incomplete Dominance: neither allele is dominant over the other (phenotype is a blend of both parents)
Codominance: both alleles are expressed/ shown equally (NOT blended)