Heredity The study of how traits are passed

from parents to offspring Perceptions have evolved over

time Incomplete Dominance Co-Dominance Mendelian Genetics

+ =

Incomplete Dominance: Offspring is an average

of the parents

Co-Dominance: showing both traits

at the same time

+ =

+ =

Gregor Johann Mendel (1822 - 1884)

The father of modern geneticsPublished one paper in 1866 that went unnoticed for 40 years Proposed heredity was controlled by paired factors that segregate with gamete production and rejoin at fertilization

Genes:•Everyone has DNA in their cells and DNA contains instructions for building a person.

•Each physical characteristic (or Trait) an organism possesses is controlled by one or more genes.

•Offspring look like parents because they inherit the same genes that the parent has.

Alleles: Alternate forms of Genes• Every Labrador dog has genes for fur, but the genes sometimes have slight variations ie, COLOR.

• Variations of genes are called alleles.

• In the blending example with the flowers, the red and white alleles were equal, and both were expressed equally in the offspring.

• In the case of Labrador fur, the alleles are NOT equal. This is an example of DOMINANCE.

Dominant Recessive

• Dominant alleles are always expressed in an offspring, and will mask any other allele present in the offsprings’ cells. In Labradors, black fur is dominant.

• Alleles which are masked in this way are called Recessive alleles. Chocolate fur is recessive. A Labrador can only have chocolate fur if there are NO alleles for black fur in its DNA.

Dominant & Recessive Genes

Dominant Alleles are always expressed in the Phenotype. Does this mean that they are always passed on to the offspring as well?

If a parent has both a dominant and a recessive allele for a trait, there is an equal chance of passing either allele on.

NO!

Every individual has 2 alleles for every gene.

The Law of Segregation

These allele pairs separate when gametes are formed….

The Law of Segregation

…and 1 of each randomly combine to create the offspring's genotype.

The Law of Segregation

Dominant & Recessive Genes

=

Genotype = Homozygous RecessivePhenotype = Chocolate

Dominant & Recessive Genes

=

Genotype = Homozygous DominantPhenotype = Black

Dominant & Recessive Genes

=

Genotype = HeterozygousPhenotype = Black

Generations

+ P-generation

(Parents)

+F1-generation

(First Filial)

F2-generation

(Second Filial)

The Summary So Far:1) The physical characteristics (traits) of individuals are

controlled by genes

2) Different forms of the same gene are called alleles.

3) The physical appearance of an organism (that you can observe) is called the Phenotype. The alleles that that individual carries (invisibly) in its’ DNA is its’ Genotype.

4) Some alleles can overpower others, and are called Dominant. These alleles are always expressed in the phenotype of the offspring.

5) Alleles that are masked by Dominant alleles are called Recessive. An individual can only show a recessive phenotype if it has NO Dominant alleles.

Monohybrid Crosses

Example: Determining the Presence of the allele for Anthocyanin

STEP 1: Assign the dominant and recessive alleles names

= A

= a

Monohybrid Crosses

STEP 2: Find out the genotype of each parent

In this lab, we starting with both heterozygous F1 plants

+Aa x Aa

Monohybrid Crosses

STEP 3: Build a Punnett Square to determine all the possible gametes each parent can produce.

Monohybrid Crosses

STEP 3: Build a Punnett Square to determine all the possible gametes each parent can produce.

A

A

a

a

Monohybrid Crosses

STEP 4: Determine the possible allele combinations

A

A

a

a

AA Aa

Aa aa

Monohybrid Crosses

STEP 5: Determine the possible phenotypes of the F2 generation

A

A

a

a

AA Aa

Aa aa

Dihybrid CrossesSTEP 1

= A

= a

= G

= g

Dihybrid CrossesSTEP 2 (These are also F1 plants)

AaGg x AaGg

Dihybrid CrossesSTEP 3 Aa Gg

AaGg

a GA ggAa G

AGaGAgag

Dihybrid CrossesSTEP 4

AG Ag aG ag

AG

Ag

aG

ag

AAGG AAGg AaGG AaGg

AAGg

AaGG

AaGg

AAgg AaGg

AaGg

Aagg

Aagg

aaGG

aaGg

aaGg

aagg

Aagg

Dihybrid CrossesSTEP 5

AG Ag aG ag

AG

Ag

aG

ag

AAGG AAGg AaGG AaGg

AAGg

AaGG

AaGg

AAgg AaGg

AaGg

Aagg

aaGG

aaGg

aaGg

aagg

Dihybrid Crosses

AAgg, Aagg=

AAGG, AAGg, AaGG, AaGg=

aaGG, aaGg=

aagg =

= 9/16 plants

= 3/16 plants

= 3/16 plants

= 1/16 plants