Gregor Mendel
learned from Doppler (physicist) and Unger (botanist) to

1. apply math to explain nature

2. learn science through experimentation

3. begin questioning the causes of plant variation

Mendel's Terminology

1. Character = a heritable feature like flower color

2. Trait = a character variant

3. True-breeding = self-pollination (offspring are of same variety)

4. Hybridization = crossing of variants

What Mendel tested

1. flower color
2. flower position
3. seed color
4. seed shape
5. pod color
6. pod shape
7. stem length

Pathway from genotype to phenotype is the key to dominant traits in living organisms.

 e.g.,  round allele codes for an enzyme that produces starch  from sugar in the seed.

blending model .	v.	particular model
"means what it says"		"the idea of genes"

Why a seed has wrinkles:
The wrinkled allele codes for a defective form of this enzyme thus sugar accumulates, osmotic pressure brings in
 HOH causing it too swell (when the seed dries, it has wrinkles).

Incomplete Dominance

F1 hybrids are "between" characters.
Intermediate Phenotype
3rd phenotype results from heterozygotes having less pigment than homozygotes.

Complete Dominance

In this case, phenotypes of heterozygotes and homozygotes are indistinguishable.

Codominance

PHENOTYPES PRESENT TOGETHER
Both alleles separately appear in the organism (eg. the 3 different human blood groups M, N, MN are based on 2 specific molecules located on the surface of blood cells).

Parent Generation First Filial Generation Second Filial Generation

x self-pollination

A Pedigree traces dominant or recessive traits through a family tree, helping us understand the past and predict the future (example:Hapsburgsandhemophilia). see Genetic Disorders

Pleiotropy

CONVERSE OF POYGENIC INHERITENCE
It is the ability of a gene to affect an organism in many ways (eg sickle-cell anemia causes multiple symptoms).

Polygenic Inheritence

CONVERSE OF PLEIOTROPY
Human height and skin color are expressed through this because they vary along a continuum. Characters that vary along a continuum are called quantative (cumulative) characters because by adding up the alleles the effect is expressed in a single phenotypic character.

Epistasis

When a gene at one locus affects the phenotypic expression of a gene at a second locus
e.g., mice: black coat (B) color is dominant to brown (b)

To have brown mice, that gene must be homozygous ;however a second gene locus determines whether or not pigment will be deposited in the hair.

For the second gene, allele C allows either black or brown pigmentation depending on the Bb situation while allele c is white recessive BUT if the alleles are cc with no C then the coat is white regardless of the genotype at the Bb locus.

Multiple alleles

This is true for most genes (eg ABO blood groups:  A, B, and O refer to different  carbohydrates on the cell surface;  O is recessive to both A and B;  A and B are codominant; 6 genotypes produce the 4 phenotypes.  If foreign blood is mixed within the recipient, antibodies are  produced that bind to the foreign cells causing them to clump in a process called agglutination.)

The Environmental Impact on Phenotype

The phenotype range is the norm of reaction (but not always the case):

A genotype provides the code for a trait that varies depending on environmental influences.  Sometimes a gene codes for a specific phenotype (blood group); on the other hand, a person's blood count of red and white cells varies depending on the altitude of the home, levels of physical activity, and air pressure.  In general, norms of reaction are broadest for polygenic characters (behavior included).

Something multi-factorial has many factors, genetic and environmental, that influence phenotype.

Next: "Genetic Disorders."