BSC 219

08/28/12

Mendel

Fundamental ideas

Time to move on

Worked with pea plants

Model systems

Large # of offspring

Easy to work with

Observations easy

Limited to what he could see with his eyes

True breeding lines

No variation from parents with respect to specific trait or traits

Had two true breeding lines for each trait.

When he crossed one of each line he got offspring that all resembled one parent.

Called F1.

When F1s crossed got 3:1 ratio

Dominant and recessive traits

Mechanism

Meiosis

Law of Independent Segregation

Parent has two alleles; one into each gamete

Alleles from different parents combine upon fertilization

Can predict outcomes of crosses

Punnett square

Look at possible gamets then do crosses

Genotype vs Phenotype

Dominant phenotype can be either homozygous or heterozygous

Recessive phenotype can only be homozygous genotype

Test cross can be used to determine which genotype a dominant phenotype has

Cross with recessive mate

Different ratios among offspring

Incomplete dominance

Heterozygotes have intermediate phenotype

Eggplant

Problem with dominance as we’ve advanced

Depends on level of observation

Dihybrid crosses-looking at two traits at one time

Law of independent assortment

Inheritance pattern of one trait does not affect the other

Traits assort by independent events

True with Mendel’s work, but only true if encoded by alleles on separate chromosomes