Transcript Inheritance What Were The Two Ideas Lacking in Darwin`s Natural

Darwin’s Explanation for Evolution
• Not created equal (variations in phenotypes &
genotypes)
• Limited stuff (finite resources)
• Produce more offspring than finite resources
can support
• Struggle for existence
• Favorable vs. unfavorable traits (relative to the
environment)
• Inheritance
What Were The Two Ideas Lacking
in Darwin’s Natural Selection Theory?
• Source of variation
• How traits are inherited
Who Solved These Problems?
• How traits are inherited: MENDEL
– Two “Particle”s for every trait; Segregation;
Independent Assortment; Dominance &
Recessive
• Ultimate source of variations: DeVRIES
– Mutations
Tao of Mendel
• Inheritance of each trait determined by
”particles" (alleles or genes) that pass on to
descendents unchanged
• An individual inherits one allele from each
parent for each trait
• A trait may not show up in an individual but
can still be passed on to next generation.
Tao of Mendel
• Genes may be one of several types (ALLELES)
– Earlobe attachment in humans: F (Free earlobe) or f
(attached earlobe)
– Blood type: A, B or o
– Lutheran saliva protein: L1, L2, . . . L22
• Some alleles are DOMINANT: F (free earlobes)
• Some alleles are recessive: f (attached earlobes)
• and some are CO-DOMINANT: A and B blood
alleles
Tao of Mendel
Law of Segregation
• For every trait an organism has, it has two
“particles” (aka alleles) for that trait: one
from one parent, the other from the other
parent
2 alleles per trait
• During gamete formation, the paired alleles
SEGREGATE, with one allele going into one
sex cell and the other allele going into a
different sex cell
Tao of Mendel
Law of Independent Assortment
• Distribution into sex cells of alleles for one
trait (e.g. earlobe attachment) is unrelated to
how alleles for a different trait (e.g. blood
type) segregate and are distributed into the
sex cells.
– AB, Rr: a person’s genotype
– Same person’s sex cell components:
• AR, Ar, BR, Br
Note: this law only valid IF alleles for one trait are on a different
chromosome (i.e., DNA strand)