Grade 11 University Biology – Unit 2 Genetics
Mendel’s Laws
Law of Segregation
 This principle states that the alleles for a trait separate when gametes are formed. These allele pairs
are then randomly united at fertilization.
 An allele is an alternative form of a gene (one member of a pair) that is located at a specific
position on a specific chromosome. These “DNA codings” determine distinct traits that can be
passed on from parents to offspring.
Law of Independent Assortment
 During gamete formation the segregation of the alleles of one pair is independent of the segregation
of the alleles of another pair.

What does this mean?
 To simplify, look at only two homogolous pairs of chromosomes (…not the 23 pairs common
in the human karoytype).
 Chromosomes can contain a dominant A or recessive a trait (i.e., a gene).
 During Interphase, the cell synthesizes more DNA and duplicates the chromosome. Thus,
we now have a gene AA or aa side-by-side on the sister chromatids.
 Another chromosome has dominant B or recessive b. After duplication, we have BB or bb.
 WITHOUT independent assortment, A and B would always sort together in the same cell.
Likewise, a and b would always sort together in the same cell. That is, one cell after division
is A and B, while the other cell is a and b.
 WITH independent assortment, the combinations could be (1) A and B, (2) a and B, (3) a and
b and (4) A and b. With his pea plant experiment, Mendel discovered independent
assortment. This is Mendel’s Second Law.
How is this possible? Crap, a problem….How do I solve it? Step 1 (…No. Do not give up or ask…)
is: “What do I know?”
 Phases of Meiosis. If I know the eight phases, where could Independent Assortment occur?
Prophase I is crossing over. So, it likely is not there. Why, the chromosomes have not
sorted entirely; rather, the homogolous pairs are “mixing” and exchanging parts of their
genetic information
To watch Independent Assortment, go to
http://bcs.whfreeman.com/thelifewire/content/chp10/1002001.html