ANT101H5 Lecture Notes - Lecture 3: Somatic Cell, Lactose Intolerance, Cell Nucleus
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Lecture 3 - Cell division and Genetic traits
January 16, 2013
Cell division: Mitosis and meiosis
Chromosomes are cellular structures, DNA wrapped around protein. They are only found
in the cell nuclei. We can only see them during the cell division phase under a light
microscope where they condense and thicken while getting ready to undergo cell
division. One DNA molecule is made up of 10's of 1000's of genes. It is like one big ball
of string which unwraps as one long string. It stores a lot of information. In the shape of a
oThere are 46 non identical chromosomes in somatic cells, since each pair comes from
a different parent. Each pair codes for the same trait, (ex. blood type or eye color), but
it won't be identical information. (Ex. one is coded for blue eyes while the other is
coded for brown eyes). It might also be same.
oIn gametes the 22 pairs are called autosomes, which code for the same trait, but are
non identical. The 23'd pair determines sex. Females have XX and males have XY
chromosomes. Have to have both pairs to get by, or organism won't survive, except
for sex chromosomes, in which you can have one. In these situations, the organism
survives and usually develops as a female.
Mitosis. Figure 3.9 and 3.11. Occurs in somatic cells. Every cell produces two identical
daughter cells with 46 chromosomes each. Produces new cells for organism to grow,
develop or repair itself.
Meiosis. Figure 3.10 and 3.11. Occurs in sex cells. One cell with 46 chromosomes
replicates and splits twice. The end product is four daughter cells which are all
genetically different from the parent cells. They have 23 chromosomes each, one from
each pair. Produces eggs and sperm cells. The process of meiosis creates diversity, since
it promotes genetic variation which evolution acts on. Sexually reproducing organisms
have an evolutionary advantage. Diversity is good because the organisms are better
resisted to disease.
During cell division, the chromosomes replicate. They are joined by a centromere.