Lecture Outline for Friday September 15, 2000
Cellular Basis of Life
Reading reference: BCC Chapter 2, 3,4
On-line resources:
Textbook
Companion Web Site
The Biology Place (login required)
Scientists of the Day: Rosalind
Franklin,
Rosalind Franklin was a chemist and who made a significant contribution
to our understanding of the structure of DNA, she found and that the sugar
phosphate backbone makes the rails of the DNA ladder and that the DNA molecule
was helical. Unfortunately, her images were shared, without her permission,
with Watson and Crick who eventually went on to win the Nobel Prize for
elucidating the structure of DNA. Franklin died of cancer before
her contributions were recognized.
Barbara McClintockA notable geneticist, McClintock was the first to show that some genes are able to move from chromosome to chromosomes. The evidence of these "jumping genes" will shortly be visible in your local supermarket in the multicolored "Indian" or Halloween corn. She was also the first women to win an unshared Nobel prize.
Today's lecture: Genes and Inheritance (note change: chapters 8-9 not 8-11)
All cells reproduce
Reproduction requires the copying and distribution of genetic material
to the descendant cells.
Chromosomes are made of large pieces of DNA. Genes are made of
DNA, so.......
In prokaryotic cells there is one large circular chromosome.
Eukaryotic cells have more genes, therefore more DNA and more, linear,
chromosomes.
In cell division, the DNA is copied and as the cell splits (fission
or mitosis) each descendant gets one copy of every chromosome.
In many eukaryotes there are two sets of nearly identical chromosomes.
(Diploid)
Some organisms, ourselves included, produce cells that contain 1/2
of the genetic material or one set of chromosomes (Haploid).
The process that accomplishes this is called meiosis.
In humans, eggs or sperm are produced after meosis depending on the
individual.
Human males produce 1012 to 1013 sperm in a lifeterm,
females mature only about 400 eggs.
When egg is fertilized by sperm, the chromosome sets combine, this
ensures that the species will have the same number of chromosomes every
generation.
In humans there are 46 chromosomes or two sets of 23, one pair is called
the sex chromosomes.
XX, XY are the most common pairing of sex chromosomes.
Human fathers contribute X or Y, human mothers one or the other X to
their offspring.
Accidents during meiosis can alter chromosome structure or number.
Abnormalities of human sex chromosomes exist (we will talk about p.
149, Turner and Klinefelter's syndrome)
Genes on chromosomes determine (in large part) what an organism looks
like and some of how it behaves.
The appearance of any one trait may be determined by a single gene,
or by multiple genes.
Each gene has its partner (or allele) on a look alike chromosome of
the other sets.
The two gene partners are often not identical, but they can be.
Some genes may "dominate" their partner gene, others may be functionally
invisible or recessive, still other situations exist in which two or more
genes are active on the same trait at the same time.
The X and Y chromosomes carry genes. X's are larger and carry
more genes than Y's.
The genes on the Y chromosome have no partners on the X.
Genes on sex chromosomes are said to be sex linked.
Do sex chromosomes dictate gender?