The Infamous BIONOTES
With your hosts:
Dr. Robert M. Pirtle - a.k.a. Mr. Middle-aged Mutant Ninja Pirtle
Covering Meiosis, Mendelian Genetics, and Population Genetics
Dr. Robert Benjamin - a.k.a. Mr. "But anyway
Covering Molecular Genetics and Sex-linked/Genetic Diseases
Typed by H.H. (of course - you think any one else is this CRAZY?)
(BTW - the Meiosis packet (w/ scans and all) is located somewhere else, not here
its too big to put on one disk
Same principles still apply. You read these and fail, cant blame me. These notes
are for me, not you
(Repeat after me, "These notes are not for me!!" -
Scream it at the top of your lungs. Now dance around like a gorilla until everyone stares
at you. Now everyone knows that you are reading these notes). I dont even know if I
can release these - I havent done much. But the test should be pretty easy,
so you probably wont need these (but remember
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Mendelian Genetics and the Gene Idea
Reading: Chapter 13, p. 238-252
Also: Work problems 1-15, and 19 on p. 259-261. The answers are in the back of the book
in Appendix A-1.
Genetics can be defined as the study of genes through their VARIATION.
The term character refers to a heritable feature (such as flower color) that
varies among individuals.
A trait is a variant for a character (such as purple of white flowers)
A gene is the basic functional unit of heredity.
EARLY IDEAS ABOUT HEREDITY: The road to MENDEL
Early genetic concepts before the 20th century: two major ideas
Heredity occurs within species: People like the Greeks thought you could
put a man and a bull together and get a minotaur. So they figured that variation and
heredity occurred within a single species.
Traits are transmitted directly: Greeks (the great thinkers once again) thought
that BODY PARTS were transmitted via sex cells. When the body parts formed together, then
you had a human. This was what people thought in the 19th century also,. Even
in 1868, Darwin said the cells and tissues excrete microscopic granules or
"gemmules" that are passed along to the offspring. Similar theories began to pop
up - ex. The example of mixing paint - somebody tall and somebody short would have medium
If no variation enters from outside species, and if variation within species is blended
with each generation
then over a period of time, all members of species would look exactly alike and would
result in little species variation. (Look in the book at the picture of the cover of Time
German botanist Josef Koelreuter experiments in 1760.
For the 1st time, he successfully hybridized tobacco plants.
Hybridized offspring appeared different from either parent - the traits did NOT blend.
Crosses of those hybrids resulted in even FURTHER variation
Offspring either resembled parents or grandparents.
He discovered that parental traits are NOT blended.
Traits masked for a generation, reappeared in next - concept of dominance.
Modern geneticist would say that alternative forms segregating among
offspring (or distributing themselves among the offspring)
T.A. Knight experiments in 1790s in England - a gentleman farmer
Crossed true breeding (varieties that were uniform from one generation to the
next) peas, purple and white flowers. Used Pisum sativum , the garden pea.
All hybrid offspring of first cross had purple flowers (This is the F1 or
FIRST FILIAL generation)
Offspring of the next cross had both color flowers (This is the F2 or SECOND
Purple flowers predominated over white flowers.
Just as in Koelreuters work with tobacco plants, a trait from one of the parents
was hidden in one generation, only to appear in the next.
So what? - summary of pre-Mendel genetics
Some forms of inherited traits masked others - this is the concept of dominance.
Forms of a trait segregate among offspring of a cross.
Some forms of a trait represented more frequently than other alternatives - different allele
GENETICS AFTER MENDEL
Gregor Mendel - born in 1822 (lots of other historic crap - you wont need for
1900. Birth of modern genetics. Rediscovery of Mendels work by three separately
working independent scientists.
Carl Correns - German
Hugo deVries - Dutch
Erich von Tschermak - Austrian
MENDEL AND THE GARDEN PEA (everybody knows this crap, right?)
For the first time, unlike others, Mendel wrote down NUMBERS (quantitative analysis)
He used the garden pea that was familiar to everyone.
See figure 13.1 on page 239.
Expected segregation of traits among offspring, from early studies.
He looked at many true-breeding traits (about 32) but only studied seven (i.e.
smooth vs. Wrinkled seeds)
See Table 13.1 on page 241
Peas were COOL - small plants that took little time to grow. Short generation time
and several generations in 1 year.
Each flower had self-fertilizing male and female parts in the same flower.
Experimental crosses possible:
See Figure 13.1
Remove the pollen from one plant, put it somewhere else
Combines traits from TWO DIFFERENT PLANTS
MENDELS EXPERTIMENTAL DESIGN
Allowed several generation of fertilization (or "self") to assure true
breeding in species.
Progeny produced only a SINGLE FORM OF A TRAIT.
Assured forms were transmitted regularly, regardless of generation #
Conducted crosses between alternate forms of a trait and tracked the heritable
characters for three generations.
See Figure 13.2 on page 240
Removed male parts from a flower with trait A1 (e.g. white flower)
Fertilized with pollen from plant with trait A2 (e.g. purple flower)
Performed reciprocal cross with A1 pollen on A2 flower.
Allowed self-fertilization of hybrids to self-pollinate for several generations
Allowed segregation of alternate forms of traits among progeny.
Counted # of offspring of each type per generation
Categorization and Quantification of results most important to studies!!
Fun with GENETICS VOCABULARY!!!
Monohybrid Cross - cross involving alternate (or allele) expression of a single
Genotype - the genetic "makeup" of an individual (The Mendelian
genotypic ration is 1:2:1)
Phenotype - the physical, chemical, behavioral, etc. expression of the genotype.
(i.e. You have RR, and therefore you are a RETARD!) (The Mendelian phenotypic ratio is
Alleles - alternate forms of expression for a given trait conventionally
designated by upper and lower case letters (i.e. "A" and "a")
Homozygous - individuals possessing the same alleles for a trait, i.e. AA or aa
Heterozygous - individuals possessing two alternate alleles for a trait (i.e.
Dominant - traits which are expressed when a single allele for that trait is
present i.e. - T__ - results in expression of a tall phenotype in garden peas (whoever
heard of tall garden peas?)
Recessive - a trait which is expressed only when a given allele occurs in the
homozygous condition, i.e. tt is the genotype for short pea plants
P1 - first parents, usually true-breeding
F1 - first group of offspring, or first "filial"
generation, usually heterozygotes expressing the dominant trait
P2 - second parents, comprised of crossing the F1
generation among themselves
F2 - second group of offspring, usually expressing a variety of
PUNNET SQUARES SUCK!!!! IF YOU DONT KNOW HOW TO DO THIS, TOUGH!!!!