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… it’s too big to put on one disk…)

Notes:

Same principles still apply. You read these and fail, can’t 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 don’t even know if I can release these - I haven’t done much. But the test should be pretty easy, though… so you probably won’t need these (but remember… I DO!!!)

------ cut here (HERE WE GO!) -----

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 20^th 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 19^th 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 tall children.

Resultant paradox

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 magazine)

German botanist Josef Koelreuter experiments in 1760.

For the 1^st 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 1790’s 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 FILIAL generation)

Purple flowers predominated over white flowers.

Just as in Koelreuter’s 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. (F₁ generation)

Forms of a trait segregate among offspring of a cross.

Some forms of a trait represented more frequently than other alternatives - different allele forms.

GENETICS AFTER MENDEL

Gregor Mendel - born in 1822 (lots of other historic crap - you won’t need for the test)

1900. Birth of modern genetics. Rediscovery of Mendel’s 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

MENDEL’S 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!!

Monohybrid Cross - cross involving alternate (or allele) expression of a single trait

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 3:1)

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. Aa)

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 phenotypes