3/10/15

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Ch 14: Mendel & the Gene Idea

Optional but fun book

Johann Gregor Mendel the “Father of Genetics”

(Read his original paper at mendelweb.org)

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2

Methods of controlling pea genetics

Hand pollination (& emasculation)

Carl Correns Hugo de Vries Erich von Tschermak

The rediscoverers

Mendel’s discoveries and insights Q: Do alleles blend (& stay blended)? Q: Are traits/characters (things we now call genes) only found in one version?

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Q: Do both parents contribute equally to their offspring?

Q: How do these alleles, if different, interact?

dominant recessive

Q: Is there an equal chance of getting either of the 2 alleles a parent has? Mendel’s Law of Segregation

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4

Do genes sort independently (travel separately) of 1 another or sort together? Y - Mendel’s Law of Independent Assortment N - genetic linkage

Genetic terminology

Monohybrid cross: following one trait Punnett square ->

(parental)

(1st filial)

(2nd filial)

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5

Test cross (when you don’t know what the genotype is)

Dihybrid cross: following two traits simultaneously

Using rules of probability Multiplication/product rule

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Multiplication/product rule

Trihybrid cross PpYyRr x Ppyyrr Q: What fraction of the offspring from this cross will exhibit at least 2 recessives? Use the multiplication/product rule to find the combined probabilities for the allele pairs: Then use the addition/sum rule to combine these mutually exclusive events.

What Mendel didn’t know:

Incomplete dominance

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7

What Mendel didn’t know: Codominance Multiple Alleles

Just FYI (optional): Glycolipids and glycoproteins play a major role in signaling cell characteristics to the outside world. For example, A, B, O blood groups result from having different carbohydrate chains on the cell surface glycolipids and glycoproteins of red blood cells and other types of cells. Everyone has glycolipids and glycoproteins which have a particular type of carbohydrate chain which signals type O. People with type A also have glycolipids and glycoproteins which have an carbohydrate called N-acetylgalactosamine added to the basic type O carbohydrate chain. People with type B have an added galactose. Those with type AB have some glycolipids and glycoproteins with N-acetylgalactosamine added and other glycolipids and glycoproteins with galactose added.

http://www.bio.miami.edu/tom/courses/bil255/bil255goods/12_membrane.html

What Mendel didn’t know: Pleiotropic traits

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What Mendel didn’t know: Epistasis

B = black

b = brown (chocolate)

E = color produced

e = no color

What Mendel didn’t know: Polygenic traits

e.g.: skin color

What Mendel didn’t know: Environmental effects

e.g.: hydrangea color (soil pH)

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Human pedigree analysis

Recessively inherited traits: albinism

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Tay-Sachs

buildup of brain lipids

Sickle cell anemia

Dr. Michael Ain

(ped-ortho)

Dominantly inherited traits: achondroplasia

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Polydactyly

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Imaging: ultrasound

DNA testing: PGD (embryo) fetal cells in mother’s blood

Phenylketonuria

Neonatal testing

A few interesting human genetics stories http://mosaicscience.com/story/man-golden-blood http://www.archives.com/genealogy/family-heritage-blue-people.html