Basic Mendelian Genetics What lovely things we pass onto our children!

Genetic Vocabulary Genetics: Heredity: Trait:

Genetic Vocabulary Gene: –DNA  RNA  Protein  How we look Allele: –Example of a gene: –Example of alleles:

History of Genetics Traditional Beliefs: Blending Traits –Definition: –Example:

Gregor Mendel Background Information about Mendel:

Mendel’s Experiments What traits did he study? How did he disprove the concept of blending traits?

Mendel’s Laws Law 1: Law of Unit Characteristics –Inherited traits are controlled by “factors” which occur in “pairs”.  Factors = __________  Pairs = __________ Law 2: Law of Dominance –One allele hides another allele in a heterozygote  Stronger allele = _____________  Weaker allele = _____________

A Quick Aside…Vocabulary Terms Genotype: The genetic makeup of an organism –The two alleles received from the parents Ex. Pure-bred white cow has a genotype of WW Phenotype: The resulting appearance because of the genotype –Ex. WW codes for a white phenotype

More Vocabulary Terms Homozygous – When a genotype has two of the same alleles –Ex. WW or ww Heterozygous – When a genotype has two different alleles –Ex. Ww

Mendel’s Laws Continued Law 3: Law of Segregation –Alleles of a gene are separated during gamete formation  Each cell only gets 1 allele for a gene A a Bb

Mendel’s Laws Continued Law 4: Law of Independent Assortment of Alleles –When alleles separate during meiosis, they do so independently of alleles of other genes  Placement of alleles is random  Not influenced by other genes A A B B a a b b

Life Beyond the Law of Dominance Not all traits are governed by the law of dominance Incomplete Dominance –Neither allele is completely dominant over the other in the heterozygote  Blending/Mixing Ex) Snap dragons WW – White flowers RR – Red Flowers RW – Pink Flowers

Incomplete Dominance

A Human Example: Eyebrow positioning

Life Beyond the Law of Dominance Codominance –Both genes express themselves FULLY at the same time Example: Roan cattle RR = Red Hair WW = White Hair RW = Roan (both red + white) Example 2: Blood type in humans (AB)

Codominance in Cows

Life Beyond the Law of Dominance Multiple Alleles –A gene possessing more than 2 alleles Example: Blood types  Blood types differ in antigens found on RBC’s AA – Homozygous AType A BB – Homozygous BType B OO – Homozygous OType O AO – Heterozygous AType A BO – Heterozygous BType B AB – Heterozygous AB Type AB

Life Beyond the Law of Dominance Polygenic Inheritance –When a trait is controlled by more than 2 genes Example: Eye color (3 genes)  Amount of pigment  Location of pigment  Tone of pigment

A Review of Mendelian Genetics 1)Neither allele is dominanta) Complete Dominance 2)More than 2 allelesb) Codominance 3)Both alleles are dominantc) Incomplete dominance 4)Many genes code for 1 traitd) Multiple alleles 5)One allele is dominante) Polygenic inheritance

Two more types of Genetic Interactions Epistasis – An allele of one gene masks the expression of an allele of a second gene Example: Red hair in humans B  Brown hair b  Blonde hair R  Normal color hair (brown or blonde) r  Red hair (Masks other gene)

Epistasis Continued Hair color –Brown hair  B_R_ –Blonde hair  bbR_ –Red hair  B_rr OR bbrr

Another example of Epistasis Labrador Retrievers –3 Coat Colors – Black, Chocolate (Brown), and Yellow Black (B) is dominant over chocolate (b) Yellow coat color comes into play at a second gene (E locus) Normal coat color (E) is dominant over yellow (e)

Epistasis in Labrador Retrievers Black Lab: B_ E_ Chocolate Lab: bb E_ Yellow Lab: _ _ ee The recessive phenotype at the E locus masks the coat color at the B locus

Another example of Epistasis Mouse coat color B  BlackC  Color is expressed b  Brownc  Color is hidden Possible combinations –Black mouse = B_C_ –Brown mouse = bbC_ –White mouse = B_cc OR bbcc

Pleiotropy – One gene affects more than one phenotype Example: Mouse coat color and death Alleles: Y  Yellow coat y  Gray coat Two more types of Genetic Interactions

Pleiotropy continued Possible Phenotypes –Yy  Yellow Mouse –yy  Gray Mouse –YY  Dead Mouse When the two dominant alleles come together the dose is lethal to the mouse Pleiotropic trait – codes for coat color and death

Pleiotropy Visualized Yy

Another Pleiotropy Example Human Example: Albinism One gene codes for multiple traits –White hair, no pigment in eyes, pale skin Labrador Retriever Example –The B gene codes for coat color in labs –It also codes for pigmentation of eyes, lips, and nose