Intro to Mendelian Genetics

What is genetics?

The science of heredity

What is genetics? The science of heredity How traits are passed to offspring

What is genetics? The science of heredity How traits are passed to offspring Gene – A section of DNA that codes for a specific protein Gene – The unit of heredity

Gregor Mendel Born in Czech Republic, settled in Austria In 1842, entered monastery at age of 21, tended to a garden of peas

Gregor Mendel In 1851 he went to the U. of Vienna to study science and statistics Returned to monastery to teach high school and study heredity through his peas. (OMG, this is like sooooo exciting! I can’t wait to hear what happens next. Seriously, I’m about to pea my pants!)

Current thoughts in 1850 Blended inheritance – Offspring are intermediate in appearance

Current thoughts in 1850 Blended inheritance – Offspring are intermediate in appearance Ex: skin tone in humans

Current thoughts in 1850 Blended inheritance – Offspring are intermediate in appearance Ex: skin tone in humans – Ink in water 1.Combined 2.Inseparable

Current thoughts in 1850 Blended inheritance – (Incorrect) – Offspring are intermediate in appearance Ex: skin tone in humans – Ink in water 1.Combined 2.Inseparable

Used peas to study inheritance Why peas?

Used peas to study inheritance Each plant has various traits to study Cheap Simple to grow Seeds easily stored for later study Short generation time Self-pollinators (flowers have male and female parts) Cloned flowers can serve as control group

Statistics was the key! Used math to explain living systems (one of the first to do so) Published his work in 1866, but mostly ignored because he didn’t know the mechanism of heredity (DNA)

Mendel’s 1 st Experiment Studied 7 characteristics with two traits each Plant height, flower color, etc.

Mendel’s 1 st Experiment Studied 7 characteristics with two traits each Plant height, flower color, etc. – Focus on plant height: Tall or short:

Mendel’s 1 st Experiment Studied 7 characteristics with two traits each Plant height, flower color, etc. – Focus on plant height: Tall or short: T or

Mendel’s 1 st Experiment Studied 7 characteristics with two traits each Plant height, flower color, etc. – Focus on plant height: Tall or short: T or t

Mendel’s 1 st Experiment Studied 7 characteristics with two traits each Plant height, flower color, etc. – Focus on plant height: Tall or short: T or t – All studied traits were heritable, not environmental – Used purebreds (clones) achieved through many generations of self-pollination

Mendel’s 1 st Experiment Crossed a purebred tall with a purebred short – Paternal: T x t – Filial (F 1 ): ??

Mendel’s 1 st Experiment Crossed a purebred tall with a purebred short – Paternal: T x t – Filial (F 1 ): 100% tall (T) Same result with all 7 characteristics Trait that showed up in F 1 generation = dominant Disappearing trait = recessive

Mendel’s 1 st Experiment Where did the recessive trait go?

Mendel’s 1 st Experiment Where did the recessive trait go? To find out, he self-pollinated the F 1 plants – F 1 : T x T

Mendel’s 1 st Experiment Where did the recessive trait go? To find out, he self-pollinated the F 1 plants – F 1 : T x T – F 2 : 75% T, 25% t

Law of segregation Law of segregation : Traits are discrete units that occur in pairs and retain their integrity

Law of segregation Law of segregation : Traits are discrete units that occur in pairs and retain their integrity Characteristics are now called genes (one or more genes lead to the appearance of a certain characteristic)

Mendelian Genetics Continued… The location (address) of a gene on a chromosome is called the locus Genes have alternate versions called alleles ex: locus for flower color

Genotype: The collection of alleles in an individual – Represented by letters

Genotype: The collection of alleles in an individual – Represented by letters P: TT x tt (T = dominant allele –> only one needed for expression) F 1:

Phenotype:

Phenotype: Physical expression of genotype + environment – Represented by

Phenotype: Physical expression of genotype + environment – Represented by descriptive words F 2 : Tt x Tt Genotypes: Phenotypes:

Genotype terminology TT = Homozygous dominant or purebred dominant Tt = tt =

Genotype terminology TT = Homozygous dominant or purebred dominant Tt = Heterozygous dominant or hybrid tt = Homozygous recessive or purebred recessive

How can you tell the difference between a homozygous dominant (DD) and a heterozygous dominant (Dd)?

Test Cross: Breed the unknown with a homozygous recessive to bring out any hidden recessive traits

Law #1: Law of segregation Law #2: Law of independent assortment – Genes located at different loci (locations) on the same chromosome assort (cross-over) independently of each other

Law #1: Law of segregation Law #2: Law of independent assortment – Genes located at different loci (locations) on the same chromosome assort (cross-over) independently of each other (Whether one gene crosses over during meiosis has no influence over whether another gene on the same chromosome crosses over)