GREGOR MENDEL“FATHER OF GENETICS”

Mendelian GeneticsAugustinian Monk at Brno Monastery in Austria (now Czech Republic)

Not a great teacher but well trained in math, statistics, probability, physics, and interested in plants and heredity.

While assigned to teach, he was also assigned to tend the gardens and grow vegetables for the monks to eat.

Mountains with short, cool growing season pea (Pisum sativum) was an ideal crop plant.

History in 1860 :

• Discovered Genes as Particles of Inheritance

• Discovered Patterns of Inheritance

• Discovered Genes Come from Both ParentsEgg + Sperm = Zygote

Nature vs Nurture

Sperm means Seed (Homunculus)

• Discovered One Form of Gene (Allele) Dominant to Another

• Discovered Recessive Allele Expressed in Absence of Dominant Allele

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Mendel worked with peas (Pisum sativum)

• Good choice for environment of monastery

• He got good varieties for testing

• Pureline

• Scientists of 1860s could not understand math

• His work lost in journals for 50 years!

• Rediscovered in 1900s independently by 3 scientists “re-discovered" in 1900, Hugo de Vries, Carl Correns, and Erich von Tschermak, and were initially very controversial. The “re-discovery” were combined with chromosome theory of inheritance by Thomas Hunt Morgan in 1915, they became the core of classical genetics.

TallP Dwarfx

F1All Tall

Phenotype

Genotype

One Example of Mendel’s Work

Clearly Tall is Inherited…What happened to Dwarf?

F1 x F1 = F2

F23/4 Tall1/4 DwarfDwarf is not missing…just masked as “recessive” in a diploid state… there IS a female contribution.

1. Tall is dominant to Dwarf

2. Use D/d rather than T/t for symbolic logic

DD dd

Dd

HomozygousDominant

HomozygousRecessive

Heterozygous

Dwarfdd

TallDd

d

TallDd

TallDD

D

dDPunnett Square:

possible gametes

possible gametes

Unknown Tall Dwarfx

Mendel as a Scientist

dd

TallDd

TallDd

D

TallDd

TallDd

D

dd

possible gametes

possible gametes

F1 x F1 = F2F2

Dwarfdd

TallDd

d

TallDd

TallDD

D

dDPunnett Square:

possible gametes

possible gametes

Test Cross:

If Unknown is DD:

Dwarfdd

Dwarfdd

d

TallDd

TallDd

D

dd

possible gametes

possible gametesIf Unknown is Dd:

Test Progeny All Tall

Test Progeny Half Tall Half Dwarf

1/3 of F2 Tall are DD

2/3 of F2 Tall are Dd

GreenP Yellowx

F1All Yellow

Phenotype

Another Example of Mendel’s Work

Clearly Yellow is Inherited…What happened to Green?

F1 x F1 = F2

F2 3/4 Yellow1/4 GreenGreen is not missing…just masked as “recessive” in diploid state

1. Yellow is dominant to Green

2. Use G/g rather than Y/y for symbolic logic

gg GG

Gg

GenotypeHomozygous

RecessiveHomozygous

Dominant

Heterozygous

Greengg

YellowGg

g

YellowGg

YellowGG

G

gGPunnett Square:

possible gametes

possible gametes NEVER use G/Y or g/y

Unknown Yellow Greenx

Mendel as a Scientist

gg

YellowGg

YellowGg

G

YellowGg

YellowGg

G

gg

possible gametes

possible gametes

F1 x F1 = F2F2

Greengg

YellowGg

g

YellowGg

YellowGG

G

gGPunnett Square:

possible gametes

possible gametes

Test Cross:

If Unknown is GG:

Greengg

Greengg

g

YellowGg

YellowGg

G

gg

possible gametes

possible gametesIf Unknown is Gg:

Test Progeny All Yellow

Test Progeny Half Yellow

Half Green

1/3 of F2 Yellow are GG

2/3 of F2 Yellow are Gg

Law of Segregation (The "First Law")

The Law of Segregation states that when any individual produces gametes, the copies of a gene separate, so that each gamete receives only one copy. A gamete will receive one allele or the other.

The direct proof of this was later found when the process of meiosis came to be known. In meiosis the paternal and maternal chromosomes get separated and the alleles with the characters are segregated into two different

Law of Independent Assortment (The "Second Law")

The Law of Independent Assortment, also known as "Inheritance Law", states that alleles of different genes assort independently of one another during gamete formation. While Mendel's experiments with mixing one trait always resulted in a 3:1 ratio between dominant and recessive phenotypes, his experiments with mixing two traits (dihybrid cross) showed 9:3:3:1 ratios . But the 9:3:3:1 table shows that each of the two genes are independently inherited with a 3:1 ratio.

Mendel was success with his experiment because he was lucky, the genes were not located in the same chromosome. What would happen if the genes were in the same chromosome?

Will be continued next week

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