The work of Gregor Mendel

• Austrian monk• Father of Genetics• Previous views of

Inheritance– Blending

– Spermists

– Ovists

“Father of Genetics”

• Mendel performed breeding experiments with garden peas

• Found mathematical patterns of inheritance

• His work was not appreciated until 1900, 16 years after his death

Mendel’s work

• Why breed peas?• They were available in many varieties,

inexpensive, short life cycle, simple procedures, easy to grow.

• The use of plants also allowed strict control over the mating.

• He chose to study only characters that varied in an ‘either-or’ rather than a ‘more-or-less’ manner.

Tracking heritable characteristics

• Mendel tracked heritable characters for 3 generations.

• When F1 hybrids were allowed to self-pollinate a 3:1 ratio of the 2 varieties occurred in the F2 generation.

Interpreting Mendel’s Data

Parent Cross

F1 generation

F2 generation

Actual Ratio

Probability Ratio

Round x wrinkled

100% round 5,474 round 1,850 wrink.

2.96:1 3:1

Yellow x green pea

100% yellow

6,022 yell

2,001 green

3.01:1 3:1

Long x short stem

100% long stem

787 long

277 short

2.84:1 3:1

Mendel’s Observations

• “dominant” vs “recessive”

• Before “genes” and “meiosis” was thought of, Mendel theorized that “inheritance factors”…– are in the pollen and ova of peas as alternate

forms for different traits.– occur in pairs, (equal contribution from both

parents)– separate during gamete formation and pair up

again at fertilization

Mendel’s Law of Segregation

• Each hereditary characteristic is controlled by two factors (alleles) that separate and pass into reproductive cells (gametes).

Mendel’s Law of Independent Assortment

• Pairs of inheritance factors (alleles) segregate independently of each other when sex cells (gametes) are formed.

Mendelian Inheritance in Humansdominant recessive

• Tongue Roller (T)• Free Earlobes (F)• Dimples (D)• Widow’s Peak (P)

• Can’t roll tongue (t)• Attached lobes (f)• No dimples (d)• Straight hairline (w)

Genetics and Probability

See handout and discuss… Coin flipping Card picking Grab colored marbles

Some Vital Vocab.

• Genetics

• Gene vs Chromosome

• Alleles

• Dominant vs Recessive

Some Vital Vocab.

• Genotype vs Phenotype

• Homozygous vs Heterozygous

• Diploid vs Haploid

• Mitosis vs Meiosis

• Zygote

Problem Solving from Mendelian Genetics

• Consider inheritance patterns for – Cystic fibrosis– Huntington’s disease– Hemophelia– Colorblindness pedigree

Exceptions to Complete Dominance

• Polygenic Traits

• Intermediate Expression (aka incomplete dominance)

• Multiple Alleles

• Several described at this link!