Gregor MendelMonk and Scientist

Father of Genetics In 1843, at the age of 21, Gregor

Mendel entered the monastery .

Born in what is now known as the Czech Republic.

Researched heredity, experiments often involved garden pea plants.

Heredity - The transmission of characteristics from parent to offspring.

Known as the “Father of Genetics”.

Genetics - Is the branch of biology that focuses on heredity. The study of the structure and function of

chromosomes & genes.

A gene is a segment of DNA on a chromosome that controls a particular hereditary trait. Genes occur in pairs.

Each of two or more alternative forms of a gene is called an allele.

Mendel’s PeasHe chose garden pea plants because: Can be grown in a small area Produce lots of offspring In peas many traits appear in two forms (i.e. tall

or short, round or wrinkled, yellow or green.) The flower is the reproductive organ and the male

and female are both in the same flower. Thus able to self pollinate.

Mendel’s Peas

Mendel’s Pea plant experiment

Used pea plants to study traits such as: height, flower position, pod color, seed texture, seed color, flower color.

Grew plants that were “true-breed” (pure) for each trait.– True breed will always give the same trait generation

after generation if self pollinated. Self pollination - The transfer of pollen from one

flower to the same or other flowers on the same plant.

Mendel’s Pea plant experiment

Then cross pollinated pairs of plants that were true breeding for contrasting traits.

Called the P generation.– Example: cross green pod plant w/ yellow

pod plant.

Allowed offspring to mature. Called the F1 generation.

Recorded the number of each type of offspring produced.

Allowed flowers from F1 generation to self pollinate and collected the seeds.

These seeds grew into what is called the F2 generation.

Mendel’s Pea plant experiment

Mendel’s Experiments He experimentally

crosses different strains to develop hybrids.

He then crossed the hybrids and analyzed the results.

Description of traits Genotype – genetic makeup, or set of

alleles that an organism has.– Represented by the letters! (TT, Tt, tt)

Phenotype – organism’s appearance.– Visual! What it looks like.

Dominant Traits RULE Strong Hereditary traits cover weak

traits.– Trait – genetically determined variant of a

characteristic. (color, height) Mendal called stronger traits

– Dominant - masks or dominates other traits.

– capital letters (T) Mendal called weaker traits

– Recessive – trait that does not appear when dominant trait is present.

– lower case letters (t)

Heterozygous – two alleles in a gene are different. (Tt)

Homozygous – two alleles in a gene are the same (TT, tt)

Punnett square – a diagram used to aid in predicting the probability of inherited traits in offspring.

Mendel’s ResultsMendel crossed purebred tall plants with purebred short plants and the first generation plants were all tall.

When these tall offspring were crossed the result was a ratio of 3 tall to 1 short.

Mendel's traits included:

a. Seed shape ---  Round (R) or Wrinkled (r)

b. Seed Color ---- Yellow (Y) or  Green (y)

c. Pod Shape --- Smooth (S) or wrinkled (s)

d. Pod Color ---  Green (G) or Yellow (g)

e. Seed Coat Color ---  Gray (G) or White (g)

f. Flower position --- Axial (A) or Terminal (a)

g. Plant Height --- Tall (T) or Short (t)

h. Flower color --- Purple (P) or white (p)

Mendel’s Observations Law of segregation – in the formation of

gametes, only one copy of each allele will be given to each sex cell.

A woman has the genotype Bb. the big B for Brown eyes, the little b for blue eyes.

Only one of them will wind up in each egg cell.

Mendel’s Observations

Law of independent assortment – each chromosome is selected independently of each other during formation of gametes.

A woman’s trait for brown eyes won't determine her hair color, because these traits assort into gametes independently.