Classical Genetics

Gregor Mendel

Pioneer of genetics.

Studied the garden pea plant.

Noticed the transmission of seven visible traits.

Traits:

Flower color 🡪 PURPLE or white

Stem Length 🡪 TALL or short

Flower Position 🡪 SIDE OF STEM or end of stem

Pod Color 🡪 GREEN or yellow

Pod Shape 🡪 INFLATEED or constricted

Seed Shape 🡪 ROUND or wrinkled

Seed Color 🡪 YELLOW or green

Gregor Mendel

Pea plant traits are expressed in one of two

forms.

Traits are now known as genes.

Genes have different forms called alleles.

Commonly these genes have a dominant trait

and a recessive trait.

Flower Color

Dominant Trait Purple

Recessive Trait White

Gregor Mendel

Mendel organized his research into generations.

P generation 🡪 parental generation the first cross

F1 generation 🡪 the offspring (progeny) of the P

generation (first filial generation)

F2 generation 🡪 the offspring (progeny) of the F1

generation (second filial generation)

The Principle of Dominance

Involves the interaction of traits.

Dominant traits overshadow recessive traits.

Traits originate from genes.

Genes have more than one form.

Each gene is made up of 2 alleles.

Each allele comes from either parent.

These alleles combine to make a genotype.

They interact to produce the physical trait of the

organism.

The Principle of Dominance

When two alleles combine they make up a genotype.

A genotype is the genetic code for the trait.

Possible Genotypes of Seed Shape

Round is Dominant to Wrinkled

Round 🡪 R

Wrinkled 🡪 r

RR 🡪 homozygous dominant genotype

Rr 🡪 heterozygous genotype

rr 🡪 homozygous recessive genotype

The Principle of Dominance

Alleles are inherited from individual parents to make up

a genotype.

RR and rr have no choice but to express both traits

they have inherited as a phenotype.

A phenotype is an observable trait.

RR = round seeds

rr = wrinkled seeds

Rr genotype expresses the principle of dominance.

Rr = round seeds

Mendel’s Principle of Segregation

Involves the separation

of alleles during meiosis.

When a plant with

homozygous round seeds

(RR) produces gametes,

each gamete will get a R

allele.

Gametes will have a

single copy (allele) of

each trait.

Mendel’s Principle of Segregation

RR genotype is a true breeding genotype because

all the gametes will contain one R allele.

rr genotype is a true breeding genotype because

all the gametes will contain one r allele.

Rr genotype is not a true breeding genotype

because all the gametes will not contain the same

allele (either R or r)

Gregor Mendel is known as the pioneer of genetics, focusing primarily on studying garden pea plants to understand heredity. He discovered the transmission of seven key traits, which have since been identified as genes, each coming in forms called alleles. Using the garden pea traits, Mendel found that dominant traits could overshadow recessive traits. He categorized his research into generations: the parental (P) generation, first filial (F1), and second filial (F2). Key principles include the Principle of Dominance and Segregation, highlighting how alleles interact and separate during reproduction, leading to observable traits (phenotypes) like seed shape, color, and more.