NOTES: Genetics Introduction

Introduction to

Mendelian
Genetics

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Gregor Mendel
(1822-1884)

Responsible
for the Laws
governing
Inheritance of
Traits

Gregor Johann Mendel

▪Austrian monk
▪Studied the
inheritance of
traits in pea plants
▪Developed the laws
of inheritance
▪Mendel's work was
not recognized until
the turn of the
20th century

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Gregor Johann Mendel

▪Between 1856 and
1863, Mendel
cultivated and tested
some 28,000 pea
plants
▪He found that the
plants' offspring
retained traits of the
parents
▪Called the “Father of
Genetics"

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Site of
Gregor
Mendel’s

experimental
garden in the

Czech

Republic

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▪Mendel stated that
physical traits are
inherited as “particles”
▪Mendel did not know
that the “particles” were
actually Chromosomes
& DNA

Particulate Inheritance

Genetic Terminology

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▪ Trait - any characteristic that can

be passed from parent to
offspring

▪ Heredity - passing of traits from

parent to offspring

▪ Genetics - study of heredity

Types of Genetic Crosses

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▪ Monohybrid cross - cross

involving a single trait
e.g. flower color

▪ Dihybrid cross - cross involving

two traits
e.g. flower color & plant height

Punnett Square

Used to help
solve genetics
problems

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Designer “Genes”

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▪ Alleles - two forms of a gene

(dominant & recessive)

▪ Dominant - stronger of two genes

expressed in the hybrid; represented
byacapital letter (R)

▪ Recessive - gene that shows up less

often in a cross; represented by a
lowercase letter (r)

More Terminology

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▪ Genotype - gene combination for

a trait(e.g. RR, Rr, rr)

▪ Phenotype - the physical feature

resulting from a genotype(e.g.
red, white)

Genotype & Phenotype in Flowers

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Genotype of alleles:
R= red flower
r= yellow flower

All genes occur in pairs, so 2
alleles affect a characteristic

Possible combinations are:
Genotypes RR

Rr

rr

Phenotypes RED RED YELLOW

Genotypes

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▪ Homozygousgenotype - gene

combination involving 2 dominant
or 2 recessive genes (e.g. RR or rr);
also calledpure

▪ Heterozygousgenotype - gene

combination of one dominant & one
recessive allele (e.g. Rr); also called
hybrid

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Genes and Environment Determine

Characteristics