Introduction

to Genetics

1822 - 1889 Austrian Monk

Gregor Mendel

1856 - 1865 Mendel’s Garden at

the Monastery

experiments

with pea plants

Living organisms inherit characteristics from their _____________

Mendel is considered the Father of _______________ - the

study of Heredity

parents

Genetics

Fertilization - the combining of a sperm with an egg

the result is called a zygote

Fertilization

Male and female reproductive cells join

Sex Cells (Gametes)

egg (ovum - animals) (ovule –

plants)

sperm (pollen – plants)

Fertilization by Pollination

Pea plants self-pollinate – the pollen of a plant

can form a zygote with the egg of the same plant

Mendel used cross-pollination – the pollen from

the stamen of one plant was transferred to the

egg in the pistil of a different plant using a

paintbrush

True-breeding means that all offspring will have the form of the

trait that the parents have.

Before starting his experiments, Mendel wanted to make

sure the original parents were “true-breeding” or “pure” for

the trait being studied.

If these parents are “pure” for seed color:

all these offspring will have

yellow seeds

all these offspring will have

green seeds

but, his first experiments studied only one trait at a time.

Mendel studied 7 different traits of the common garden pea plant

smooth vs. wrinkled seeds

green vs. yellow seeds

smooth vs. wrinkled seed pods

green vs. yellow seed pods

purple vs. white flowers

axial vs. terminal flower position

tall vs. short plants

Trait – a specific _____________ characteristic

Each trait had ________ different forms (round or wrinkled shaped)

inherited

two

Mendel’s First Crosses P generation = original parents

F1 generation = first generation = 1st “Filial” (means sons

or daughters)

All offspring (F1) were hybrids, each showing

characteristics of only one parent

_________ - offspring between parents different for a certain trait Hybrid

Mendel’s Conclusions

1 1. Principal of Unit Factors - offspring receive ___ unit factor

from each parent for a trait

2. Principal of ____________- some factors are dominant (always

appear) and some are recessive (masked out by the dominant

factor)

Dominance

What We Know Today of Mendel’s Conclusions

genes Mendel’s Factors were _________ located on chromosomes

factor

Chromosome

Gene

alleles Different

An organism with a dominant allele will exhibit that form of the

trait

An organism with a recessive allele will exhibit it only if a

dominant allele is ________ present not

Mendel’s First Results

Used parents that were true-breeding, such as tall x short

dominant

•100% offspring were tall

•“tall” factor was ___________ over “short” factor

Review of Generations

1st set of

offspring

(F1

generation)

original

parents

(P generation)

2nd set of

offspring

(F2

generation)

Mendel called the parents for an experiment the P generation.

Mendel called the first generation of offspring the F1 generation.

Mendel called the second generation of offspring the F2 generation

(2nd “filial” generation).

Law of Segregation

dominant

• Mendel continued by crossing

the F1 offspring to produce the

F2 generation

• All F1 generation were _______ hybrids

• Result of the F1 generation

cross producing the F2

generation:

•___% of offspring were

dominant (tall)

•___% of offspring were

recessive (short)

75

25

Mendel’s Conclusions of the F1 Cross 2 1. Each parent had ___ factors for each trait (one from each of

its parents

2. Each parent had a dominant and a _____________ factor

• only way an F2 offspring could

end up with recessive trait

recessive

separate 3. 2 factors had to __________ when

sex cells (gametes) formed

• otherwise, offspring would always

get a dominant factor & have the

dominant trait

Law of ______________- two

alleles must separate

when gametes form

Segregation