Lesson 1: Mendelian Genetics

Question 1

Vocabulary Review

Answer 1

Gene
Segment of DNA. Genetic Unit of instruction, the code for a trait.

Allele
Version of a gene

Genotype
The combination of alleles that code for a trait.

Phenotype
The physical representation of a trait (what the trait looks like)

Homozygous
A genotype that contains 2 of the SAME alleles

Heterozygous
A genotype that contains 2 DIFFERENT alleles

Dominant
The version of a trait (phenotype) that is more commonly seen

Recessive
The version of a trait (phenotype) that is less commonly seen

Question 2

The “Blending” Theory of Inheritance

Answer 2

Before Mendel’s work, the most popular theory of inheritance stated that the
qualities of the parents blended to form the qualities of the child (offspring).

Ex. A tall parent and a short parent would produce a child of medium height

Question 3

Gregor Mendel

Answer 3

Gregor Mendel was an
Austrian monk who worked
with pea plants.

The first to identify discrete
units of heredity (genes)

Discredited the blending
theory
He was the first person to
predict how traits were
transferred from one generation
to the next

Concluded that inherited
characteristics were carried in
discrete, independent units
(later called genes)

Question 4

Mendel’s Peas

Answer 4

The four main reasons Mendel
worked with pea plants were:

The common pea plant was
available throughout Europe

It is easy to grow and matures
quickly

Pea plants self – pollinate,
allowing Mendel to control
which plants reproduced

Different varieties of pea
plants have different traits
that can be easily observed
from one generation to the
next.

Question 5

Mendel’s
Experiment

Answer 5

Mendel selectively fertilized pea plants with
the pollen from other plants and analyzed the
hereditary patterns of certain traits

The first thing Mendel needed to do was
obtain purebred plants for the traits he
wanted to study.

A purebred organism results from many
generations of selective breeding.

Plant height was one of the traits Mendel used
in his studies of the pea plant.

Once he had a purebred short and a purebred
tall plant he would cross – pollinate them and
observe the results.

Mendel called this purebred cross the parent
or P generation.

Question 6

The Results

Answer 6

The offspring of the P
generation were called the F1
generation.

These pea plants were all
tall.

Mendel then cross –
pollinated these plants with
each other and created the F2
generation.

These plants were 75%
tall and 25% short.

Question 7

Mendel’s Conclusions

Answer 7

1. The Principle of Dominance

These results led Mendel to conclude that the tall trait was dominant and the
short trait was recessive.

2. The Principle of Segregation

Genes are normally paired but are separated during gamete formation.

3. The Principle of Independent Assortment

Each factor’s distribution in the gametes is not related to the distribution of
any other factor