Download 8.1 INTRO to Genetics Practice Monohybrid Crosses

8.1 GENETICS - Key Concepts and
Vocabulary
Key Concepts:
1. What is a gene?
2. Gregor Mendel’s laws
of genetics
3. Predicting the results
of genetic crosses
4. How to use a
Punnett square
Key Vocabulary:
 Gene
 Allele
 Dominant
 Recessive
 Heterozygous
 Homozygous
 Genotype
 Phenotype
Genetics

The study of how traits are
passed from parents to offspring

The study of inheritance
What traits are genetic?

Genes

Segments of
DNA on
chromosomes that control a
trait


Alleles are different versions of a
gene for the same trait


Ex. Height
Ex. Tall or short for the trait of height.
How many copies of each gene do
organisms have?
Gregor Mendel


Austrian monk who observed how traits were inherited in pea
plants
Mendel’s work is the basis of all genetics What are some traits
that Mendel could have observed?
Mendel’s Laws

Mendel’s work with pea plants helped him develop three laws
of genetics:
1. Law of DOMINANCE
2. Law of Segregation
3. Law of Independent
assortment
Law of Dominance


One allele for a trait is expressed more than the other
The dominant factor is expressed and dominates the
other factor


Always represented by a capital letter
The recessive factor is hidden by the dominant factor

Always represented by a lower-case letter
Law of Dominance
What letters should be used to
represent the following traits?
 Yellow seeds 
Wrinkled seeds -

Green pods -

Tall plants -

Dwarf plants -
Law of Segregation



Genes separate during meiosis
and the chromosome number is
reduced
Each egg or sperm produced by
meiosis only has one copy of
every gene
When egg and sperm join
during fertilization the new cells
has genes from both parents
Will baby be
tall or short?
Genetics Vocabulary

Genotype is the
genetic make-up of an organism


Represented by code letters
Phenotype is
the physical appearance of an organism


The actual trait represented by code letters
A homozygous organism has
two of the same alleles for a trait


Example - AA or aa
A heterozygous organism has
two different alleles for a trait

Example - Aa
Genetics Vocabulary

The parental generation (P) is the Starting Generation

The first filial generation (F1) is the offspring of the
parental generation
The second filial generation (F2) is the offspring of the F1
generation

Punnett Squares

Punnett squares are used to predict the probability of
traits being passed from parents to offspring
Steps of using Punnett squares:
1. Determine alleles of parents
2. Place alleles on top or sides of square
3. Combine alleles inside square
4. Determine genotypes and phenotypes of offspring
Monohybrid Cross


Genetic cross between ONE pair of alleles for a trait
Example: In rabbits, black fur color is dominant to brown
fur color. Use a Punnett square to predict the results of a
cross between a homozygous black rabbit and a
homozygous brown rabbit
Law of Independent Assortment

Genes for
different traits
are passed
down
separately
from parents
to offspring

Dihybrid Cross

Genetic cross between TWO pairs of alleles for different
traits

Example: In pea plants, the allele for round seeds is
dominant over the allele for wrinkled seeds. The allele
for yellow seeds is dominant over the allele for green
seeds. Use a Punnett square to predict the results of a
cross between a plant homozygous dominant for both
traits and a recessive plant