Download Mendel and Punnett squares notes

Gregor Mendel
Mendel’s Conclusions
• In his crosses each trait had a Dominant Factor
which masked, or dominated the other factor for a
specific trait.
• the other trait we call the Recessive Factor.
• In a true-breeding cross (BBxbb) the recessive
factor is masked in F1 but appears in F2
Mendel’s Conclusions
• Law of Segregation: Each organism
contains two factors for each trait; factors
segregate in the formation of gametes.
When two gametes combine during
fertilization, the offspring have two factors
controlling a specific trait.
• Law of Independent Assortment: states
that factors for different characteristics
are distributed to gametes independently.
Genetics Vocabulary
• Gene - the unit of heredity; a section of DNA
sequence encoding a single protein
• Alleles - two genes that occupy the same position on
homologous chromosomes and cover the same trait
• Locus - a fixed location on a strand of DNA where a
gene or one of its alleles is located
Genetics Vocabulary
• Homozygous - having identical genes (one from each
parent) for a particular characteristic.
• Heterozygous - having two different genes for a
particular characteristic.
Genetics Vocabulary
• Phenotype - appearance
• Genotype - genetic makeup
Genetics Vocabulary
• Dominant - the trait that appears in the
heterozygous condition.
• Recessive - the trait that is masked in the
heterozygous condition.
Genetics Vocabulary
• Monohybrid cross - cross involving a
single pair of genes, one trait
• P – “parents”
• F1 – “kids”
• F2 – “grandkids”
Genetics Vocabulary
• Punnett squares - used to aid in
predicting the probability that certain traits
will be inherited by offspring
• Probability - is the likelihood that a
specific event will occur or is the likely
outcome a given event will occur from
random chance
How To: Monohybrid Crosses
On the Back of Your Notes
Steps
Notes
Examples
Monohybrid Crosses
(only one trait)
• Ineeda Know Ph.D. is trying to identify the
potential genotypes of offspring of a white male
rabbit and a heterozygous black female rabbit.
Ineeda Know Ph.D. is trying to identify the potential
genotypes of offspring of a White male rabbit and a
heterozygous black female rabbit. Black is dominant to
white in bunnies.
Step
Notes
1. Determine the Will be stated in
dominant and
the problem
Recessive trait
Example
Black is
dominant to
white in bunnies
Ineeda Know Ph.D. is trying to identify the potential
genotypes of offspring of a White male rabbit and a
heterozygous black female rabbit. Black is dominant to
white in bunnies.
Step
Notes
Example
2. Assign letters
for the trait
Dominant trait
gets the capital
letter
B = black
b = white
Recessive traits
gets the lower
case letter
Ineeda Know Ph.D. is trying to identify the potential
genotypes of offspring of a White male rabbit and a
heterozygous black female rabbit. Black is dominant to
white in bunnies.
Step
Notes
Example
3. Determine Each parent has White male = bb
genotype for two alleles
parents
Heterozygous
black female = Bb
Ineeda Know Ph.D. is trying to identify the potential
genotypes of offspring of a White male rabbit and a
heterozygous black female rabbit. Black is dominant to
white in bunnies.
Step
Notes
4. Put parents on Separate
the square
parental alleles
Example
Bb x bb
B
b
b
b
Ineeda Know Ph.D. is trying to identify the potential
genotypes of offspring of a White male rabbit and a
heterozygous black female rabbit. Black is dominant to
white in bunnies.
Step
Notes
Example
5. Determine
genotype of
offspring
Punnett square
holds offspring
genotypes
Bb x bb
Genotype =
letter code
B
b
b
Bb
bb
b
Bb
bb
Ineeda Know Ph.D. is trying to identify the potential
genotypes of offspring of a White male rabbit and a
heterozygous black female rabbit. Black is dominant to
white in bunnies.
Step
Notes
Example
6. Determine
genotype ratio
Count offspring
in the Punnett
square
genotype ratio =
2 Bb: 2 bb
There are two
correct ways to
represent your
data
2/4 Bb, 2/4 bb
Ineeda Know Ph.D. is trying to identify the potential
genotypes of offspring of a White male rabbit and a
heterozygous black female rabbit. Black is dominant to
white in bunnies.
Step
Notes
Example
7. Determine
phenotype
ratio
Phenotype =
what they look
like
*ratio MUST add
up to the number
of boxes*
Count offspring in
the Punnett square
phenotype ratio
2 black:2 white
Practice Problems
A pure-breed white flower crosses with a pure-breed
purple flower. Purple is dominant to white.
•
•
•
•
Determine the genotypes of the flowers.
Show the punnett square
What is the genotype of the F1 generation
What is the phenotype of the F1 generation
Genotype = Pp
Phenotype = Purple
More Practice
A homozygous black guinea pig is crossed with a
heterozygous black guinea pig .
B = black
b = brown
• Determine the genotypes of the parental guinea
pigs.
• Show the punnett square.
• What are the genotypes?
• What are the genotype ratio?
• What are the phenotypes?
• What are the phenotype ratios?
Genotypes = BB and Bb
Genotype Ratio =
2BB:2Bb
Phenotypes = All Black
Even More Practice
If you had a black guinea pig how could you tell
it’s genotype was homozygous and
heterozygous?
Use a test cross:
cross with a pure
breed recessive
and look at the F1
generation