Download Genetics 3-2 Power point

APW
• If you flip a coin, what are the chances that it will
land on heads? Tails?
• Suppose you flip the coin once, get heads, and then
flip it again. What are the chances that you will get
heads again? Explain.
APW 3-20-08
• Fill in the following Punnett Square.
D
d
d
• Define: Purebred • Define: Hybrid• Define: Testcross-
d
APW 3-20-08
• Fill in the following Punnett Square.
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d
d
Dd
dd
d
Dd
dd
• Define: Purebred-having the same alleles
• Define: Hybrid-having two different alleles
• Define: Testcross-when you cross an organism with a
homozygous recessive genotype with a dominant
phenotype to figure out the dominant trait organisms
genotype.
APW 3-24-08
• Fill in the following Punnett Squares.
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Chapter 3 Section 2
Traits and Inheritance
Objectives
1. Explain how genes and alleles are related to
genotype and phenotype
2. Use the information in a Punnett square
3. Explain how probability can be used to predict
possible genotypes in offspring.
4. Describe three exceptions to Mendel’s observations
Genes
• Genes are one set of
instructions for an inherited
trait.
• Each parent gives one set of
genes to offspring.
• Therefore, offspring has two
sets of a gene for every
characteristic.
• Genes are located on
chromosomes.
Bigger
Smaller
Alleles
• Alleles are the
different forms of a
gene.
• Characteristics are to
traits as genes are to
alleles.
Phenotype vs. Genotype
• A phenotype is any observed
quality of an organism, such
as its morphology,
development, or behavior.
• A genotype is the inherited Genotype
instructions an organism
carries, which may or may not
be expressed.
Phenotype
Phenotypes of Pea Plants
• Name 2 possible phenotypes for flower color.
______________
_______________
• Name 2 possible phenotypes for seed shape.
______________
_______________
• Name 2 possible phenotypes for seed color.
______________
_______________
Genotypes of Pea Plants
• Name 3 possible genotypes for flower color if the
alleles are F and f.
___________
___________
___________
• Name 3 possible genotypes for seed shape if the
alleles are S and s.
___________
___________
___________
• Name 3 possible genotypes for seed color if the
alleles are C and c.
___________
___________
___________
Genotype: Homozygous vs.
Heterozygous
• A Homozygous plant
is one with two
dominant or two
recessive alleles.
HH or hh
• A Heterozygous plant
is a plant with two
different alleles
Hh
Punnett Squares
• Punnett Squares are used to
organize all of the possible
combinations of offspring
from particular parents.
• What is the ratio of dominant
phenotypes to recessive
phenotypes?
_______________
Using a punnett square to model
Mendel’s first experiments
Punnett Squares
• Punnett Squares are used to
organize all of the possible
combinations of offspring
from particular parents.
• What is the ratio of dominant
phenotypes to recessive
phenotypes?
_______________
Using a Punnett square to model
Mendel’s second experiments
What are the chances?
• When the alleles a parent has are different,
the chances of receiving them are fifty-fifty,
like a coin toss.
• Probability is the mathematical chance that
something will happen. In this case, it is the
chance that a trait will be inherited.
• Probability is usually written as a fraction or a
percentage.
Probability Practice
• If you roll a pair of dice, what is the probability that
you will roll 2 threes?
______ x ______ = ______
• If you flip a coin twice, what is the probability that
you will get 2 heads?
______ x ______ = ______
• If you roll a single die, what is the probability you will
roll an even number?
______ + ______ + ______ = ______
Probability Practice
• If both parents have Pp genes, what is the probability
that the offspring will have PP genes?
______ x ______ = ______
• If both parents have Pp genes, what is the probability
that the offspring will have Pp genes?
______ x ______ + ______ x ______ = ______
• If both parents have Pp genes, what is the probability
that the offspring will have pp genes?
______ x ______ = ______
Exceptions to Mendel’s Principles
•
•
•
•
•
Incomplete Dominance
Codominance
One gene, many traits
Many genes, one trait
Environmental Effects
Incomplete Dominance
• When an individual is
heterozygous for a trait,
instead of one trait being
completely dominant over
another, the traits mix.
• Thus, you can tell the
genotype by looking at the
phenotype for incomplete
dominance.
R
r
R
RR
Rr
r
Rr
rr
Codominance
• In codominance, neither
phenotype is recessive. Both
traits are fully expressed.
• However, both codominant
traits are dominant over the
recessive trait.
• Blood type is an example
IA
i
IB
IAB
IBi
i
I Ai
ii
One Gene, Many Traits
• What do you notice
about the tiger?
• Sometimes one gene
influences more than
one trait.
• In tigers, the gene that
influences eye color
also influences hair
color.
Many genes, One trait
• Skin color and eye color are
influenced by many genes.
• That is why there are intermediary
colors.
Environment
• Environments can also affect
phenotype (hair cutting)
Objectives
1. Explain how genes and alleles are related to
genotype and phenotype
2. Use the information in a Punnett square
3. Explain how probability can be used to predict
possible genotypes in offspring.
4. Describe three exceptions to Mendel’s observations