Transcript Ch. 10- Genetics

Ch. 10- Genetics
Patterns of Inheritance
The Blending Hypothesis
of Inheritance


Trait- a variation of a particular
character
Is the blending hypothesis true??
Gregor Mendel



Austrian Monk
Grew pea plants in 1800’s to study
patterns of inheritance
Genetics- study of heredity
The work of Mendel


Pea plants can self-pollinate and
reproduce sexually.
1st steps- identify “true-breeding”
plants
– If they self-pollinate, they would produce
offspring identical to themselves
The work of Mendel


Pea plants can also cross-pollinate (2
plants as parents)
Studied 7 pea plant traits
Probability



The likelihood that a particular event
will occur.
Probability = number of events of
choice/ number of possible events
Example:
Probability

Past outcomes don’t influence future
ones.
– Prob. 1 flip is heads = ½
– Prob. 3 flips is heads= ½ x ½ x ½ = 1/8
Genetics Vocabulary






P generation- “parents”; original pair of
plants
F1 generation- 1st offspring
F2- offspring of F1 plants
Hybrid- offspring of 2 different truebreeding parents
Gene- chemical factor that determines traits
Allele- different forms of a gene
More genetics vocab…



For each inherited characteristic, an
organism has 2 alleles (1 from each
parent)
Homozygous- alleles are the same
(AA, aa)
Heterozygous- alleles are different
(Aa)
More genetics vocab…


Dominant- when only 1 of the 2
different alleles in a heterozygous
individual appears to affect the trait
(upper case letter)
Recessive- the other allele that does
not appear to affect the trait (lower
case letter)
Mendel’s Principle of
Dominance

Principle of Dominance- Some
alleles are dominant and some are
recessive
And more vocab…


Genotype- shows alleles for a trait
(Aa)
Phenotype- how a trait is expressed
(brown eyes)
Mendel’s Law of
Segregation
Each parent has two factors (genes) for a
particular trait, but only gives one to
offspring.
Probability & Punnett
Squares



Principles of probability can be used to
predict the outcomes of genetic
crosses.
Punnett Square- shows all possible
outcomes of a genetic cross.
Bill Nye video
Monohybrid Cross



1 trait is analyzed
Let’s try one!
Steps:
– Assign letters to DOMINANT and RECESSIVE
alleles
– Derive genotypes of parents
– Complete punnett square!
– Determine probabilities of genotypes and
phenotypes.
Example

In pea plants purple flowers are
dominant to white flowers.
If two white flowered plants are
crossed, what percentage of their
offspring will be white flowered?
Testcross


To find out if parent
with dominant trait is
homozygous (YY) or
heterozygous (Yy),
cross with homozygous
recessive mate (yy).
Appearance of the
offspring will reveal the
genotype of the
mystery plant.
Testcross

Short hair is dominant over long hair
in guinea pigs. A short haired guinea
pig was mated with a long-haired
guinea pig. If all of the offspring had
long hair, what would the genotype of
the short haired guinea pig be?
Incomplete Dominance


For some characteristics, neither allele
is dominant.
Heterozygotes have an “intermediate”
phenotype
Incomplete Dominance

Purebred Andalusian chickens have
either black or white feathers. A hybrid
chicken has feathers that appear blue.
– Two hybrid chickens produce offspring.
Codominance

Codominance- a heterozygote
expresses BOTH traits
Codominance


In cattle, red is dominant and white is
dominant. Offspring with a red and
white gene are a roan color.
a. A homozygous white cow is
crossed with a roan bull.
Multiple Alleles

Many genes have
several alleles for
each inherited
character.
– i.e. blood types
– A & B are
codominant, O is
recessive
Multiple Alleles

A heterozygous women with blood
type A is married to a man with blood
type O. What are the genotypes and
phenotypes of the offspring?
The Importance of the
Environment

An individual’s phenotype depends on
the environment as well as on genes.
Sex-Linked Traits




Females XX
Males XY
Any gene that is located on a sex
chromosome (i.e. the “x”) is called a
sex-linked gene.
In humans, most sex-linked genes are
found on the X chromosome.
– ** Y does not carry any genes**
Sex-Linked Traits

In humans, colorblindness is a sexlinked recessive trait.
a. A colorblind man has a baby with a
hybrid woman.