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Chapter 12Chapter 12
Mendelian GeneticsMendelian Genetics
Important TermsImportant Terms
Character--something that is inherited.Flower color
Trait--a variant of a character.Purple flower vs. white flower
Allele--an alternative version of a gene.Brown hair or blond hair.
Character--something that is inherited.Flower color
Trait--a variant of a character.Purple flower vs. white flower
Allele--an alternative version of a gene.Brown hair or blond hair.
Important TermsImportant Terms
Hybridization--crossing of two variants of a true breeding plants. The hybrid contains genes from both parents which likely come out in the next generation.
Hybridization--crossing of two variants of a true breeding plants. The hybrid contains genes from both parents which likely come out in the next generation.
More Useful TermsMore Useful Terms
Homozygous--organisms with identical alleles for a trait in question.
Heterozygous--organisms with different alleles for a trait in question.
Phenotype--the outward appearance of an organism--blue eyes.
Genotype--the genetic makeup of an organism--QQ.
Homozygous--organisms with identical alleles for a trait in question.
Heterozygous--organisms with different alleles for a trait in question.
Phenotype--the outward appearance of an organism--blue eyes.
Genotype--the genetic makeup of an organism--QQ.
Important TermsImportant Terms
True breeding--describes an organism that is homozygous--either dominant or recessive, for example TT, or tt.
Heterozygous--describes the genotype of an organism that has a dominant and a recessive allele, for example Tt.
Monohybrid--cross of one character.Dihybrid--cross of two characters.
True breeding--describes an organism that is homozygous--either dominant or recessive, for example TT, or tt.
Heterozygous--describes the genotype of an organism that has a dominant and a recessive allele, for example Tt.
Monohybrid--cross of one character.Dihybrid--cross of two characters.
Important TermsImportant Terms
P generation--Usually true breeding and start the experiment.
F1 generation--1st filial which are hybrid offspring of the parents.
F2 generation--2nd filial which is offspring of the hybrids. This is when we start to see the traits reappear from the P generation.
P generation--Usually true breeding and start the experiment.
F1 generation--1st filial which are hybrid offspring of the parents.
F2 generation--2nd filial which is offspring of the hybrids. This is when we start to see the traits reappear from the P generation.
Important Term: Test Cross
Important Term: Test Cross
Suppose we have a purple flower and we want to know if it is homozygous dominant or heterozygous, (recessive will be white).
To do this, cross the organism with a homozygous recessive and observe the offspring. If any white are produced, the trait is said to be heterozygous, and will be produced in a 1:1 ratio.
Suppose we have a purple flower and we want to know if it is homozygous dominant or heterozygous, (recessive will be white).
To do this, cross the organism with a homozygous recessive and observe the offspring. If any white are produced, the trait is said to be heterozygous, and will be produced in a 1:1 ratio.
Gregor MendelGregor Mendel
He studied garden peas.What made Mendel’s work so good
was that he kept excellent records of what he did and the results of his experiments.
He studied garden peas.What made Mendel’s work so good
was that he kept excellent records of what he did and the results of his experiments.
MendelMendel
At the time, people believe in a “blending hypothesis.” They believed that the traits of a particular organism would be blended together.
Mendel’s experiments abolished this notion.
At the time, people believe in a “blending hypothesis.” They believed that the traits of a particular organism would be blended together.
Mendel’s experiments abolished this notion.
MendelMendel
Mendel crossed true-breeding purple flowers and true-breeding white flowers and the offspring (F1) were all purple.
When he crossed the F1 purple flowers, he got purple and white in a 3:1 ratio.
He determined that purple was dominant to white.
Mendel crossed true-breeding purple flowers and true-breeding white flowers and the offspring (F1) were all purple.
When he crossed the F1 purple flowers, he got purple and white in a 3:1 ratio.
He determined that purple was dominant to white.
MendelMendel
The “blending hypothesis” was wiped out because none of the flowers were pale purple.
He also gave rise to the term “heritable factor” which we now call genes. He said heritable factors must somehow determine flower color.
The “blending hypothesis” was wiped out because none of the flowers were pale purple.
He also gave rise to the term “heritable factor” which we now call genes. He said heritable factors must somehow determine flower color.
AllelesAlleles
These heritable factors are what we now call genes.
Minor differences in the DNA account for the different versions of these genes which we call alleles.
These heritable factors are what we now call genes.
Minor differences in the DNA account for the different versions of these genes which we call alleles.
The Law of SegregationThe Law of Segregation
The 2 alleles for a heritable characteristics segregate during gamete formation and end up in different gametes.
This makes up what is known as the Law of Segregation.
The 2 alleles for a heritable characteristics segregate during gamete formation and end up in different gametes.
This makes up what is known as the Law of Segregation.
Law of SegregationLaw of SegregationIf different
alleles are present, there is a 50/50 chance that the gamete will receive a copy of one gene vs. another.
If different alleles are present, there is a 50/50 chance that the gamete will receive a copy of one gene vs. another.
Law of Independent Assortment
Law of Independent Assortment
Mendel demonstrated this using a dihybrid cross.
Mendel demonstrated this using a dihybrid cross.
The CrossThe Cross
Plants producing yellow colored, round seeds were crossed with plants producing green colored, wrinkled seeds.
If they assort independently, a 9:3:3:1 ratio should be produced.
If they don’t assort independently, if they are somehow linked, a different ratio will be observed.
Plants producing yellow colored, round seeds were crossed with plants producing green colored, wrinkled seeds.
If they assort independently, a 9:3:3:1 ratio should be produced.
If they don’t assort independently, if they are somehow linked, a different ratio will be observed.
ConclusionsConclusions
From the cross, Mendel concluded that no matter how many characteristics are observed, they always separate independently of one another when the traits are on different chromosomes.
From the cross, Mendel concluded that no matter how many characteristics are observed, they always separate independently of one another when the traits are on different chromosomes.
The Law of Independent Assortment
The Law of Independent Assortment
As a result of the dihybrid cross, Mendel arrived at what is known as the Law of Independent Assortment.
It says that all alleles of a gene pair will separate independently of other alleles from other gene pairs during gamete formation.
The “green/yellow” alleles will separate independently from the “round/wrinkled” gene pair.
As a result of the dihybrid cross, Mendel arrived at what is known as the Law of Independent Assortment.
It says that all alleles of a gene pair will separate independently of other alleles from other gene pairs during gamete formation.
The “green/yellow” alleles will separate independently from the “round/wrinkled” gene pair.
2 Rules of Probability2 Rules of Probability
Two rules help us determine the probability of chance events.
1. The multiplication rule.2. The addition rule.
Two rules help us determine the probability of chance events.
1. The multiplication rule.2. The addition rule.
The Multiplication RuleThe Multiplication Rule
To determine the probable outcome of a chance event, multiply the probability of each possible outcome.
Coin example: 1/2 • 1/2 = 1/4
To determine the probable outcome of a chance event, multiply the probability of each possible outcome.
Coin example: 1/2 • 1/2 = 1/4
The Multiplication RuleThe Multiplication RuleAnother example: Suppose we roll
one die followed by another and want to find the probability of rolling a 4 on the first die and rolling an even number on the second die.
P(4) = 1/6P(even) = 3/6
The probability of rolling a 4 and an even is 1/6 • 3/6 = 3/36, or 1/12.
Another example: Suppose we roll one die followed by another and want to find the probability of rolling a 4 on the first die and rolling an even number on the second die.
P(4) = 1/6P(even) = 3/6
The probability of rolling a 4 and an even is 1/6 • 3/6 = 3/36, or 1/12.
The Addition RuleThe Addition Rule
Allows us to determine the probability of any mutually exclusive events by adding together their individual probabilities.
Allows us to determine the probability of any mutually exclusive events by adding together their individual probabilities.
The Addition RuleThe Addition Rule For instance: Suppose you are going to pull one card out of
a deck. What is the probability of pulling a king or an
ace?
P(King) = 4/52 P(Ace) = 4/52
The probability of pulling a King or an Ace is 4/52 + 4/52, which is 8/52, or 2/13.
There is a 2 in 13 chance of pulling a King or an Ace.
For instance: Suppose you are going to pull one card out of
a deck. What is the probability of pulling a king or an
ace?
P(King) = 4/52 P(Ace) = 4/52
The probability of pulling a King or an Ace is 4/52 + 4/52, which is 8/52, or 2/13.
There is a 2 in 13 chance of pulling a King or an Ace.
}Each are mutually exclusive
The Addition RuleThe Addition RuleSo, how does this
apply to us?Use a monohybrid
heterozygous F2 cross to illustrate.
What is the possibility of getting a heterozygous F2 offspring?
1/4 + 1/4 = 1/21/2 of the offspring
should be heterozygous.
So, how does this apply to us?
Use a monohybrid heterozygous F2 cross to illustrate.
What is the possibility of getting a heterozygous F2 offspring?
1/4 + 1/4 = 1/21/2 of the offspring
should be heterozygous.
DominanceDominance
There are varying degrees of dominance. Some characters are completely dominant to others. For instance, purple is completely dominant to white; round is completely dominant to wrinkled.
When you begin looking at things, there are varying forms of dominance.
There are varying degrees of dominance. Some characters are completely dominant to others. For instance, purple is completely dominant to white; round is completely dominant to wrinkled.
When you begin looking at things, there are varying forms of dominance.
Complete DominanceComplete Dominance
Mendel’s peas showed complete dominance. One trait was completely dominant to another (purple to white).
Mendel’s peas showed complete dominance. One trait was completely dominant to another (purple to white).
CodominanceCodominanceThis is where both alleles are
expressed.MN blood group is the example.There are 2 variations of alleles at the
gene locus.MM individuals have “M” proteins on
their surface.NN individuals have “N” proteins on
their surface.MN have both “M” and “N” proteins on
their surface.There is no intermediate phenotype.
This is where both alleles are expressed.
MN blood group is the example.There are 2 variations of alleles at the
gene locus.MM individuals have “M” proteins on
their surface.NN individuals have “N” proteins on
their surface.MN have both “M” and “N” proteins on
their surface.There is no intermediate phenotype.
Incomplete DominanceIncomplete Dominance
Some alleles exhibit incomplete dominance--certain characteristics fall somewhere in between the phenotypes of the 2 homozygotes.
For example: pink snapdragons.
Some alleles exhibit incomplete dominance--certain characteristics fall somewhere in between the phenotypes of the 2 homozygotes.
For example: pink snapdragons.
Incomplete DominanceIncomplete Dominance
With pink snapdragons, a red and a white will produce a pink flower--incomplete dominance.
Less red pigment is made and an intermediate phenotype is seen.
Why is it not “blending?”
With pink snapdragons, a red and a white will produce a pink flower--incomplete dominance.
Less red pigment is made and an intermediate phenotype is seen.
Why is it not “blending?”
Multiple AllelesMultiple Alleles
Thus far we have been talking about 2 alleles that govern certain traits. Often times there are multiple alleles that govern traits within a population.
For example:3 alleles which code for 4 different
blood types.AB blood is also a case of
codominance.
Thus far we have been talking about 2 alleles that govern certain traits. Often times there are multiple alleles that govern traits within a population.
For example:3 alleles which code for 4 different
blood types.AB blood is also a case of
codominance.
Polygenic InheritancePolygenic Inheritance
Polygenic inheritance is the case where many genes act on a single characteristic.
For example: skin color is determined by at least 3 separately inherited genes. Variations of the genotype of these individuals produces all of the varieties of skin color we see.
Polygenic inheritance is the case where many genes act on a single characteristic.
For example: skin color is determined by at least 3 separately inherited genes. Variations of the genotype of these individuals produces all of the varieties of skin color we see.
PleiotropyPleiotropy
Pleiotropy is where one gene has many characteristics features.
CF is caused by a mutation in one gene and causes all sorts of problems-thick mucous in the lungs, digestive problems, excessively salty skin, etc.
Pleiotropy is where one gene has many characteristics features.
CF is caused by a mutation in one gene and causes all sorts of problems-thick mucous in the lungs, digestive problems, excessively salty skin, etc.
