Download Mendel`s Principle of Segregation:

What is heredity? ______________________________________
What is a trait?_______________________________________
What is an allele?_____________________________________
Key Terms to Know!
• phenotype
• genotype
• homozygous
•
•
heterozygous
hybrid
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•
•
•
•
dominant
recessive
Punnett square
monohybrid cross
dihybrid cross
Mendel’s Principle of Segregation:
Alleles separate in meiosis, then come back together in the zygote (offspring)
through Fertilization
Parents = “P” generation Offspring = “F1” generation Their offspring =“F2”
generation
What was the PHENOTYPE of F1 hybrid
plants like? Which parent did they
resemble? ______________________
What about the F2?
______________________
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Explain: MENDEL’S CONCLUSIONS
1. Inheritance is determined by what he called “factors.” What are these? ____________
2. The Principal of Dominance means: _______________________________________
_______________________________________________________________________
3. Did the recessive allele disappear in the F1 plants? ____________________________
________________________________________________________________________
4. How could he test this? _________________________________________________
The F1 Cross:
Phenotypes:
Genotypes:
Define the Principal of SEGREGATION: ____________________________________
________________________________________________________________________
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Explaining the F1 Cross—Mendel’s Hypotheses
1. There are alternative forms of genes called ___________________.
2. How many alleles does an organism have for each gene? _________________
3. If the alleles are the SAME, the individual is __________________ for that trait.
4. If the alleles are DIFFERENT, the individual is _________________ or a
________________for that trait.
5. In a heterozygous individual the allele that appears in the Phenotype is called the
_______________________allele (P)
6. The other allele that does not appear called the _________________allele. (p)
7. The two alleles for a trait segregate (separate) during the formation of _____________
(sex cells), so that each carries only one allele for each characteristic.
8. This is known as Mendel’s ______________________________________
9. The joining of gametes during __________________ reforms allele pairs in the offspring.
10. By what process that we studied do alleles SEGREGATE? ______________
11. What types of cells are produced as a result? (haploid/diploid? Why does it
matter?)___________________________
12. How many copies of an allele does an offspring inherit from the male parent?___
13. How many copies of an allele does an offspring inherit from the female parent?___
14. An observable trait (such as purple flowers) is called the _____________________
15. The genetic makeup, or combination of alleles (such as PP), is called the
____________________
Punnett Square
Shows all possible outcomes of a genetic cross.
Used to predict probabilities of types of offspring if you know the genetic makeup
(genotype) of both parents.
How is a Punnett Square an abbreviation of Meiosis (gametes) and Fertilization (Zygotes)?
________________________________________________________________________
Cross two parents that are both Heterozygous for free earlobes.
Aa x Aa (Monohybrid Cross)
Allele Key:
A = Free earlobe
a = attached earlobe
RESULTS: (Ratio or Percentages)
Parent #1 Gametes
A
Parent
#2
Gametes
F1 Offspring
A
a
F1Offspring
a
1. Phenotype: # _______ Free earlobe
# _______ Attached earlobe
F1 Offspring
F1Offspring
2. Genotype: #_______ Homozygous Dominant
# _______ Heterozygous
# _______Homozygous Recessive
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Monohybrid Practice Problems:
1.
In pea plants, round peas are dominant over wrinkled peas.
Use a Punnett square to predict the phenotypic and genotypic outcome (offspring) of a cross
between a plant homozygous for round peas (RR) and a plant homozygous for wrinkled peas (rr).
2.
Jake’s second toe is much longer than his thumb toe – at least an inch! This is a recessive trait. If
he marries Emma, who is a heterozygous for having her second toe shorter than her thumb toe,
answer the following questions. Use the letter T to represent this allele.
a. Which trait is dominant – long second toe or short second toe?
b. What are Jake’s and Emma’s genotypes?
c. If Jake and Emma have children, what are the possibilities of their children’s phenotype?
d. What are the possibilities of their children’s genotype?
3.
Jack is so double jointed that his thumb can bend over backwards to touch his watch. His father is
double jointed also, but his mother is not. If being double jointed is a recessive trait, what is the
genotype of Jack and his parents? Use the letter “D” to represent the allele for this trait.
Mendel’s Principle of Independent Assortment
Define Independent Assortment:
Define DiHybrid Cross:
Trait #1
Trait #2
Dominant = Round shape
Dominant = Yellow
Recessive = Wrinkled shape
Recessive = Green
***Alleles for different traits are located on different Homologous Chromosome Paris,
therefore they assort and separate during Meiosis INDEPENDENTLY from each other!****
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The Dihybrid Cross
Round & Yellow Pea Plant (RRYY) (Parent #1)
x
Wrinkled & Green Pea Plant (rryy) (Parent #2)
What gametes would these two Parents produce? In other words, how will the alleles for
these two traits segregate (Pull apart in meiosis)?
(Parent #1) RRYY: _________________________
(Parent #2) rryy: __________________________
Set up the Punnett Square to Cross these parents:
(Notice this Punnett Square has only one box for offspring. That’s because each parent above only made
________ kind of gamete, so only one kind of offspring is possible)
Parent #1
Gametes
RESULTS:
Phenotype of all F1 offspring:
______________
Parent #2
Gametes
Offspring
Genotype of all F1 offspring:
______________
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Before we Cross the two Dihybrids, let’s look at:
Independent Assortment of Alleles during Meiosis
F1 Geneotype = RrYy
In Possibility #1: The Paternal
Chromosomes RANDOMLY lined up one
on top of the other during Metaphase I
ending up together in the Haploid gametes
R & Y ended up together in one cell
R= Round
r = wrinkled
Y = Yellow
y = green
In Possibility #2: One Paternal
Chromosome RANDOMLY Lined up
above one Maternal Chromosome (and vice
versa), creating Haploid gametes that were
a mixture of paternal and maternal alleles.
R & y ended up together in one cell
and
r & y ended up together in another cell
and
r & Y ended up together in another cell
What are the four different allele combinations the F1 parent can make in its gametes?
1. ______________
2. ______________
3. ______________
4. ______________
These are the four different allele combinations that are ALWAYS made in a Dihybrid’s
gametes!
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Now we are ready to Cross the two Dihybrids! (RrYy x RrYy)
The DiHybrid Cross: F1
This is a Dihybrid Cross: Crossing two organisms that are hybrid for Two Traits!
RrYy x RrYy
1.
What types of GAMETES can these Parents produce, assuming that the alleles segregate independently?
(**Hint: Principle of Independent Assortment: Genes for different Traits
segregated independently during the formation of gametes)
2.
Set up the Punnet Square—place the alleles for the gametes of one parent across the top and the
alleles for the other parent down the side.
3.
Fill in the possible offspring types.
Gametes Parent #1
Gametes
Parent #2
4.
How many offspring of the 16 possibilities are:
a. Yellow and Round (Dominant/Dominant) _____________________
b. Yellow and Wrinkled (Dominant/ Recessive) __________________
c. Green and Round (Dominant /Recessive) ______________________
d. Green and Wrinkled (Recessive/Recessive) ____________________
5.
Summarize Mendel’s Principle of Independent Assortment:
6.
What would the probability have been of producing a Yellow Wrinkled offspring if the parents
had been RRYY x rryy?
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Dihybrid Practice Problems:
1) For eye color, brown “B” is the dominant allele, and blue “b” is the recessive allele.
For the shape of the nose, pointy “P” is the dominant allele, and flat “p” is the
recessive allele. Dassa is heterozygous brown eyed and has a flat nose. She marries
Oliver who is heterozygous brown eyed and a heterozygous pointy nosed person.
What are the possible genotypes and phenotypes for their children?
2) In newts, skin color (blue verses green) and ruffle patterns (fringed verses spiked) are
genetically inherited. A blue, fringed female whose father was green, spiked is mated
to a blue, fringed male.
a) In looking at all of the offspring from their matings, one finds that roughly 56%
are blue, fringed; roughly 6% are green spiked; roughly 18% are blue, spiked;
roughly 18% are green, fringed. What were the genotypes of the parents?
b) If a blue, spiked was mated with green, fringed from this generation, what are the
possible phenotypes (and the ratio) and the possible genotypes of the offspring?
(assume both are heterozygous for the dominant trait)
3) What kind of gametes can be produced by the organisms with the following
genotypes?
a) AAbb __________________________________________
b) AABB _________________________________________
c) Aabb __________________________________________
d) AaBb __________________________________________
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Multiple Alleles
& CoDominance
In CoDominance, the Heterozygous Individual shows what Phenotype?
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Genetic Linkage and Crossing Over
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Linked Genes
1. Homologous chromosomes may bear either the same alleles or different ones at a
particular location, making the organism either _____________________ or
_______________________ for each gene.
2. When genes are located on separate chromosomes, they sort _____________ of each
other during meiosis.
3. But what happens when genes are located on the same chromosome? The alleles for
these genes would not be sorted into gametes independently since they would stay
together during meiosis. The only way such alleles can sort independently is if they
_____________________ during Prophase I of Meiosis.
4. When alleles are located on the same chromosome and inherited together, they are
called ____________________ genes
Sex-Linked Genes
Any gene that is located on a sex chromosome is called a
____________________
In humans, most sex-linked genes are found on the
__________, which is considerably larger than the _____
chromosome.
Explain why none of the flies with white eyes
was female in F1 generation. ____________
_____________________________________
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More Practice Problems:
1. A woman has a baby and wants to prove who the father is. Her blood type is B and the
baby is A. There are 2 possible fathers: Sam, who is type A and Matthew who is type O.
Which man could be the father?
a. Either
b. Sam
c. Matthew
d. Neither
e. Impossible to tell
2. In certain breeds of dogs, black color is dominant and red color is recessive; solid
color is dominant and white spotting is recessive. A homozygous black-and-white
spotted male is crossed with a red-and-white spotted female. What is the
probability of their producing a solid black puppy?
3. A female fruit fly whose body is covered with forked bristles is mated with a male
fly with normal bristles. Their offspring are 121 females with Normal bristles and
138 males with forked bristles. (ie: NO females with forked and NO males with
bristles) Explain the inheritance pattern for this trait.
What were the genotypes of the parents?
What must be the genotypes of the male and female offspring?
4. Hemophilia (recessive sex-linked disorder)
Normal male = ______________
Normal female = _____________
Hemophiliac Male = ___________ Carrier female = ______________
Hemophiliac Female = __________
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Summary
1. Punnett Squares are Meiosis (gametes) along the sides and Fertilization (zygotes) on
the inside squares.
2. In a Hybrid, the allele that shows up as the Phenotype is the Dominant allele, the
other one is Recessive. This is the only way to tell which allele is dominant.
3. Segregation of alleles happens during Meiosis, when homologous pairs split and
haploid cells (gametes) are formed because we never give our offspring BOTH copies
of our alleles, only one or the other.
4. Independent Assortment is when you’re looking at two traits at a time, one trait on
one homologous chromosome pair, and another trait on a different pair. When they
line up in Metaphase I, maternal and paternal chromosomes of the pair randomly line
up over other maternal and paternal chromosomes independent of one another. In a
dihybrid, that gives you 4 gamete outcomes.
5. Linked Genes are when the genes for two different trait happen to be on the same
chromosome, so they do not independently assort. Example, sex-linked traits
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