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Genetics Guided Notes
To be used with Genetics PowerPoint
History of Genetics:
Gregor Mendel:
o Austrian monk lived from 1822-1884
o Mendel developed principles of heredity
without any knowledge of genes or
chromosomes
o His principles were established through
experiments with pea plants
Why was Mendel so successful with pea plants?
• Used pure breeding, contrasting traits
• Studied characteristics one at a time for many
generations
• Used mathematics in analyzing his results
• Obtained large numbers of offspring
• Chose pea plants which normally self-fertilize
• Used scientific method
• Inexpensive
Define genes: factors that control organism’s traits.
-the part of chromosome that contains the genetic code.
 Every organism requires a set of coded instructions for specifying its traits
 For offspring to resemble their parents, their must be a reliable way to transfer hereditary
information from one generation to the next
Genetic Terms:
•
(
•
:(
): the alleles on homologous chromosomes are the same
): the alleles on homologous chromosomes are different
•parental generation (P): the two original organisms being crossed - usually pure
•first filial generation(F1): the first generation of offspring from the parents
• second filial generation(F2): generation of offspring arising from the first filial generation
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Genotype: the ___________ makeup of an organism
•Homozygous Dominant: ____
•Homozygous Recessive: ____
•Heterozygous: ____
Phenotype: the ___________ of an organism
Describes what the organism looks like
TT - _________
tt - _________
Tt - _________
______________
_______:
a model used to predict the
results of a genetic cross
Three Laws by Mendel:
1. Law of Dominance: a pattern of heredity in which one allele of a gene may express
itself by masking the presence of the other allele
Define Dominant Trait:
Define Recessive Trait:
Example:
____________________ x ____________________  ___________________
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Example of Dominance:
R = red
r = white
Problem: Cross homozygous dominant with homozygous recessive
___ ___ x ___ ___
What are the results?
Phenotype:
____ % red,
____ %white
Genotype:
____ % homozygous or heterzygous
2. Law of Segregation and Recombination Mendel’s Second Law:
When gametes are formed during meiosis three things happen. What are they?
When gametes are formed during meiosis:
There is a random segregation of homologous chromosomes
Random segregation of sister chromatids & alleles
The result: new gene combinations are likely to be produced
Segregation means separation and can lead to genetic recombination.
Example of Segregation:
Problem: Cross two offspring from the 1st filial generation (both are heterozygous)
___ ___ x ___ ___
Results?
Phenotype:
_____% red, ____% white
Phenotypic ratio:
___ red : ___ white
Genotype:
___% homozygous dominant
___% homozygous recessive
___% heterozygous
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3. Law of Independent Assortment Mendel’s Third Law
Scenario: Two different traits located on two different chromosomes
Explain what two things can happen to these traits during meiosis:
• They segregate randomly during meiosis
• May be inherited independently of each other
The cross of two organisms heterozygous for a trait is known as a dihybrid cross
Punnett Square Problem #3: Dihybrid Cross
T = tall
Q = wrinkled
t = short
q = smooth
Problem: Cross homozygous tall and homozygous wrinkled seeds with homozygous short and
homozygous smooth seeds
Genotypes for this cross: TTQQ x ttqq
What are the phenotypes for these plants?
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Punnett Square Problem #3: Dihybrid Cross
Genotypes for this cross: TtQq x TtQq
T = tall
Q = wrinkled
t = short
q = smooth
What are the phenotypes for these plants?
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Incomplete Inheritance:
Two examples of Incomplete Inheritance:
Incomplete Dominance & Codominance
Define Incomplete Dominance:
Name one example of incomplete dominance
________________________________________________________________
Problem:
Cross offspring from 1st cross (2 heterozygous parents)
R = red
r = white
Rr x Rr
Results:
Phenotype:
___% red, ___% pink, ___% white
Phenotype ratio:
__ red : __ pink : __ white
Genotype:
___% homozygous dominant
___% heterozygous
___% homozygous recessive
Genotype ratio:
1: 2 : 1
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Define Codominance:
Name the first example of Codominance:
_______________________________________
Example of Codominance:
Problem:
Cross offspring from 1st cross (2 heterozygous parents)
R = red
r = white
Rr x Rr
Results:
Phenotype: 50% red & white 25% red, 25% white
Phenotyp ratio: 1 red : 2 red & white : 1 white
Genotype: 25% homozygous dominant
25% homozygous recessive
50% heterozygous
Problem 1
Phenotype of tt ------------------------Genotype of tt--------------------------Phenotype of TT ----------------------Genotype of TT------------------------Phenotype of pure dominant-------Genotype of pure dominant--------Phenotype of pure recessive-------Genotype of pure recessive--------7
__ __ x __ __
Problem
2:
Problem 3: Cross two
A married couple want to know
heterozygous parents
their chances of having girl
Key:
Male
XY
Female
Phenotype: ____% Male
XX
____% Female
Problem 3:
Cross two heterozygous parents
R = Red
R = white
__ __ X __ __
Results:
Phenotype: ___% red, white ___%
Phenotype Ratio:
Genotype:
____ : ___
___% heterozygous
___% homozygous dominant
___% homozygous recessive
Problem 4: Pure dominant crossed with hybrid
R = red
r = white
__ __ x __ __
Results:
Phenotype: ___% red, white ___%
Phenotypic Ratio:
Genotype:
__
:
_ __
___% heterozygous
___% homozygous dominant
___% homozygous recessive
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Problem 5: The male’s genotype is homozygous recessive.
The female is phenotypically dominant but does carry the recessive allele.
R = red
r = white
__ __ x __ __
Results:
Phenotype: ___% red, white ___%
Phenotypic Ratio:
Genotype:
_____
:
_ ___ __
___% heterozygous
___% homozygous dominant
___% homozygous recessive
Problem 6: Law of Codominance
Problem: Cross two heterozygous parents.
R = red
r = white
__ __ x __ __
Results:
Phenotype:
___% red, ___& red and white, ___% white
Phenotypic Ratio:
__ ___ : _ _ __ _______ __ :
Genotype:
________
___% heterozygous
___% homozygous dominant
___% homozygous recessive
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Problem 7: Law of Incomplete
Dominance
Problem: Cross two heterozygous parents.
R = red
r = white
__ __ x __ __
Results:
Phenotype:
___% red, ___& pink, ___% white
Genotype:
___% heterozygous
___% homozygous dominant
___% homozygous recessive
Problem 8: A test cross uses an individual
that is homozygous recessive. It will determine if the
dog in question is pure or carrying a recessive gene.
B = brown
b = white
__ __ x __ __
or
__ __ x __ __
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Multiple alleles
Traits that are controlled by more than 2 alleles
Results in multiple phenotypes
Examples:
Pigeons
BA dominant over B
BA and B are dominant over
Blood groups in humans
Four blood types A B AB & O
Polygenic Inheritance
A pattern of a trait that is controlled by 2 or more genes.
Phenotype express a range of variability.
Examples:Stem length, human height, eye color & skin color
Stem length for a totally recessive plant is____ cm.
aabbcc = 4 cm
Aabbcc = cm
AAbbcc = cm
AABbcc = cm
AABBcc =
AABBCc =
AABBCC =
cm
cm
cm
Gene Expression
Influence of External Environment:
Examples: Temp., nutrition, light, chemicals
Color of rabbit in the summertime: brown
Color of rabbit in the winter: white
The temperature effects what color fur (or what proteins) are expressed
Temp also determines the sex of a gator
Light determines color of bacteria
Influence of Internal Environment:
Examples: Hormonal influences
•Horn size in mountain sheep
•Male pattern baldness
•Peacock feathers
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