Download Mendelian Genetics Ch. 6.3 through 6.6 Notes

MENDELIAN GENETICS–
CHAPTER 6.3 – 7.4
Mrs. Williams
Freshman Biology Honors; Semester Two
Pre-Test
Get out your cell phones!
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Genetics
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Genetics is the study of traits and how they are
passed from one generation to the next.
BrainPop
Greatest Discoveries
Gregor Mendel
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Austrian monk
Performed genetic experiments in the 1850’s and
1860’s
Considered the “Father of Genetics”
His work was performed with no knowledge of
DNA, cells, or meiosis!
Mendel’s Experiments
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Worked with pea
plants in the monastery
gardens
Followed the
inheritance patterns of
seven different traits
(characteristics) in the
plants
Creating the F1 Generation

For each trait:
 Mendel
used a true-breeding plant for each form of
the trait for the parent (P) generation
 Ex-
True-breeding purple flower x true-breeding white
flower
 Cross-pollinated
the plants to produce offspring
 Created F1 generation which only displayed one form
of the trait (hybrids)
 Ex-
all F1 plants were purple flowered
Conclusions

Pea plants were passing a chemical message from
one generation to the next that was controlling the
trait (Ex- flower color)
 This
is a gene (Ex- gene for flower color)
 Genes
are sections of DNA on chromosomes that code for a
trait
 Different
 There
forms of a trait are called alleles
is a purple and a white allele for flower color
More Conclusions

Principle of Dominance
 One
allele is dominant over the other
 Dominant will always be displayed when present
 Recessive is only seen when it is the only allele present
Review – Grab a set of flip cards!

1. Meiosis occurs in what type of cells?
 A.
Somatic Cells
 B. Gametes

2. How many times does DNA replicate during
meiosis?
 A.
Once
 B. Twice
 C. Three Times
 D. Four Times
Review Continued
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3. What are the steps, in order, of meiosis I?
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A. Metaphase I, Telophase I, Interphase I, Anaphase I
B. Interphase, Metaphase I, Prophase I, Telophase I, Anaphase I
C. Interphase, Prophase I, Metaphase I, Anaphase I, Telophase I
D. Telophase I, Metaphase I, Anaphase I, Prophase I
4. How many functional egg cells are made during each
cycle of meiosis?
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A. Four
B. Three
C. Two
D. One
Review Continued
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5. Who is considered the “Father of Genetics”?
A. Gregorovich Butinsky
 B. Gregor Mendel
 C. Viktor Krum
 D. Anton von Leuweenhoek
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6. What plants were used to do genetics experiments?
A. Pea plants
 B. Petunias
 C. Pansies
 D. Tomato plants

Review Continued
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7. What states that if a dominant allele is present, it
will always be expressed?
A. The Law of Independent Assortment
 B. The Principle of Dominance
 C. The Law of Segregation
 D. The Order of the Phoenix
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8. In order for a recessive trait to be expressed, both
parents must donate a
A. Dominant allele
 B. Recessive allele
 C. One parent gives a dominant, and one parent gives a
recessive

Creating the F2 Generation
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For each trait
 Mendel
 Ex- F1
self-pollinated plants from the F1 generation
purple flower is crossed with itself
 Created
the F2 generation which displayed both traits
in a 3:1 ratio
 For
every 4 flowers, 3 were purple flowered and one was
white flowered
Conclusions

Each pea plant has two copies of every gene
 Each
copy is found on one of the homologous
chromosomes
 Each individual has three possible types of
combinations
 Two
dominant alleles- homozygous dominant
 Two recessive alleles- homozygous recessive
 One of each- heterozygous
More Conclusions

Principle of Segregation
 The
two copies of a gene that an individual has
separate (segregate) from each other during
gamete formation
 The copy to be put in the gamete is chosen at
random
 This happens during Anaphase I when the tetrads
separate
Tetrad Separation
Predicting Inheritance Outcomes
Probability- rules that predict the likelihood of
an event occurring
 Punnett squares- tool used in genetics to figure
out the probability of a genetic cross

 Monohybrid
cross- Punnett square showing the
outcome of the inheritance of one trait
 Dihybrid cross- Punnett square showing the outcome
of the inheritance of two traits
Information About Traits
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Physical form of the trait seen is the phenotype (show
either dominant or recessive)
Genotype is the alleles that an individual has for a
trait (2 alleles/trait)
Represented by letters (capital for dominant, lower-case for
recessive)
 Letter is chosen based on dominant allele
 Possibilities (using flower color as example)
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Homozygous dominant PP
Heterozygous Pp
Homozygous recessive pp
 Heredity
Setting Up a Punnett Square
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One parent’s possible
gametes go on the top
Other parent’s possible
gametes go on the side
Squares are filled in
with the column and
row header

Dominant letter is written
first
Mendel’s Dihybrid Experiment
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Mendel crossed two plants that were true-breeding
for two traits
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Ex- True-breeding round and yellow peas (RRYY) x Truebreeding wrinkled and green peas (rryy)
F1 generation was all round and yellow
F1 generation was self-pollinated to create F2
F2 generation showed all 4 possible phenotype
combinations in a 9:3:3:1 ratio
Conclusions

Law of Independent Assortment
 Each
gene segregates on its own
 The inheritance of one trait does not influence the
inheritance of another; each trait is chosen
randomly and independent from each other
 For
example, a pea plant that inherited the dominant
yellow pea color did not automatically inherit the round
(dominant) pea shape.
Setting Up a Dihybrid Punnett Square

All possible allele combinations from one parent are
placed along the top (4 total)
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For example- an F1 round and yellow pea plant (RrYy)
could produce RY, Ry, rY, and ry gametes
All possible allele combinations from the other parent
are placed along the side (4 total)
Square are filled with the column and row headers
(16 squares)
Letters from one trait go first, then the other
 Capital letter for that trait are put in front

Dihybrid Punnett Square
Uses for Punnett Squares
Give all possible outcomes for a cross
between two different parents
 Predicts expected (not actual) ratios
among the offspring
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Beyond Mendelian Genetics
Incomplete dominance
 Codominance
 Multiple alleles
 Polygenic traits
 Multifactorial traits
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Incomplete Dominance
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One allele is not completely dominant over the
other; heterozygotes show a blending of the trait
Codominance
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Neither allele is
dominant over the other;
heterozygotes express
both alleles at the same
time (not a blending)
Ex: Both black and white
feathers in chickens
Ex: Both white and red
hairs in roan cattle
Multiple Alleles
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Gene has more than just two alleles possible
Remember- each individual still just has 2
Ex- rabbit fur color (4 alleles)
Human Blood Types
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Human Blood Types have a gene that displays
multiple alleles and codominance
ABO gene has three alleles
 IA
codes for a A-type ID tag on red blood cells
 IB codes for a B-type ID tag on red blood cells
 i codes for no ID tag on red blood cells
 A
I and IB alleles are codominant
Human Blood Types Continued
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Possible Phenotypes and Genotypes
blood type (IAIA or IAi)
 B blood type (IBIB or IBi)
 AB blood type (IAIB)
 O blood type (ii)
A
Polygenic Traits
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More than one gene codes for a trait
Wide range of phenotypes and genotypes possible
Ex- eye color
Multifactorial Traits
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Phenotype is a blend between genetic
inheritance and environment
Revisiting Independent Assortment
Not all genes independently assort
 Only happens with genes on different
chromosomes
 Genes on the same chromosome are linked
(where one goes the others go too)
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For example, if
 One homologous chromosome has alleles A, B, and c for
three genes
 The other homologous chromosome has alleles A, b, and C
 Then the offspring cannot get A, B, and C or a, b, and c
or any other combinations
Crossing-Over Revisited
Crossing-over can change the combinations of
linked genes
 The further apart that two genes are on a
chromosome, the more likely that they are to
cross-over
 Gene maps are maps of chromosomes that
show the locations of genes and the distances
between them
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