Gregor Mendel conducted experiments with garden peas in the 1850s to study inheritance of traits. He found that traits are passed from parents to offspring in predictable ratios. Some key findings were that traits are controlled by discrete units (now known as genes), alleles can be dominant or recessive, and genes assort independently during reproduction. Mendel's work established the foundations of classical genetics but was not widely recognized until the early 1900s.

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Genetics

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Genetics & Inheritance
What you get isn’t always what you get

3. Intro to Inheritance
 http://learn.genetics.utah.edu/content/begin/t
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Gregor Mendel (7/22/1822 - 1/6/1884)
 “Father of Modern Genetics”
 Born in 1822 in Heinzendorf Moravia
in what is now the Czech Republic
 Born in Heinzendorf, Austria on July
22, 1822. He died in Brno, Austria
January 6, 1884
 Augustinian monk employed as high
school natural science teacher for 20
years

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Gregor Mendel (7/22/1822 - 1884)
 Experimented with garden peas Pisum
sativum
 Tested some 28,000 pea plants in 7 years
 Used artificial feritization
 Worked in limited space in monastery
garden
 First to consider single traits of
hybridization experiments results
 Devised precise mathematical pattern
 Did not understand biological process, eg.
chromosomes & DNA
 1900 three botanists “discovered” his
papers while researching their own
findings
Mendel, O.S.A., experimental garden
(35x7 meters) in the grounds of the
Augustinian Monastery in Old Brno.
Its appearance before 1922.

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Mendel’s Pea Plants
 Pisum sativum
 Diploid
 Seven pairs of traits
• Axial / terminal
flowers (Aa)
• Purple / white Flower
coats (Pp)
• Tall / short (Tt)
• Round / wrinkled (Ss)
• Green / yellow seeds
(Gg)
• Inflated / constricted
(Ii)
• Green / yellow unripe
pods (Gg)

7. Mendel’s Pea Plants
 Pisum sativum
 Mendel fertilized the
pea flowers and
removed other
underdeveloped
reproduction parts
before self-fertilization
could take place.
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8. William Bateson, English
 Gave name genetics
based on Greek term
"to generate"
 Promoted Mendell's
view of paired genes
using term allelomorph,
shortened to allele.
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Basic Ideas
 Mendel used term unit
characters based on
physical elements and
occurring in pairs of
allele. We now call
these genes.
 The paired genes (allele
pairs) separate form one
another and are
distributed to different
sex cells through
meiosis

10. Mendel's 3 Laws
1. The Law of
Dominance
 In a cross of parents
that are pure for
contrasting traits,
only one form of the
trait will appear in
the next generation.
Offspring that are
hybrid for a trait
will have only the
dominant trait in the
phenotype.
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11. Mendel's 3 Laws
2. The Law of
Segregation
 During the formation
of gametes (eggs or
sperm), the two alleles
responsible for a trait
separate from each
other.
 Alleles for a trait are
then "recombined" at
fertilization, producing
the genotype for the
traits of the offspring.
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12. Mendel's 3 Laws
3. The Law of
Independent
Assortment
 Alleles for different
traits are
distributed to sex
cells (& offspring)
independently of
one another.
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Terms
 Allele: an alternate form of a
gene. Variants that occur at
the same locus.
 Homozygous: having the
same alleles for same trait
 Heterozygous: having
different alleles for same trait
 Phenotype — physical looks
of genes
 Genotype — the actual genes
 Dominance — phenotypic
recognition
 Recessive —carriers

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Labeling:
The standard way of
labeling the variation
information of a trait in a
particular organism is using
two letters.
 Capital letters represent
information which is
dominant.
 Lowercase letters
represent the recessive.
The letter being used
describes a variation
(usually the recessive) of
the trait.
GG stands for a plant where both
pieces of color information are
dominant - yellow. The plant is
yellow.
Gg stands for a plant where one
piece of color information is
dominant - yellow, and the
other is recessive - green. The
plant is yellow.
Gg stands for a plant where one
piece of color information is
recessive - green, and the other
is dominant - yellow. The plant
is yellow.
gg stands for a plant where both
pieces of color information are
recessive - green. The plant is
green.

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Pea Plant Traits
Trait:
Dominant
Expression:
Recessive
Expression:
1 Form of ripe seed Smooth Wrinkled
2 Color of seed albumen Yellow Green
3 Color of seed coat Grey White
4 Form of ripe pods Inflated Constricted
5 Color of unripe pods Green Yellow
6 Position of flowers Axial Terminal
7 Length of stem Tall Dwarf

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Examples of genetic traits studied by
Mendel

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Examples of Phenotypes & Genotypes
 Phenotypes for
garden peas
 Genotypes for
garden peas

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Terms
 Codominance
 Heterozygote expressing
each allele equally
 Semidominance
 Similar to codominance, but
not equal expression of both
alleles
 Filial
 Latin for progeny
 F1 --
 F2 --

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Law of Probability
 The chance of two
or more independent
events occurring
together is the
product of the
chances for their
separate
occurrences.

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Terms

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Monohybrid Cross

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Punnett Square
 Diagram of a Monohybrid
Cross

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Monohybrid Cross—Punnett Square

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Monohybrid Cross, P1
Genotype Phenotype
Gg Green
Homozygous Green
X
Homozygous Yellow

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Monohybrid Cross, ƒ1
Genotype Phenotype
GG Green
Gg Green
gg Yellow
Heterozygous Green
X
Heterozygous Green

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Monohybrid Ratios
 Genotypic Ratio
 1:2:1
 Phenotypic Ratio
 3:1
# Genotype Phenotype #
1 GG Green 3
2 Gg Green
1 gg Yellow 1

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Dihybrid Cross

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Dihybrid Cross

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Dihybrid Cross

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Dihybrid Punnett Square

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Dihybrid Punnett Square

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Dihybrid Punnett Square

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Dihybrid Punnett Square

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Dihybrid Punnett Square

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Dihybrid Punnett Square
 Genotypes
 GGRR
 GGRr
 GgRR
 GgRr
 GGrr
 ggRR
 Ggrr
 ggRr
 ggrr
 Genotypic Ratio
 1:1:2:2:4:2:2:1:1

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Dihybrid Punnett Square

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Dihybrid Punnett Square

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Dihybrid Punnett Square
 Phenotypes
 Green Round
 Green Wrinkled
 Yellow Round
 Yellow Wrinkled
 Phenotypic Ratio
 9:3:3:1

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Partial Dominance
 When one allele isn't
fully dominant over its
partner

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Partial Dominance Example
Genotype Phenotype
RR Red
Rr Pink
rr White
Pink flowers
X
Pink flowers

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Epistiasis - two genes affecting property do not have
equal vote
 Example: melanin and
melanin deposition
(black, white, and
brown coat of guinea
pig). Black is dominant
brown is recessive
when melanin
producing gene is
present. Coat is white
when no melanin is
deposited.

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Collaboration - two genes interact
to produce a novel phenotype
 Example: comb types
in chickens

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Multiple Gene Inheritance
(polygenic)
 Nilsson-Ehle's trigenic
cross of wheat (10-8)
 Frequency distribution
(10-9)

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Sex-related Characteristics
 Holandric - genes
unique to Y
chromosome, hair
pinna on ears
 Eye color in fruit flies
 Hemophilia
 Color blindness

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Sex-linked Inheritance
 Drosophila

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Sex-linked Inheritance
 Hemophilia

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Pedigree

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Slugs Mating

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Webpage Links
 The Genetic Code - S.D. Black, U. of Texas Health Center at Tyler Table relating nucleic
acid triplet to the corresponding amino acid.
 Molecular Biology - The Biology Project, Biology, University of Arizona Activities, Problems
sets, and Tutorials: Molecular Genetics; Nucleic Acids; Recombinant DNA Technology;
Eukaryotic Gene Expression
 Prokaryotic Genetics and Gene Expression from the MIT Hypertextbook - M.I.T. Tools for
studying prokaryotic genetics, biochemical genetics, Lac operation, etc.
 The making of the nucleosome - D. Pruss Simplified images and a tour.
 http://www.agen.ufl.edu/~chyn/age2062/lect/lect_10/lect_10.htm
 http://www.borg.com/~lubehawk/mendel.htm
 http://www.sonic.net/~nbs/projects/anthro201/disc/