3. Intro to Inheritance
http://learn.genetics.utah.edu/content/begi
n/tour/inheritance.swf
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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. Offspri
ng 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 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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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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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/
