Gregor Mendel
• Gregor Mendel:
– Austrian monk lived from
1822-1884
– Mendel developed
principles of heredity
without any knowledge of
genes or chromosomes
– His principles were
established through
experiments with pea plants
Why was Mendel successful with the pea?
• Used pure breeding, 7 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
• Inexpensive
• Used scientific method
• Easy to pollinate (transfer of male pollen to egg)
Mendel’s 7 contrasting traits
Genes and Heredity
• Genes: factors that control organism 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, there
must be a reliable way to transfer hereditary
information from one generation to the next
Genes and Heredity
• Heredity the passing of traits from parents to offspring.
• Genetics the study of heredity (the passing of traits)
• Each human cell contains 30 thousand different genes
Alleles
• Alleles: part of a gene associated with a particular
characteristic & located on a specific chromosome
• Example:
– Height is a gene(height is a trait)
– tallness or shortness are alleles
• The alleles determine
how each gene is expressed.
At least 2 alleles for one gene.
T
TT
t
t
Chromosomes and Traits
• chromosomes: hereditary units of an organism
-carries genetic information
-made of DNA
-consists of two identical sister
chromatids and a centromere.
• locus: particular point where a certain
gene is found on a chromosome
cenrtomere
Sister
chromatids
Homologous Chromosomes pair of associated chromosomes
one from mom & one from dad
-
always the same size (EXCEPT XY)
- centromere always in the same spot
- genes on sister chromatids are identical
- the alleles on homologous chromosomes are coded
for the same gene, but could be different.
Asexual vs. Sexual
Reproduction
• Asexual reproduction:
– All the genes come from
a single parent
– These genes are normally identical to the parent (clone)
• Sexual reproduction:
– Organisms receive half their genetic information from the
Mother's egg and half from their Father's sperm
– Sexually reproduced offspring resemble but are not
identical to their parents
Back to Mendel
• The significance of Mendel's work was not
immediately recognized
• Mendel's hereditary factors, now called genes,
exist at definite loci on chromosomes
• The gene-chromosome theory provides the
mechanism to account for the hereditary
patterns which Mendel observed
Genetics Terms
• homozygous (pure): the alleles on homologous
chromosomes are the same
• heterozygous: (hybrid): the alleles on
homologous chromosomes are different
• parental generation (P): the two original
organisms being crossed - usually pure
• first filial generation: the first generation of
offspring from the parents
• second filial generation: generation of
offspring arising from the first filial generation
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
– Example:
red flower (RR) X white flower (rr)  red flower (Rr)
X

Law of Dominance
• Dominant Trait: the trait or allele that is
expressed (capital letter) R
• Recessive Trait: the trait or allele that is
present but that is not expressed
(lowercase letter) r
Punnett Squares
• Punnett square: a model used to predict the
results of a genetic cross
• Genotype: the genetic makeup of an organism
– Homozygous Dominant: TT
– Homozygous Recessive: tt
– Heterozygous: Tt
• Phenotype: the appearance of an organism
– Describe what it looks like
TT - Tall
tt - short
Tt - Tall
Example of Dominance
Problem:
Cross homozygous
dominant with
homozygous recessive
• R = red
• r = white
• RR x rr
R
r
Results:
1st Generation Flowers:
Phenotype: 100%
red
Genotype: 100%
heterozygous
r
Rr
Rr
R
Rr
Rr
2. Law of Segregation
Mendel’s second law
– 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 _______________
and can lead to genetic recombination.
Example of Segregation
Problem:
Cross offspring from 1st
cross (2 heterozygous
parents)
• R = red
• r = white
• Rr x Rr
Results:
2nd Generation Flowers:
Phenotype: 75% red, 25%
white
Genotype: 25% homozygous
dominant, 25% homozygous
recessive, 50% heterozygous
R
r
R
r
RR
Rr
Rr
rr
Law of Independent
Assortment
Mendel’s third Law
– Scenario: Two different traits located on two different
chromosomes
• 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
Law of Independent Assortment
Incomplete Inheritance
• Two examples:
– Incomplete Dominance
– Codominance
• Incomplete Dominance:
– Case where one allele is partially dominant over the other
– Examples: red X white snapdragons  pink snapdragons
cross between black and white Andulusian
fowl gives blue (gray) fowl
Example of Incomplete
Problem:
Cross offspring from 1st
cross (2 heterozygous
parents)
• R = red
• r = white
• Rr x Rr
R
R
RR
r
Rr
Results:
2nd Generation Flowers:
Phenotype: 50% pink, white 25%, 25% red
Genotype: 50% heterozygous
25% homozygous dominant
25% homozygous recessive
r
Rr
rr
Intermediate Inheritance
• Codominance: a case in which neither allele is
dominant over the other
– Alleles have equal power
• Examples:
– Cross between red and white short horned cattle
gives roan cattle
– Checkered black & white chicken
– Sickle-cell Anemia - a blood disease where RBCs are
sickle shaped or half moon. Most common African.
– Heterozygous - half normal half sickle shape
Example of Codominance
Problem:
Cross offspring from 1st
cross (2 heterozygous
parents)
• R = red
• r = white
• Rr x Rr
R
R
RR
r
Rr
Results:
2nd Generation Flowers:
Phenotype: 50% red & white 25% red, 25% white
Genotype: 25% homozygous dominant
25% homozygous recessive
50% heterozygous
r
Rr
rr
Pink Snapdragons
X

Roan Cattle
X
Red Cattle

Roan Cattle
White Cattle
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 b
– Blood groups in humans
Four blood types A B AB & O
Dihybrid Cross
Problem:
Cross homozygous tall
and homozygous
wrinkled seeds with
homozygous short and
homozygous smooth
seeds
T = tall
t = short
Q = wrinkled
q = smooth
What are the genotypes
for these plants?
TTQQ x ttqq
TTQQ x ttqq
TQ TQ
TQ
TQ
tq
TtQq
TtQq
TtQq
TtQq
tq
TtQq
TtQq
TtQq
TtQq
tq
TtQq
TtQq
TtQq
TtQq
tq
TtQq
TtQq
TtQq
TtQq
Phenotype: 100% Tall & Wrinkled
Dihybrid Cross
• What is the phenotype from this cross?
– 100% Tall and Wrinkled
• What is the genotype from this cross?
– We don’t worry about genotype for dihybrid
crosses
Complete the following Dihybrid cross
Step 1 - set up gamettes(sex cells)
(1 3, 1 4, 2 3, 2 4)
TtQq x TtQq
Complete the following Dihybrid cross
TtQq x TtQq
TQ
tq
Tq
tQ
TQ TTQQ
TTQq
TtQQ
TtQq
Tq
TTQq
TTqq
TtQq
Ttqq
tQ
TtQQ
TtQq
ttQQ
ttQq
tq
TtQq
Ttqq
ttQq
ttqq
What are the phenotypes for the
above cross???
• 9 - Tall & Wrinkled
• 3 - Tall & round
• 3 - Short & wrinkled
• 1 - Short & round
Changing Chromosome Structure
Translocation: transfer of one section of a chromosome
Addition: a portion of one chromosome is attached to
another chromosome
Deletion: a portion of a chromosome is taken away from a
chromosome
Inversion: a portion of a chromosome breaks off and then
becomes reattached to the same chromosome in an
inverted (upside down) fashion
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
Gene Expression
• Influence of Internal Environment:
• Examples: Hormonal influences
– Horn size in mountain sheep
– Male pattern baldness
– Peacock feathers
Gene Expression
• Influence of Internal Environment:
• Examples: Hormonal influences
– Horn size in mountain sheep
– Male pattern baldness
– Peacock feathers
Problem 1
Phenotype of tt ------------------------- Short
Genotype of tt--------------------------- Homozygous recessive
Phenotype of TT ----------------------- Tall
Genotype of TT------------------------- Homozygous dominant
Phenotype of pure dominant-------- Tall
Genotype of pure homozygous----- TT
Phenotype of pure recessive-------- Short
Genotype of pure recessive--------- tt
Problem 2
Problem:
A married couple want to know
their chances of having girl
X
Y
X
XX
XY
X
XX
XY
X __
Y x __
X __
X
__
Results:
2nd Generation Flowers:
Phenotype: 50% BOY,
50% GIRL
Problem 3
Problem:
Cross 2 heterozygous parents
• R = red
• r = white
R
R
R __
r
r x __
• _R_ __
r
Results: 2nd Generation Flowers:
Phenotype: 75% red, white 25%
Genotype:
50% heterozygous
25% homozygous dominant
25% homozygous recessive
r
RR
Rr
Rr
rr
Problem 4: Law of dominance
Pure dominant cross with hybrid
• R = red
• r = white
R __
R x __
R __
r
• __
R
R
RR
r
Rr
Results: 2nd Generation Flowers:
Phenotype: 100% red
Genotype:
50% homozygous dominant
50% heterozygous
R
RR
Rr
Problem 5: Law of dominance
Problem:
The male’s genotype is
heterozygous. The female is
phenotypically dominant but
does carry the recessive allele.
• R = red
• r = white
r x _R _r
•R
_ _
R
R
RR
r
Rr
r
Rr
rr
Results: 2nd Generation Flowers:
Phenotype: 75% red, white 25%
Genotype: 50% heterozygous
25% homozygous dominant
25% homozygous recessive
Problem 6: Law of Codominance
Problem:
Cross 2 heterozygous parents
• R = red
• r = white
R r_ x _R _r
• _
R
R
RR
r
Rr
Results: 2nd Generation Flowers:
Phenotype: 25% red, white 25% 50 % red & white
Genotype:
25% homozygous dominant
25% homozygous recessive
50% heterozygous
r
Rr
rr
Nature vs. Nurture
• In many cases it is not only the genes that
we have that determine what we look like
• Scenario: If identical twins (same DNA)
were separated at birth and lived in 2
different environments and then brought
together 25 years later would they look the
same? Why or why not?
Nature vs. Nurture
• Answer:
The identical twins would have similar features
(eye color, size of nose, etc.) but may look very
different. What they did throughout their lives
effects what they look like
– For example: sun exposure, diet, hygiene, injuries,
etc.
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
Crossing Over
• Crossing Over: during meiosis
homologous chromosomes often:
– Twist around each other and break then
– Exchange segments and rejoin
• Crossing over results in:
– The rearrangement of genes
– An increased variability of offspring
Karyotypes
• Karyotype: an enlarged photograph of the
chromosomes in an organism
Human Karyotype
• Human diploid cells contain 23 pairs of chromosomes
• Autosomes: body chromosomes (22 pr. in humans)
• Homo sapiens have one pair of sex chromosomes
– Males: each sex chromosome is unlike and is
designated XY
– Females: each sex chromosome is alike and is
designated XX
• The sex of a human is genetically determined at
fertilization when a sperm cell containing either an X or a
Y chromosome unites with an egg cell containing an X
chromosome
Fertilization
Mutations
• Mutation: change in DNA
– Mutations in body cells effect present
organism, but CAN NOT BE PASSED ON to
offspring
– Mutations in sex cells CAN be passed on to
the offspring
• WHY?: Nonsex cells are not apart of the
fertilization process—only sex cells are
Mutations
• Chromosomal Alterations:
– Nondisjunction
• Example: Down’s Syndrome
– Polyploidy
• Example: 3n or 4n set of chromosomes
• Most mutations are harmful and recessive
Mutagenic Agents
• Mutagenic Agents: increase the possibility of
mutations
– Radiation: X-rays, ultraviolet, radioactive & substances
– Chemicals: formaldehyde, asbestos, and nicotine
• The adaptive value of a gene mutation is
dependent upon the nature of the mutation and
the type of environment with which the
organism interacts
Genes and the environment
• The environment interacts with
genes in the development and
expression of inherited traits
• Here is an example…
Types of Selective Breeding
• Artificial Selection: individuals with
desirable traits are mated to produce
offspring with those traits
• Inbreeding: offspring produced by
artificial selection are mated with one
another to reinforce those desirable traits
Selective Breeding
• Hybridization: crossing two individuals
with different desirable traits to produce
offspring with a combination of both
desirable traits
– English shorthorn cattle
(good beef) X Brahman
cattle (heat resistant) 
Santa Gertrudis cattle
(good beef and heat
resistance)
Types of Selective Breeding
• Mutations may be preserved by vegetative
propagation
– Example: seedless oranges and bananas
Types of Selective Breeding
• Recombinant DNA:
– Also called genetic engineering
– Creates new varieties of plants and animals
by manipulating the genetic instructions of
these organisms to produce new
characteristics
Genetic Research
• Knowledge of genetics is making possible new
fields of health care
• Mapping of genetic instructions in cells makes it
possible to detect, and perhaps correct,
defective genes that may lead to poor health.
• Substances from genetically engineered
organisms may reduce the cost and side effects
of replacing missing body chemicals.
Genetic Research
• Cloning: producing a group of genetically
identical offspring from the cells of an
organism
• This technique shows great promise in
agriculture
– Plants with desirable qualities can be rapidly
produced from the cells of a single plant
Genetic Research
• Genetic engineering: (recombinant DNA)
– transfer of genetic information from one
organism to another
– includes the transfer of entire genes and gene
splicing
– Genetic engineering can correct genetic
defects & produce agriculturally more
efficient plants and animals
Recombinant DNA
• A cell can synthesize a new chemical
coded for by its new genes
• Examples:
– Interferon: helps fight infections
– Insulin: combat diabetes
– Growth hormone: help stimulate growth
Recombinant DNA
X
(X)
How Recombinant DNA Works
• Restriction Enzymes: enzymes used to cut
segments of DNA in one organism so they can
be transferred into another organism
– Characteristics produced by the segments of DNA
may be expressed when these segments are inserted
into new organisms such as bacteria.
– Inserting, deleting, or altering DNA segments can
alter genes. An altered gene may be passed on to
every cell that develops from it.
Difficulties with Genetic
Engineering
•
•
•
•
The moved gene may not be expressed
It is difficult to isolate the gene
The trait may be recessive
There may be unintended adverse
qualities
Human Genome Project
• Human Genome Project: has allowed
humans to know the basic framework of
their genetic code
– Knowledge of genetics is making possible
new fields of health care
– Genetic mapping is making it possible to
detect and possibly correct, defective genes
that may lead to poor health.
More on Genetic Research
• A down side to this is that health insurance
agencies and other organizations may use
this genetic information against
individuals.
• Substances from genetically engineered
organisms may reduce the cost and side
effects of replacing body chemicals.
Human insulin produced in bacteria is
already an example of this.
Future of Genetic Engineering?
Genetic Disorder
Name of
Technique used to
Characteristic
Disorder
Diagnose
of Disorder
Sickle Cell Microscopic
Low oxygen
Anemia
examination of blood supply of cells
Down’s
Karyotype
Syndrome
Mental
Retardation
PKU
Mental
retardation
Urine analysis
Amniocentesis
• One final way to check for genetic
diseases is through amniocentesis
– Checks the proteins of the developing fetus
while in the womb