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CHARACTERISTICS OF LIFE
All Living Things reproduce!!!!!
All Living Things Have DNA!!!!
Cladogram
WHY ARE WE ALL DIFFERENT?
We all inherited different genes from our parent
which determines our traits.
Heredity – Passing on of traits from parents
to offspring.
23 chromosomes from
each parent.
Autosomal vs. Sex Chromosomes
• ALL OF THE TRAITS THAT
MENDEL STUDIED WERE
AUTOSOMAL TRAITS.
THAT IS WHY PEA PLANT
WAS AN EASY STUDY. NO
WEIRD TRAITS LIKE
BLENDING!!!
Genes – Pieces of DNA that carry heredity
instructions and are passed from parents.
Traits – A distinguishing characteristic that is
passed from parents to offspring.
Genetics – Study of heredity(passing
on of genes)
JOHANN Gregor Mendel was born July 22,
1822. Mendel became a friar at the Augustinian
monastery in Brno, Czechoslovakia. From 1868
until his death, Mendel was the abbot of the
monastery.
Mendel was experimenting with flowers in
the monastery's gardens. He wondered how
traits were passed from parent to offspring. He
studied the relations between parents and
children with mathematical symbols.
Father of Modern Genetics
•The first person to trace the characteristics of successive generations of a living
thing
•He was not a world-renowned scientist of his day.
• Rather, he was an Augustinian monk who taught natural science to high school
students.
• Second child of Anton and Rosine Mendel
• They were farmers in Brunn
• They couldn’t afford for him to attend
college
• Gregor Mendel then attended the
Augustinian Monastery and became a monk
The Monastery Garden with the greenhouse which
Gregor J. Mendel, O.S.A., had built in 1870. Its appearance
before 1902.Courtesy of Villanova University Archives.
Gregor J. Mendel, O.S.A., experimental garden (35x7
meters) in the grounds of the Augustinian Monastery in
Old Brno.Its appearance before 1922. Courtesy of
Villanova University Archives.
The Birth of the idea: Heredity
• On a walk around the monastery, he found an
atypical variety of an ornamental plant.
• He took it and planted it next to the typical
variety.
• He grew their progeny side by side to see if
there would be any approximation of the traits
passed on to the next generation.
• This experiment was "designed to support or to
illustrate Lamarck's views concerning the
influence of environment upon plants.“
GREGOR MENDAL
He chose to study 7 different traits,only one
at a time, so he could understand the
mathematical results.(tall, flower color and
position, pod color and shape, etc.)
He learned that each plant had two genes for
each trait. One from each parent.
He Argued!!!!
• Parents pass on their offspring
heritable traits(genes) SO two
alleles for every trait. One from
each parent!!!
• Genes retain their individuality.
There is no blending.
Why Did He Chose Peas?
• Short generation times
• Large number of offspring
• Many different traits(varieties)
Why did Mendal work with peas?
• Good choice for environment of monastery(food)
• Network provided unusual varieties for testingseveral traits.
• Obligate self-pollination reproductive system
• Crosses easy to document
• Short life cycle
• Easy to track he traits.
Character vs. trait
• Character – heritable trait varies
that varies among individual. Hair
color, eye color, etc
• Trait – Variant for a character –
brown , black, blonde hair
Self- pollination Vs. Cross
Pollination
Self – pollination – plant pollinates itself.
Peas do this. Mendel could decide on
the test crosses.
Cross pollination – Mendel crossed one
plant with another by taking pollen
from one type of plant and placing it
on the other.
Mendel crosspollinated pea
plants
• He cut away the
male parts of one
flower, then dusted
it with pollen from
another
• He found that the
plants' respective
offspring retained the
essential traits of the
parents, and therefore
were not influenced
by the environment.
Mendel’s 4 Conclusion
1. There are alternative versions of
gene that account for variations in
inherited characters.
Alleles: Alternate versions of a
gene!!!
Mendel’s 4 Conclusion
2. For each character, an organism
inherits two alleles. They can be
the same or different.
Homozygous – identical alleles
Heterozygous – two different alleles.
Mendel’s 4 Conclusion
3. If the 2 alleles of an inherited pair
differ, then one determines the
organism’s appearance. It is
called DOMINANT.
Recessive – no affect on organism
unless dominant is not present.
Mendel’s 4 conclusions
• A sperm or egg carries only one allele
for each inherited character because
allele pairs separate from each other
during gamete formation.
• Law of segregation – Sperm and egg
carries only one allele which separate
during meiosis.
MENDAL’S EXPERIMENT
PART 1He bred a pure tall pea
plant with a pure short pea
plant. ALL the offspring were
TALL.
TT X tt = Tt
PART 2 - F1
He crossed 2 of the
offspring from the above
cross.
Results – 75% Tall
25% Short
Tt X Tt = TT, Tt, tt
Mendelian genetics
• Character (heritable feature, i.e., fur
color)
• Trait (variant for a character, i.e.,
brown)
• True-bred (all offspring of same
variety)
• Hybrid (crossing of 2 different truebreds)
• P generation (parents)
• F1 generation (first filial generation)
Parent Generation
F1 Generation
F2 Generation, 3:1 ratio
Three Conclusions to His Research
1. Principle of Dominance and
Recessiveness
One allele in a pair may mask the
effect of the other
2. Principle of Segregation
The two alleles for a characteristic
separate during the formation of
eggs and sperm
3. Principle of Independent Assortment
The alleles for different
characteristics are distributed to
reproductive cells independently
of the other genes on the
chromosome.
This means all
gametes will be
different!
Independent
Assortment
• Chromosomes separate
independently of each
Bb
other
B
Ff
B
F
b
f
Bb
Bb
Ff
f
b
b
Ff
B
meiosis I
B
B
Bb
diploid (2n)
B
meiosis II
b
F
sperm
haploid (n)
Independent Assortment
• Genes for different traits can segretate
independently during the formation of gametes
without influencing eachother
• Question: How many gametes will be produced
for the following allele
arrangements?
• Remember:
1. RrYy
2n (n = # of heterozygotes
2. AaBbCCDd
3. MmNnOoPPQQRrssTtQq
Mendal’s Death
• Died in 1884 of Nephritis(kidney
inflammation). After his death, his
papers were burnt by his abbott
because they went against beliefs of
the times.
• His work was lost for 50 years!!
Genetic vocabulary…….
• Punnett square:
• Gene: point on a chromosome
that controls the trait
• Allele: an alternate form of a
gene A or a
• Homozygous: identical
alleles for a character
• Heterozygous: different
alleles for a gene
• Phenotype: physical traits
• Genotype: genetic makeup
• Testcross: breeding of a
recessive homozygote X
dominate phenotype (but
unknown genotype)
Vocabulary
• Diploid – Full number of chromosomes in a
somatic cell
• Haploid – Half number of chromosomes in
a gamete.
Dominant and Recessive alleles
Dominant alleles – upper-case
a. homozygous dominant
(BB – Brown eyes)
Recessive alleles – lower case
a. homozygous recessive
(bb – blue eyes)
b. Heterozygous (Bb – Brown eyes)
Dominant gene – Stronger of the two
traits and masked(hides) the recessive
trait.
Recessive gene – Weaker trait.
For these reasons, he is called the
Father of Genetics.
GENETICS RULES
GENETIC SYMBOLS
Use symbols to represent different forms of a
gene.
Capital Letters – Represents dominant
trait.
Lower Case Letters – Represents recessive
trait.
Examples- B – Brown eyes
b – blue eyes
GENETIC RULES
Every organism has TWO forms of every gene.
One from each parent. Each form is called
an ALLELE. You could have got a blue eye gene
from mom and a brown eye gene from dad.
Examples – Bb, WW, gg, Rr
An organism can have the same gene for the
trait or they can have two different genes.
If the genes are the same, then they
are called HOMOZYGOUS or purebred.
Examples – aa(one antenna),
AA(2 antenna), LL(different
colored legs), ll(clear legs), TT(curly
Tail), tt(straight tail)
If the genes are different, then they
are called HETEROZYGOUS or hybrid
Examples – Aa(2 antenna),
Ll(different color leg),
Tt(curly tail)
Phenotype vs. Genotype
• Outward appearance • Arrangement of
• Physical
genes that
characteristics
produces the
• Examples:
1.Brown eyes
2.blue eyes
phenotype
• Exmple:
1. TT, Tt
2.
tt
GENETIC PROBABILITY
Mendal crossed yellow and green pea plants
and discovered that 1 out of 4 were green.
He was using probability.
Probability – The possibility or likelihood that
a particular event will occur.
Used to predict – the results of genetics
crosses.
The squares contain the gene combinations
that could occur in the cross.
The genotype is the letter combination or
gene combinations in the squares.
Example – Tt, Aa, bb,or Ll
The phenotype is the actual appearance of
the organism.
Example – curly tail, 2 antennas, 3 body
Segments, different color legs
PUNNETT SQUARES
A Punnett square is a special chart used to
show the possible gene combinations in a
cross between 2 organisms.
Developed by an English genetists by the
name of Reginald Punnett.
5 Steps of Punnett Square
1. Determine the genotypes of parents.
2. Set up your Punnett Square. Dad’s
genotype on top and Mom’s on side.
3. Fill in squares by combining sperm with
egg.
4. Write out possible combos(genotype).
5. Determine phenotype ratio.
How does a Punnett Square Work?
1. Draw a square and divide
it into 4 sections.
2. Write the gene pairs
across the top of the
box, then the
other down the side
3. In each box, place
the correct gene to see
the possible combinations.
Each square
represents a 25%
possibility of getting
that trait.
PARTS OF A PUNNETT SQUARE
Male Genes
Female
Genes
Offspring
Combinations
Tt
Tt
Tt
Tt
Cross between
homozygous
dominant and
recessive.
What are the percent of the offspring?
What are the genotypes?
What are the phenotypes?
TT
Tt
Tt
tt
Cross between
two heterozygous
parents.
What are the percentages of offspring?
What are the genotypes?
What are the phenotypes?
Mathematical Computations
In a Punnett Square where both parents are
Hybrids the percents are listed below:
25% purebred(homozygous) black – BB
50% hybrid(heterozygous) black - Bb
25% purebred(homozygous) white - bb
% of same genotype as parents - 50 %
% of same phenotype as parents - 75%
What about 2 Traits?
• BbTt x BbTt
• The Gametes contain one of each of the
alleles. (BT).
• Each of the offspring contain four alleles
exactly like the parents.(BbTt).
• Notice the number of possible offspring
has increased.
• The phenotypic ratio is 9:3:3:1
Steps of Dihybrid Cross
Dihybrid Cross
Dihybrid Cross
RY
RY
Ry
rY
ry
Ry
rY
ry
Dihybrid Cross
RY
RY RRYY
Ry
Ry
RRYy
rY
RrYY
ry
RrYy
Round/Yellow:
9
Round/green:
3
RRYy
RRyy
RrYy
Rryy
rY RrYY
RrYy
rrYY
rrYy
wrinkled/green:
ry RrYy
Rryy
rrYy
rryy
9:3:3:1 phenotypic ratio
wrinkled/Yellow: 3
1
Dihybrid Cross
• Example:cross between round and yellow
heterozygous pea seeds.
R
r
Y
y
= round
= wrinkled
= yellow
= green
RrYy x RrYy
RY Ry rY ry
x
RY Ry rY
possible gametes produced
Genetics Beyond Mendel
•
•
•
•
Sex linked
Incomplete dominance
Codominance
Pedigrees
Incomplete Dominance
• One allele is not
completely dominant over
another. THEY BLEND
TOGETHER!!
R
R
W
RW
RW
produces the
F1 generation
W
RW
RW
All Rr = pink
(heterozygous pink)
INCOMPLETE DOMINANCE
Sometimes, you may notice that traits can blend
Together. The blending of two traits is call
incomplete
dominance. Two capital letters are used. For
example, from baby marmellow RY = orange nose,
RR = red nose, and RY = yellow nose
Examples – palomino in horses, pink color in
flowers are red and white combined.
Cat Examples
• Black cat mated to a white cat can get a
gray cat!!!
What is meant by
MULTIPLE ALLELES?
• A trait that is controlled by more
than two alleles is said to be
controlled by multiple alleles
• Traits controlled by multiple alleles
produce more than three phenotypes
of that trait.
• Codominance – situation where both
alleles are expressed.
Multiple Alleles and Codominance
• Ex )Blood type
• Blood type A and B are co-dominant,
while O is recessive.
• Forms possible blood types of A, B, AB,
and O.
Codominance
• Both alleles are
expressed
1.
type A=
IAIA
or
IAi
2. type B= IBIB or IBi
3. type AB= IAIB
4. type O= ii
Black cow + white cow =
spotted cow
Blood Also Shows Codominance
Where are Disorders Located?
• Autosomal chromosomes: 1 - 22
– The disorder is caused by a gene or
nondisjunction of chromosomes 1 - 22.
* Sex Linked disorders: Located on the X
or Y chromosomes.
Sex Linked Genes
Sex Linked Traits or Disorders - The X and
Y chromosomes carry the genes that
determine gender traits so the genes located
on X and Y are called sex linked.
• X – 1098 genes
• Y – 26 genes much smaller!!!
Sex Linked Genes
• The genes that are on the X are expressed in
the phenotype of the male because it is the
only gene they carry. If the gene is a
recessive for a disorder, the male will have
the disorder.
• Ex: hemophilia, duchene muscular, fragileX syndrome, high blood pressure(some),
night blindness, and red-green color
blindnesss.
Sex-Linked Inheritance
• Traits that are only found on the X
chromosome
• Colorblindness and Hemophilia are
examples of sex-linked traits.
• These genes are recessive and found only
on the X chromosome.
How Would a Female Have a
Sex Linked Disorder?
• She would have to receive a recessive gene
from both parents.
Queen Victoria of England
• Carrier of hemophilia
• X-linked traits to one of her sons. He died
but all of her daughters were carriers.
• They married into the Russia royal families
and spread it to the Russian royality.
• By 20th century, 20 of her descendants had
hemophilia.
History
• Her daughter Alexandra married Tsar Nicholas of
Russian. Finally had a son Alexei. He had
hemophilia. He was the only son and only heir to
become Tsar. To keep people from learning of his
disease, they withdrew from society. The people
mistook this as they did not care. Alexei had som
internal bleeding and a man by the name of
Rasputin stopped the bleeding. He was let into the
inner circle. Many thought he led to revolution.
Why do Pedigrees?
• Punnett square tests work well for organisms
that have large numbers of offspring and
controlled matings, but humans are quite
different:
1. small families. Even large human families
have 20 or fewer children.
2. Uncontrolled matings, often with
heterozygotes.
3. Failure to truthfully identify parentage.
Today... Pedigree analysis
 In humans, pedigree analysis is an important
tool for studying inherited diseases
 Pedigree analysis uses family trees and
information about affected individuals to:
figure out the genetic basis of a disease
or trait from its inheritance pattern
predict the risk of disease in future
offspring in a family (genetic counseling)
Goals of Pedigree Analysis
• 1. Determine the mode of inheritance:
dominant, recessive, partial dominance, sexlinked, autosomal, mitochondrial, maternal
effect.
• 2. Determine the probability of an affected
offspring for a given cross.
Basic Symbols
More Symbols
Today... Pedigree analysis
 How to read pedigrees
 Basic patterns of inheritance
autosomal, recessive
autosomal, dominant
X-linked, recessive
X-linked, dominant (very rare)
 Applying pedigree analysis - practice
Sample pedigree - cystic fibrosis
male
female
affected individuals
Dominant vs. Recessive
• Is it a dominant pedigree or a recessive pedigree?
• 1. If two affected people have an unaffected child, it must
be a dominant pedigree: D is the dominant mutant allele
and d is the recessive wild type allele. Both parents are Dd
and the normal child is dd.
• 2. If two unaffected people have an affected child, it is a
recessive pedigree: R is the dominant wild type allele and r
is the recessive mutant allele. Both parents are Rr and the
affected child is rr.
• 3. If every affected person has an affected parent it is a
dominant pedigree.
Assigning Genotypes for Dominant
Pedigrees
• 1. All unaffected are dd.
• 2. Affected children of an affected parent and an
unaffected parent must be heterozygous Dd, because they
inherited a d allele from the unaffected parent.
• 3. The affected parents of an unaffected child must be
heterozygotes Dd, since they both passed a d allele to their
child.
• 4. Outsider rule for dominant autosomal pedigrees: An
affected outsider (a person with no known parents) is
assumed to be heterozygous (Dd).
• 5. If both parents are heterozygous Dd x Dd, their affected
offspring have a 2/3 chance of being Dd and a 1/3 chance
of being DD.
Autosomal Dominant
• Assume affected
outsiders are assumed
to be heterozygotes.
• All unaffected
individuals are
homozygous for the
normal recessive
allele.
Autosomal dominant pedigrees
• Trait is common in the pedigree
• Trait is found in every generation
• Affected individuals transmit the trait to ~1/2 of
their children (regardless of sex)
Dominant Autosomal Pedigree
I
2
1
II
1
2
3
4
5
6
III
1
2
3
4
5
6
7
8
9
10
Autosomal dominant traits
There are few
autosomal dominant
human diseases
(why?), but some
rare traits have this
inheritance pattern
ex. achondroplasia
(a sketelal disorder
causing dwarfism)
Assigning Genotypes for Recessive
Pedigrees
• 1. all affected are rr.
• 2. If an affected person (rr) mates with an unaffected person, any
unaffected offspring must be Rr heterozygotes, because they got a r
allele from their affected parent.
• 3. If two unaffected mate and have an affected child, both parents must
be Rr heterozygotes.
• 4. Recessive outsider rule: outsiders are those whose parents are
unknown. In a recessive autosomal pedigree, unaffected outsiders are
assumed to be RR, homozygous normal.
• 5. Children of RR x Rr have a 1/2 chance of being RR and a 1/2
chance of being Rr. Note that any siblings who have an rr child must
be Rr.
• 6. Unaffected children of Rr x Rr have a 2/3 chance of being Rr and a
1/3 chance of being RR.
Autosomal Recessive
• All affected are
homozygotes.
• Unaffected outsiders
are assumed to be
homozygous normal
• Consanguineous
matings are often (but
not always) involved.
Autosomal recessive traits
• Trait is rare in pedigree
• Trait often skips
generations (hidden in
heterozygous carriers)
• Trait affects males and
females equally
Recessive Autosomal Pedigree
Autosomal recessive diseases in humans
Most common ones
• Cystic fibrosis
• Sickle cell anemia
• Phenylketonuria (PKU)
• Tay-Sachs disease
For each of these, overdominance
(heterozygote superiority) has been suggested
as a factor in maintaining the disease alleles at
high frequency in some populations
Y-Linked Inheritance
• We will now look at how
various kinds of traits are
inherited from a pedigree
point of view.
• Traits on the Y
chromosome are only
found in males, never in
females.
• The father’s traits are
passed to all sons.
• Dominance is irrelevant:
there is only 1 copy of
each Y-linked gene
(hemizygous).
X-linked recessive pedigrees
• Trait is rare in pedigree
• Trait skips generations
• Affected fathers DO
NOT pass to their sons,
• Males are more often
affected than females
X-linked recessive traits
ex. Hemophilia in European royalty
X-linked recessive traits
ex. Glucose-6-Phosphate Dehydrogenase deficiency
• hemolytic disorder causes jaundice in infants and
(often fatal) sensitivity to fava beans in adults
• the most common enzyme
disorder worldwide, especially
in those of Mediterranean
ancestry
• may confer malaria resistance
X-linked recessive traits
ex. Glucose-6-Phosphate-Dehydrogenase deficiency
X-linked dominant pedigrees
• Trait is common in pedigree
• Affected fathers pass to ALL of their daughters
• Males and females are equally likely to be affected
Sex-Linked Dominant
• Mothers pass their X’s to both
sons and daughters
• Fathers pass their X to
daughters only.
• Normal outsider rule for
dominant pedigrees for females,
but for sex-linked traits
remember that males are
hemizygous and express
whichever gene is on their X.
• XD = dominant mutant allele
• Xd = recessive normal allele
Sex-Linked Recessive
• males get their X from their
mother
• fathers pass their X to daughters
only
• females express it only if they
get a copy from both parents.
• expressed in males if present
• recessive in females
• Outsider rule for recessives
(only affects females in sexlinked situations): normal
outsiders are assumed to be
homozygous.
X-linked dominant diseases
• X-linked dominant diseases are extremely unusual
• Often, they are lethal (before birth) in males and
only seen in females
ex. incontinentia pigmenti (skin lesions)
ex. X-linked rickets (bone lesions)
Pedigree Analysis in real life: complications
Incomplete Penetrance of autosomal dominant traits
=> not everyone with genotype expresses trait at all
Ex. Breast cancer genes BRCA-1 and BRCA-2
& many “genetic tendencies” for human diseases
What is the pattern of inheritance?
What are IV-2’s odds of being a carrier?
What is the inheritance pattern?
What is the genotype of III-1, III-2, and II-3?
What are the odds that IV-5 would have an affected son?
Sample pedigree - cystic fibrosis
What can we say about
I-1 and I-2?
What can we say about
II-4 and II-5?
What are the odds that
III-5 is a carrier?
What can we say about
gene frequency?
III-1 has 12 kids with an unaffected wife
8 sons - 1 affected
4 daughters - 2 affected
Does he have reason to be concerned about paternity?
Breeding the perfect Black Lab
How do we get a true-breeding line for both traits??
black individuals = fetch well
grey individuals = don’t drool