Download Gregor Mendel

UNIT 3-GENETICS
What is Genetics?

The branch of biology that studies
heredity
What is heredity?
 The passing of characteristics from
parents to offspring. The fittest survive
to reproduce and pass on traits that
improve survivability
What are Characteristics?
 Are traits that are inherited from the
parents (i.e. flower color, plant
height, eye color, hair color )
Who is the founder of
Genetics ?
Gregor Mendel
a Monk in Austria
Mendel

Modern genetics had its beginnings in an
abbey garden in the 1850’s, where a monk
named Gregor Mendel documented a
mechanism of inheritance.
 He discovered the basic principles of heredity
by breeding garden peas in carefully planned
experiments.
 His approach to science had been influenced
at the University of Vienna by one of his
professors: the physicist Doppler.

He was the first person to succeed in
predicting how traits are transferred
from one generation to the next.
Why did Mendel Succeed?
In order to study inheritance, Mendel
chose to use peas.
 His use of plants also allowed strict
control over the crosses/mating.
 He chose to study only characteristics
that varied in an ‘either-or’ rather than a
‘more-or-less’ manner. (i.e.white or
purple, tall or short)


He chose his subject carefully. Mendel
chose the garden pea for his
experiments for several reasons:
-Garden peas reproduce sexually-they
produce male and female sex cells
called GAMETES
-Male gametes form in the pollen
produced in male reproductive organ
-The female gametes form in the
female reproductive organ
He chose his subject carefully. Mendel
chose the garden pea for his
experiments for several reasons:
 Garden peas reproduce sexually-they
produce male and female sex cells
called GAMETES
 Male gametes form in the pollen which
is produced in male reproductive organ
 The female gametes form in the female
reproductive organ

Perfect Flowers have both male and female
parts. Imperfect flowers have one or the other.
Male
Parts
Female
Parts

The male and female gametes unite in
a process called fertilization

The resulting fertilized cell is called a
zygote and develops into a seed.

The transfer of pollen grains from a
male reproductive organ to a female
reproductive organ is called
Pollination.
What was his procedure?

To hybridise 2
varieties of pea plants,
Mendel used an
artist’s brush.
 He transferred pollen
from a true breeding
white flower to the
carpel of a true
breeding purple
flower.

When he wanted to breed, or cross, one
plant with another, Mendel opened the
petals of a flower and removed the male
organs called Stamens.

He then dusted the female organs
with pollen from the plant he
wished to cross it with.
The process Mendel used is called
cross-pollination.
 By using this technique, Mendel could
be sure of the parents in his cross.
 Each seed was a single offspring
 He studied only one trait at a time to
control variables, and he analyzed his
data mathematically. (Remember the
scientific method?)

He used plants that breed true. This
means if the plants are allowed to selfpollinate, they show characteristics that
never vary from the parent. (white
flower parents-white flower offspring)
 The tall pea plants he worked with were
from populations of plants that had been
tall for many generations and had
always produced tall offspring.

Mendel’s Experiments
The first parent generation is called the
P1
 The offspring of the first mating is called
the F1 generation (first filial which
means son in Latin)
 Mendel let the F1 Generation to selfpollinate to produce the F2 generation

Tracking heritable characteristics
Mendel tracked
heritable characters
for 3 generations.
 When F1 hybrids
were allowed to selfpollinate a 3:1 ratio
of the 2 varieties
occurred in the F2
generation.

WHAT TOOL CAN WE USE TO MAKE
PREDICTIONS?

PUNNETT SQUARES
Do you remember how to set one up?

Two columns and Two rows
P
p
P
PP
Pp
p
P-Purple Dominant
p- White Recessive
F1 Generation
Pp
pp
Mendel’s Results

In the P1, he crossed true breeding plants that had
purple flower with other plants that had white
flowers.
 All of the F1 plants had purple flowers. There
were not any plants with white flowers
 He let the F1 plants self-pollinate to produce the F2
Generation. The F1 had 705 purple flowers and
224 white flowers (ratio 3:1)

Mendel repeated his experiment many times with
the same results
Punnett Squares
Capital letters are used for the dominant
trait
 Lower case letters are used for a
recessive trait.
 The presence of a Dominant allele
cancels out the expression of
Recessive allele
 For a recessive allele to show itself
offspring must get one recessive allele
from each parent


Two alleles together determine how a
trait will be expressed

One allele comes from each parent

Homozygous for a trait- Both alleles are
the same for a trait (BB or bb)

Heterozygous for a trait- Both alleles
are different for a trait (Bb or Ww)

Mendel derived three main laws of
Genetics

It is amazing that he came up with the right
conclusions in the 1850s even though he
knew nothing about chromosomes, genes or
DNA
4 letters in the
DNA Alphabet
Chromosome
Genes
DNA

DNA was not discovered until 100 years
later by Watson and Crick

Each trait or characteristic exists in
two versions. These two versions of a
gene are called alleles (one allele for
purple flowers and one for white
flowers)
1. Law of Dominance- one allele shows itself
 For each trait or characteristic, an individual
inherits two alleles…..one from each parent.


True breeding plants had two identical alleles
This is called homozygous or pure (PP or
pp)
 PP could also be called homozygous
dominant
 What would pp be called
homozygous recessive

Plants in the F1 generation had two different
alleles for flower color (one purple and one
white). Organisms with two different alleles
are said to be hybrid or heterozygous (Pp)
 Genotype-The two letters representing the
two alleles (Pp, PP, Ww, Tt)
-The genotype for purple flowers would be
-PP or Pp
-The genotype for white flowers would be
It is recessive so the ONLY possibility is pp
-The genotype for brown hair could be
BB or Bb
-The genotype for blond hair would be
Only possibility is bb

Phenotype-The actual physical expression of
the two alleles. (What we see with our eyes)
-The phenotype of Pp would be
purple
-The phenotype of PP would be
purple
-The phenotype of pp would be
white
-The phenotype of BB for hair color would
be
brown hair
-The phenotype of bb would be
blond hair

The allele that shows itself is called the
dominant allele. In the F1 generation all
flowers were purple (purple was
dominant (Big P) and white was
recessive (Little p) )

The allele that doesn’t show itself when
the dominant allele is present is called
the recessive allele
2. Law of Segregationone allele comes
from each parent

The two alleles for each trait separate when
the organism makes gametes (sex cellssperm, eggs or pollen).
 When an organism makes gametes the
chromosome number is reduced by half
(results in one allele from each parent)

How many chromosomes do humans have?
–46 Chromosomes
By the law of segregation, the two alleles for
a characters are packaged into separate
gametes

If the blending model were correct, the F1
hybrids from a cross between purple-flowered
and white-flowered pea plants would have pale
purple flowers.
 Instead, the F1 hybrids
all have purple flowers,
just a purple as the
purple-flowered
parents.
Fig. 14.2
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Law of Segregation - the two alleles for
each character segregate during gamete
production
If humans have 46 chromosomes, how
many chromosomes are in the sex cells
(eggs and sperm)?
The egg and sperm
combine to make 46
chromosomes. So the
egg has 23 and
the sperm has 23.
 What alleles could a heterozygous
parent (Pp) contribute ?
Either a “Big P” or a “Little p”

What alleles could a homozygous
 parent (PP or pp) contribute ?

PP only “Big P”
pp only “little p”
3. Law of Independent Assortment

More than one characteristic or trait is
inherited simultaneously with each
fertilization.(flower color, tall or short, eye
color, curly vs straight hair etc.)
 The inheritance of one trait has nothing to do
with the inheritance of another trait.
 Human eye color from your parent is a totally
separate event regarding whether you get the
allele for straight or curly hair.
Mendel’s terminology






True breeding: When the plants self-pollinate,
all their offspring are of the same variety.
Hybridisation: Mating, or crossing, of two
varieties.
Monohybrid cross: A cross that tracks the
inheritance of a single character.
P generation: True breeding parents.
F1 generation: (first filial) Hybrid offspring of
the P generation.
F2 generation: (second filial) Offspring from
the self-fertilization of the F1 hybrids.
Mendel’s impact
Mendel’s theories of inheritance, first
discovered in garden peas, are equally
valid for figs, flies, fish, birds and human
beings.
 Mendel’s impact endures, not only on
genetics, but on all of science, as a
case study of the power of
hypothesis/deductive thinking.

Scientists found that Mendel’s
principles applied not only to peas but
other organisms as well.
 Much of the genetic research
since Mendel’s work has been
done with the common fruit fly
(Dropsophilia melanogaster).


Why is the fruit fly a good organism to
study genetics?

Why is the fruit fly a good organism to
study genetics?
-new generation can be reproduced
every 14 days
-two flies can produce 100 offspring
every two weeks

Why aren’t humans good organisms to
study genetics?
-new generation can be reproduced
about every 20 years.
-gestation is long (9 months)
Genetics Vocabulary

Allele- a version of a particular gene (one
trait or characteristic)
 Phenotype- Physical expression of an
inherited trait in an individual (What you can
see or easily test)
 Genotype-the combination of alleles in an
individual ( TT, Tt). Not easy to determine
except in the case of individuals exhibiting
recessive traits. Can require test crosses or
other tests to determine the actual genotype.

Gene-The segment of DNA that contains the
genetic information for a given trait or
characteristic. Located at specific points on
the chromosomes in the nucleus and made of
two alleles.
 Chromosome-a structure composed of DNA
that contains the genetic material and is
located in the nucleus of the cell. Arranged in
homologous pairs

Incomplete Dominance-when the
heterozygous offspring has a phenotype
that is a mixture of the homozygous
parent’s phenotype.
Co- dominance
Occurs when alternative alleles are
present in the genotype and fully
observed in the phenotype
 ABO blood grouping system, where a
single gene locus features multiple
alleles- IA, IB, and i. Individuals
carrying alleles for both A and B
express both in the blood phenotype
AB.

Co- dominance
Roan Cattle- both Red and White alleles are
expressed resulting in cattle that are red,
white or roan.

Multiple Alleles-many genes
have more than two alleles.This
means that more than two possibilities exist.
Multiple Alleles
Antigens found in blood given in a
transfusion that is foreign to the body produces
antibodies which causes the blood to clump up
and cause serious problems.
Look at the right side of the chart on the previous page and see if
you can answer the following questions.
What blood type would be a universal
donor? (could give a transfusion to any other blood type)
A person with Type O blood can donate blood to individuals of
any ABO blood group (ie A, B, O or AB). Blood group O
individuals do not have either A or B antigens on the surface of
their RBCs, but their blood serum contains IgM anti-A antibodies
and anti-B antibodies against the A and B blood group antigens.
What blood type would be a universal
recipient? (could get a transfusion of any type of blood)
Therefore, an individual with type AB blood can receive blood
from any group (with AB being preferable), but can donate
blood only to another type AB individual. Blood group AB
individuals have both A and B antigens on the surface of their
RBCs, and their blood serum does not contain any antibodies
against either A or B antigen.
Is there anything else that needs to be
considered before blood transfusions?
Rh Factor
Rh Factor

The Rh system was named after rhesus
monkeys , since they were initially used in the
research to make the antiserum for typing
blood samples.
 The inheritance of this trait usually can be
predicted using a punnett square in which
there are two alleles, D and d.
 Individuals who are homozygous dominant
(DD) or heterozygous (Dd) are Rh+.
 Those who are homozygous recessive (dd)
are Rh- (i.e., they do not have the key Rh antigens).
Mother-fetus incompatibility

The greatest problem with the Rh group is not
so much incompatibilities following
transfusions as those between a mother and
her developing fetus.
 Mother-fetus incompatibility occurs when
the mother is Rh- (dd) and the father is Rh+
(DD or Dd). Maternal antibodies can cross
the placenta and destroy fetal red blood
cells.
 The risk increases with each pregnancy as
the level of antibodies increases

Rh type mother-fetus incompatibility occurs
only when an Rh+ man fathers a child with an
Rh- mother. Since an Rh+ father can have
either a DD or Dd genotype, there are 2
mating combinations possible:

The fetus can be protected by giving Rhwomen with Rh+ mates a serum (Rho-GAM )
containing anti-Rh+ antibodies.

Polygenic Traits –involves the
interaction of MORE than one gene. In
humans this results in a wide range of
phenotypes for skin color.
Polygenetic Inheritance



Qualitative variation
usually indicates
polygenic inheritance.
This occurs when there
is an additive effect from
two or more genes.
Pigmentation (amount of
melanin) in humans is
controlled by at least
three (3) separately
inherited genes.
There are some exceptions to Mendel’s law.
Some alleles do blend (white and red
snapdragons do produce pink flowers)
1. Eye color
(brown, blue,
hazel,green etc)
A closer look at chromosomes





Humans have 23 pairs of Chromosomes
Autosomes include the 22 pairs that are not
the sex chromosomes
Karyotypes are prepared
to look for chromosome
abnormalities
We say each chromosome
Pair is homologous
Is this Karyotype for a male or Female?
Male? (look at Chromosome #23)
»MALE
»Sex Chromosome on #23
Autosome VS Sex Chromosomes
Some Genetics Disorders are
associated with Chromosomes 1-22
 Other Genetic disorders are associated
with the sex chromosomes #23
 Sex linked disorders behave a bit
differently. So it is useful to look at them
separately.

Genetic Disorders
P-Point Mutation
D-Deletion of Gene
C-Whole Chromosome extra, missing or both
Disorder
Mutation
Chromosome
Angelman Syndrome
DCP
22
Color Blindness
P
23 (X)
Cystic Fibrosis
P
7
Down Syndrome
C
21 (extra copy)
Duchenne Muscular D.
D
23 (X)
Haemophilia
P
23 (X)
Klinefelter’s Syndrome
C
X (male XXY)
Phenylketonuria
P
12
Sickle Cell Disease
P
11
Turner Syndrome
C
X (female XO)
Syndrome-a number of symptoms occurring together and
characterizing a specific disease or condition
Technology
And
Genetic testing
Fetal testing
Carrier
Recognition
1.
2.
3.
4.
Amniocentesis
Chorionic villus
sampling (CVS)
Ultrasound
Fetoscopy
Newborn
screening
Image of the karyotype of a child with Down
syndrome or Trisomy 21: Do you see anything that
looks abnormal?
-In 1866 a physician named John Langdon Down published
an essay in England describing the symptoms .
-Medical research has shown that age of mother is a factor
Under age 30-1:900 chance and Over age 40 1:100 chance.
Amniocentesis

Amniocentesis is a diagnostic procedure performed by inserting a
needle through the abdominal wall into
the uterus and withdrawing a small
amount of amniotic fluid surrounding
the fetus.

Amniocentesis can detect chromosomal
disorders, such as Down syndrome,
structural defects, such as spina bifida
(open spine, where the vertebrae fail
to close), anencephaly (a condition in
which the brain is incomplete or missing.
Ultrasound
•The most well known application of ultrasound is its use in
sonagraphy to produce pictures of fetuses in the human
womb.
Ethical Questions?

Ethical motive: motivation based on ideas of
right and wrong
 How do we use ultrasound and
amniocentesis as it develops further ?
 Terminate a fetus if….
-Has Down Syndrome? Is that morally right or morally
wrong? When is a fetus a human?
-It is a boy fetus and the parents want a
girl? Short and want tall?

You may have to make some ethical
decisions using this technology during your
life time.
Autosomal Dominant Inheritance
 Dominant gene located on 1 of the
autosomes (all chromosomes except sex chromosomes)
 Usually rare, Individual may not live to
produce offspring
 Affected individuals have to carry only 1
dominant gene (can be heterozygous or homozygous)
 Passed onto both males and females
 Every person affected must have
at least 1 parent with the trait
 Does not skip generations
 E.g. Huntington’s disease, Marfan syndrome
 Do you know the symbols used to identify
male and female?

Marfan syndrome is a heritable condition that
affects the connective tissue which holds the
body together and provides a framework for
growth and development.
 In Marfan syndrome, the connective tissue is
defective and does not act as it should.
 Connective tissue is found throughout the
body, Marfan syndrome can affect many body
systems, including the skeleton, eyes, heart
and blood vessels, nervous system, skin, and
lungs. (Some Scientist’s think President
Lincoln may have had it …tall and lanky)
Autosomal Dominant- Marfan
syndrome
General Pedigree
Autosomal Dominant Pedigree
Unaffected
Female
Unaffected
Male
Look for:
 Trait in every
generation
– Once leaves the
pedigree does not
return


Every person with the
trait must have a
parent with the trait
Males and females
equally affected
Autosomal Recessive Inheritance

The recessive gene is located on 1 of the autosomes
 Letters used are lower case ie bb
 Unaffected parents (heterozygous) can produce
affected offspring (if they get both recessive genes)
We call the result homozygous recessive)
 Inherited by both males and females
 Can skip generations
 If both parents have the trait then all offspring will
also have the trait. The parents are both homozygous
recessive.
 E.g. Albinism, thalassemia, sickle cell anaemia and
cystic fibrosis.
Autosomal Recessive Pedigree
Affected
Male
Unaffected Male
Look for:
 Skips in generation
 Unaffected parents
can have affected
children
 Affected person must
be homozygous
 Males and females
affected equally
Autosomal recessive
Albinism- Albinism is an inherited condition present at
birth, characterized by a lack of pigment that normally
gives color to the skin, hair, and eyes.
Albinism
Thalassemia is an blood disorder passed
down through families (inherited) in which
the body makes an abnormal form of
hemoglobin, the protein in red blood cells
that carries oxygen.
Sickle cell anemia is a disease passed down through
families in which red blood cells form an abnormal
crescent shape. Sickle cells contain abnormal
hemoglobin that causes the cells to have a sickle
shape. Sickle-shaped cells don’t move easily through
your blood vessels.
Sex linked inheritance Dominant

Male sperm determines the
sex of the individual at
fertilization
-Sperm contains a Y- male offspring
-Sperm contains a X- female offspring

Dominant gene on X chromosome

Affected males pass to all daughters and
none of their sons
– Genotype= XAY
Sex linked inheritance
Genes are carried on the sex
chromosomes (X or Y)
 Sex-linked notation

– XBXB normal female
– XBXb carrier female
– XbXb affected female
– XBY normal male
– XbY affected male
Sex linked dominant disorders

If the mother has an X- linked dominant
trait and is homozygous (XAXA) all children
will be affected
 If Mother heterozygous (XAXa) 50% chance
of each child being affected
 E.g. dwarfism, rickets, brown teeth
enamel.
Rickets can be genetic or
from a vitamin D
deficiency
Sex linked Inheritance Recessive

Gene located on the X chromosome

More males than females affected

Y does not contain a second allele
so Males have the trait if they get
ONE recessive allele from their mother.

Females can only inherit if the father is
affected and mother is a carrier (hetero)
or affected (homo)

Males cannot be carriers (only have 1 X so either affected or
not)
Can skip generations
E.g. color blindness, hemophilia, Duchene muscular
dystrophy


Sex linked recessive pedigrees
More males being affected
 Affected female will pass onto all her
sons
 Affected male will pass to daughters
who will be a carrier (unless mother
also affected)
 Unaffected father and carrier mother
can produce affected sons

Sex linked recessive
Sex linked recessive problem



8-10% of males and 1/200 females (0.5%) are born
with red or green color deficiency.
XcY or XcXc results in color blindness
Females with XcX are carriers and have normal
vision
Can a color blind father have normal sons?
X
X
Xc
Y
XcX
XY
XcX
XY
Yes, but all of his daughters will
be carriers
X
Xc
Can a carrier mother have normal sons?
X
Y
XcX
XcY
XX
XY
Yes, 50% of her sons will have normal color
vision and 50% of daughters will be carriers
Environmental Impact on Phenotype
Are these different species?
No. Increasing the pH of the soil will change the color of
hydrangea flowers from blue to pink

The expression of genes in an organism can
be influenced by the environment
 Drugs, chemicals, temperature, and light are
among the external environmental factors
that can determine which genes are turned
on and off
 The environment can influence
the way an organism develops
and functions.
Effect of the Environment
Only difference is the
soil
Which color variation in
hares is useful in
winter?
The pigment Chlorophyll
makes grass green. What
happens to grass’s color
in winter?
Identical Twin and Environmental influences
When you study psychology in college you will study
“Nature VS Nuture”
What is more important in making us who we are today?
Is it how we are brought up?
Is our genetic make-up more important?
Why do these identical twins separated
At birth look so different?

Epigenetics is the study of changes in
phenotypes (appearance) or gene expression
caused by mechanisms other than changes
in the underlying DNA sequence, (Greek:
επί- over, above) -genetics.
Allele

A different form of a particular gene, positioned
in the same relative position (locus) on
homologous chromosomes
Homologous chromosomes
Gene locus –
position on the
chromosome
Alleles (diff versions of
the genes)
DNA nucleotides
Phosphate group
Nitrogenous base
Pentose sugar
Phosphodiester bond
Nucleotide
Polynucleotide
chain
Sugar phosphate
backbone
4 different bases
G
C
A
T
Double helix
5’end
3’end
3’end
5’end
Organism
chromosomes












Human
Chimpanzee
Dog
Horse
Chicken
Goldfish
Fruit fly
Mosquito
Nematode
Horsetail
Sequoia
Round worm
No.
46
48
78
64
78
94
8
6
11(m), 12(f)
216
22
2
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