Introduction To GeneticsChapter 11
1
The work of Gregor Mendel
Gregor Mendel was born in 1822 and after
becoming a priest; Mendel was a math
teacher for 14 years and a monastery. Mendel
was also in charge of the monastery garden.
.
2
• Mendel carried out his
work with garden peas
3
• Fertilization is the fusion of an egg and
a sperm.
• True breeding plants are plants that
were allowed to self-pollinate and the
offspring would be exactly like the
parent.
4
5
Genes and Dominance
• The different forms of a gene is
called and an alleles.
1. The principle of dominance states
that some alleles are dominant
and others are recessive.
6
Pinky Finger Traits
At John Burke High School they tested dominant and recessive traits in
our school population. We tested pinky finger traits, whereby, the bent
finger is dominant and the straight finger is recessive.
7
Segregation
• Each trait has two genes, one from the
mother and one from the father.
• Traits can be either dominant or
recessive.
• A dominant trait only needs one gene in
order to be expressed.
8
• A recessive trait needs two genes in
order to be expressed.
9
10
• Egg and sperm are sex cells called
gametes.
2. The Principle of Segregation
–Segregation is the separation of alleles
during gamete formation.
11
12
Probability and Punnett Squares
• Genetics and Probability
–The likelihood that a particular event
will occur is called probability.
–The principals of probability can be used
to predict the outcome of genetic
crosses.
13
PROBABILITY
14
Lets Predict:
Punnett Squares
• The gene combination that might result
from a genetic cross can be determined by
drawing a diagram known as a Punnett
square.
• Punnett squares can be used to predict
and compare the genetic variations that
will result from a cross.
15
16
• Each trait has two genes- one from the
mother and one from the father.
• Alleles can be homozygous – having
the same traits.
• Alleles can be heterozygous- having
different traits.
17
18
• Physical characteristics are called the
phenotype.
• Genetic make up is the genotype.
19
20
Exploring Mendalian Genetics
3. The Principle of Independent
assortment
–Genes segregate independently.
21
• The principle of independent assortment
states that genes for different traits can
segregate independently during the
formation of gametes.
• Independent assortment helps account
for the many genetic variations observed
in plants, animals and other organisms.
22
23
A summary of Mendel’s Principals
• Genes are passed from parent to
offspring.
• Some forms of a gene may be
dominant and others recessive.
24
• In most sexually producing organisms,
each adult has two copies of each geneone from each parent. These genes are
segregated from each other when
gametes are formed.
• The alleles for different genes usually
segregate independently of one another.
25
26
Review (PDN)
• What does it mean to be “dominant” and
“recessive”??
• How can you write out “dominant” and
“recessive”? -- use brown hair (B) is dominant
over red hair (b)
27
Beyond Dominance
and Recessive Alleles
• Some alleles are neither dominant nor
recessive, and many traits are controlled
by multiple alleles or multiple genes.
• Cases in which one allele is not
completely dominant over another are
called incomplete dominance.
28
• Example: White (W) and Red (R) is both
dominate.
If WW X RR the F1 generation would be
What?
29
1. Cross a red flower with a white
flower, showing incomplete dominance.
Red=R
White=W
W
W
R
R
RW
RW
RW
RW
Genotype: 100% RW
Phenotype: PINK!
Incomplete dominance:
Alleles are expressed as a blend.
Each allele has a capital letter.
Red= R
Yellow= Y
• Codominance is when both alleles contribute
to the phenotype.
Example: Feather colors
34
Codominance
• Both traits dominate, seen separately!
Red Horse
White Horse
Give you ROAN!
Example of Codominant Problem
Red feathers are codominant to white feathers in chickens.
CR= red
CW= white
Cross a homozygous Red with a homozygous white feathered
chicken.
CR
CW
CW
CR CW
CR CW
CR
CR CW
CR CW
GENOTYPE:
100% CR CW
PHENOTYPE:
100%
Red and white mixed
feathers
• Many genes have more than two
alleles and are referred to have
multiple alleles.
• This means that more than two
possible alleles exist in a population.
–Like eye color… hair / fur color…
38
39
C. Multiple Alleles
• One trait, many allele options!
• But remember: an individual cannot inherit more
than two actual alleles, even if more than two
possible alleles exist.
Another Example:
Blood type
A, B, AB, O!
Rabbits have 4 basic
colors (alleles!)
• brown
• chinchilla or grey
• It is recessive to brown.
• himalayan or white with black tips.
• It is recessive to both brown and chinchilla.
• albino
• It is recessive to all.
Full color
Himalayan
Chinchilla
AIbino
Polygenic Traits
• Traits produced by many genes with
many alleles
• Most human traits are polygenic
• Most variety of expression
• There are 3 genes that contribute to
skin color.. And many alleles for
each gene!
Traits that are controlled by two or more genes
are said to be polygenic traits, which means,
“having many genes.”
Example: eye color has many different genes.
44
More examples:
•
•
•
•
Height
Weight
Intelligence
Eye color
Sex Determination
In humans, the
X and Y
chromosomes
control the sex
of offspring.
Outcome is always 50% chance of a
male, and 50% chance of a female
Sex-linked traits
• Traits controlled by genes on the sex
chromosomes are called sex-linked.
• Alleles for sex-linked traits are written as
superscripts on the X chromosomes only.
Example: Red eyes in fruit flies
found in females
Males tend to have white eyes,
which is recessive.
XR XR
Xr y
• X and Y sex
chromosomes are nonhomologous
• Any allele on the X
chromosome will NOT
be masked by a
matching allele on the Y
chromosome.
Why are sex-linked disorders more common in
males than in females?
• Males have just one X chromosome containing an
allele. So all X-linked alleles are automatically
expressed in males, even if they are recessive.
Why is Mendel’s Work so
IMPORTANT??
Applying Mendel’s principles
Mendel’s principals do not
only apply to plants.
51
THE END
52