Download Gregor Mendel - HCC Learning Web

2/10/2016
o
x x
xo x x
x
1. Source of
variation
x
o
o
3. Differential
Survival
2. Selective Pressure
o
xo o
o o
oo
The Next
Generation
but...HOW are traits passed on to offspring?
Gregor Mendel
-
-
Observed that the inheritance of
traits from one generation to the
next followed certain patterns
Ideas changed biology but went
unnoticed for 40 years
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Mendel’s
Genetics
Before Mendel
-People had interbred animals and
plants for nearly 10,000 years
-People also knew where babies
came from
-However, it was assumed that
“information” mixed during
reproduction
Evolution of corn
+
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Mendel’s first experiment (color)
What he EXPECTS
(1st generation [p])
(1st generation [p])
(2nd generation [F1])
+
=
What he GETS
(1st generation)
(2nd generation)
(1st generation)
+
=
Mendel’s second experiment
(3rd generation [F2])
(2nd generation [F1])
(2nd generation [F1])
=
+
Some traits skip generations....
Mendel’s theories
*trait / gene
1. There is a factor* for pea
color
2. Each parent contributes one
determining factor to the
offspring
3. Factors remain separate;
they do not blend
4. Factors are either dominant
or recessive
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Alleles & Loci

LOCUS (pl. loci) - Each determinant (gene) has a specific location
inside reproductive cells (chromosomes)

ALLELE - Alternate forms of each determinant (gene) that occurs
at a given locus.



Loci may have only one allele - fingernail growth rate
Loci may have two alleles - boys and girls
Loci may have multiple alleles - A,B,O blood types (but any
individual organism can only have two)
Genotypes

Genotypes - the genetic endowment of an individual

example - Mendel’s pea plants
PEA COLOR
Allele 1
Allele 2
YELLOW
green
Phenotypes

Phenotypes - the physical manifestation of the
genotype (e.g. - the actual observable trait)
...but what about
that green allele?
Why does it get no
love?
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Law of Segregation

The genetic basis of
any trait is
determined by an
allele from each
parent.


Mendel’s Law of
Segregation states
that within body cells,
alleles occur in pairs.
When sex cells are
formed, only one of
each pair is passes
on.
stuff



A corrected reading calendar will be uploaded to the
course website by the end of the day
Quiz #1 - point adjustment
Homework #1 – come talk to me if you have questions
about how your point total was determined
Dominant and Recessive Alleles


There is a reason why crossing yellow and green peas
can result in only yellow peas
Dominant and Recessive Alleles

Dominant Alleles - Manifest themselves even if there is only one
of them present at a loci.


Represented by a Capital letter (R - dominant allele for tongue
rolling)
Recessive Alleles - Can be MASKED by dominant genes. The only
way for recessive alleles to be manifested is if the locus has
TWO recessive alleles

Represented by a lowercase letter (r – recessive allele for tongue
rolling)
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Homozygous vs Heterozygous


A homozygous factor (gene) is one where both alleles
are the same (either dominant or recessive)
A heterozygous factor (gene) is one where the alleles
from each parent are different.


In a heterozygous gene, the recessive allele will be masked by
the dominant allele
So for tongue rolling....



Homozygous Dominant = RR (tongues will roll)
Homozygous Recessive = rr (no tongue rolling)
Heterozygous = Rr (tongues will roll)
Tongue rolling (dominant trait)
Father - RR
Mother - rr
Female
r
r
R
Rr
Rr
R
Rr
Rr
100 % of children will roll tongues
Tongue rolling (dominant trait) Second generation
Father - Rr
(child of the
first couple)
Female
r
r
R
Rr
Rr
r
rr
rr
Mother - rr
50 % of children will roll tongues
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Tongue rolling (dominant trait) - your
turn
Father - Rr
Female
Mother - Rr
R
r
R
?
?
r
?
?
Tongue rolling (dominant trait) - your
turn
Father - Rr
Female
Mother - Rr
R
r
R
RR
Rr
r
Rr
rr
75 % of children will roll tongues
Factors vs. Alleles


Alleles may be dominant or recessive

R for dominant tongue rolling

r for recessive NO tongue rolling
Factors (genes) may ALSO be dominant or recessive

That is, they may only express themselves in certain combinations
of alleles
What?
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Tongue folding (inverse trait)
Father - Ff
Female
Mother - Ff
F
f
F
FF
Ff
f
Ff
ff
25 % of children will fold their tongues
Imagine a car with 2 gas tanks
Tank 1
Tank 2
Result
Genotype
No gas
No gas
No go
homozygous
recessive
Some gas
No gas
Car is go!
heterozygous
Some gas
Some gas
Car is go!
homozygous
dominant
Now a biological example
Tank 1
Tank 2
Result
Genotype
No melanin No melanin Blue eye
homozygous
recessive
Some
melanin
No melanin Brown eye
heterozygous
Some
melanin
Some
melanin
homozygous
dominant
Brown eye
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Rolling and Folding!!!


RF
Father - Rr Ff (roller / non folder)
Mother - Rr Ff (roller / non folder)
RF
Rf
rF
rf
RR FF
RR Ff
Rr FF
Rr Ff
Rf
rF
rf
Rolling and Folding!!!


Father - Rr Ff (roller / no folder)
Mother - Rr Ff (roller / no folder)
RF
Rf
rF
rf
RF
RR FF
RR Ff
Rr FF
Rr Ff
Rf
RR Ff
RR ff
Rr Ff
Rr ff
rF
Rr FF
Rr Ff
rr FF
rr Ff
rf
Rr Ff
Rr ff
rr Ff
rr ff

Genotypes






RRFF = 1
RRFf = 2
RrFF = 2
RrFf = 4
RR ff = 1
Rr ff = 2

rr FF = 1
rr Ff = 2

rr ff = 1

Phenotypes
Rollers / Non-folders
9/16 (56.25%)
Rollers / Folders
3/16 (18.75%)
Non-rollers / Non-folders (3/16)
Non-rollers / Folders (1/16 or 6.25%)
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Law of Independent Assortment


The distribution of one pair of genes does not influence
the distribution of other pairs of genes
So....the presence tongue rolling will not affect the
presence of tongue folding
Codominant Alleles
Alleles
are codominant when they both
affect the phenotype of a heterozygous
genotype. Neither is dominant over the
other.
In complex genetic systems with more
than two alleles, some alleles may be
dominant and some may be codominant.
Example - blood types (A,B,O)
A and B are codominant
Pleiotropy



a gene pair that influences the physical expression of a
number of different characteristics and traits
example - Phenylketonuria
 PKU is determined by a single gene and can lead to:
mental retardation, reduced hair and skin
pigmentation, and brain seizures
Antagonistic pleiotropy

a type of pleiotropy in which some gene expressions are positive
and some are negative
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Antagonistic Pleiotropy


Gene p53
Pros



Regulates cell cycles
Suppresses the development of tumors
Cons

Suppresses the production of stem cells


- in adults, stem cells replace worn out cells
So, the p53 gene prevents cancer
and “causes” you to get old
Sex linked
traits

Henry VIII



King of England (15091547)
Had six wives...whom
he got rid of through
various means because
he wanted a son
Thing is....it was his
fault (sort of)
Sex chromosomes


There are two sex chromosomes: X and Y
There are (generally) two genotypes and two
phenotypes


XX woman
XY man
X
Y
X
XX
XY
X
XX
XY
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Sex-linked traits

The X chromosome is much larger than the Y chromosome

That means that there is more information contained in X
chromosomes
Some evidence for the
idea that “men” are a
mutation!!
There are many traits that
are carried along the X
chromosome (carried by
mother)
Sex linked traits





Traits carried on X chromosome
Females need two affected chromosomes to manifest a
trait
Females with one affected chromosome is a carrier
but is not affected
Males only get one X, so if they have the affected X
chromosome, then they manifest the trait
This is why men manifest MORE sex-linked traits than
women.
Example - hemophilia



Hemophilia is a disorder that prevents blood from
clotting
When creating Punnett squares for sex traits, we place
a superscript letter next to the sex chromosome
So...
XHXH
female with hemophilia
XHX
female carrier of hemophilia
XHY
male with hemophilia
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Mendelian Genetics is concerned
with patterns and processes of
inheritance
Law of Segregation
Law of Independent
Assortment
Homozygous dominant
Homozygous recessive
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