Transcript 11–3 Exploring Mendelian Genetics

11–3 Exploring Mendelian
Genetics
11-3 Exploring Mendelian Genetics
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11–3 Exploring Mendelian Genetics
The Law of
Segregation
• It states that when an
organism produces
gametes its two alleles for
a trait separate and go
into different gametes.
• Therefore, when gametes
from 2 parents join to
produce a new organism,
the offspring receive one
allele from each parent.
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11–3 Exploring Mendelian Genetics
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Does the gene for one trait have
anything to do with whether the
gene for another trait is
inherited?
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Mendel showed that….
Different traits are inherited
separately
This is called the Law of
Independent Assortment
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11–3 Exploring Mendelian Genetics
Independent Assortment
• The alleles for rolling your tongue
segregate independently of those
for hair or eye color.
• This leads to genetic variation.
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11–3 Exploring Mendelian Genetics
Beyond Dominant and
Recessive Alleles
Some traits cannot be explained by
simple dominant or recessive
alleles.
In fact, most genes have more than
2 alleles.
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11–3 Exploring Mendelian Genetics
Beyond Dominant and
Recessive Alleles
Incomplete Dominance
When one allele is not completely dominant over
another it is called incomplete dominance.
Blending!
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11–3 Exploring Mendelian Genetics
Beyond Dominant and
Recessive Alleles
RR
A cross between
red (RR) and
white (WW)
snapdragons
produces pinkcolored flowers
(RW).
WW
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11–3 Exploring Mendelian Genetics
Beyond Dominant and
Recessive Alleles
Codominance
In codominance, both alleles contribute to the
phenotype.
In certain varieties of chicken, the allele for black
feathers is codominant with the allele for white
feathers.
Heterozygous chickens are speckled with both
black and white feathers. The black and white
colors do not blend to form a new color, but appear
separately and equally.
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11–3 Exploring Mendelian Genetics
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11–3 Exploring Mendelian Genetics
Beyond Dominant and
Recessive Alleles
Multiple Alleles
Each organism has only 2 alleles for a trait
however, more than 2 alleles exist in a population.
For example: a rabbit’s coat color.
The coat color is determined by a single gene that
has at least 4 different alleles.
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11–3 Exploring Mendelian Genetics
Beyond Dominant and
Recessive Alleles
Different combinations of alleles result in the colors
shown here.
KEY
C=
full color; dominant
to all other alleles
cch = chinchilla; partial
defect in pigmentation;
dominant to
ch and c alleles
ch = Himalayan; color in
certain parts of the
body; dominant to
c allele
chhc
ch,cCc
h
ch
Chinchilla:
Himalayan:
Full
color: CC,
cc
c,hCc
, or
cch
c,hhor
, or
cch
Cc
c
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c = albino; no color;
recessive to all other
alleles
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11–3 Exploring Mendelian Genetics
Beyond Dominant and
Recessive Alleles
Polygenic Traits
Traits controlled by two or more genes are said to
be polygenic traits “having many genes.”
Height in humans is a polygenic trait because it is
controlled by multiple genes.
Other examples include: eye color and skin color.
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11–3 Exploring Mendelian Genetics
Pattern of Inheritance
Description
Example
Incomplete Dominance
One allele is not
Snapdragon plant: A
completely dominant over plant with red flowers is
another
crossed with a plant with
white flowers, producing
heterozygous plants with
pink flowers.
Codominance
Both alleles contribute to
the phenotype
One variety of chicken: A
black feathered chicken is
crossed with a white
feathered chicken,
producing heterozygous
speckled chickens.
Multiple Alleles
A gene has more than
two alleles
Rabbit fur color
Polygenic Traits
Traits controlled by more
than one gene
Human skin color:
Several genes control this
trait, leading to a wide Slide
range of colors.
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