Transcript Patterns of inheritance!

Patterns of inheritance!
Although we are SOOOO thankful for Mendel,
there are many exceptions to Mendel’s Laws
of Heredity….
Genetics is more
complicated!
Incomplete dominance:
One allele is not completely
dominant over another
Incomplete dominance
Heterozygous offspring have an appearance in
between the phenotype of the parents!
Example: Snapdragons (flower)
Red (RR) x White (rr)
Incomplete dominance
Heterozygous phenotype is between the
dominant & recessive phenotype!
r
r
R
Rr
Rr
R
Rr
Rr
All F2 generation
Are Rr
Rr = PINK flowers!!!!!
Incomplete dominance
Incomplete dominance
Quick tip….
Codominance
BOTH alleles contribute to
the phenotype!!!
Codominance
When heterozygous, BOTH alleles act
dominant…BOTH alleles are seen!
Example: Chickens
BB = black bb = white
BB = black feathers
bb = white feathers
Codominance
Heterozygous offspring show both phenotypes!!
Example: Chickens
BB = black feathers
bb = white feathers
All F1 generation are
B
Bb …
Bb = black and white speckles!
B
b
b
Bb
Bb
Bb
Bb
Codominance in Chickens
P generation
Codominance is SOOO beautiful!
Quick tip…
Review:
Mendel Complete Dominance
Red (RR)
Red (Rr)
White (rr)
Yellow #12
Incomplete dominance
-Long tails (L)
-Short tails (S)
Multiple Alleles
Genes that have
more than two
alleles
Color coat in rabbits is determined by a single
gene that has at least four different alleles.
Different combinations of these alleles result
in the four colors you see here.
• In some rabbits, there are four alleles for fur color but
each rabbit only has two alleles. Depending on which two
alleles they have, they will be one of four colors!
Red is dominant over Tan, which is dominant over Black, which is dominant over Albino
(R)
(T)
(B)
(A)
Red > Tan > Black > Albino
• If a heterozygous black male rabbit mates with a
homozygous tan rabbit, what will the babies look like?
Another example of multiple alleles…
(Codominance, TOO!)
Human blood type
A B O
Three alleles for one trait!
Human Blood Type
•Blood type is determined by an antigen found on the surface of
the blood cell (protein that can stimulate the production of
antibodies)
Blood Type
Phenotype
•
A
B
O
•Everybody receives one allele for
blood type from each parent!
•A and B are CODOMINANT!
•O is recessive!
So…there are FOUR blood types
A
B
AA
Blood Type A
AB
Blood Type AB
AO
Blood Type A
BB
Blood Type B
BO
Blood Type B
OO
Blood Type O
AB
O
Multiple Allele & Codominance
Problem:
Homozygous male Type B (BB)
X
Heterozygous female Type A (AO)
B
B
A
AB
AB
O
BO
BO
½ = AB
½ = BO
SO, what are there
actual blood types?
If a boy has a blood type O and his sister has
blood type AB, what are the genotypes and
phenotypes of their parents?
Quick tip…
Polygenic Traits
Traits controlled by two
or more genes
The wide range of skin color in humans is due to
more than four different genes that control
this trait!
And eye color!
Quick Tip…
Polygenic traits are
more complex than
our punnett
squares!
Sex-Linked traits
Genes that are carried on
the X or Y chromosomes
(the sex chromosomes)!
Ex: Colorblindness, Hemophilia and
Duchenne Muscular Dystrophy
First, remember how to determine
gender…
Females have XX chromosomes
Males have XY chromosomes
Sex-Linked traits
BUT…the X chromosome is BIGGER and holds
WAY more genes than the Y
-The Y chromosome appears to only contain a
few genes total
-Currently 100 x-linked genetic disorders have
been mapped
Sex-Linked Traits
FEMALES:
R
r
XX
R
R
XX
•MALES:
R
XY
r
XY
Carriers
• Since females have two copies of the X chromosome, it is
possible to have certain alleles “hidden” by a dominant allele.
She is a healthy “CARRIER”
• However, because males only have one X chromosome, they
either have it…or they don’t. They can NOT be carriers!
B: Healthy
b: Muscular Disorder
FEMALE
Bb Healthy Phenotype
“Carrier”
MALE
b Muscular Disorder
Healthy Father, Carrier Mom
2 out of 4 children will
have the hemophilia
allele.
-The female: Carrier
-The male : HAS
hemophilia
The infected son has children with a
healthy woman
•None of the children
would have
hemophilia.
ALL females: Carriers
•This is why sex-linked
traits often disappear
and reappear from
generation to
generation!
Quick Tip!
Sex-linked traits affect
males and females
differently!!!
Genetics and Environment
• Traits are determined by a combination of
genes and environment!!!
A sunflower gene for height or flower size
BUT, these are influenced by: sunlight, soil,
water
Genes provide a plan for
development…but how
that plan unfolds depends
on the environment!
Some more examples….
-Blood Pressure
-Intelligence
-High yielding tomato plant
-Fair skin prone to cancer
-Woman baldness
Practice Problems
Incomplete dominance:
In a particular species of bird, feather color shows incomplete dominance. A
cross between a blue bird (BB) & a white bird (bb) produces offspring that
are silver (Bb). If two silver birds were to mate, what would the genotypes
& phenotypes be of their babies?
Practice Problems
Codominance:
Cow coloration is commonly an example of codominance. Homozygous cows
can be white or brown and heterozygous cows are called roan. Describe
the appearance of the baby cows if a white cow crosses with a brown cow:
Practice Problems
Multiple Alleles:
In one kind of mouse, fur color is a multiple allele trait because there are
three alleles. Black (B), Tan (T), and white (W) are all alleles that mice can
have but each mouse only has two alleles.
Black is dominant over Tan, which is dominant over White.
Often written: Black > Tan > White
If a homozygous black mouse mates with a heterozygous tan mouse, what will
the genotypes & phenotypes be of the offspring?
Practice Problems
Sex Linked Trait:
The bison herd on Konza Prairie shows a sex linked genetic defect carried on the X
chromosomes. Some males have a malformed back leg that interferes with its
normal motion. If a healthy male bull mates with a female cow that is a carrier,
what are the chances of producing a normal son?
Male Genotype:
Female Genotype:
If he mates with this cow every year, what percentage of their daughters will have normal knees?
What percentage of their daughters will be carriers of this disease?