Download Different Forms of Genetic Expression

Different Forms of Genetic
Expression
Genetic expression is how a gene is “shown”
(phenotype)
We have been using a model known as complete
dominance.
Complete Dominance
 The form of genetic expression discovered
by Gregor Mendel.
 Only 2 alleles for each gene.
 One is dominant – shown with a capital
letter.
 One is recessive – shown with a lower case
letter.
 If one dominant allele is present, that is the
only trait that will be expressed!
Incomplete Dominance
 Dominant alleles combine to form a new trait.
 Each allele is represented with its own capital
letter.
 R = red
 W = white
 A red plant would have the genotype _______.
 A white plant would have the genotype _______.
 The heterozygous plant, RW, has two dominant
alleles, it would form a new phenotype which mixes
the two.
 RW = _________
Incomplete Dominance – Practice!
 The two alleles for an aliens skin color
are black and white, and is
genetically expressed through
incomplete dominance.
 Show a Punnett square for a mix
between a gray and white alien.
Co-dominance
 Dominant alleles are both expressed but do
not mix. (Huh?)
 In a particular breed of horse, there are two
alleles for coat color.
 CW = white coat
 CR = red coat
 Note the use of superscripts. The base
“C” is for coat or color, and the
superscripts represent red and white, the
allele varieties.
Co-dominance continued…
 What is the genotype of a red horse?_______
 What is the genotype of a white
horse?_______
 What happens in the heterozygous condition?
 CRCW = roan, this is a horse that has both
red hairs and white hairs.
Co-dominance – Human Example!
 People can have four different blood
types.
 ______, _____, _____, or _____.
 Blood type AB is a result of an
individual having alleles for both the
A and B antigen and they are both
present on cells. (Co-dominant)
IAIB
Multiple Alleles
 Multiple alleles are combinations of
different kinds of genetics due to
more than two forms of alleles
present.
 A good example of this is human
blood type.
 There are 3 alleles: IA , IB, i.
 IA is the “A” allele, IB is the “B” allele,
and i = the “O” allele.
Multiple Alleles continued…
 What genotypes are possible for
individuals with blood type…




A–
B–
AB –
O–
Multiple Alleles – Practice!
 A female with blood type AB marries
a man with blood type B. The mans
mother was blood type O.
 What is the chance that they have a
child with blood type A?
Sex-Linked Traits
 Remember that there are two types
of sex chromosomes.




X
Y
Males have the genotype XY.
Females have the genotype XX.
 Genes that are found on the sex
chromosomes are called sex-linked.
Sex-Linked Traits continued…
 There is a gene for color-blindness found on
the X chromosome.
 XB = not color blind
 Xb = color blind
 Females can possess the color-blind allele
without being color-blind.
 XBXb
 Males can be color-blind even though they
may only have one color-blind allele.
 XbY
Sex-Linked Traits – Practice!
 The gene for eye color in fruit flies is
found on the X chromosome.
 XR = red eyes
 Xr = white eyes
 What is the genotype of…




a
a
a
a
red-eyed male –
white-eyed female –
white-eyed male –
red-eyed female -
Sex-Linked Traits – More practice!
 Cross a white-eyed male fruit fly with
a pure red-eyed female.
 What is the chance that a white-eyed
male fruit fly will be born?