Download p. Codominance

p.
Codominance
► Codominant
alleles do not mask each
other but are dominant together.
► An
example in humans is blood type.
► Blood type AB has the IA and IB alleles
which are codominant.
► Codominant
alleles are written as capital
letters with capital superscripts—FB, FW, IA
► Punnett
Square for codominant alleles
► A black chicken crossed with a white
chicken produces offspring that are black
and white (FBFW)
►
►
FW
►
FW
FB FB
F BF W
►
Punnett Square for blood type
IA
i
IB
i
Possible genotypes?
Possible blood types?
Patterns of Inheritance
in Humans
Patterns of Inheritance in Humans
► Single
genes with two alleles
example of a trait with two alleles is widow’s
peak (W or w)
► Single
genes with multiple alleles
example of a trait with multiple alleles is
blood type (IA, IB, or i)
► Traits
controlled by many genes
example of a trait controlled by many genes is skin
color
The Sex Chromosomes
► The
X and Y chromosomes carry genes that
determine whether a person is a male or
female.
► They
also carry genes that determine other
traits.
► Genes on the X and Y chromosomes are
called sex linked genes.
X or y?
► Half
of a males sperm cells carry an X
chromosome.
► The
other half carry a y chromosome
► If
a sperm carrying X fertilizes an egg, the child
will be a girl. If a sperm carrying a y fertilizes an
egg, the child will be a boy.
► The
y chromosome is smaller and is lacking
some genetic information that X chromosomes
have.
Sex-Linked Genes
► Sex
linked genes are traits controlled by genes on
the X and y chromosomes.
Examples of sex-linked genes —color blindness and
pattern baldness
► Because
the y chromosome is smaller
► having only one recessive allele on the X
chromosome will result in the male having the trait
because there is nothing on the y chromosome to
mask it.
► How
gender (sex) is determined.
X
X
X
y
X X
X X
XX = female
Xy = male
► How
color blindness is inherited
C
►X is the allele for normal color vision
c
►X is the allele for colorblindness
Xc, he will be colorblind.
c c
► If a female inherits X X , she’ll be
► If
a male inherits
colorblind.
► Punnett
Square for color blindness
XC Xc
Is the father colorblind?
Xc
y
Could they have a colorblind male child?
Could they have a colorblind female?