Download Complex patterns of inheritance

Complex patterns of
inheritance
Section 12.2
Incomplete dominance
• Phenotype of heterozygous individuals is
intermediate between those of the 2
homozygotes.
Incomplete Dominance example
CRCR
CRCW
CRCW
CWCW
Codominance
• Phenotypes of both homozygotes
produced in heterozygous individuals.
(both alleles expressed equally).
Codominance Example
RR
RW
RW
WW
Multiple Alleles
• An inheritance pattern
in which traits are
controlled by more
than 2 alleles
Multiple Alleles example
IA
IA
IAIA
IAIA
IAIi
IAIi
IA
Ii
Sex Determination
• Humans have 23 pairs of chromosomes
Sex Determination
• Of the 23 pairs of chromosomes in
humans, 22 are autosomes (pairs that look
alike) and 1 are sex chromosomes.
Sex Determination
• A karyotype is a diagram of the
chromosomes (arranged in order for
study)
Sex Determination
• Sex chromosomes are indicated by the
letters X and Y
• Females sex chromosomes are XX
• Male sex chromosomes are XY
• Who controls the sex of offspring?
– Males (Sperm)
• Why?
– All female eggs carry X chromosome. Sperm
carry X or Y
Sex-linked inheritance
• Sex-linked traits: characteristics
determined by genes on sex
chromosomes
• Can sex-linked traits be on the X or Y
chromosome?
– Yes
• Which is more common?
– X chromosome
Sex-linked inheritance
• Alleles are written as superscripts for X
and Y for sex linked traits
• What does it look like?
– XRXr or XrY
Color Blindness
•
•
•
•
C = normal
c = color blind
Male with color blindness = XcY
Female with color blindness = XcXc
Color Blindness
• Female carrier of color blindness = XCXc
• Normal (non-carrier) = XCXC
• Why can only females be carriers of X-linked
traits?
– Males only have one X-chromosome. If the
trait is on the X chromosome they will be
colorblind.
• Can males or females pass on y-linked traits?
– Only males
Practice
Hemophilia is a lethal recessive sex linked trait. It
causes your blood to be unable to clot. So, if you
fall and cut your chin open, the blood will keep
spurting out of your chin! If Queen Victoria
carries a recessive trait for hemophilia XHXh and
marries Albert who has hemophilia XhY. How
many of their children will die from hemophilia?
Polygenic traits
• Traits caused by more than one gene