Download Complex Patterns of Inheritance

Complex Patterns of Inheritance
Incomplete Dominance
Codominance
Polygenic Inheritance
Sex Linkage
Incomplete Dominance

The active allele does not compensate for the
inactive allele.
 The heterozygous phenotype is somewhere in
between the homozygous phenotype.
Dominant
Actual
RR
Rr
Expected
rr
Codominance

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A condition in which both alleles of a gene
are expressed.
Codominant alleles are written as capital
letter with either subscripts or superscripts.
HR is the allele for red hair in cattle.
HW is the allele for white hair in cattle.
HRHR cattle have red hair.
HWHW cattle have white hair.
HRHW cattle are called roan they have a mix
of both colored hairs.
Polygenic (Poly = many; Genic = gene)

Involves traits controlled by the interaction of more
than one gene.
 Occurs in traits that have more than 2 phenotypes.
(e.g. hair color, eye color, skin color)
 All traits in Mendel’s experiments involved simple
traits with 2 outcomes (e.g. Tall vs. Short)
Sex-Linked Traits

The first twenty two pairs of human
chromosomes do not determine the sex of
the individual and are therefore called
autosomal.

The chromosomes that determine the sex of
the individual are the sex chromosomes and
are represented by the letters “X” & “Y”.

Female is XX and male is XY (in humans).
Sex-Linked Traits

Traits controlled by genes on the sex
chromosome are said to be sex-linked.
Two examples are:

[Colorblindness ]- Colorblindness is a
recessive disorder in which a person cannot
distinguish between certain colors.

[Hemophilia ]- is another recessive gene on
the X chromosome which is sometimes
called the “bleeder’s disease”.
Sex-Linked Traits

Colorblindness:

XX = normal vision female
 XC X = carrier female
 XC XC = colorblind female

XY = normal vision male
 XCY = colorblind male
Sex-Linked Traits

Hey, male pattern baldness is not sex-linked.
 It is actually caused by a gene on an autosomal
chromosome.
 That makes it sex-influenced, a trait that is
caused by a gene whose expression differs in
males and females.