Transcript 12.2 Complex patterns of inheritance

12.2 Complex
patterns of inheritance
Complex patterns of inheritance
Mendel’s experiments show simple
inheritance with recessive and dominant
alleles
 Some patterns of inheritance are more
complex

Complex patterns of inheritance
Incomplete dominance
 Codominance
 Multiple alleles
 Sex-linked inheritance
 Polygenic inheritance
 Environmental factors

Incomplete dominance
Phenotype of the heterozygote is in
between the phenotypes of the
homozygotes
 RR=red pigment
R1R1=white, no pigment
RR1=pink

Codominance
Phenotypes of both homozygotes are
produced in heterozygote, both alleles are
expressed equally
 BB=black feather
WW= white feather
BW= checkered

Multiple alleles
Traits controlled by more than two alleles
 Each pigeon has two alleles
for feather color, but there
are many possible alleles
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Sex-linked inheritance
In humans have 46 chromosomes, 23 pairs
 22 pairs autosomes
 one pair sex chromosomes, determine sex
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Sex-linked inheritance
Sex-linked traits are controlled by genes
located on the sex chromosomes
 Alleles are carried on
the X chromosome,
not the Y chromosome

Polygenic inheritance
A trait that is controlled by
more than one gene
 Genes may be on different
chromosomes
 Each gene may have more
than one allele
 Trait usually expressed in a
continuous range of variability
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Environmental factors

External
 Gene
may not be expressed due to
temperature, nutrition, light, chemicals,
infection
 For example, this bacteria
is different color when
grown at different temperature
Environmental factors

Internal
 Males
and females differ due to hormones
 Age may change trait expression
Complex patterns of inheritance
Mendel’s idea that heredity is a composite
of many traits still holds
 Later researchers have filled in details
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