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 thereare many possible alleles

Sex-linked inheritance

In humans have 46 chromosomes, 23 pairs 22 pairs autosomes one pair sex chromosomes, determine sex

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

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

InternalMales and females differ due to hormonesAge 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