Patterns of inheritance review

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Patterns of Inheritance Review

Degrees of Dominance

Complete Dominance - AA and Aa same phenotype

Incomplete Dominance - Aa has in-between/blended phenotype Codominance - Aa has both A and a

phenotype

Simple (Complete) Dominance

• LL or L l - short hair • l l - long hair

Co-dominanceBoth gene versions (alleles) are shownExample:

BB – black hairOO- orange hairBO – both black and orange hair

Incomplete Dominance

• Piebald spotting• ss - No white fur • SS- More than 50% white fur • Ss - Less than 50% white fur

The dominant allele cannot completely mask the recessive allele

What kind of dominance?

X-linked traits• genes found on the

X chromosome.• Females XX• Males XY• Orange and black

are codominant and on the X chromosome

Y-linked traits• Y-linked traits called

holandric inheritance.• Y-chromosome is small and

does not contain many genes

• Deletions on y chromosome male infertility

• SRY gene sex determining region

X-linked or holandric?

Multiple Alleles

More than 2 versions (alleles) for a single trait

Can have any dominance pattern

Multiple Alleles

• BB, Bb, Bbl – black hair• bb, bbl – brown hair• bl bl – cinnamon hair

Epistasis – when one gene controls the expression of another gene

• Most cats have the tabby gene

• Non-Agouti trait masks the tabby trait

Epistasis(standing upon)

• Dilute gene• DD and Dd – not dilute• dd – dilute – black become gray and orange

becomes cream

Epistasis or multiple alleles?

Pleiotropy A single gene can have

multiple effects on phenotype

ex multiple symptoms of sickle cell anemia (pain, jaundice, infections, fatigue, etc)

Pleiotropy in cats

• Dominant white gene can also cause blue eye color and deafness

Polygenic Inheritance

2 or more genes affect a single phenotypic trait Ex: Eye color, skin color, height

some traits also influenced by the environment - multifactorial inheritance

Pleiotropy, multifactorial, or polygenic?

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