Incomplete Dominance Codominance Sexlinked and Polygenic Inheritance Incomplete

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Incomplete Dominance, Codominance, Sexlinked and Polygenic Inheritance

Incomplete Dominance, Codominance, Sexlinked and Polygenic Inheritance

Incomplete Dominance • Offspring have an appearance somewhat in between the phenotypes of the

Incomplete Dominance • Offspring have an appearance somewhat in between the phenotypes of the two parents – “Mixed” – Blended R R W RW RW F 1 generation W RW RW All Rr = pink (heterozygous pink)

Incomplete Dominance • Incomplete dominance occurs when two or more alleles influence the phenotype

Incomplete Dominance • Incomplete dominance occurs when two or more alleles influence the phenotype • Neither allele is completely dominant over the other

Incomplete Dominance

Incomplete Dominance

Codominance • BOTH alleles are expressed equally in heterozygous individuals • Neither allele is

Codominance • BOTH alleles are expressed equally in heterozygous individuals • Neither allele is dominant over the other – Example: blood type • Determined by whether or not you have A or B proteins • IA = A protein • IB = B protein • I = no protein • Another example Is the speckled chicken

Codominance

Codominance

Codominance Problem • Example: homozygous male Type B (IBIB) • x heterozygous female Type

Codominance Problem • Example: homozygous male Type B (IBIB) • x heterozygous female Type A (IAi) IB IB IA I AI B i I Bi 1/2 = IAIB 1/2 = IBi

Another Codominance Problem Example: male Type O (ii) x female type AB (IAIB) IA

Another Codominance Problem Example: male Type O (ii) x female type AB (IAIB) IA IB i I Ai I Bi 1/2 = IAi 1/2 = IBi

Codominance • Question: If a boy has a blood type O and his sister

Codominance • Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents? boy - type O (ii) X girl - type AB (IAIB)

Codominance • Answer: IA IB i i I AI B ii Parents: genotypes =

Codominance • Answer: IA IB i i I AI B ii Parents: genotypes = IAi and IBi phenotypes = A and B

Sex-linked Traits • Traits (genes) located on the sex chromosomes • Sex chromosomes are

Sex-linked Traits • Traits (genes) located on the sex chromosomes • Sex chromosomes are X and Y – XX genotype for females – XY genotype for males • Many sex-linked traits carried on X chromosome

Sex – Linked Traits • Example: Colorblindness – If the mother carries the colorblindness

Sex – Linked Traits • Example: Colorblindness – If the mother carries the colorblindness gene on her X chromosome, her son could get it. – As long as one X chromosome X y is ok, a female will not c. X c y X X C express the trait X X XX Xy

Sex-linked Traits Example: Colorblindness Sex Chromosomes Colorblindness XX chromosome - female Xy chromosome -

Sex-linked Traits Example: Colorblindness Sex Chromosomes Colorblindness XX chromosome - female Xy chromosome - male

Polygenic Inheritance • Inheritance pattern controlled by two or more genes • Genes can

Polygenic Inheritance • Inheritance pattern controlled by two or more genes • Genes can be on the same chromosome or on different chromosomes • Genotypes are written as AA, Aa, or aa except you will have three or more genes each with a dominant and recessive trait • Skin color is influenced by the additive effects of melanin by three to six genes. Eye color is also a result of melanin added from multiple genes.

Polygenic Inheritance a pedigree

Polygenic Inheritance a pedigree

Polygenic Inheritance of Skin Color Gametes ABC ABc ABC AABBCc Ab. C Abc a.

Polygenic Inheritance of Skin Color Gametes ABC ABc ABC AABBCc Ab. C Abc a. BC AABb. Cc Aa. BBCC a. Bc Ab. C Abc a. BC AAbbcc aa. BBCc a. Bc ab. C abc aa. Bbcc The table shows typical ranges of skin color combinations. Other polygenic influenced conditions include Spina bifida and Cleft palate. ab. C abc