Warm Up Who is Gregor Mendel? What’s the difference between “true breeds” and “hybrids”? Explain his experimentations and their impact in genetics.

Non-Mendelian Genetics

Some traits don’t follow the simple dominant/recessive rules that Mendel first applied to genetics. Traits can be controlled by more than one gene. Some alleles are neither dominant nor recessive.

Incomplete Dominance NO allele is completely dominant over the other. The heterozygous phenotype is a blending of the two homozygous phenotypes. Example: four o’clock flowers R=red r=white Rr=pink (blending of the two alleles)

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Codominance Two alleles are both expressed as dominant Coat color in cows –RR: Red –WW: White –RW: Roan, white with red spots (NOT pink!)

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Multiple-Allele Series Codominance More than two choices of alleles are present for a trait ABO blood type has three alleles ABO Blood types: –If both A and B are present, type is AB –Neither is recessive Individuals can be type A, B, AB, or O (recessive)

OO

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Sex-Linked Inheritance

Review Males have an X and a Y chromosome Females have two X chromosomes These chromosomes determine sex, so genes located on these chromosomes are known as sex-linked genes.

Disorders that are sex-linked are much more common in males, because they would only need 1 recessive allele to have the trait; rather than the two recessive alleles the females need. The X chromosome is much larger than the Y, so it carries more genes than the Y chromosome.

X-Linked (recessive) Traits/Disorders carried on the X chromosome –Females receive 2 X chromosomes If a female gets only 1 affected X chromosome, she will not express that trait/disorder, but will be a carrier If a female gets only 2 affected X chromosomes, she will express that trait/disorder Males receive 1 X chromosome –Males receive 1 X chromosome & 1 Y chromosome If a male gets an affected X chromosome, he will express that trait/disorder

Y-Linked (recessive) Traits/Disorders carried on the Y chromosome –Females receive 2 X chromosomes Females CANNOT receive a Y chromosome, so they will NEVER have a Y-linked trait (cannot be carriers either) –Males receive 1 X chromosome & 1 Y chromosome If a male gets an affected Y chromosome, he will express that trait/disorder

Sex Linked Inheritance Regardless of whether the sex-linked recessive trait is being carried on the X or the Y, boys are more likely to express the trait than girls. Sorry boys! 

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HOMEWORK Page 3 – Q 2 Page 4 – Q 3(#6)