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Types of Complex Inheritance Incomplete Dominance Codominance Multiple Alleles Polygenic Traits

Incomplete dominance Both alleles partially show by blending together Analogy: Mixing Together Paint Blue Green Yellow

Both alleles are completely expressed at the same time. codominance Both alleles are completely expressed at the same time. -Analogy: Mixing Together Pebbles Yellow AND Blue Yellow Blue

Multiple alleles Having more than two alleles for a specific trait Ex. An example is blood groups in humans. Blood type, for example, is determined by three alleles. A is codominant IA B is codominant IB O is recessive i

Blood Types Alleles (Genotype) Blood Type (Phenotype) AA or Ao IAIA or IAi Type A BBor Bo IBIB or IBi Type B AB only IAIB Type AB oo only ii Type O

Polygenic Traits Traits that are determined by the interaction of multiple pairs of genes Ex: skin color, height

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Multiple Allele Traits: Blood Type Blood type exhibits codominance and multiple alleles. The chart below shows the phenotype and genotype of blood types. Phenotype Genotype Type A AA or Ao IAIA or IAi Type B BB or Bo IBIB or IBi Type AB AB IAIB Type O oo ii Blood Type is controlled by 3 alleles: A, B, O. A & B are codominant, O is recessive.

1. a) What are the two genotypes possible for a person who as A blood 1. a) What are the two genotypes possible for a person who as A blood? IAIA or IAi b) What genotype does a person with AB blood have? IAIB c ) What genotype does a person with O blood have? ii d) What are the two genotypes possible for a person who as B blood? IBIB or IBi

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Sex-Linked

Which Chromosome Determines our Sex? Introduction: A human has 23 pairs of homologous chromosomes Pairs 1-22 are called Autosomes – chromosomes not involved in determining sex Pair 23 – Sex Chromosomes

How is Sex Determined? Sex chromosomes are X and Y Females are XX Males are XY

How is Sex Determined? Females can only make eggs with the X chromosome Males make sperm with the X or Y chromosome, so it is the male that determines the sex of a baby

How is Sex Determined? 50% chance male 50% chance female

Discovery of Sex-Linked Genes Discovered in fruit flies (drosophila melanogaster) by Thomas Hunt Morgan

Discovery of Sex-Linked Genes Eye color is sex-linked in fruit flies. He discovered that alleles for eye color is carried on the X chromosome ONLY! NO ALLELES ON THE Y CHROMOSOME

Why Fruit Flies? Easy to maintain 10 – 15 day life cycle Many offspring produce in a short time

Sex-Linked Traits Traits that are controlled by the sex chromosomes Colorblindness – can’t see the difference between certain colors Hemophilia – blood does not clot properly

Example H = Normal h = hemophilia Important Rule: Only write the gene over the X chromosome

Female Genotypes XHXH : Normal Female (Homozygous Dominant) XHXh : Normal Female Carrier (Heterozygous) XhXh : Female with hemophilia (Homozygous Recessive)

Male Genotypes XHY : normal male without hemophilia XhY : male with hemophilia

Sex-linked traits occur more in males than females because Males only need one “bad” gene on the X chromosome But females need two “bad” genes on both X chromosomes