Complex Patterns of Inheritance Mendel said that each trait has one gene, which has two alleles, one dominant and one recessive. Many traits are more complex than this.

Polygenic Traits Polygenic: “many genes”, when several genes influence a trait Examples: – Eye color, height, weight, hair and skin color. – All these conditions have intermediate conditions between one extreme and the other.

Polygenetic Traits

Incomplete Dominance: alleles “blend” Betta Fish Snapdragons x x = =

Incomplete Dominance Situation: If red and white flower alleles show incomplete dominance, what offspring ratios will you see if you cross a Red-flowered plant with a white-flowered plant? Parent Genotypes: RR x WW Offspring Ratios -Genotype: 100% RW -Phenotype: 100% Pink RR W W RW

Codominance: both alleles show up in their “pure form” Chickens Blood Types x= speckled

Codominance Situation: If red and white flower alleles show codominance, what offspring ratios will you see if you cross a red-flowered plant with a white-flowered plant? Parent Genotypes: RR x WW Offspring Ratios -Genotype: 100% RW -Phenotype: 100% “splotchy” RW RR W W

Multiple Alleles Multiple Alleles: Genes with more than two alleles that could code for a trait. There are three or more possible alleles, but an individual will still only have two alleles for each trait.

Multiple Alleles: Human Blood Types Three different alleles: I A, I B, and i. A and B are types of carbs cell surface. I A and I B are dominant over i, but are codominant with one another. Four different blood types: – A from I A I A or I A i – B from B I B or I B i – AB from I A I B – O from ii

Blood Type Problem I A and I B are co-dominant i is recessive. AB blood type mother says that John Doe is the father of an AB baby. His blood type is O – could he be? IAIA IBIB i i Possible blood types: A or B Not AB! NOT the father. IBiIBi IAiIAiIBiIBi IAiIAi

Blood Types Blood Type% of Americans with this blood type Who can receive this type O+37%O+, A+, B+, AB+ O-6%All blood types A+34%A+, AB+ A-6%A+, A-, AB+, AB- B+10%B+, AB+ B-2%B+, B-, AB+, AB- AB+4%AB+ AB-1%AB+, AB-

Sex linked genes You have two copies of almost all genes What two chromosomes do not have all the same genes?

Sex-linked Genes = genes found on the X chromosome Males are XY so they only have 1 copy of the X chromosome Females are XX so they have two copies of X Recessive genes on X chromosome show up more in males.

Heterozygous Red-Eyed Female x Red-Eyed Male Genotypes: Phenotype Ratio: 50% Red-eyed females 25% Red-eyed males 25% White-eyed males XRXR XrXr XRXR Y XRXRXRXR XRXrXRXr XRYXRY XrYXrY X R X r x X R Y Question: Can a father pass on an x-linked trait to son?

Human Examples of Sex Linkage Hemophilia is a disorder that causes blood to clot incorrectly  patient bleeds out after minor cut – Common in royal families because of inbreeding Red-green color blind Male pattern baldness …Can identify patterns using pedigrees

Pedigree: shows how a trait is passed down in a family Unaffected Affected Carrier Female Male Carrier = individual who has ONE copy of a recessive allele (doesn’t have disease, but can pass it on to children)

If the phenotype is more common in males, the gene is likely sex-linked. If it is even between male and female, it is autosomal. Autosomes = chromosome other than X & Y

Dominant or Recessive? If the trait is dominant, every individual with the trait will have a parent with the trait If individual has the trait and neither parent had the trait, it must be recessive.

Recessive or dominant?

Autosomal or Sex-Linked?

Many inherited diseases are usually recessive – why do you think that is?

What type of inheritance?

Dihybrid Crosses Dihybrid Crosses: a cross between individuals that involves two traits (e.g., pod color and plant height) Tall = H, Short = h…. Green = G, Yellow = g Example: 1) Parent 1: HHGG  Tall, Green 2) Parent 2: hhgg  Short, Yellow

Finding the Gametes for Dihybrid Crosses Remember, each gamete must have ONE COPY of the two genes To find possible gametes for each parent, use the FOIL method (x + 3)(x + 4) = x 2 + 4x + 3x +12

Another Example: Heterozygous x Heterozygous Parent 1: H h G g Parent 2: H h G g Possible Gametes: HGHG HgHg hGhG hghg HGHG HgHg hGhG hghg

Heterozygous x Heterozygous Parent Genotypes: HhGg x HhGg Offspring Ratios -Genotype: too complicated! -Phenotype: Next Slide! HGHG HgHghGhG hghg HGHG HgHg hGhG hghg HhGg HHGG HHGgHhGG HHGgHHggHhGg Hhgg HhGGHhGghhGGhhGg HhgghhGghhgg HGHG HgHg hGhG hghg Possible Gametes:

Another Example: Heterozygous x Heterozygous Parent Genotypes: HhGg x HhGg Phenotype: 9: 3: 3: 1 9 Tall, Green 3 Tall, Yellow 3 Short, Green 1 Short, Yellow HGHG HgHghGhG hghg HGHG HgHg hGhG hghg HhGg HHGG HHGgHhGG HHGgHHggHhGg Hhgg HhGGHhGghhGGhhGg HhgghhGghhgg