Review of Mendel’s Laws Law of Dominance - some alleles are dominant others are recessive. Law of Segregation - Organisms inherit 2 copies of each gene, 1 from each parent. Organisms donate only 1 copy of each gene in their gametes (egg or sperm). Law of Independent Assortment – genes for different traits can segregate independently during the formation of gametes (egg and sperm).

Chromosome Theory of Inheritance Genes are located on chromosomes and the behavior of chromosomes during meiosis accounts for inheritance patterns.

Exceptions to Mendel’s Laws Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes. Exceptions to Mendel’s Laws include: Incomplete dominance - Codominance Multiple Alleles - Polygenic traits

Ex. Red and white flowers make pink flowers Incomplete Dominance The heterozygous phenotype is somewhere between the two homozygous phenotypes. Neither allele is completely dominant or recessive. Ex. Red and white flowers make pink flowers

Incomplete Dominance Example #1 In humans, curly hair (HH) is incompletely dominant to straight hair (H’H’).  The heterozygous individual has wavy hair (HH’).  Cross two people with wavy hair. Genotype Ratio: Phenotype Ratio:

Incomplete Dominance Example #2 Fitz loves growing flowers for his friend Olivia. Her favorite flowers, roses, are found in red (RR), blue (R’R’), and purple (RR’). What would happen if Fitz crossed a blue rose with a purple rose? Genotype Ratio: Phenotype Ratio:

Codominance Both traits are fully and separately expressed. Ex. Red and white flowers make red and white speckled flowers. Ex. Blood Type (AB blood type is fully A and fully B) Blood type is also an example of multiple alleles

Codominance Example #1 In horses, gray horses (GG) are codominant to white horses (WW).  The heterozygous horses(GW) is an appaloosa horse (a white horse with gray spots on the rump and loins). Cross a white horse with an appaloosa horse. ________      X      ________   Genotypic Ratios: Phenotypic Ratios:

Blood Type An example of Codominance AND Multiple Alleles Blood Type AB is fully A and fully B Multiple Alleles Alleles = A, B, and i

Blood Type An example of Codominance AND Multiple Alleles Ex. If a mother has Type AB blood and a father has Type B blood, what are the possible blood types of their children?

Blood Type Who’s Your Daddy? Genetics Oh no! The hospital has made a big mistake and lost track of which baby belongs to each parents. Can you help them fix this before they get sued? Babies: Baby 1: O Baby 2: AB Baby 3: A Parents: Mr. and Mrs. Allele: AB and AB Mr. and Mrs. DNA: O and AB Mr. And Mrs. Gene: B and O

Multiple Alleles Having more than two alleles for one gene Ex. Alleles for blood type = A, B, i Ex. Fur color in rabbits

Multiple Alleles Example Example: What are the possible fur colors of the offspring if you cross a dark grey rabbit (Ccch) and a Himalayan rabbit (chc)? Phenotype Key: Full color = CC, Ccch, Cch, Cc Chinchilla = cchch, cchcch, cchc Himalayan = chc, chch Albino = cc

Polygenic Inheritance A trait produced by two or more genes Usually shows a RANGE in phenotype Ex. skin color, eye color, height, personality Occasionally, epistasis can occur When one gene overshadows all of the others Ex. Labrador retriever fur colors, eye color, Albinism Eye Color (in general) TWO Genes = B gene and G gene BB or Bb = Brown bb = not brown GG or Gg + bb = green gg + bb = blue Lab Fur Color: TWO Genes = B gene and E gene BB or Bb = Black bb = Brown EE or Ee + bb = Brown ee = masks ALL b genotypes (epistasis) and makes YELLOW

Linked Genes Linked genes: genes that are physically located on the same chromosome will be inherited together. Ex. Blonde hair and blue eyes, red hair and freckles, large ears and broad nose Linked genes can only be separated or broken apart during Crossing Over

Sex-Linked Traits Males and females have exactly the same chromosomes for pairs 1-22. These are autosomes. The last pair of chromosomes, called sex chromosomes, determine the gender of the individual. Females have XX Males have XY

X vs. Y Chromosome Y chromosome carries FEW genes. X chromosome contains MANY genes that affect MANY traits. Sex-Linked Genes = genes on sex chromosomes (X or Y) Image © NIH Image Gallery 2014: https://flic.kr/p/JWZHC6

Genes on the X chromosome are X-Linked. X-Linked Genes Genes on the X chromosome are X-Linked. Females inherit gene as normal & principle of dominance applies. Males inherit the gene on the X, but not the Y. Because males have only one X, they express that trait whether it is dominant or recessive! Carrier Daughter Normal Son Affected Son Normal Daughter

Sex-Linked Example Colorblindness - located on X chromosome Normal vision = XB Colorblindness = Xb Y chromosome does NOT have the gene Ex. Cross a woman who is a carrier for color blindness with a man who is normal. Image: © Christian Heilmann 2011 https://flic.kr/p/9eE3Cc