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Objective: 1) Provide an example for codominance, incomplete dominance, and multiple alleles. 2) Define karyotype. SOME TRAITS THAT ARE DOMINANT INCLUDE: HITCHHIKER’S THUMB, ALMOND-SHAPED EYES, THICK LIPS, HAIR ON MIDDLE SECTION OF FINGER. . Human Traits: autosomal Oval dominant, square recessive 1. Shape of face (probably polygenic) 2. Cleft in chin No cleft dominant, cleft recessive 3. Hair curl (probably polygenic) Assume incomplete dominance Curly: Wavy: Straight: homozygous 4. Hairline Widow peak dominant, straight hairline recessive 5. Eyebrow size Broad dominant, slender recessive 6. Eyebrow shape Separated dominant, joined recessive 7. Eyelash length Long dominant, short recessive 8. Dimples Dimples dominant, no dimples recessive 9. Earlobes Free lobe dominant, attached recessive homozygous heterozygous 10. Eye shape Almond dominant, round recessive 11. Freckles Freckles dominant, no freckles recessive 12. Tongue rolling Roller dominant, nonroller recessive 13. Tongue folding Inability dominant, ability recessive 14. Finger mid-digital hair Hair dominant, no hair recessive 15. Hitch-hiker's thumb Straight thumb dominant, hitch-hiker thumb recessive 16. Bent little finger Bent dominant, straight recessive 17. Interlaced fingers Left thumb over right dominant, right over left recessive 18. Hair on back of hand Return to Menu 19. Tendons of Palmar Muscle Hair dominant, no hair recessive Two tendons dominant, three tendons recessive INCOMPLETE DOMINANCE: THE PHENOTYPE OF THE HETEROZYGOUS CONDITION IS A CROSS BETWEEN THE DOMINANT AND RECESSIVE TRAITS. EXAMPLE: IN CARNATIONS, R=RED r=WHITE RR= RED CARNATION Rr= PINK CARNATION rr= WHITE CARNATION CODOMINANCE: THE PHENOTYPES OF BOTH ALLELES ARE EXPRESSED IN A HETEROZYGOUS INDIVIDUAL. EXAMPLE: IN CHICKENS, B= BLACK FEATHERS, W= WHITE FEATHERS BB = BLACK FEATHERS BW = BLACK AND WHITE FEATHERS WW = WHITE FEATHERS MULTIPLE ALLELES: SOMETIMES MORE THAN 2 ALLELES CONTROL A TRAIT. 3 ALLELES DETERMINE PIGEON FEATHER COLOR Occurs when one gene controls the expression of a second gene. In mice, one gene controls whether the mouse will have coloration (dominant) or albinism/white (recessive). IF coloration is dominant, THEN a second gene will determine if the mouse will be brown or black. Pleiotropy is a condition that occurs when 1 gene controls many phenotypes. A classic example of pleiotropy is the human disease PKU (phenylketonuria). This disease can cause mental retardation and reduced hair and skin pigmentation, and can be caused by a mutation in a single gene that codes for an enzyme (phenylalanine hydroxylase) that converts the amino acid phenylalanine to tyrosine, another amino acid. One trait or phenotype is controlled by many genes. For example between 4 to 10 genes control human height. Genes linked to human height: ZBTB38, HHIP, CDK6, HMGA2, GPR126, ADAMTSL3, GDF5, LCORL, EFEMP1, and HIST1H1D AUTOSOMES: THERE ARE 22 PAIRS OF HOMOLOGOUS CHROMOSOMES (TOTAL CHROMOSOMES =44) SEX CHROMOSOMES: 1 PAIR OF CHROMSOMES THAT DETERMINE THE SEX OF AN ORGNANISM. SOME TRAITS ARE CONTROLLED BY GENES LOCATED ONLY ON THE SEX CHROMOSOMES (EXAMPLE: COLOR BLINDNES AND HEMOPHILIA). YOUR CHROMOSOMES ORGANIZED AS A KARYOTYPE (CHROMOSOME MAP) YOUR CHROMOSOMES DURING METAPHASE SEX-LINKED TRAITS: TRAITS CONTROLLED BY GENES LOCATED ON THR SEX CHROMOSOMES. X = FEMALE SEX CHROMOSOME Y = MALE SEX CHROMOSOME (SMALLER THAN X AND DOES NOT CONTAIN AS MANY GENES) THOMAS HUNT MORGAN DISCOVERED TRAITS LINKED TO SEX CHROMOSOMES. HE FIRST NOTICED THIS IN FRUIT FLY EYE COLOR. MORGAN’S 1ST EXPERIMENT: X FEMALE Xr Y XR XRXr XRY XR XRXr XRY MALE OFFSPRING: ALL RED EYES