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INHERITANCE PATTERNS AND HUMAN GENETICS Chapter 12 Slide 2 Quick review Genetics is the field of biology devoted to understanding how characteristics are transmitted form parents to offspring. Slide 3 The DOMINANT factor/gene masks the effect of the other factor in the F1 generation. Use CAPS ex. T for tall The RECESSIVE factor/genes effect can only be seen in the P generation or F2 generation when the DOMINANT gene is absent. Use lower case ex. t for short Generations: P Tall x Short F1 Tall (tall is dominant) F2 3 Tall : 1 short Slide 4 MENDELS 2 LAWS: #1 LAW OF SEGREGATION: A pair of factors is segregated, or separated, during the formation of gametes. Factors for different characteristics are distributed to gametes independently. #2 LAW OF INDEPENDENT ASSORTMENT: Slide 5 GENOTYPE is the genetic makeup of the organism. TT = homozygous dominant Tt = heterozygous tt = homozygous recessive PHENOTYPE is the physical appearance of that organism. Ex. Tall or short MENDELIAN INHERITANCE- DOMINANCE. 2 phenotypes only. If someone has the dominant phenotype but you arent sure of Their genotype use a pedigree (humans) or do a test cross. Slide 6 Other Patterns of Inheritance: 1.Incomplete Dominance- blending seen in heterozygote (ex. pink flowers, brown hair) 2.Codominance- both dominant and recessive phenotypes seen in heterozygote. (ex. type AB blood, roan horse fur color) 3.Polygenic- more than 1 gene determines the phenotype. (Ex. Eye color, Hair color aabbcc) 4.Multiple alleles- more than just 2 alleles (Ex. Blood type = A allele, B allele, O allele is recessive.) Slide 7 EX. Polygenic Inheritance- when the trait is controlled by multiple genes so many phenotypes are possible. AaBbCc x AaBbCc Huge variety in possible Phenotypes of the offspring - skin, hair, eye color - foot size - nose length - height Slide 8 Multiple alleles- trait controlled by three or more alleles. -Ex. ABO blood groups: - TYPE A - TYPE B - TYPE AB Shows Codominance! - TYPE O Slide 9 The process of using phenotypes to deduce genotypes When someone has the DOMINANT phenotype you are uncertain of their genotype. TT or Tt When someone has the recessive phenotype you can be sure of their genotype. tt Slide 10 DIRECTIONS: For each of the following single gene/ Mendelian traits, write your phenotype on the line. Write as much of your genotype as you can be certain. - both alleles if RECESSIVE (rr) - one allele if DOMINANT (R __) Repeat the process by studying two blood relatives (parents work the best) Use a pedigree. Slide 11 1. HAIR TYPE very curly or straight TT, Tt tt Slide 12 2. Hair Color Dark or Light DD, Dd dd Slide 13 3. Hair Line Continuous or Widows Peak WW, Ww ww Slide 14 4. Iris Color Pigmented or Blue EE, Ee ee Slide 15 5. Lens of Eye Astigmatism or Normal AA, Aa aa Slide 16 6. Nose Shape Roman (convex) or Concave NN, Nnnn Slide 17 7. Ear Lobe Free/Long or Attached LL, Llll Slide 18 8. P.T.C. Taster Tasteror Nontaster RR, Rrrr Slide 19 9. Tongue Curling Can curlor Can not curl CC, Cc cc Slide 20 10. Point of chin Dimpled or NO dimple II, Iiii Slide 21 11. Number of Fingers Polydactylism or Normal # PP, Pp pp Slide 22 Slide 23 12. Little Finger Bent or Straight FF, Ff ff Slide 24 13. Hypermobility of Thumb Loose Jointed or Not so HH, Hhhh Slide 25 14. Thumb Extension Hitchhikers Thumb or Not HH, Hh hh Slide 26 15. Middigital Hair Present or Absent MM, Mm mm Slide 27 16. Palmar Muscle Normal (2) or Long (3) UU, Uu uu Slide 28 17. Allergies Tendency Or No tendency AA, Aa aa Slide 29 18. Veins VaricoseorNormal VV, Vvvv Slide 30 19. White Skin Spotting Freckles or No freckles SS, Ssss Slide 31 20. White Forelock Slide 32 LIST OF STRANGE MENDELIAN TRAITS Ear wiggling Misshapen toes or teeth Inability to smell musk or skunk Lack or teeth, eyebrows, nasal bones or thumbnails Whorl in the eyebrow Tone Deafness Hairs that are triangular in cross-section or that have multiple hues (colors) Hairy knuckles, palms, soles, or elbows Egg-shaped pupils Magenta urine after eating beets Sneezing fits in bright sunlight. Slide 33 DNA in chromosomes contain information to make proteins. Geneticists use their knowledge of DNA and the way chromosomes behave to study how traits are inherited and expressed. Slide 34 The parents genotype can be a gene pair of either: - TT homozygous dominant - tt homozygous recessive - Tt heterozygous The parent can make gametes (sperm or eggs), through the process of MEIOSIS, that have either one or the other of the gene pair in it. Slide 35 SEX DETERMINATION MORGANs Fruit fly (Drosophila) breeding experiments of the 1900s revealed the identity of sex chromosomes. In males they were different XY; in females they were the same XX. The other chromosomes (22 in humans) are AUTOSOMES. Slide 36 The male determines the sex of the offspring


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