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Biology I S409 Notes: The Genetics Unit. Name: Hour: Date:. Chapter 10.2: Mendelian Genetics (Pgs 277-282) Chapter 11: Complex Inheritance and Human Heredity (Pgs 294- 315). www.acad.swarthmore.edu/.../ the_history_of_gene_testin.htm. T: 1, 2a. How Genetics Began.

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  1. Biology I S409 Notes: The Genetics Unit Name: Hour: Date: Chapter 10.2: Mendelian Genetics (Pgs 277-282) Chapter 11: Complex Inheritance and Human Heredity (Pgs 294- 315)

  2. www.acad.swarthmore.edu/.../ the_history_of_gene_testin.htm T: 1, 2a How Genetics Began Heredity- the passing of traits from parent to offspring (the next generation) Genetics – is the science of heredity • The Father of Genetics: Gregor Mendel • An Austrian monk & plant breeder in 1866) • Studied pea plants (a “true-breeding” simple, predictable plant; consistently produce offspringwith only one form of a trait = complete dominance) • Kept precise records of 7 traits • Seed shape and color • Flower color and position • Pod color and shape • Plant height

  3. The Inheritance of Traits • 2 different plants crossed. (P1) “crosspollinate” • Tall plant X short plant • Results (offspring): F1 generation • Found all were tall (Same for all 7 traits) • One trait “masks the other” • F1 was allowed to “self pollinate” to produce F2 • Results: Majority tall and some short • Found ¾ tall : ¼ short • 3:1 ratio for all 7 traits • Must be a pairof factors (genes) • one gene from each parent

  4. T: 2 f, g, h Genes & Dominance • Genes are represented by letters of the alphabet • Good letters  = Aa, Bb, Rr • Bad Letters  = Cc, Oo, Ww(look too similar! ) • Genes represented in pairs (1 individual has 2 letters) • One from mom, one from dad Principle of Dominance • One gene masks the other from being expressed • A gene that “masks” is Dominant = R • A gene that gets “masked” is Recessive = r • Two identical genes are homozygous (purebred) • RR = homozygous dominant (shows dominant trait) • rr = homozygous recessive (shows recessive trait) • One of each gene is heterozygous (hybrid) • Rr = heterozygous (shows dominant trait)

  5. T: 2 b-i Vocabulary Summary • Allele – different forms of the same gene; tall/short, brown/blue (represented by letters) • Chromosome- DNA containing structure that carries genetic material from one generation to another • Gene- functional unit that controls inherited trait expression that is passed from one generation to another; section of DNA found on a chromosome; i.e. the gene for eye color • Genotype – an organism’s allele pairs (letters) • Phenotype – observable characteristic; what organism looks like (words) • Homozygous – an organism with two of the same alleles for a particular trait (RR or rr) • Heterozygous – an organism with 2 different alleles (Rr) ; called hybrids • Dominant- allele that will mask a recessive gene (R) • Recessive- allele that is masked (r)

  6. Probability & Genetics • Probability = likelihood an event occurs • Example: coin flip • Either heads or tails • There is a 1 out of 2 chance it is heads • ½ or 50% probability • Each flip is independent of other • What if you flip a coin 3 times? • The probability of all heads ½ X ½ X ½ = 1/8 • You can use this to predict genetic cross outcomes

  7. Punnett Squares(Dr. Reginald Punnett) • Used to predict & compare results of a cross • Types of gametes (sex cells) produced are shown along the top and left side of the square • Possible combinations of the offspring appear in the boxes (zygotes; a.k.a. fertilized egg) • Consider one of Mendel’s Experiments:Tall plants are considered dominant to short plants regarding pea plant height. If two pea plants heterozygous for height are crossed, the following genotypes and phenotypes may be determined regarding the possible offspring.

  8. One Trait is being considered: plant height (T, t) Key: TT = tall Tt = tall tt = short P1: Tt x Tt Punnett Square: Genotype: (letters) 1 TT: 2 Tt : 1 tt Phenotype: (words) 3 Tall Pea Plants: 1 Short Pea Plant

  9. Probability & Segregation • In the previous example the results of the cross were… • Genotype • ¼ TT ; 2/4 or ½ Tt; ¼ tt • Phenotype • ¾ tall; ¼ short • 75% tall; 25% short • Remember these are predictions; • They hold true for large #s • Not necessarily for individual/small events

  10. T: 3a Complete Dominance Cross (4 Boxes 1 trait) • When looking at the shape of peas on pea plants, round peas are dominant to wrinkled peas. Using a Punnett Square, determine the genotype and phenotype of the possible offspring when you cross a plant that is heterozygous for pea shape WITH a homozygous recessive plant for the same trait. Trait: shape (R, r) Key: R R = round R r= round r r = wrinkled P1Rr Xr r Punnett Square: Genotype: (letters)2 Rr : 2 rr Phenotype: (words) 2 Round Peas: 2 Wrinkled Peas

  11. Incomplete Dominance Cross T: 3b Trait: Flower color(R, r) • In four o’clock plants, the alleles for red and white flowers show incomplete dominance. When alleles are mixed, pink flowers result. If a red flower is crossed with a white flower, the following genotypes and phenotypes may be determined regarding the possible offspring. Key: RR = red Rr = pink rr = white P1: RRxrr Punnett Square: Genotype: (letters) 4 Rr Phenotype: (words) 4 Pink (All Pink)

  12. Co-Dominance Cross T: 3b Trait: fur color (R, r) • In cows, the alleles for fur color show co-dominance. Fur color may be red or white in cows, however, when alleles are mixed fur will have red and white spots. If a red cow is crossed with a white cow, the following genotypes and phenotypes may be determined regarding the possible offspring. Key: RR = red fur Rr = red & whitespots rr = white fur P1: RR x rr Punnett Square: Genotype: (letters) 4 Rr Phenotype: (words) 4 (All)red & whitespots

  13. Co-Dominance Cross T: 3b Trait: attitude (L, l) • In cats, the alleles for attitude show co-dominance. Cats can have attitudes that are snotty or lazy, however, when alleles are mixed a cat with a snotty & lazy attitude results. If two heterozygous cats are crossed, what are the genotypes and phenotypes of the possible offspring? Key: LL = snotty cat Ll = snotty & lazy cat ll = lazy cat P1: Ll x Ll Punnett Square: Genotype: (letters) 1 LL : 2 Ll : 1 ll Phenotype: (words) 1 snotty : 2 snotty & lazy: 1 lazy

  14. Multiple Alleles Cross T: 3d Trait: eye color(E, eR, er) • Set of 3 or more alleles determine 1 trait • In fruit flies, there are multiple alleles for eye color. 3 alleles produce different eye colors. Red eyes are dominant to purple and white eyes, however, purple eyes are dominant to white eyes. If you cross a heterozygous red eye fly that carries the white eye allele with a heterozygous purple eye fly will the offspring be? Key: EE = red eyes EeR = red eyes Eer = red eyes eReR= purple eyes eRer = purple eyes erer = white eyes Genotype: (letters) 1 EeR: 1 Eer: 1 eRer : 1 erer Phenotype: (words) 2 red eye : 1 purple eye: 1 white eye P1: Eer x eRer Punnett Square:

  15. Multiple Alleles Cross T: 3d Trait: ear length(E, eL, el) • In bunnies, there are multiple alleles for ear length. Different combinations of 3 alleles produce ear lengths. Long ears are dominant to floppy ears and short ears, however, floppy ears are dominant to short ears. If you cross a heterozygous long ear bunny that carries the floppy ears allele with a short ear bunny what offspring will result? Key: EE = Long ears EeL = Long ears Eel = Long ears eLeL = Floppy ears eLel = Floppy ears elel = short ears Genotype: (letters) 2 Eel: 2 eLel Phenotype: (words) 2 long ears : 2 floppy ears P1: EeL x elel Punnett Square:

  16. T: 3e Sex-Linked Traits • Each cell in your body, except your gametes, contains 46 chromosomes (23 from mom, 23 from dad) • 22 pairs of chromosomes are called autosomes • 1 pair of chromosomes is called your sex chromosomes (determines gender) • Sex chromosomes (gametes) are called: X & Y • Males = XYFemales = XX • Thomas Hunt Morgan (Early 1900’s) discovered sex-linked genes in Drosophila. (Fruit flies) • Most Sex-linked genes are on the X, not the Y. • Why? The X chromosome is physically larger! • Most sex-linked genes are recessive • One gene, from mom, gives males mutant trait. • Two genes, from each parent, are needed to give a female offspring the mutant trait(that’s why there are fewer females with sex-linked traits)

  17. T: 3e Examples of Sex-linked Traits • Again, females are less likely to express a recessive X-linked trait because the other X chromosome may mask the effect of the trait! • Red-green color blindness(~8% of males in US) • Hemophilia(inability to clot blood)

  18. T: 3e Sex-Linked Cross • In fruit flies, eye color is sex-linked. Normal eye color is red, and recessive eye color is white. If you cross a white-eyed male with a normal red-eyed female what offspring result? • XR = female sex chromosome w/ normal dominant gene for red eyes • Xr = female sex chromosome w/ mutant recessive gene for white eyes • Y = male sex chromosome

  19. T: 3e Trait: eye color (XR, Xr, Y) Key:XRXR = Normal Female, Red Eyes XRXr = Carrier Female, Red Eyes XrXr = Mutant Female, White Eyes XRY = Normal Male, Red Eyes XrY = Mutant Male, White Eyes P1: XrY x XRXR Punnett Square: Genotype: (letters) 2 XRXr: 2 XRY Phenotype: (words) 2 Carrier Females, red eyes : 2 Normal Males, red eyes

  20. T: 3e Sex-Linked Cross • Hemophilia is a disease that results from the bloods inability to clot. This disease has been found to be a sex-linked trait in humans. The hemophilia allele is recessive to the normal allele. If you cross a female carrier with a normal male what offspring result?

  21. T: 3e Trait: blood’s ability to clot (XB, Xb, Y) Key:XBXB = Normal Female; Can Clot XBXb = Carrier Female; Can Clot XbXb = Mutant Female, hemophiliac XBY = Normal Male; Can Clot XbY = Mutant Male, hemophiliac P1: XBY x XBXb Punnette Square: Genotype: (letters) 1XBXB: 1XBXb : 1XBY : 1XbY Phenotype: (words) 1 Normal Female Can Clot : 1 Carrier Female Can Clot:1 Normal Male Can Clot: 1 Mutant Male, hemophiliac .

  22. T: 3c Dihybrid CrossTwo Traits (16 Boxes) • Principle of Independent Assortment • States that genes for different traits segregate (separate) independently during gamete formation • This holds true for more than one trait  • Plant height and flower color are being studied. Tall plants are dominant to short plants and red flowers are dominant to white. A white plant heterozygous for height is crossed with a short plant heterozygous for flower color. Using this cross, the following genotypes and phenotypes may be determined regarding the possible offspring.

  23. T: 3c Traits: height (H, h) color (R, r) Key: HH = Tall Hh = Tall hh = Short RR = Red Rr = Red rr = White P1: Hhrr x hhRr

  24. T: 3c Traits: height (H, h) Cont. color (R, r) P1: H h r r x h h R r Punnett Square: Genotype: (letters) 4 HhRr : 4 hhRr : 4 Hhrr : 4 hhrr Phenotype: (words) 4 Tall & Red : 4 short & red : 4Tall & white : 4 short & white

  25. T: 3c Dihybrid Cross • Number of spots and tail length are being studied in leopard. Even numbers of spots are dominant to odd numbers of spots and long tails are dominant to short tails. A leopard with a odd number of spots a short tail is crossed with a leopard who is heterozygous for both traits. Using this cross, the following genotypes and phenotypes may be determined regarding the possible offspring.

  26. T: 3c Traits: Number of spots (E, e) Tail length (L, l) Key: EE = Even # Ee = Even # ee = Odd # LL = Long Tail Ll = Long Tail ll = Short Tail P1: eell x EeLl

  27. T: 3c Traits: Number of spots (E, e) Tail length (L, l) P1: eell x EeLl Punnett Square: Genotype: (letters) 4 EeLl : 4 Eell : 4 eeLl : 4 eell Phenotype: (words) 4 Even #ed Spots & Long Tail : 4 Even #ed Spots & Short Tail : 4 Odd #ed Spots & Long Tail : 4 Odd #ed Spots & Short Tail

  28. 11.1: Basic Patterns of Human Inheritance • RecessiveGenetic Disorders • Mendels work was ignored for about 30 years and “rediscovered” in the early 1900’s by Dr. Garrod & genetic studies now continue today…

  29. 11.1: Basic Patterns of Human Inheritance • DominantGenetic Disorders • Not all genetic disorders are caused by recessive inheritance. Some are caused by dominant alleles. That means those who do NOT have the disorder are homozygous recessive for the trait.

  30. T: 3f Pedigrees – Pg 299 • Pedigrees can be used to track genetic information through generations of a family “family history” • Pedigrees have a few simple rules: • Men are shown as squares • Woman are shown as circles • Each generation is given a Roman Numeral (I, II, III, IV, V) • Each individual within a generation is given a number(1, 2, 3, 4, 5) • Shadedindividuals have the trait being tracked in the pedigree

  31. T:f Pedigree Practice • Problem #1: The trait shown below is the ability to taste PTC (phenylthiocarbamide) paper. This trait is controlled by a dominant gene represented by T, and is transmitted by normal inheritance. Nontasters are, therefore, Homozygous for the recessive trait and are represented by tt. The shaded figures below are both homozygous recessives (tt) and are nontasters. All unshaded symbols have two possible genotypes: TT or Tt. Determine the genotypes of all the individuals in the pedigree below: tt Tt Tt Tt Tt Tt tt Tt/TT Tt

  32. T: 3f Pedigree Practice Problem #2 • Write the correct Roman numeral for each generation. • Write the correct number for each individual. • Assume the shaded symbols represent the recessive homozygous genotype rr. Which, individuals show the homozygous recessive trait? • In the spaces below each symbol, write as much of the genotype of each individual as can be determined from the information provided. I 1 Rr 2 rr II 1 Rr 2 Rr 3 rr 4 Rr 5 Rr 6 rr III 1 rr 2 Rr 3 Rr

  33. T: 3f Pedigree Practice • Problem #3 Colorblindness in humans is caused by a sex-linked recessive gene on the X-chromosome. In this pedigree chart, both of the first generation parents are colorblind. Assuming that none of the in-laws are colorblind or are carriers, what is the maximum number of descendants that could be colorblind? • 3 • 4 • 5 • 12

  34. T: 4,5 11.3: Chromosomes & Human Heredity • Karyotypes are a way of studying chromosomes • Used to identify genetic disorders. • You can not see changes in genes, but you can see changes in chromosome number. • There are 22 autosomes matched together with 1 pair of nonmatching sex chromosomes. (find X & Y) • Is this karyotype from a male or female?

  35. T: 4, 5 Nondisjunction • Nondisjunction: when sister chromatids fail to separate properly during cell division • Down syndrome: one of the earliest known human chromosomal disorders. It is usually the result of an extra chromosome 21; often called trisomy 21

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