What is Genetics? - The science that deals with heredity and variation. - Heredity: the transmission of traits from parents to offspring

Transcription

1 Genetics

2 What is Genetics? - The science that deals with heredity and variation. - Heredity: the transmission of traits from parents to offspring - Variation: similarities and differences

3 What is Heredity? t/basics/inheritance/ What is a Trait? t/basics/traits/

4 What is a Gene? Gene = segment of DNA on a chromosome that controls a trait. Genes are made up of DNA and act as instructions to make proteins Genes are passed onto offspring Every person has two copies of each gene, one inherited from each parent Trait: a quality of characteristic Different forms of each gene are called Alleles. You inherit one from each parent. Letters represent Alleles Allele H = black hair Allele h = brown hair Capital letters = dominant alleles Lowercase letters = recessive alleles

5 Dominant alleles are notated with capital letters Ex: B= Brown Recessive alleles are notated with lower case letters Ex: b=grey **Remember, individuals get one allele from each parent

6 Copy from mother Copy from father

7 Homozygous v. Heterozygous Homozygous = both alleles of a pair are alike for that characteristic P P PP homozygous dominant pp homozygous recessive PP Heterozygous = two alleles are different for that characteristic P p Pp Pp

8 P= Purple p= White

9 Trait specific characteristic of an organism The genetic contribution to a trait is called the genotype ex:tt The genotype is the DNA or the genetic makeup The outward expression of the genotype is called the phenotype. The phenotype is what is actually expressed or what you see

10 The picture to the right shows several common human traits Stop and work on Genetics Practice Problems Sections 1-3

11 Do Now Take out your notes. What is the difference between genotype and phenotype? Give an example. What is the difference between homozygous and heterozygous? Give an example.

12 Monohybrid Punnett Squares Letters outside Punnett = possible gametes (egg/sperm) formed from meiosis Letters inside Punnett = possible offspring Practice: Red is dominant over white. Two heterozygous flowers are crossed. Use a Punnett square to determine the probability of one of their offspring having a red color. R=red r=white Predicted outcome of Punnett: Genotypic ratio of offspring: 25%RR : 50% Rr : 25% rr Phenotypic ratio of offspring: 75% red and 25% white Answer: 75 % or ¾ will have red flowers R R r r

13 Monohybrid Punnett Squares Practice: H = brown hair h = black hair. Determine the possible genotypes for each cross below: Mom is Hh and Dad is hh Mom is hh and Dad is HH Mom is Hh and Dad is Hh

14 Practice Monohybrid Cross In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a genetic cross of two plants that are heterozygous for the seed shape trait, what fraction of the offspring should have spherical seeds? Draw a Punnett square

15 Practice Monohybrid Cross Genotypes that resulted from this monohybrid cross (Ss x Ss) homozygous dominant heterozygous homozygous recessive Phenotypes that resulted from this monohybrid cross (Ss x Ss)

16 Recessive Inheritance Normal Dd Parents Deafness is a recessive disorder D=normal d=deaf If we cross heterozygous parents with normal hearing, what will the Punnett Square look like? Normal Dd Sperm D D d DD Normal Dd Normal (carrier) Dd Normal (carrier) dd Deaf Eggs d Offspring

17 Practice Questions: Draw Punnett squares to answer the questions. 1. In mussels, brown (B) coloring is dominant, and blue (b) coloring is recessive. If a blue mussel has two brown parents, what percentages of the total offspring of these brown parents are expected to be blue? a. 100% b. 75% c. 50% d. 25% 2. In cats, the allele for short hair (H) is dominant to the allele for long hair (h). If a heterozygous short-hair cat is crossed with a long-hair cat, what percentage of the offspring is expected to be heterozygous for hair length? a. 0 % b. 25 % c. 50 % d. 75 % 3. In pigeons, the allele B produces ash-red feathers. The allele b produces blue feathers. The B allele is dominant to the b allele. A pigeon with genotype Bb is crossed with a pigeon with the genotype bb. What percent of the offspring are expected to have ash-red feathers? a. 0 % b. 25 % c. 50 % d. 100 % Stop and work

18 Do Now Take out your homework (yellow WS) Work on your salmon colored packet. You have 10 minutes to finish. HW for tonight: 8.3 R&Q

19 MENDEL S LAWS

20 Gregor Mendel (7/22/ ) Experimented with garden peas Pisum sativum Tested some 28,000 pea plants in 7 years Used artificial fertilization (he physically added the sperm (pollen) to the eggs Worked in a small space in monastery garden Devised precise mathematical pattern for inheritance Did not understand biological process, eg. chromosomes & DNA Not until 1900 that three botanists discovered his papers while researching their own findings Mendel, O.S.A., experimental garden (35x7 meters) in the grounds of the Augustinian Monastery in Old Brno. Its appearance before 1922.

21 Gregor Mendel discovered principles of genetics in experiments with the garden pea Mendel showed that parents pass heritable factors to offspring (heritable factors are now called genes) Advantages of using pea plants Controlled matings Self-fertilization or cross-fertilization Observable characteristics with two distinct forms True-breeding (pure) strains Copyright 2009 Pearson Education, Inc.

22 Label the flower in your notes Petal Stamens (contain male gametes in the pollen) Carpel (contains female gametes)

23 White 1 Removed stamens from purple flower Stamens Carpel Parents (P) 2 Purple Transferred pollen from stamens of white flower to carpel of purple flower

24 White 1 Removed stamens from purple flower Stamens Carpel Parents (P) 2 Purple 3 Transferred pollen from stamens of white flower to carpel of purple flower Pollinated carpel matured into pod

25 White 1 Removed stamens from purple flower Stamens Carpel Parents (P) 2 Purple 3 Transferred pollen from stamens of white flower to carpel of purple flower Pollinated carpel matured into pod 4 Offsprin g (F1) Planted seeds from pod

26 Pea plant traits Flower color Purple White Axial Terminal Seed color Yellow Green Seed shape Round Wrinkled Pod shape Inflated Constricted Pod color Green Yellow Tall Dwarf Flower position Stem length stop and work

27 Mendel's 3 Laws Law of Dominance, Law of Segregation, and Law of Independent Assortment 1. The Law of Dominance In a cross of parents that are pure (homozygous) for contrasting traits, only one form of the trait will appear in the next generation. Offspring that are hybrid (heterozygous for a trait will have only the dominant trait in the phenotype. 27

28 Mendel's 3 Laws 2. The Law of Segregation During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring. 28

29 Mendel s law of segregation describes the inheritance of a single character Example of a monohybrid cross Cross between parents who are true breeding for a trait i.e. both are homozygous for one allele of a gene Ex: PP x pp P=purple flowers p=white Parental generation: purple flowers white flowers F1 (1st) generation: all plants with purple flowers F2 (2nd) generation: 3/4 of plants with purple flowers 1/4 of plants with white flowers Mendel needed to explain Why one trait seemed to disappear in the F1 generation Why that trait reappeared in one quarter of the F2 offspring

30 P generation (true-breeding parents) Purple flowers (PP) White flowers (pp)

31 P generation (true-breeding parents) Purple flowers F1 generation White flowers All plants have purple flowers

32 P generation (true-breeding parents) Purple flowers (PP) White flowers (pp) F1 generation All plants have purple flowers Fertilization among F1 plants (F1 F1) F2 generation ¾ of plants have purple flowers ¼ of plants have white flowers

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34 Practice Monohybrid Cross In pea plants, spherical seeds (S) are dominant to dented seeds (s). In a genetic cross of two plants that are heterozygous for the seed shape trait, what fraction of the offspring should have spherical seeds?

35 Practice Monohybrid Cross Genotypes that resulted from this monohybrid cross (Ss x Ss) homozygous dominant heterozygous homozygous recessive Phenotypes that resulted from this monohybrid cross (Ss x Ss)

36 Mendel s law of segregation describes the inheritance of a single character Four Hypotheses 1. Genes are found in alternative versions called alleles; a genotype is the listing of alleles an individual carries for a specific gene 2. For each characteristic, an organism inherits two alleles, one from each parent; the alleles can be the same or different A homozygous genotype has identical alleles A heterozygous genotype has two different alleles Copyright 2009 Pearson Education, Inc.

37 9.3 Mendel s law of segregation describes the inheritance of a single character Four Hypotheses 3. If the alleles differ, the dominant allele determines the organism s appearance, and the recessive allele has no noticeable effect The phenotype is the appearance or expression of a trait The same phenotype may be determined by more than one genotype 4. Law of segregation: Allele pairs separate (segregate) from each other during the production of gametes so that a sperm or egg carries only one allele for each gene Copyright 2009 Pearson Education, Inc.

38 Genetic makeup (alleles) pp PP P (parent) plants Gametes All p All P F1 plants (hybrids) Gametes All Pp 1 2 P 1 2 p Sperm P F2 plants P Phenotypic ratio 3 purple : 1 white PP p Pp Eggs Genotypic ratio 1 PP : 2 Pp : 1 pp p Pp pp stop and work

39 Draw Punnett squares to answer the questions. 1. In mussels, brown (B) coloring is dominant, and blue (b) coloring is recessive. If a blue mussel has two brown parents, what percentages of the total offspring of these brown parents are expected to be blue? a. 100% b. 75% c. 50% d. 25% 2. In cats, the allele for short hair (H) is dominant to the allele for long hair (h). If a heterozygous short-hair cat is crossed with a long-hair cat, what percentage of the offspring is expected to be heterozygous for hair length? a. 0 % b. 25 % c. 50 % d. 75 % 3. In pigeons, the allele B produces ash-red feathers. The allele b produces blue feathers. The B allele is dominant to the b allele. A pigeon with genotype Bb is crossed with a pigeon with the genotype bb. What percent of the offspring are expected to have ash-red feathers? a. 0 % b. 25 % c. 50 % d. 100 %

40 Mendel's 3 Laws 3. The Law of Independent Assortment Alleles for different traits are distributed to sex cells (& offspring) independently of one another. 40

41 The law of independent assortment is revealed by tracking two characters at once Example of a dihybrid cross Parental generation: round yellow seeds (RRYY) wrinkled green seeds (rryy) F1 generation: all plants with round yellow seeds F2 generation: 9/16 of plants with round yellow seeds 3/16 of plants with round green seeds 3/16 of plants with wrinkled yellow seeds 1/16 of plants with wrinkled green seeds Mendel needed to explain Why nonparental combinations were observed Why a 9:3:3:1 ratio was observed among the F2 offspring Copyright 2009 Pearson Education, Inc.

42 9.5 The law of independent assortment is revealed by tracking two characters at once Law of independent assortment Each pair of alleles segregates independently of the other pairs of alleles during gamete formation For genotype RrYy, four gamete types are possible: RY, Ry, ry, and ry Copyright 2009 Pearson Education, Inc.

43 Hypothesis: Independent assortment Hypothesis: Dependent assortment P generation rryy RRYY ry Gametes RY F1 generation rryy RRYY RrYy RrYy Sperm Sperm 1 2 F2 generation ry Gametes RY 1 2 RY 1 2 ry RY Eggs ry 1 4 RY 1 4 ry Eggs Hypothesized (not actually seen) 1 4 Ry 1 4 ry RY 1 4 ry 1 4 Ry 1 4 ry RRYY RrYY RRYy RrYy RrYY rryy RrYy rryy RRYy RrYy RRyy Rryy RrYy rryy Rryy rryy Actual results (support hypothesis) Yellow round Green round Yellow wrinkled Green wrinkled

44 Dihybrid Cross Practice In guinea pigs, the allele for black fur (B) is dominant over that for brown fur (b). Similarly, the allele for short fur (S) is dominant over that for long fur (s). Draw a Punnett square that shows a cross between two guinea pigs with the genotype BbSs. Describe the genotypes and phenotypes of the cross. What is the ratio? What is the phenotypic outcome of the offspring produced by this cross? 9 black short fur, 3 black long fur, 3 brown short fur, 1 brown long fur

45 Do Now - Take out your homework (8.3) -Take out your white Genetics Worksheet -Turn to page 3 and complete the first dihybrid cross and answer the questions. If you finish, move on to #2

46 Do Now: Read the paragraph and answer the questions. PTC: The Genetics of Bitter Taste In 1931, a chemist named Arthur Fox was pouring some powdered PTC into a bottle. When some of the powder accidentally blew into the air, a colleague standing nearby complained that the dust tasted bitter. Fox tasted nothing at all. Curious how they could be tasting the chemical differently, they tasted it again. The results were the same. Fox had his friends and family try the chemical then describe how it tasted. Some people tasted nothing. Some found it intensely bitter, and still others thought it tasted only slightly bitter. Soon after its discovery, geneticists determined that there is an inherited component that influences how we taste PTC. Today we know that the ability to taste PTC (or not) is conveyed by a single gene that codes for a taste receptor on the tongue. The PTC gene, TAS2R38, was discovered in There are two common forms (or alleles) of the PTC gene: Taster allele= T (dominant) Non taster allele= t (recessive) Questions: What are the possible genotypes of PTC tasters? What are the genotypes for non-tasters? Next, we will figure out your genotype!!

47 Pedigrees: Genetic traits in humans can be tracked through family pedigrees A pedigree Shows the inheritance of a trait in a family through multiple generations Demonstrates dominant or recessive inheritance Can also be used to deduce (determine) genotypes of family members Copyright 2009 Pearson Education, Inc.

48 First generation (grandparents) Ff Ff ff Ff Ff Ff ff ff FF or Ff Second generation (parents, aunts, and uncles) Third generation (two sisters) FF or Ff Female Male Affected Unaffected ff ff

49 Albinism is a recessive disorder affecting humans. In order to get it, a person must receive 2 copies of the recessive allele for the trait. If someone has this disorder, they can not produce skin pigment, and have the genotype aa. The pedigree below shows people with albinism. On the pedigree, mark each person s genotype. If a dominant individual s genotype is unknown, write A. How many people have the disorder? Both generation I-1 and I-2 must have what genotype? How do you know? If generation III-4 marries an albino woman and has a child, what is the probability that the child will have the disorder? Use a Punnett square to justify your answer. Side note-- many animals can have albinism. Not just humans. A= normal a=albinism

50 Aa Aa Albinism is a recessive disorder affecting humans. If someone has this disorder, they can not produce skin pigment, and have the genotype aa. The pedigree below shows people with albinism. On the pedigree, mark each person s genotype. If a dominant individual s genotype is unknown, write A. How many people have the disorder? Both generation I-1 and I-2 must have aa what genotype? How do you know? If generation III-4 marries an albino woman and has a child, what is the probability that the child will have the disorder? Use a Punnett square to justify your answer. aa A_ aa Aa A_ Aa Aa Aa A= normal a=albinism A_ Aa

51 Do Now Take out your pedigree packet from Thursday and start the problems. HW for tonight: Read section 8.3 and complete the Directed Reading WS: Patterns of Inheritance (yellow)

52 Complex Genetics: Different types of Inheritance Patterns So far we have talked about dominant/recessive inheritance pattern where one trait is always dominant, but there are other types of interference patterns as well that don t follow the same rules. Types of Inheritance: Dominant/Recessive (complete dominance) Codominance Incomplete dominance Multiple alleles Polygenic

53 Incomplete dominance results in intermediate (in between) phenotypes Neither allele is dominant over the other Both alleles are present in heterozygotes often described as blending No dominant allele Copyright 2009 Pearson Education, Inc.

54 Examples of incomplete dominance Human Hair: If a straight-haired person and a curly haired person have a child, the child will likely have wavy hair Andalusian Chicken Feathers: If a black Andalusian chicken mates with a white Andalusian chicken, their offspring spring will most likely be Blue or a blend of black and white

55 Example of Incomplete Dominance Crossing homozygous red flowers with homozygous white flowers produces heterozygotes that pink (blend of white and red)

56 Examples of incomplete dominance Human Hair: If a straight-haired person and a curly haired person have a child, the child will likely have wavy hair Andalusian Chicken Feathers: If a black Andalusian chicken mates with a white Andalusian chicken, their offspring spring will most likely be Blue or a blend of black and white

57 Complete Simpsons Problem #1: Incomplete Dominance

58 Codominance Many genes have more than two alleles in the population Neither allele is dominant over the other Expression of both alleles is observed as a distinct phenotype in the heterozygous individual Observed for type AB blood

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62 Complete Simpsons Problem #2: Codominance

63 Do Now -Take out your notes -What is the difference between codominance and incomplete dominance? Give and example of each.

64 Multiple alleles More than two alleles in the population individuals can carry any two of these alleles The ABO blood group has three alleles: leading to four phenotypes: type A, type B, type AB, and type O blood Copyright 2009 Pearson Education, Inc.

65 ABO Blood Type - blood type gene is found on the 9th chromosome AO genotype will have an A phenotype - blood type results from inheritance of 1 of 3 alleles (A, B, or O) from each parent. 2 alleles total. BO genotype will have an B phenotype - Types A and B are dominant. Type O is recessive. OO genotype will have an O phenotype - Possible outcomes: AB genotype will have an AB phenotype

66 Blood Type Practice Problem The police have rounded up the usual suspects in the latest rash of bookstore robberies. The thief got a nasty paper cut at the scene of the crime. The suspects are of blood types O, A, B and AB. The blood at the crime scene contained O alleles. Which suspect therefore cannot have been involved? Explain. Release Suspect #4 because his blood contains no O alleles.

67 Complete Simpsons Problem #3: Multiple Alleles

68 SEX CHROMOSOMES AND SEX-LINKED GENES Copyright 2009 Pearson Education, Inc.

69 Chromosomes determine sex in many species X-Y system in mammals, fruit flies XX = female; XY = male X-O system in grasshoppers and roaches XX = female; XO = male Z-W in system in birds, butterflies, and some fishes ZW = female, ZZ = male Chromosome number in ants and bees Diploid = female; haploid = male Copyright 2009 Pearson Education, Inc.

70 X Y

71 Determining Sex in Humans --Sex is determined by the father Parents Male XY Fill in the boxes in your notes! Female XX Meiosis Gametes Produced (n) Y X X Eggs Sperm Fertilization Offspring (2n) XX Female XY Male

72 Sex-linked genes exhibit a unique pattern of inheritance Sex-linked genes are located on either of the sex chromosomes X-linked genes are passed from mother to son and mother to daughter X-linked genes are passed from father to daughter Y-linked genes are passed from father to son Copyright 2009 Pearson Education, Inc.

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74 Sex-linked (x) disorders affect mostly males If a male inherits only one sex linked allele from his mother the allele will be expressed -----> Xr Y A woman must inherit two X chromosomes (one from each parent) and therefore 2 alleles ---->XR Xr or Xr Xr or XR XR

75 Female Example of a sex-linked gene (x-linked gene) Male Xr Y XR XR Because the alleles are found on X chromosomes, we show them as a superscript on the X. Remember that females can only produce gametes with a single X chromosome and males can produce gamete with either an X or a Y chromosome. Sperm Eggs XR Xr Y XR Xr XR Y R = red-eye allele r = white-eye allele

76 Female Male XR Xr XR Y R = red-eye allele r = white-eye allele Sperm X R XR Y XR XR R X Y Xr XR Xr Y Eggs Xr 3 Red-eyed 1 White-eyed

77 Female Male XR Xr Xr Y Sperm Xr Y XR XR Xr XR Y Xr Xr Xr Xr Y Eggs 2 Red-eyed 2 White-eyed

78 Hemophilia is a sex-linked (x) trait A high incidence of hemophilia plagued royal families of Europe. -Queen Victoria of England carried the hemophilia allele XR Xr - She passed it onto one of her sons and two of her daughters (only her daughter Alice is shown) -Via marriage, her grand daughters introduced the gene to royal families of Spain and Russia. - Thus the age-old practice of using marriage to strengthen international alliances effectively spread hemophilia to several nations. Hemophilia in the royal families of England and Russia. Half filled shapes represent unaffected heterozygous carriers.

79 More examples of sex-linked disorders 1. red-green color blindness 2. Duchenne muscular dystrophy

80 Do Now Take out your notes and answer the following question: Neither Tom nor Sue has hemophilia, but their first son does. If the couple has a second child, what is the probability that this child will also have the disease? Draw a Punnett square as evidence for your response. Remember that x-linked alleles are notated with superscripts about the X. What type of inheritance pattern is this?

81 Sex-linked genes Practice Problem Neither Tom nor Sue has hemophilia, but their first son does. If the couple has a second child, what is the probability that this child will also have the disease? Draw a Punnett square as evidence for your response. Remember that x-linked alleles are notated with superscripts about the X. ¼ (25% chance)

82 Complete Simpsons Problem #4: Sex-linked Traits

83 Can two unrelated people with different DNA look the same? Do you have a doppelganger? in-portraits-quebec-photographer-francois-brunelle-ta kes-pictures-look-alikes.html

84 Polygenic inheritance A single characteristic may be influenced by many genes Many genes influence one trait Skin color is affected by at least three genes Copyright 2009 Pearson Education, Inc.

85 At last count, the International Federation of Pigment Cell Society has determined that there are a total of 378 genetic loci involved in determining skin color in human and mice. The picture at right, shows only 3.

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