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Mendel and Heredity Chapter 8. 8.1 The Origins of Genetics Heredity is the passing of characters from parents to offspring Heredity is the passing of.

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Presentation on theme: "Mendel and Heredity Chapter 8. 8.1 The Origins of Genetics Heredity is the passing of characters from parents to offspring Heredity is the passing of."— Presentation transcript:

1 Mendel and Heredity Chapter 8

2 8.1 The Origins of Genetics Heredity is the passing of characters from parents to offspring Heredity is the passing of characters from parents to offspring Used throughout history to alter crops and domestic animals Used throughout history to alter crops and domestic animals Gregor Johann Mendel – Austrian Monk Gregor Johann Mendel – Austrian Monk Used pea plants and bred different varieties Used pea plants and bred different varieties Developed rules to accurately predict patterns of heredity Developed rules to accurately predict patterns of heredity

3 Why Peas? 2 characters have clearly different forms 2 characters have clearly different forms Character = inherited characteristic (color) Character = inherited characteristic (color) Trait = single form of character (purple) Trait = single form of character (purple) Male and female reproductive parts are in same flower Male and female reproductive parts are in same flower Can control fertilization Can control fertilization Flower can fertilize itself (self- fertilization) or can cross pollen from 1 plant to another (cross-pollination) Flower can fertilize itself (self- fertilization) or can cross pollen from 1 plant to another (cross-pollination) Peas are small, grow easily, mature quickly, and produces many seeds so results obtained quickly Peas are small, grow easily, mature quickly, and produces many seeds so results obtained quickly

4 Traits Expressed as Simple Ratios Mendel started by looking at 1 characteristic (monohybrid), such as color, with 1 pair of contrasting traits, purple or white flowers Mendel started by looking at 1 characteristic (monohybrid), such as color, with 1 pair of contrasting traits, purple or white flowers Only allowed plants to self-pollinate for many generations Only allowed plants to self-pollinate for many generations True-breeding – all offspring show only 1 trait True-breeding – all offspring show only 1 trait Parental (P) generation Parental (P) generation Cross pollinated 2 P generation plants with contrasting traits Cross pollinated 2 P generation plants with contrasting traits Offspring called filial (F 1 ) generation Offspring called filial (F 1 ) generation Counted numbers of each trait Counted numbers of each trait

5 Allowed F 1 generation to self pollinate Allowed F 1 generation to self pollinate Offspring called F 2 generation Offspring called F 2 generation Each characterized and counted Each characterized and counted

6 Mendels Results F 1 showed only 1 form of character other had disappeared F 1 showed only 1 form of character other had disappeared When F 1 self pollinates other trait reappears in some of F 2 When F 1 self pollinates other trait reappears in some of F 2 Found ratio of traits to be 3 to 1 Found ratio of traits to be 3 to 1 3 white flowers to 1 purple flower 3 white flowers to 1 purple flower Same ratio found for any trait he studied Same ratio found for any trait he studied

7 8.2 Mendels Theory We used to think offspring were blend of traits We used to think offspring were blend of traits Tall x short = medium Tall x short = medium Mendels experiments showed us this is not entirely true Mendels experiments showed us this is not entirely true

8 Mendels Hypothesis There are 2 copies of a gene, one from each parent, for each inherited characteristic There are 2 copies of a gene, one from each parent, for each inherited characteristic There are different versions of genes called alleles There are different versions of genes called alleles Tall or short Tall or short When both versions are present one may be dominant (completely expressed) and the other may be recessive (not expressed when dominant is present) When both versions are present one may be dominant (completely expressed) and the other may be recessive (not expressed when dominant is present) When you form gametes, alleles separate independently so only one allele in each gamete When you form gametes, alleles separate independently so only one allele in each gamete

9 Mendels Finding in Modern Terms Use letters to show alleles Use letters to show alleles Capitol = dominant (T, P, Y, etc…) Capitol = dominant (T, P, Y, etc…) Lower case = recessive (t, p, y, etc…) Lower case = recessive (t, p, y, etc…) Homozygous = letters are same Homozygous = letters are same Homozygous dominant = TT, PP Homozygous dominant = TT, PP Homozygous recessive = tt, pp Homozygous recessive = tt, pp Heterozygous = letters are different Heterozygous = letters are different Tt, Pp Tt, Pp Only dominant allele is expressed Only dominant allele is expressed

10 Genotype = set of alleles Genotype = set of alleles What you actually have What you actually have TT, Tt, or tt TT, Tt, or tt Phenotype = what is expressed Phenotype = what is expressed How it looks How it looks Tall, Tall, or Short Tall, Tall, or Short

11 Mendels Laws of Heredity Law of Segregation Law of Segregation 2 alleles for a character segregate when gametes are formed 2 alleles for a character segregate when gametes are formed Behavior of chromosomes during meiosis Behavior of chromosomes during meiosis Law of Independent Assortment Law of Independent Assortment 1 character does not affect another 1 character does not affect another Alleles of different genes separate independently of on another Alleles of different genes separate independently of on another Now know this only applies to genes located on different chromosomes or that are far apart on same chromosome Now know this only applies to genes located on different chromosomes or that are far apart on same chromosome

12 8.3 Studying Heredity: Punnett Squares Breeders want certain characteristics when they breed (cross) animals Breeders want certain characteristics when they breed (cross) animals Horticulturists produce plants with specific characteristics Horticulturists produce plants with specific characteristics

13 Punnett Square Punnett Square Used to predict outcomes Used to predict outcomes Shows all possible combinations of gametes Shows all possible combinations of gametes Put 1 st parents genotype on top Put 1 st parents genotype on top Put 2 nd parents genotype on side Put 2 nd parents genotype on side Do the cross Do the cross TT Tt tt

14 So in Mendels F1 generation, a pure Tall plant bred with a pure short plant can only give 1 kind of offspring due to dominance of tall allele

15 Determining Unknown Genotypes How do you know if a tall plant is homozygous or heterozygous? They both look tall How do you know if a tall plant is homozygous or heterozygous? They both look tall Can do a Test Cross Can do a Test Cross If dominant phenotype is shown with unknown genotype, cross it with homozygous recessive If dominant phenotype is shown with unknown genotype, cross it with homozygous recessive

16 Test Cross Results If unknown is homozygous dominant, all offspring of test cross will have dominant trait If unknown is homozygous dominant, all offspring of test cross will have dominant trait

17 Test Cross Results If unknown is heterozygous, offspring of test cross will have 2 dominant and 2 recessive phenotypes If unknown is heterozygous, offspring of test cross will have 2 dominant and 2 recessive phenotypes

18 Can use probability calculations to predict results of genetic crosses Can use probability calculations to predict results of genetic crosses Probability is the likelihood a specific event will occur Probability is the likelihood a specific event will occur Probability = # of 1 kind of possible outcome divided by total number of possible outcomes Probability = # of 1 kind of possible outcome divided by total number of possible outcomes We will express these as fractions We will express these as fractions Chance a coin will come up heads Chance a coin will come up heads 1 head / 2 sides = ½ 1 head / 2 sides = ½

19 DD = ¼ DD = ¼ Dd = 2/4 or ½ Dd = 2/4 or ½ dd = ¼ dd = ¼

20 Dihybrid Cross Uses a Punnett Square to determine outcomes of 2 traits at one time Uses a Punnett Square to determine outcomes of 2 traits at one time Example: Surface and Color Example: Surface and Color Surface:RR, Rr, or rrround or wrinkled Surface:RR, Rr, or rrround or wrinkled Color:YY, Yy, yyyellow or green Color:YY, Yy, yyyellow or green What are the possible combinations? What are the possible combinations? RY, Ry, rY, ry RY, Ry, rY, ry

21 So if you have 2 purebred homozygous parents RRYY and rryy and you mate them, what do you get? So if you have 2 purebred homozygous parents RRYY and rryy and you mate them, what do you get? All offspring will be RrYy All offspring will be RrYy What if you have F1 breed? What if you have F1 breed? Make a Punnett Square of possible gametes for each parent Make a Punnett Square of possible gametes for each parent What possible combos can parents offer? What possible combos can parents offer? Do you remember FOIL? Do you remember FOIL? RY, Ry, rY, ry RY, Ry, rY, ry

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23 You never have to count the results of a dihybrid cross between heterozygotes! 9 with both dominant traits 9 with both dominant traits 3 with first dominant and second recessive 3 with first dominant and second recessive 3 with first recessive and second dominant 3 with first recessive and second dominant 1 with both recessive traits 1 with both recessive traits So 9:3:3:1 So 9:3:3:1

24 Inheritance of Traits Pedigree Pedigree Family history that shows how a trait is inherited over several generations Family history that shows how a trait is inherited over several generations Helpful in tracking genetic disorders Helpful in tracking genetic disorders Carrier – have allele for trait but show no symptoms Carrier – have allele for trait but show no symptoms

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26 Things You Can Find From A Pedigree Autosomal or Sex- Linked? Autosomal or Sex- Linked? If autosomal it will be equal in both sexes If autosomal it will be equal in both sexes If sex linked generally only found in males If sex linked generally only found in males Y linked Y linked Hairy ear rims Hairy ear rims X linked X linked Color-blindness Color-blindness Hemophilia Hemophilia

27 Dominant or recessive Dominant or recessive Autosomal Dominant – every individual with condition will have parent with condition Autosomal Dominant – every individual with condition will have parent with condition Achondroplasia – type of dwarfism Achondroplasia – type of dwarfism Huntingtons Disease – brain degenerates Huntingtons Disease – brain degenerates Autosomal Recessive – 1, 2, or no parents with condition Autosomal Recessive – 1, 2, or no parents with condition Cystic fibrosis Cystic fibrosis Sickle cell anemia Sickle cell anemia Albinism Albinism

28 Heterozygous or Homozygous Heterozygous or Homozygous Autosomal homozygous dominant or heterozygous phenotype will show dominant allele Autosomal homozygous dominant or heterozygous phenotype will show dominant allele Homozygous recessive will show recessive allele Homozygous recessive will show recessive allele 2 heterozygous of recessive allele dont show condition but can have children that do 2 heterozygous of recessive allele dont show condition but can have children that do

29 8.4 Complex Patterns of Heredity Complex Control Complex Control Most of the time characters display much more complex patterns than simple dominant- recessive patterns Most of the time characters display much more complex patterns than simple dominant- recessive patterns Characters can be influenced by several genes Characters can be influenced by several genes

30 Polygenic Inheritance Several genes affect a character Several genes affect a character These genes may be scattered along same chromosome or on different chromosomes These genes may be scattered along same chromosome or on different chromosomes Determining the effect of any one gene is difficult Determining the effect of any one gene is difficult Crossing over and independent assortment create many different offspring combos Crossing over and independent assortment create many different offspring combos Eye color, height, weight, hair, intelligence, and skin color Eye color, height, weight, hair, intelligence, and skin color Usually gives a range of expression Usually gives a range of expression

31 Polygenic Inheritance

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34 Intermediate Characters Incomplete dominance Incomplete dominance Phenotype that is intermediate between 2 parents, neither is completely dominant Phenotype that is intermediate between 2 parents, neither is completely dominant White x red = pink White x red = pink Straight hair x curly hair = wavy hair Straight hair x curly hair = wavy hair

35 Multiple Alleles Characters controlled by genes with 3+ alleles Characters controlled by genes with 3+ alleles Humans have ABO blood types Humans have ABO blood types I A, I B, i I A, I B, i Letters A and B refer to carbohydrates on surface of red blood cells Letters A and B refer to carbohydrates on surface of red blood cells i has neither carbohydrate i has neither carbohydrate I A and I B are dominant over I, but not over each other (codominant) I A and I B are dominant over I, but not over each other (codominant) Still only 2 possibilities in a person Still only 2 possibilities in a person

36 Blood Types 2 forms are displayed at the same time 2 forms are displayed at the same time Codominance – both expressed, not blended Codominance – both expressed, not blended I A I B both expressed I A I B both expressed ii = Type O ii = Type O

37 Characters Influenced by Environment Plants may change color based on pH of soil Plants may change color based on pH of soil Arctic fox Arctic fox Summer – enzymes produce pigments for darker fur Summer – enzymes produce pigments for darker fur Winter – no enzymes, no pigments to darken fur Winter – no enzymes, no pigments to darken fur Siamese cats Siamese cats Dark fur in cooler parts Dark fur in cooler parts Humans Humans Height related to nutrition Height related to nutrition Skin color based on sun exposure Skin color based on sun exposure Twins are genetically identical, any difference is due to environment Twins are genetically identical, any difference is due to environment

38 Genetic Disorders Proteins encoded by genes must function precisely for normal development and function Proteins encoded by genes must function precisely for normal development and function Genes may be damaged or copied wrong causing faulty proteins Genes may be damaged or copied wrong causing faulty proteins Mutation = changes in genetic material Mutation = changes in genetic material Rare because cells try to correct errors Rare because cells try to correct errors Harmful effects produced by inherited mutations Harmful effects produced by inherited mutations Many carried by recessive alleles Many carried by recessive alleles

39 Sickle Cell Anemia Recessive genetic disorder Recessive genetic disorder Mutated allele produces defective form of hemoglobin causing red blood cells (rbc) to be misshapen Mutated allele produces defective form of hemoglobin causing red blood cells (rbc) to be misshapen These rupture easily causing less O 2 to be carried and may get stuck and cut off blood supply These rupture easily causing less O 2 to be carried and may get stuck and cut off blood supply Recessive allele protects heterozygous individuals from malaria Recessive allele protects heterozygous individuals from malaria Parasites in sickle rbc die Parasites in sickle rbc die Normal rbc still transport oxygen Normal rbc still transport oxygen

40 Cystic Fibrosis Most common fatal, hereditary, recessive disorder in Caucasions Most common fatal, hereditary, recessive disorder in Caucasions 1 in 25 has at least 1 copy of defective gene that makes a protein needed to move chloride in and out of cells 1 in 25 has at least 1 copy of defective gene that makes a protein needed to move chloride in and out of cells Mucus clogs organs Mucus clogs organs 1 in 2,500 homozygous for cystic fibrosis 1 in 2,500 homozygous for cystic fibrosis No cure No cure

41 Hemophilia Impairs bloods ability to clot Impairs bloods ability to clot Sex-linked Sex-linked Dozen+ genes code for clotting proteins Dozen+ genes code for clotting proteins 1 mutation on X chromosome causes Hemophilia A 1 mutation on X chromosome causes Hemophilia A Males only get 1 X chromosome Males only get 1 X chromosome

42 Huntingtons Disease dominant allele on autosome dominant allele on autosome 1 st symptoms - mild forgetfulness and irritability in 30s and 40s 1 st symptoms - mild forgetfulness and irritability in 30s and 40s Eventually lose muscle control, spasms, severe mental illness, and death Eventually lose muscle control, spasms, severe mental illness, and death

43 Treating Genetic Disorders Most cant be cured Most cant be cured Genetic Counseling – tells of possible genetic problems with offspring, may be treated if early enough Genetic Counseling – tells of possible genetic problems with offspring, may be treated if early enough

44 Phenylketonuria (PKU) Lack enzyme that converts amino acid phenylalanine into tyrosine so it builds up in the body and causes severe mental retardation Lack enzyme that converts amino acid phenylalanine into tyrosine so it builds up in the body and causes severe mental retardation Can be placed on phenylalenic diet Can be placed on phenylalenic diet

45 Gene Therapy Replace defective genes with normal ones Replace defective genes with normal ones Isolate copy of gene Isolate copy of gene Put working copy into a virus Put working copy into a virus Virus infects and puts gene in Virus infects and puts gene in Infected cells are cured Infected cells are cured Still trying to get this to work Still trying to get this to work


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