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Biology 12

Biology 12. Definitions. Allele - alternative form of a gene Chromosome – chunk of DNA DNA – the genetic information in a nucleus Gene – section of chromosome that controls one characteristic Dominant – the allele that is expressed in a heterozygote

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Biology 12

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  1. Biology 12

  2. Definitions • Allele - alternative form of a gene • Chromosome – chunk of DNA • DNA – the genetic information in a nucleus • Gene – section of chromosome that controls one characteristic • Dominant – the allele that is expressed in a heterozygote • Co-dominant – both alleles are expressed in a heterozygote • Recessive – the allele that is not expressed (hidden) in the heterozygote • Autosomal – carried on one of the non-sex chromosomes (autosomes) • Sex-linked – carried on one of the sex chromosomes (X or Y) • Multiple alleles – more than 2 alleles exist for 1 characteristic • Genotype – alleles present in an organism • Phenotype – alleles expressed in an organism (ie its appearance) • Heterozygous – has 2 different alleles for a characteristic • Homozygous – has 2 alleles the same for a characteristic • Hybrid – has 2 different alleles for a characteristic • Pure-breeding – has 2 alleles the same for a characteristic • Hemizygous – has only 1 allele for a characteristic eg males with sex linked condition

  3. Tabby is dominant to black coat colour in cats. Predict the genotype and phenotype ratios expected from a cross between a hybrid tabby and a black cat. Tongue rolling is dominant to non-tongue rolling in humans. Predict the genotype and phenotype ratios expected from a cross between a heterozygous tongue roller and a non tongue roller. Short hair is dominant to long hair colour in cats. Predict the genotype and phenotype ratios expected from a cross between a hybrid short-haired cat and a long hair cat. Astigmatism is dominant to normal vision in humans. Predict the genotype and phenotype ratios expected from a cross between a person heterozygous for astigmatism and a normally sighted person. Genetics problems 1

  4. Tabby is dominant to black coat colour in cats. Predict the genotype and phenotype ratios expected from a cross between a hybrid tabby and a black cat. Astigmatism is dominant to normal vision in humans. Predict the genotype and phenotype ratios expected from a cross between a person heterozygous for astigmatism and a normally sighted person. Genetics problems 1 Short hair is dominant to long hair colour in cats. Predict the genotype and phenotype ratios expected from a cross between a hybrid short-haired cat and a long hair cat. T = tabby t = black Cross is Tt x tt Genotypes ½ Tt, ½ tt Phenotypes ½ tabby, ½ black t t H = short h = long Cross is Hh x hh Genotypes ½ Hh, ½ hh Phenotypes ½ short, ½ long h h T Tt tt H Hh hh t Tt h Hh hh tt Tongue rolling is dominant to non-tongue rolling in humans. Predict the genotype and phenotype ratios expected from a cross between a heterozygous tongue roller and a non tongue roller. T = tongue roller t = non tongue roller Cross is Tt x tt Genotypes ½ Tt, ½ tt Phenotypes ½ tongue roller, ½ non tongue roller A = astigmatism a= normal vision Cross is Aa x aa Genotypes ½ Aa, ½ aa Phenotypes ½ astigmatism, ½ normal t t a a T Tt tt A Aa aa T Tt tt a Aa aa

  5. Predict the genotypes and phenotypes expected from crossing a white flowered plant and a red flowered plant Predict the genotypes and phenotypes expected from crossing a pink flowered plant and a white flowered plant Predict the genotypes and phenotypes expected from crossing a pink flowered plant and a red flowered plant Predict the genotypes and phenotypes expected from crossing 2 pink flowered plants Genetics problems 2 Red flower colour is co-dominant with white flower colour in snap dragons, with the heterozygote showing pink flowers

  6. Predict the genotypes and phenotypes expected from crossing a white flowered plant and a red flowered plant Predict the genotypes and phenotypes expected from crossing a pink flowered plant and a red flowered plant Genetics problems 2 Red flower colour is co-dominant with white flower colour in snap dragons, with the heterozygote showing pink flowers FRFR = red, FWFW = white, FR FW = pink FRFR x FW FR FR FW FWFW x FRFR  allFWFRpink FR FRFR FRFW ½ FRFR = red, ½ FRFW = pink FR FRFR FRFW Predict the genotypes and phenotypes expected from crossing a pink flowered plant and a white flowered plant Predict the genotypes and phenotypes expected from crossing 2 pink flowered plants FWFW x FW FR FR FW FR FW FW FRFW FWFW FRFW x FR FW FR FRFR FRFW FWFW FW FRFW FRFW FWFW FW ½ FRFR = red, ½ FRFW = pink 1 FRFR = red : 2 FR FW = pink : 1 FWFW = white

  7. What genotypes and phenotypes are expected if a haemophiliac male marries a homozygous normal female? What genotypes and phenotypes are expected if a haemophiliac male marries a heterozygous female? What genotypes and phenotypes are expected if a normal male marries a heterozygous female? What is the probability of having a son with haemophilia, if a haemophiliac male marries a heterozygous female? Genetics problems 3 Haemophilia is a disease carried as a sex-linked recessive trait.

  8. What genotypes and phenotypes are expected if a haemophiliac male marries a homozygous normal female? What genotypes and phenotypes are expected if a normal male marries a heterozygous female? Genetics problems 3 Haemophilia is a disease carried as a sex-linked recessive trait. XHXH = normal female, XHXh = carrier female, XhXh = haemophiliac female XHY = normal male, XhY = haemophiliac male XHXH x XhY XHXh x XHY XH XH XH Xh All females carriers XHXh all males normal XHY Xh XHXh XHXh XH XHXH XHXh Y XHY XHY Y XHY XhY What genotypes and phenotypes are expected if a haemophiliac male marries a heterozygous female? What is the probability of having a son with haemophilia, if a haemophiliac male marries a heterozygous female? XH Xh XH Xh XHXh x XhY XHXh x XhY Xh XHXh XhXh Xh XHXh XhXh Probability is 1/4 Y Y XHY XhY XHY XhY ½ females are XHXh = carrier, ½ females are XhXh = haemophiliac ½ males are XHY = normal, ½ males are XhY = haemophiliac

  9. Pedigrees These are diagrams that show the inheritance of characteristics within families They allow us to determine the pattern of inheritance and predict characteristics of future offspring Conventions include

  10. Autosomal dominant recessive crosses Pedigrees will show 2 phenotypes. Crossing a homozygous dominant with a homozygous recessive leads to heterozygous offspring with the dominant trait Crossing 2 heterozygous individuals leads to offspring which could show either trait bb BB Bb Bb Bb B_ B_ bb B_

  11. Autosomal co-dominant crosses Pedigrees will show 3 phenotypes. Crossing a homozygous dominant with a homozygous recessive leads to heterozygous offspring with the intermediate trait Crossing 2 heterozygous individuals leads to offspring which could show any of the three phenotypes SBSB SWSW SBSW SBSW SBSB SBSW SWSW SBSW

  12. Determining patterns of inheritance 1 • Autosomal recessive • Heterozygotes don’t show trait so it may skip generations • If both parents have it, all offspring will have it • Parents don’t have to have it • Autosomal dominant • Heterozygotes do show trait so it can’t skip generations • Even if both parents have it, offspring don’t have to show it • At least one parent must have it • Autosomal co-dominant • 3 phenotypes are present

  13. Sex linked inheritance Males and females have different chromosomes Males can only show 2 phenotypes (ie males can not be carriers) Females can show 3 phenotypes (if codominant) or 2 phenotypes (if dominant recessive, with a carrier) Males and females will show different patterns of inheritance

  14. Determining patterns of inheritance 2 In sex-linkage mothers pass to sons, fathers pass to daughters • Sex-linked recessive • Mainly in males • Females can only have it if father has it and mother is at least a carrier • Affected females pass it to all their sons • Sex-linked dominant • Fathers pass to all daughters • Mothers pass to half their sons • Sex-linked co-dominant • Only females can show intermediate trait

  15. Reading pedigrees Autosomal recessive Autosomal dominant Sex linked recessive Autosomal recessive

  16. Pedigree problem 1 a) How many males are there? b) How many females are there? c) How many males have long fur? d) How many females have short fur? e) What type of inheritance is this? f) Write the most likely genotype of each individual on the pedigree. g) Which individuals are definitely homozygous? h) Which individuals are definitely heterozygous? i) How could you confirm the genotypes of the short haired cats in the fourth generation? j) What offspring would you expect from a cross of III1 and II6?

  17. Pedigree problem 1 L = short fur l = long fur ll ll LL LL a) How many males are there? 9 b) How many females are there? 9 c) How many males have long fur? 4 d) How many females have short fur? 3 e) What type of inheritance is this? Autosomal recessive f) Write the most likely genotype of each individual on the pedigree. g) Which individuals are definitely homozygous? Shaded ones h) Which individuals are definitely heterozygous? Unshaded ones with shaded children and/or a shaded parent i) How could you confirm the genotypes of the short haired cats in the fourth generation? Test cross (breed to long haired cat) j) What offspring would you expect from a cross of III1 and II6? Ll x ll = 50% Ll (short hair) 50% ll (long hair) ll ll ll ll LL LL LL LL L l Ll Ll Ll Ll ll l Ll Ll Ll ll Ll l ll

  18. Pedigree problem 2 a. What is the pattern of inheritance is this? b. Write the genotype for each individual. c. What offspring would you expect if you mated individual III 1 to: i) III 2? ii) III 3? iii) I 1?

  19. Pedigree problem 2 CSCS = spotted CDCD = dark CDCS = sable CSCS a. What is the pattern of inheritance is this? codominance b. Write the genotype for each individual. c. What offspring would you expect if you mated individual III 1 to: i) III 2? x = ii) III 3? x = ½ : ½ iii) I 1? x = CDCD CS CD CDCS CDCS CDCS CDCD CD CDCD CDCS CDCS CDCD CDCSD CDCD CDCD CD CDCS CSCS CDCS CDCD CSCS CDCD CDCS CDCD CDCS CDCD CSCS CDCS

  20. Pedigree problem 3 • Is this trait dominant or recessive? Give reasons to justify your answer. • Is this trait autosomal or sex-linked? Give reasons to justify your answer. • Which individuals are definitely homozygous? • Which individuals are definitely heterozygous? • What is the probability of individuals II2 and II8 having white coated offspring? Show all working.

  21. Pedigree problem 3 B = black b = white • Is this trait dominant or recessive? Give reasons to justify your answer. recessive • Is this trait autosomal or sex-linked? Give reasons to justify your answer. autosomal • Which individuals are definitely homozygous? Shaded ones • Which individuals are definitely heterozygous? Unshaded ones with shaded children and/or a shaded parent • What is the probability of individuals II2 and II8 having white coated offspring? Show all working. Bb x bb = ½ Bb black ½ bb white

  22. Pedigree problem 4 • Is this trait dominant or recessive? Give reasons to justify your answer. • Is this trait autosomal or sex-linked? Give reasons to justify your answer. • Which individuals are definitely heterozygous? • What is the probability of individuals II1 and II7 have white coated offspring? Show all working.

  23. Pedigree problem 4 r = dark R = white • Is this trait dominant or recessive? Give reasons to justify your answer. dominant • Is this trait autosomal or sex-linked? Give reasons to justify your answer. autosomal • Which individuals are definitely heterozygous? Shaded ones with unshaded children and/or an unshaded parent • What is the probability of individuals II1 and II7 have white coated offspring? Show all working. rr x rr = all rr dark

  24. Pedigree problem 5 • Is this trait dominant or recessive? Give reasons to justify your answer. • Is this trait autosomal or sex-linked? Give reasons to justify your answer. • Which individuals are definitely homozygous? • Which individuals are definitely heterozygous? • Individuals II8 and II9 are expecting another child. What is the probability it will be normal? Show all working. • Individual II1 is marrying a woman from a family which is free of this disease. What is the probability of their children having this disease? Show all working.

  25. Pedigree problem 5 XD Xd Xd XDXd XdXd • Is this trait dominant or recessive? Give reasons to justify your answer. Recessive : d = disease, D = normal • Is this trait autosomal or sex-linked? Give reasons to justify your answer. Sex linked • Which individuals are definitely homozygous? Shaded females • Which individuals are definitely heterozygous? Unshaded females with shaded children and/or a shaded parent • Individuals II8 and II9 are expecting another child. What is the probability it will be normal? Show all working. XDXd x XdY = 50% won’t have disease • Individual II1 is marrying a woman from a family which is free of this disease. What is the probability of their children having this disease? Show all working. XDY x XdXd = all XdXd or XdY = 0% with disease Y XDY XdY

  26. Pedigree problem 6 • Is this trait dominant or recessive? Give reasons to justify your answer. • Is this trait autosomal or sex-linked? Give reasons to justify your answer. • Which individuals are definitely homozygous? • Which individuals are definitely heterozygous? • Individuals II8 and II9 are expecting another child. What is the probability it will not have the disease? Show all working.

  27. Pedigree problem 6 XD Xd • Is this trait dominant or recessive? Give reasons to justify your answer. Dominant : D = disease, d = normal • Is this trait autosomal or sex-linked? Give reasons to justify your answer. Sex linked • Which individuals are definitely homozygous? Unshaded females • Which individuals are definitely heterozygous? Shaded females with unshaded children and/or an unshaded parent • Individuals II8 and II9 are expecting another child. What is the probability it will not have the disease? Show all working. XDY x XDXd = 25% chance of normal child XD XDXD XDXd Y XDY XdY

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