Biology 2B Pedigrees
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
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_
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
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
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
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
Reading pedigrees Autosomal recessive Autosomal dominant Sex linked recessive Autosomal recessive
Pedigrees Identify the most probable mode of inheritance for these:
Pedigrees Autosomal dominant Autosomal recessive Identify the most probable mode of inheritance for these: Autosomal dominant Autosomal recessive Autosomal or sex linked dominant Sex linked recessive
Pedigrees 2 Identify the modes of inheritance possible for these
Pedigrees 2 Identify the modes of inheritance possible for these Autosomal dominant Autosomal recessive Sex linked dominant Autosomal dominant Autosomal recessive Autosomal dominant Autosomal recessive Sex linked recessive Autosomal dominant Autosomal recessive
Genetics
Genetics Recessive Dominant Sex linked Sex linked Recessive Autosomal
Pedigrees
Pedigrees Autosomal recessive Autosomal dominant Sex-linked recessive
Genetics problem 1 This pedigree shows the inheritance of a rare characteristic in guinea pigs a) Identify the type of inheritance shown. b) Identify the genotypes of i) I2 ii) II1 iii) III3 iv) III7 c) What is the probability that the next offspring of individuals II1 and II2 will have this characteristic? d) What is the probability that the next offspring of individuals II5 and II6 will have this characteristic?
Genetics problem This pedigree shows the inheritance of a rare characteristic in guinea pigs a) Identify the type of inheritance shown. Autosomal recessive b) Identify the genotypes of i) I2 nn ii) II1 Nn iii) III3 N_ iv) III7 Nn c) What is the probability that the next offspring of individuals II1 and II2 will have this characteristic? Nn x Nn ¼ NN, ½ Nn, ¼ nn, so 25% d) What is the probability that the next offspring of individuals II5 and II6 will have this characteristic? Nn x nn ½ Nn, ½ nn, so 50%
WATP short answers 2 A B C Explain whether this trait is sex-linked or autosomal, dominant or recessive. Give reasons in your answer. Explain how you could determine the genotype of individual B. What genotypes and genotypes would you expect to see from a cross between individuals A and C?
WATP short answers 2 A B C Explain whether this trait is sex-linked or autosomal, dominant or recessive. Give reasons in your answer. Autosomal(1)-Second generation individual IV would have the condition if it was sex linked, sex-linked conditions are always passed on from affected mother to son.(1) Recessive(1)-Second generation individuals I and II neither have condition but son does. If it were dominant, this would not be possible.(1) Explain how you could determine the genotype of individual B. A test cross can be used to determine the unknown genotype of an organism when the trait is determined by an autosomal gene.(1) You must cross the unknown individual with a homozygous recessive individual.(1) If the unknown individual was homozygous dominant then all of the offspring will have the dominant trait.(1) If the unknown individual was heterozygous then half of the offspring will be dominant and the other half will be recessive.(1) What genotypes and genotypes would you expect to see from a cross between individuals A and C? Nn x Nn ¼ NN, ½ Nn, ¼ nn; ¾ would not show it, ¼ would
Human Biology Q43 The pedigree drawn below represents the inheritance of a rare genetic condition that affects normal liver functions. Individuals who inherit this condition experience no symptoms until they become middle-aged (40-55 years). At this point in their life, affected individuals will present with severe digestive and blood composition problems. a) What is the mode of inheritance for this condition? (2 marks) b) Outline the evidence in the pedigree that provides definite support for your answer in part (a) above. (3 marks) c) What is the chance that another child of individuals 5 and 6 will be affected? Show some working. (2 marks) d) Despite a clear understanding of how this condition is inherited, it continues to appear in populations and families. Give a reason for its continued appearance. (1mark)
Human Biology Q43 The pedigree drawn below represents the inheritance of a rare genetic condition that affects normal liver functions. Individuals who inherit this condition experience no symptoms until they become middle-aged (40-55 years). At this point in their life, affected individuals will present with severe digestive and blood composition problems. a) What is the mode of inheritance for this condition? (2 marks) Autosomal recessive Outline the evidence in the pedigree that provides definite support for your answer in part (a) above. (3 marks) Recessive – individuals 5 & 6 don’t have it but individual 11 does Autosomal – individual 1 has it, but her son 4, doesn’t - individual 11 has it and her father 6 doesn’t
Human Biology Q43 The pedigree drawn below represents the inheritance of a rare genetic condition that affects normal liver functions. Individuals who inherit this condition experience no symptoms until they become middle-aged (40-55 years). At this point in their life, affected individuals will present with severe digestive and blood composition problems. c) What is the chance that another child of individuals 5 and 6 will be affected? Show some working. (2 marks) N n 1/4 N NN Nn n Nn nn Despite a clear understanding of how this condition is inherited, it continues to appear in populations and families. Give a reason for its continued appearance. (1mark) It can skip generations as it is recessive It doesn’t appear until later in life – often after the affected individual has had offspring (and passed on the gene)
e) What is the chance that Jane is a carrier? (1 mark) Human Biology Q43 A family with a history of haemophilia (X-linked recessive) has the following pedigree: e) What is the chance that Jane is a carrier? (1 mark) f) What is the chance that Jane will have an affected daughter? g) What is the chance that Jane will have an affected child?
e) What is the chance that Jane is a carrier? (1 mark) Human Biology Q43 A family with a history of haemophilia (X-linked recessive) has the following pedigree: Normal = XH Haemophilia = Xh Carrier female XH Xh XH XH XH XH Xh Normal male Xh Y Y XH Y e) What is the chance that Jane is a carrier? (1 mark) ½ (mother is carrier) f) What is the chance that Jane will have an affected daughter? (1 mark) 0 – her husband is unaffected What is the chance that Jane will have an affected child? (1 mark) If she is a carrier, she has ¼ chance of affected child She has ½ chance of being a carrier Her chance = ¼ x ½ = 1/8
Human Biology Q46 The pedigree shown below represents the inheritance of a genetic condition that affects normal vision. A student examined this pedigree and concluded that the condition must be inherited in an autosomal fashion. On the basis of this information, answer the questions below. In your analysis, use the letters N or n. a) What is the probability that individual III-4 is heterozygous? Show your working. (2 marks) b) List all the individuals for whom genotype is uncertain. (2 marks) c) If individual III-2 married and had children with an affected person, what is the chance that their child will have the condition? Show your working. (2 marks) d) A second student examined this pedigree and made the statement: "There is evidence on the pedigree that this condition could also be inherited as a sexlinked recessive condition". Is this statement correct or incorrect? Use evidence from the pedigree to support your answer. (2 marks)
List all the individuals for whom genotype is uncertain. (2 marks) Human Biology Q46 The pedigree shown below represents the inheritance of a genetic condition that affects normal vision. A student examined this pedigree and concluded that the condition must be inherited in an autosomal fashion. On the basis of this information, answer the questions below. In your analysis, use the letters N or n. N = normal, n = disease What is the probability that individual III-4 is heterozygous? Show your working. (2 marks) 100% - she doesn’t show the condition so must have N, and mother has the condition, so must have given her a n List all the individuals for whom genotype is uncertain. (2 marks) II4, II5, II7, III2
Human Biology Q46 The pedigree shown below represents the inheritance of a genetic condition that affects normal vision. A student examined this pedigree and concluded that the condition must be inherited in an autosomal fashion. On the basis of this information, answer the questions below. In your analysis, use the letters N or n. If individual III-2 married and had children with an affected person, what is the chance that their child will have the condition? Show your working. (2 marks) His parents are both Nn, so he has 2/3 chance of being Nn If he is Nn his children have ½ chance of being nn, as their mother is nn d) A second student examined this pedigree and made the statement: "There is evidence on the pedigree that this condition could also be inherited as a sexlinked recessive condition". Is this statement correct or incorrect? Use evidence from the pedigree to support your answer. (2 marks) No – II6 has it and her father doesn’t - II6 has it and her son doesn’t