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HMB265H1 Lecture Notes - Proband, Autosome, Zygosity

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School
UTSG
Department
Human Biology
Course
HMB265H1
Professor
Stephen Wright

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HMB265H1 Full Course Notes
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HMB265H1 Full Course Notes
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Document Summary

Propositus: in a human pedigree, the person which first came to the attention of the geneticists; usually the phenotype of the propositus exceptional in some way. To see single-gene inheritance the patterns in the pedigree have to be interpreted according to mendel"s law of segregation but humans -> few kids -> 3:1 ratios & 1:1 ratios not usually seen until many similar pedigrees are combined. The affected phenotype of an autosomal recessive disorder is inherited as a recessive allele unaffected allele = dominant allele. Disorder appears in the progeny of unaffected parents. Affected progeny include both males and females-> dealing with simple mendelian inheritance of a gene on an autosome rather than a gene on a sex chromosome. Shows up in groups of affected siblings; ppl earlier and later in the generation tend not to be affected. Inbreeding increases the chances that two heterozygotes will mate -> higher chance of producing recessive disorders.

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Related Questions

Shown below is the pedigree of a rare neurodegenerative diseasein humans.

a. Based on the pedigree,characterize each of the following modes of inheritance as likely,unlikely, or impossible: autosomal dominant, autosomal recessive, Ylinked, X-linked dominant, and X-linked recessive. Justify yourreasoning.

Further scrutiny of members of this family reveals thefollowing: 1) The disease’s degree of expression varies amongindividuals, with some mildly affected, others moderately affectedand still others severely affected; and 2) Individual III-14 waspreviously married. Her ex-husband is phenotypically normal, withno history of the disease in his family going back tengenerations. He has custody of the couple’s two children, a girland a boy, both of whom are affected with the disease. The partialpedigree is shown below (the “slash” represents separation ordivorce)

b. Do these findingseliminate any of the remaining “likely or unlikely” modes ofinheritance listed in part (a)? Are any of thesemodes of inheritance still possible? If so, which one(s) andwhy?

c. Is mitochondrialinheritance a likely, unlikely or an impossible mode of inheritancefor this disease? Does it provide an explanation for the disease’svariable expressivity?

d. How can mitochondrialinheritance explain individual III-14?

Shown below is the pedigree of a rare neurodegenerative diseasein humans.

a. Based on the pedigree, characterize each of the following modes ofinheritance as likely, unlikely, or impossible: autosomal dominant,autosomal recessive, Y linked, X-linked dominant, and X-linkedrecessive. Justify your reasoning.

Further scrutiny of members of this family reveals thefollowing: 1) The disease’s degree of expression varies amongindividuals, with some mildly affected, others moderately affectedand still others severely affected; and 2) Individual III-14 waspreviously married. Her ex-husband is phenotypically normal, withno history of the disease in his family going back tengenerations. He has custody of the couple’s two children, a girland a boy, both of whom are affected with the disease. The partialpedigree is shown below (the “slash” represents separation ordivorce)

b. Do these findings eliminate any of the remaining “likely orunlikely” modes of inheritance listed in part (a)?Are any of these modes of inheritance still possible? If so, whichone(s) and why?

c. Is mitochondrial inheritance a likely, unlikely or an impossiblemode of inheritance for this disease? Does it provide anexplanation for the disease’s variable expressivity?

d. How can mitochondrial inheritance explain individual III-14?

a) List the characteristic features of autosomal dominant inheritance. How might reduced penetrance obscure this mode of inheritance in a pedigree?

b) Describe two molecular mechanisms that can give rise to autosomal dominant alleles, and describe an example of each.

c) List the characteristic features of mitochondrial inheritance. Explain why mitochondrial disorders typically demonstrate both variable expressivity and delayed onset after birth.

d) List the characteristic features of X-linked recessive patterns of inheritance. Describe circumstances in which the daughter of an affected male may display clinical features of the disorder.