02BIS1012013XLinkLect3

Genetic counselors try to establish the proband as

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Unformatted text preview: S101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 26 Pedigree Analysis (p.51) A pedigree is a diagram of family relationships that uses symbols to represent people and pedigree lines to represent genetic relationships. These diagrams make it easier to visualize relationships within families, particularly large extended families. Pedigrees are often used to determine the mode of inheritance (dominant, recessive, etc.) of genetic diseases. to BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 27 Pedigree Symbols (p.51) ­ The “propositus” (also The known as the “proband”) is a male who first exhibits a medical condition (e.g, color blindness) in the family. The feminine of propositus is “proposita”. Genetic counselors try to establish the proband as part of the pedigree analysis. analysis. BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 28 Ancient inferences about genetics The Talmud made an ahead-of-its-time observation that inferred the existence of genes. The sages of the Talmud ruled that if a woman bears two sons who die of bleeding after circumcision, any additional sons that she has, should not be circumcised. The Talmud further states that the sons of her sister must not be circumcised, whereas her brothers should be circumcised, reflecting a clear understanding this is a disease transmitted to the male through the female. BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 29 General Characteristics of X-Linked Inheritance ­ The simple rules provided in your text will help in The evaluating these pedigrees. These rules are summarized below. summarized ­ Sex linked traits sometimes show a “cris-cross” Sex pattern of inheritance because fathers pass the trait through the unaffected daughter, who in turn, passes it on to her affected sons. passes ­ Reciprocal crosses resulting in different phenotypic Reciprocal ratios in the sexes often indicate X-linkage. ratios BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 30 Characteristics of X-linked Recessive Traits ­ 1. Males are mostly affected because of their Males hemizygous condition. hemizygous ­ 2. Affected males result from mothers who are Affected carriers (heterozygous) of the X-linked trait. carriers ­ 3. Approximately half of the sons of a carrier female should be affected. ­ 4. The sons of affected females must be affected. ­ 5. Affected females come from affected fathers and Affected carrier mothers. carrier ­ 6. Males that are not affected carry the wild-type Males allele in their X chromosome. allele BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expr...
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This note was uploaded on 02/12/2014 for the course BIS 101 taught by Professor Simonchan during the Spring '08 term at UC Davis.

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