JAIPUR NATIONALUNIVERSITY

SUBMITTED TO-PRATIBHA MAAM

SUBMITTED BY-SANJEET YADAVROLL NO.-6BT11

SEMINAR ON

PEDIGREE ANALYSIS

A pedigree is a chart of the genetic history of family over several generations.

Scientists or a genetic counselor would find out about your family history and make this chart to analyze.

What is a Pedigree?

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Gregor Mendel(1822-1884)Responsible for the Laws governing Inheritance of Traits

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Genetic Terminology

Trait - any characteristic that can be passed from parent to offspring

Heredity - passing of traits from parent to offspring

Genetics - study of heredity

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Alleles - two forms of a gene (dominant & recessive)

Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R)

Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r)

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More Terminology

Genotype - gene combination for a trait (e.g. RR, Rr, rr)

Phenotype - the physical feature resulting from a genotype (e.g. red, white)

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Genotypes

Homozygous genotype – When the two alleles are same (dominant or 2 recessive genes) e.g. TT or tt; also called pure 

Heterozygous genotype – When the 2 alleles are different- one dominant & one recessive allele    (e.g. Tt); also called hybrid

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Types of Genetic Crosses

Monohybrid cross - cross involving a single traite.g. flower color

Dihybrid cross - cross involving two traits e.g. flower color & plant height

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INTERPRETING A PEDIGREECHART

Determine whether the disorder is dominant orrecessive.

If the disorder is dominant, one of theparents must have the disorder.

If the disorder is recessive, neitherparent has to have the disorder.

THE STEPS WHEN INTERPRETINGA PEDIGREE CHART

Determine if the pedigree chart shows an autosomal or X linkeddisease.

If most of the males in the pedigree areaffected, then the disorder is X-linked

If it is a 50/50 ratio between men andwomen the disorder is autosomal.

Rules of InheritanceX-Linked Dominant• Both males and females are affected; often morefemales than males are affected• Does not skip generations.• Affected sons must have an affected mother;• affected daughters must have either anaffected mother or an affected father• Affected fathers will pass the trait on to all theirdaughters• Affected mothers if heterozygous will pass thetrait on to 1/2 of their sons and 1/2 of theirdaughters

Rules of InheritanceX-Linked Recessive• More males than females are affected• Affected sons are usually born to unaffectedmothers, thus the trait skips generations• Approximately 1/2 of carrier mothers’ sons areaffected• It is never passed from father to son• All daughters of affected fathers are carriers

Autosomal Dominant

Equal in Males and Females:

Rules of InheritanceAutosomal Dominant• Appears in both sexes with equal frequency• Both sexes transmit the trait to their offspring• Does not skip generations• Affected offspring must have an affected parentunless they posses a new mutation• When one parent is affected (het.) and the otherparent is unaffected, approx. 1/2 of the offspringwill be affected• Unaffected parents do not transmit the trait

Rules of InheritanceAutosomal Recessive•Appears in both sexes with equal frequency• Trait tend to skip generations• Affected offspring are usually born tounaffected parents• When both parents are hetrozygout,approx. 1/4 of the progeny will be affected• Appears more frequently among thechildren of consanguine marriages

Y-Linked Dominant

• Only males are affected

• It is passed from father to all sons

• It does not skip generations

Mitochondrial InheritanceFathers don’t transmit, justmothersAll offspring at risk

Sickle Cell / Malaria Connection

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