Pedigree Analysis

Pedigree analysis is the study of inheritance patterns of traits through generations using family trees called pedigrees. It is one of the most important topics in Genetics for CSIR-NET because questions are frequently asked from inheritance patterns, probability, and genotype prediction.

1. Standard Symbols Used in Pedigree

SymbolMeaning□Male○Female■ / ●Affected individual◐Carrier─Marriage│OffspringDouble lineConsanguineous marriageRoman numeralsGenerationsArabic numeralsIndividuals

2. Types of Inheritance Patterns

A. Autosomal Dominant (AD)

Important Features

Trait appears in every generation.

Both males and females affected equally.

Affected individual usually has an affected parent.

Father-to-son transmission possible.

Unaffected individuals do not transmit the trait.

Probability

If heterozygous affected parent × normal parent:

Examples

Huntington disease

Achondroplasia

Marfan syndrome

Identification Trick

“Vertical transmission” → every generation affected.

B. Autosomal Recessive (AR)

Important Features

Trait skips generations.

Affected individuals often born to unaffected parents.

Males and females equally affected.

Consanguinity common.

Probability

Carrier × Carrier:

Affected probability:

Examples

Albinism

Sickle cell anemia

Phenylketonuria

Identification Trick

“Horizontal pattern” → affected siblings but parents normal.

C. X-linked Recessive (XLR)

Important Features

Mostly males affected.

No father-to-son transmission.

Trait may skip generations.

Affected male passes allele to all daughters.

Cross

Carrier mother × normal father:

Results:

50% sons affected

50% daughters carriers

Examples

Haemophilia

Colour blindness

Duchenne muscular dystrophy

Identification Trick

More males affected + no male-to-male transmission.

D. X-linked Dominant (XLD)

Important Features

Both sexes affected.

Affected father → all daughters affected.

No father-to-son transmission.

Trait appears every generation.

Examples

Vitamin D resistant rickets

E. Y-linked (Holandric)

Important Features

Only males affected.

Father transmits to all sons.

Never found in females.

Examples

Hairy pinna

F. Mitochondrial Inheritance

Important Features

Transmitted only through mother.

All children of affected mother affected.

Affected father does not transmit.

Example

Leber hereditary optic neuropathy

3. Most Important Rules for Solving Pedigrees

Rule 1: Check Generation Pattern

Every generation → dominant

Skipping generations → recessive

Rule 2: Check Sex Ratio

Equal males/females → autosomal

Mostly males → X-linked recessive

Rule 3: Father-to-Son Transmission

ObservationConclusionPresentNot X-linkedAbsentCould be X-linkedAll sons affectedY-linked

This is one of the most important CSIR-NET tricks.

4. Carrier Probability Problems

Example

Unaffected brother of affected AR individual:

Parents are:

Possible unaffected genotypes:

AA

Aa

Aa

Therefore:

Very important for CSIR-NET numerical questions.

5. Bayesian Probability in Pedigree

Used when extra information changes probability.

Formula

Used in advanced pedigree questions.

6. Common CSIR-NET Tricks

ObservationInterpretationTrait skips generationRecessiveMore males affectedX-linked recessiveAffected father → all daughters affectedX-linked dominantOnly males affectedY-linkedAffected mother → all children affectedMitochondrialConsanguinityAutosomal recessive

7. Frequently Asked CSIR-NET Concepts

Incomplete Penetrance

Genotype present but phenotype absent.

Example:

Dominant trait may appear to skip generation.

Variable Expressivity

Same genotype shows different phenotypes.

Consanguinity

Increases autosomal recessive disorders.

8. Strategy to Solve Any Pedigree Question

Observe generations.

Check affected sexes.

Look for father-to-son transmission.

Identify dominant/recessive.

Assign genotypes.

Solve probability.

This systematic approach is highly recommended for CSIR-NET pedigree problems.

9. Important Disorders for Exam

DisorderInheritanceHaemophiliaX-linked recessiveColour blindnessX-linked recessiveHuntington diseaseAutosomal dominantSickle cell anemiaAutosomal recessiveAlbinismAutosomal recessiveHairy pinnaY-linked

10. Previous Year CSIR-NET Focus Areas

Identification of inheritance type

Carrier probability

Bayesian pedigree problems

Sex-linked inheritance

Pedigree with Hardy-Weinberg integration

Видео Pedigree Analysis канала Umair Alam