Pedigree Notes

Pedigree Analysis

  • Definition: A visual representation of the genetic relationships among a group of individuals or animals within a family.

  • Importance:

    • Useful in biology and animal breeding.

    • Helps track the inheritance of specific traits or characteristics across generations.

Pedigree Chart Overview

  • Purpose: Represents the genetic family history of a particular trait.

  • Applications:

    • Determines the risk and presence of a disease in the next generation.

    • Analyzes the inheritance of a particular trait among family members, typically over three generations or more.

Representation of Inheritance

  • Inheritance Pathways: In pedigree analysis, marriages are represented by lines.

  • Trait Presence:

    • If the analyzed trait is present in any individual, it is represented in black or shaded.

Genetic Diseases in Pedigree Analysis

  • Family Members: Some members of the family within the pedigree may be affected by a genetic disease.

  • Example Individuals:

    • Individuals I-1, I-2, II-4, and II-5 do not have the genetic disease but are presumed to be heterozygotes (carriers).

  • Recessive Patterns:

    • The pedigree indicates a recessive pattern of inheritance for a genetic disease.

    • Two unaffected individuals (I-1 and I-2) have produced an affected offspring (II-3).

Karyotype

  • Definition: An organized picture of chromosomes used to check for genetic conditions.

  • Human Genome Structure: In the human genome, there are 23 homologous chromosome pairs:

    • 22 are autosomal chromosome pairs.

    • 1 pair is a sex chromosome.

Comparisons between Pedigree and Karyotype

Similarities

  1. Genetic Analysis: Both are used to study genetics and inheritance patterns.

  2. Identification of Genetic Disorders: Both help detect genetic abnormalities and inherited conditions.

  3. Visual Representation: Each provides a visual tool for analyzing genetic information.

  4. Application in Genetic Counseling: Commonly used to assess the risks of genetic disorders in families.

Differences

  1. Definitions:

    • Pedigree: A chart showing family relationships and the inheritance of specific traits across generations.

    • Karyotype: An organized image of an individual's chromosomes, used to examine chromosome structure and number.

  2. Purpose:

    • Pedigree: Tracks the inheritance of traits or genetic disorders in a family over generations.

    • Karyotype: Detects chromosomal abnormalities, such as extra or missing chromosomes.

  3. Type of Information:

    • Pedigree: Shows phenotypic information (observable traits) and relationships within a family.

    • Karyotype: Displays chromosomal information, revealing the physical characteristics of chromosomes.

  4. Applications:

    • Pedigree: Analyzes inheritance patterns and predicts genetic risks within families.

    • Karyotype: Used in diagnosing chromosomal disorders like Down syndrome or Turner syndrome.

Chromosomal Counts and Arrangements

  • Dogs: 78 chromosomes in total, arranged in 39 pairs.

    • 38 pairs of autosomes and 1 pair of sex chromosomes (XX for females, XY for males).

  • Mice: 40 chromosomes in total.

    • 19 pairs of autosomes and 1 pair of sex chromosomes (XX for females, XY for males).

Genetic Inheritance Principles

Incomplete Dominance

  • Definition: The phenotype of a heterozygote is intermediate between the two homozygous phenotypes.

  • Example:

    • One allele (R) codes for red color, and the other for white color (r).

    • The heterozygous individual (Rr) exhibits a pink phenotype (blend of red and white).

  • Results:

    • A blend of both alleles results in a phenotype.

Punnett Square Example

  • Common Example: Flower color in snapdragons.

    • Crossing red (C R C R) and white (C W C W) produces pink (C R C W).

Additional Examples of Incomplete Dominance

  • In Horses:

    • Crosses between chestnut brown and creamy white produce palomino (distinctive golden coat with white mane and tail).

  • Hair Types:

    • Curly Hair (HH) crossed with Straight Hair (H'H') results in Wavy Hair (H'H).

Codominance

  • Definition: Both alleles in a heterozygous organism are fully and equally expressed, without blending.

  • Phenotype Result: Offspring displays traits from both alleles simultaneously.

  • Example:

    • Black and white chickens can express both colors when crossed (checkered pattern).

  • Human Blood Types: The ABO blood group system is a classic example where both A and B are equally expressed in blood type AB.

Key Differences Between Codominance and Incomplete Dominance

  • Codominance: Both alleles are fully and equally expressed, leading to separate traits appearing side by side.

  • Incomplete Dominance: The heterozygous phenotype is a blend of the two alleles.

Role of Environment in Phenotype

  • Gene-Environment Interaction: Different environmental conditions can activate or suppress specific genes, leading to variations in phenotype.

  • Influencing Factors:

    • Temperature and Light: Temperature extremes can influence gene expression in organisms such as Himalayan rabbits, where pigmentation changes at different temperatures.

    • Example:

    • Gene C controls fur pigmentation, active between 15 and 25°C, leading to color changes based on the environment encountered.

    • Light Influence:

    • Vanessa caterpillars exposed to different light colors exhibit differences in butterfly wing coloration.

    • Chemical Exposure:

    • Amphibians are sensitive to environmental chemicals, with exposure linking to developmental abnormalities, e.g., exposure to atrazine and glyphosate affecting frogs.

Closing Remarks

  • Summary and Questions:

    • Presented material summary and invited questions regarding the topics discussed.

    • Instructor: Siamak Shirani Bidabadi

    • Contact: sbidabad@asu.edu