Lecture 7- Knowt

Human Heredity Principles & Issues

• Author: Michael R. Cummings

• Edition: Eleventh Edition, Cengage Learning, 2016

Pedigree Analysis in Human Genetics

Overview

• Pedigree analysis is a crucial method used in human genetics to trace inheritance patterns.

Key Functions of Pedigree Analysis

• Reveals the inheritance pattern of a trait:

  • Dominant vs. Recessive Traits

  • Identifies the chromosomal locus of the gene involved.

  • Classifies the inheritance type:

    • Autosomal Recessive (AR)

    • Autosomal Dominant (AD)

    • X-linked Recessive (XR)

    • X-linked Dominant (XD)

    • Y-linked (Y)

    • Mitochondrial (M)

Disorders with Autosomal Dominant Inheritance Patterns

Characteristics

• Every affected individual typically has at least one affected parent.

• The traits are distributed equally among males and females.

• Heterozygotes express the abnormal phenotype; they are often less severely affected than homozygous dominant individuals.

Inheritance Implications

• Two affected heterozygous parents may have an unaffected child.

• Heterozygous individuals with unaffected partners have a 50% chance of having affected offspring.

Examples of Autosomal Dominant Traits

Sex-Linked and Non-Mendelian Inheritance Patterns

Pedigree Analysis Insights

• Pedigree analysis can reveal complex inheritance patterns that deviate from simple Mendelian inheritance.

Sexual Chromosomes Inheritance

• Males (XY) pass Y chromosomes to sons and X chromosomes to daughters.

• Females (XX) pass one X chromosome to all offspring.

X-Linked Dominant Inheritance Patterns

Characteristics

• Affected males pass the trait to all daughters and no sons.

• Heterozygous females pass the trait to half of their children.

• More affected females than males due to heterozygous expression in females.

• X-linked dominant disorders include but are not limited to:

  • Rett syndrome

  • Alport syndrome

  • Goltz syndrome

  • Fragile X syndrome

X-Linked Recessive Inheritance Patterns

Characteristics

• X-linked recessive traits are generally more common in males due to hemizygosity.

• Affected males only pass the trait to daughters who become carriers.

• Examples:

  • Haemophilia A and B

  • Color blindness (affecting approximately 8% of the male population)

Key Traits and Disorders - X-Linked Recessive

Y-Linked Traits and Inheritance

Characteristics

• Y-linked genes are passed directly from father to son.

• Males express all Y-linked genes and are hemizygous for these genes.

• Only 60 Y-linked traits identified, mostly related to male sexual development.

Maternal Inheritance: Mitochondrial Genes

Characteristics

• Mitochondria contain their own DNA essential for energy conversion.

• Females pass their mitochondrial DNA to all offspring; this trait affects all children but only daughters pass it on.

Examples of Mitochondrial Disorders