Chromosomes, Genes, and Inheritance: A Comprehensive Overview

Sutton's Chromosome Theory of Inheritance

• Chromosomes occur in pairs.
• Chromosome pairs separate during meiosis.
• Each gamete carries one chromosome from each pair.
• Pairs of chromosomes separate independently of other pairs.
• Fertilization restores the paired condition of chromosomes in the zygote.

Mendel's Laws of Inheritance

• Factors (genes) occur in pairs.
• Factors segregate to form gametes.
• Each gamete carries a single factor.
• Pairs of factors separate independently of other pairs.
• Fertilization restores the paired condition of factors in the zygote.

Chromosomal Abnormalities

Trisomies

• Down Syndrome (Trisomy 21): Congenital mental disability, distinct facial profile, increased risk of illness, and heart defects.
• Patau Syndrome (Trisomy 13): Nerve abnormalities, body malformations, increased risk of illness, polydactyly, kidney and heart defects.
• Edwards Syndrome (Trisomy 18): Birth defects and cardiac dysfunction.

Other Chromosomal Disorders

• Angelman Syndrome (Chromosome 15): Eating disorders, hyperactivity, cranial deformity, often with blue eyes and blond hair.
• Tourette Syndrome: Linked to a sex chromosome, characterized by spasms, tics, and attention deficit.
• Klinefelter Syndrome (XXY): Affects males, resulting in underdeveloped secondary sexual characteristics, language delay, and tall stature.
• Turner Syndrome (Monosomy X): Affects females, characterized by the absence of one X chromosome, leading to underdeveloped secondary sexual characteristics.

Sex-Linked Inheritance

Example: Hemophilia

• X^DX^D: Normal female
• X^DX^d: Carrier female
• X^dX^d: Affected female
• X^DY: Normal male
• X^dY: Affected male

Note: Males cannot be carriers of X-linked recessive traits.

Gene Interactions

Key Concepts

• Genes occupy a specific location on a chromosome called a locus.
• Genes occupying the same locus on a pair of homologous chromosomes are called alleles.
• Alleles do not necessarily carry the same information.
• Genes found on the same chromosome are called linked genes.

Types of Gene Interactions

• Multiple Alleles: More than two alleles can exist for a trait, but only two occupy the loci for each characteristic.
• Epistasis: One gene can mask the expression of another gene. Example: Coat color in animals.
• Polygenic Inheritance: A characteristic is regulated by the additive action of many pairs of genes. Example: Skin color in humans, determined by multiple gene pairs.

Blood Groups

Blood groups are determined by the presence or absence of specific antigens on red blood cells.