Genetics Chapter on Inheritance Patterns

Pattern of Inheritance

• Inheritance patterns depend on whether alleles are on autosomal or sex chromosomes and whether they are dominant or recessive.
• Five basic modes of single-gene inheritance:
  • Autosomal dominant
  • Autosomal recessive
  • X-linked dominant
  • X-linked recessive
  • Y-linked
  • Mitochondrial

Homogametic and Heterogametic

• Females are homogametic, producing gametes with only X chromosomes (XX).
• Males are heterogametic, producing gametes with both X and Y chromosomes (XY).
• During meiosis, sex chromosomes are separated into different gametes.

Non-Mendelian Inheritance

• Complex traits show continuous variation, influenced by both genetics and environmental factors.
• Example traits include human height and weight, affected by gene interactions and environmental influences.
• Such traits are classified as complex or multifactorial.

Autosomal Inheritance

• Autosomal Dominant:
  • Phenotype observed with one copy of the dominant allele (heterozygous or homozygous).
• Autosomal Recessive:
  • Phenotype observed only with two copies of the recessive allele (homozygous).
  • Heterozygous individuals (carriers) do not express the phenotype but can pass it on.

Sex-linked Inheritance

• Most sex-linked characteristics are X-linked due to limited genetic information on the Y chromosome.
• X chromosome contains hundreds of genes unrelated to sex determination.
• Males express all alleles on their single X chromosome, making dominance or recessiveness irrelevant for X-linked traits.
• Conditions linked to the X chromosome include haemophilia, muscular dystrophy, and color blindness.

Historical Context

• Thomas Hunt Morgan's experiments with Drosophila (fruit flies) advanced understanding of X-linked inheritance.
• Morgan aimed to challenge Mendelian ratios and discovered a white-eyed male fly, crucial for his studies.
• The notation used: XR indicates the red eye allele (dominant), while Xr indicates the white eye allele (recessive).

Explore the various patterns of inheritance in genetics, including autosomal and sex-linked traits. This quiz covers both Mendelian and non-Mendelian inheritance types, explaining complex traits and their genetic basis. Test your understanding of how these patterns influence phenotype and inheritance in organisms.