Topic 08 Part 2_ Chromosome Theory of Inheritance

Chromosome Theory of Inheritance

Overview

  • Mendelian inheritance is linked to chromosome behavior.

  • Key topics include:

    • Morgan’s experiments

    • Sex determination and sex-linked traits

    • Linked genes and linkage maps

    • Statistical analysis: Chi square (Χ²)

    • Chromosome number/structure alterations

    • Human disorders from chromosome changes

    • Organelle genes

Chromosomes and Inheritance (15.1)

  • Discovery of mitosis and meiosis post-Mendel's work.

  • Chromosome Theory of Inheritance:

    • Genes are located on chromosomes.

    • Chromosomes undergo segregation and independent assortment.

  • Explains Mendel’s laws through chromosome behavior during meiosis and fertilization.

Morgan’s Experiments (15.1)

  • Thomas Morgan linked specific genes to specific chromosomes using fruit flies (Drosophila melanogaster).

  • Key attributes of Drosophila:

    • Rapid breeding cycle (two weeks).

    • Four pairs of chromosomes.

Sex Determination (15.2)

  • Sex in humans is determined by X and Y chromosomes.

  • Conditions for male development:

    • Presence of Y chromosome.

    • Functional SRY gene on Y.

    • Response to testosterone during fetal development.

Sex-Linked Genes (15.2)

  • The X chromosome carries many non-sex-related genes; the Y primarily has sex-determining genes.

  • X-linked recessive disorders are more prevalent in males due to their single X chromosome.

Linked Genes (15.3)

  • Genes located on the same chromosome are termed linked genes, inherited together.

  • Non-parental phenotypes indicate genetic recombination via crossing over.

Alterations of Chromosome Number (15.4)

  • Chromosomal alterations can lead to disorders:

    • Aneuploidy: Abnormal chromosome numbers due to nondisjunction during meiosis.

    • Example: Trisomy (three copies of a chromosome).

    • Polyploidy: More than two complete chromosome sets, common in plants.

Disorders from Chromosome Alterations (15.4)

  • Trisomy 21 leads to Down syndrome, with increased risk associated with maternal age.

  • Turner syndrome (XO) is a known monosomy, causing infertility in females.

  • Klinefelter syndrome (XXY) results in infertility in males.

  • Cri du Chat syndrome is caused by a deletion in chromosome 5, leading to developmental issues.

Inheritance of Organelle Genes (15.5)

  • Extranuclear genes found in mitochondria and chloroplasts resemble prokaryotic DNA.

  • Maternal inheritance due to zygote cytoplasm originating from the egg.

  • Defects in mitochondrial genes can affect ATP production, impacting muscles and brain function.