Biology 2E Lecture PowerPoint Slides (Chapter 13): Modern Understanding of Inheritance PDF

11/2/2024 BIOLOGY 2E Chapter 13 MODERN UNDERSTANDING OF INHERITANCE Lecture PowerPoint Slides PART 1 This work is licensed under a Creative Commons Attribution-NonCommercial- Share...

11/2/2024 BIOLOGY 2E Chapter 13 MODERN UNDERSTANDING OF INHERITANCE Lecture PowerPoint Slides PART 1 This work is licensed under a Creative Commons Attribution-NonCommercial- ShareAlike 4.0 International License. 1 CELEBRATING BIOLOGISTS!!! Angel Alcala, Carmen C. Anthony Oro, PhD Velasquez, PhD MD/PhD 2 1  11/2/2024 Shortly after the rediscovery of Mendel’s work a search for the physical basis of the gene began. Mendel’s findings were based in statistical results from numerous crosses and his “Laws” were purely conceptual deductions. Mendel had no idea as to the actual physical nature of his conceptual “hereditary particles” (genes). Rediscovery and recognition of the importance of his work triggered many into trying to find the physical cause of Mendel’s observations. By 1900 microscopy was a well-developed technology and the importance of the cell was well known. Many microscopic studies of cells were undertaken to look for the physical gene. 3 Technological Advances Advances in microscopy and staining techniques allowed the visualization of chromosomes that appeared to behave in accordance with Mendel’s observations 4 2  11/2/2024 Chromosomes Today we know that chromosomes are threadlike nuclear structures consisting of DNA and proteins that serve as the repositories for genetic information. 5 CHROMOSOMAL THEORY OF INHERITANCE Each pair of homologous chromosomes sorts randomly and independently of other chromosome pairs Male and female gametes contain half the genetic material of the parent cell 6 3  11/2/2024 CHROMOSOMAL THEORY OF INHERITANCE During meiosis, chromosome pairs migrate as discrete structures. Chromosome sorting from each homologous pair into pre-gametes appears to be random. Each parent synthesizes gametes that contain only half their chromosomal complement. Even though male and female gametes (sperm and egg) differ in size and morphology, they have the same number of chromosomes, suggesting equal genetic contributions from each parent. The gametic chromosomes combine during fertilization to produce offspring with the same chromosome number as their parents. 7 THE CHROMOSOMAL BASIS OF MENDEL’S LAWS (PART 1: P GENERATION) 8 4  11/2/2024 THE CHROMOSOMAL BASIS OF MENDEL’S LAWS (PART 2: F1 GENERATION) During metaphase I of meiosis I 9 THE CHROMOSOMAL BASIS OF MENDEL’S LAWS (PART 2: F1 GENERATION) During anaphase I of meiosis I 10 5  11/2/2024 Chromosomal Theory of Inheritance Proposed long before there was any direct evidence that traits were carried on chromosomes. Working with sea urchins and grasshoppers, Boveri and Sutton (respectively) independently demonstrated that chromosomes occur in matched maternal and paternal pairs that segregate in meiosis. Early support for their theory came from the work of Eleanor Carothers demonstrating independent assortment of chromosomes in grasshoppers. Discovery of X and Y chromosome-based inheritance of sex and T.H. Morgan’s subsequent work on genetic linkage in Drosophilia melanogaster led to the first real proof of a chromosome role in heredity. 11 Drosophilia melanogaster Human karyotype Drosophilia melanogaster karyotype 12 6  11/2/2024 T. H. Morgan showed that the white eye mutant allele was inherited along with sex (the X chromosome). This sex linkage was the first demonstration that genes were on chromosomes. 13 The concept of linkage was further extended to map genes to chromosome positions – genetic linkage maps. Morgan’s work with sex linkage showed that the trait for sex and the trait eye color were inherited together. They did not segregate independently – violated Mendel’s second law. When other traits were examined, it was found that those on the same chromosome did not always segregate independently. Traits on the same chromosome did segregate, however. Far apart traits segregated independently. Traits closer together segregated less often than independence predicted. Cross over between homologous chromosomes was the mechanism that segregated genes on the same chromosome. When genes were far apart crossover happened all the time. When the were close together, cross overs happened less frequently. 14 7  11/2/2024 END OF PART 1 15 8