Transcript Genetics
Genetics Chapter 11 Homologous Chromosomes Half of an offspring’s chromosomes come from it’s mother Half of it’s chromosomes come from it’s father These chromosomes are considered homologous- each of the chromosomes from the father has a corresponding chromosome from the mother ho·mol·o·gous (h -m l -g s, h )adj. 1. 2. 3. Corresponding or similar in position, value, structure, or function. Biology Similar in structure and evolutionary origin, though not necessarily in function, as the flippers of a seal and the hands of a human. Genetics Having the same morphology and linear sequence of gene loci as another chromosome.5. The American Heritage® Dictionary of the English Language, Fourth Edition copyright ©2000 by Houghton Mifflin Company. Ploidy A cell that contains both sets of homologous chromosomes is said to be diploid (2N) A cell with only one set is called haploid (N) and is known as a sex cell ( ex. egg or sperm) Meiosis Cell Division DNA Replication Cell Division Mitosis Outcomes Meiosis Mitosis Gregor Mendel Austrian monk sometimes known as the “father of genetics” Experimented with pea plants that are self-pollinating so all genetic traits are identical between parent plant and seed Used true-breeding plants-allowed to selfpollinate they produce identical offspring Gregor Mendel b. 1822 Fertilization During sexual reproduction, male and female reproductive cells join Produces a new cell which has a mixture of the genetic information from the male and female parent cells If self-fertilization happens offspring may be identical to parent If fertilization from another individual takes place, genetic variations can occur Cross Pollination Test Subject: Pea Plant Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Cross Pollination Mendel cut away the male pollen producing parts of pea plants and pollinated those plants with pollen from other flowers This made it possible for Mendel to crossbreed plants with different traits and follow the patterns of occurrence Genes and Dominance Trait- a specific characteristic P – parental generation F1 – filial generation 1 (filial means children) F2 – filial generation 2 (children of F1s, could be called grandchildren) Hybrid – offspring of genetic crosses Mendel Drew Two Conclusions Conclusion 1 Biological inheritance is determined by factors that are passed from one generation to the next Today we call these factors genes The different forms of variation produced by a gene are called alleles Mendel Drew Two Conclusions Conclusion 2 Mendel’s second conclusion is known today as the principle of dominance Principle of Dominance states that some alleles are dominant and others are recessive Segregation Segregation in the F1 Cross Has the recessive allele disappeared or is it still present in the F1 plants? Mendel allowed all seven types of F1 hybrids to produce an F2 generation (self pollinating) Amazing! Results non-existent in the F1 generation reappear in 25% of F2 Segregation The alleles separate or “segregate” during the formation of gametes (sex cells) Offspring then have the possibility of inheriting two recessive genes, though they statistically get at least one dominant Each gamete carries only one copy of the gene either the dominant OR the recessive, not both Punnet Square ¾ of the offspring have purple phenotype ¼ of offspring have white phenotype ½ heterozygous ½ homozygous (¼ recessive white, ¼ dominant purple)