inheritance chapter 29. gregor mendel “father of genetics” 1822 - 1884

Download Inheritance Chapter 29. Gregor Mendel “Father of Genetics” 1822 - 1884

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  • Inheritance Chapter 29
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  • Gregor Mendel Father of Genetics 1822 - 1884
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  • What Mendel did He bred peas in the monastery garden at Brno, Czech Republic (then part of the AustroHungarian Empire). Observed occasional variations in the appearance of these plants. Selectively bred plants to consistently produce characteristics that were unusual. Saw a pattern in the way that the unusual characteristics showed up. Was the first to propose that these characteristics were passed from one generation to another by the gametes.
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  • The Abby where Mendel worked
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  • What Mendel did not do He didnt use the word gene to refer to subject of his work. He didnt see chromosomes. He never used a Punnett square. He never achieved fame in his lifetime for his work.
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  • Charles Darwin 1809 - 1882 Proposed the Theory of Evolution. Actually, talked about descent with modification from a common ancestor. He didnt use the word evolution very often. Voyage of the Beagle 1831 1836. Presented paper with Alfred Russell Wallace in 1858. Published first edition of Origin of Species in 1859.
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  • Some Vocabulary Genetics study of inheritance. Autosomes the 22 pairs of chromosomes that do not determine genetic sex. Sex chromosomes the 23 rd pair, the X and the Y. Karyotype the diploid chromosomes displayed in their condensed form and paired as homologs
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  • A typical karyotype
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  • More Vocabulary Alleles - a matched pair of two genes, coding for the same or alternative forms of a particular trait. Found at the same location (locus) on homologous chromosomes. Homozygous having the same alleles for a trait Heterozygous having different alleles for the same trait.
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  • More words Dominant an allele that expresses itself and masks its partner. Example: brown hair is dominant over blond. Recessive the reverse of the above. The allele that is masked Allele pairs are expressed as a pair of letters representing the trait. Example: Mendals peas came in tall and short. Tall is the dominant allele for height in peas. Therefore it is written as a capital T. A heterozyote for height would be Tt, with the lowercase t representing the recessive.
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  • Genotype vs. Phenotype Genotype the actual alleles an organism has is its genotype. In our heterozygote pea plant that would be Tt. Phenotype that which is expressed. Our pea plant maybe genotypically heterozygotic but phenotypically it is tall. Homozygote dominant = TT phenotype = tall Homozygote recessive = tt phenotype = short Heterozygote= Tt phenotype = tall
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  • Mendels Laws Mendal discovered that if you bred plants that had two alleles for each trait that you would get the same ratios of phenotypes & genotypes whenever you crossed heterozygotes. It was like clockwork! This was because of independent assortment and segregation, which became known as Mendals Laws
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  • It works like this Phenotypic ratio = 3:1 or 3 tall : 1 short Genotypic ratio = 1:2:1 or 1 homozygote dominant 2 heterozygotes 1 homozygote recessive
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  • Example: PKU
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  • Violation of Mendels Laws Mendals laws only hold if: there is random fertilization there is random fertilization the alleles are located on separate chromosomes the alleles are located on separate chromosomes the alleles have a simple dominant/recessive relationship the alleles have a simple dominant/recessive relationship there are only two alleles for that trait there are only two alleles for that trait they are not lethal to the zygote they are not lethal to the zygote
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  • Penetrance Percentage of individuals with particular genotype that shows expected phenotype Expressivity Extent to which particular allele is expressed
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  • Teratogens Factors that result in abnormal development
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  • Sources of variation: segregation & independent assortment Assortment leads to many possibilities as far as gamete formation goes. For any genome it can be calculated as 2 n, where n=the number of chromosome pairs.
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  • So for a human with 23 chromosome pairs, the possible combinations of gametes = 2 23 or 8,388,608! (and thats with out recombination)
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  • Suppression 1 gene suppresses other Second gene has no effect on phenotype
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  • Complementary Gene Action Dominant alleles on 2 genes interact to produce phenotype different from when 1 gene contains recessive alleles
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  • Sources of Individual Variation During meiosis, maternal and paternal chromosomes are randomly distributed Each gamete has unique combination of maternal and paternal chromosomes
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  • Crossing Over and Translocation Figure 2917
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  • Genetic Recombination During meiosis, various changes can occur in chromosome structure, producing gametes with chromosomes that differ from those of each parent Greatly increases range of possible variation among gametes Can complicate tracing of inheritance of genetic disorders
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  • Crossing Over Parts of chromosomes become rearranged during synapsis When tetrads form, adjacent chromatids may overlap
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  • Translocation Reshuffling process Chromatids may break, overlapping segments trade places
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  • Genomic Imprinting During recombination, portions of chromosomes may break away and be deleted Effects depend on whether abnormal gamete is produced through oogenesis or spermatogenesis
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  • Chromosomal Abnormalities Damaged, broken, missing, or extra copies of chromosomes Few survive to full term Produce variety of serious clinical conditions
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  • Mutation Changes in nucleotide sequence of allele
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  • Spontaneous Mutations Result of random errors in DNA replication Errors relatively common, but in most cases error is detected and repaired by enzymes in nucleus Errors that go undetected and unrepaired have potential to change phenotype Can produce gametes that contain abnormal alleles
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  • A Map of Human Chromosomes
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  • Human Genome Project Goal is to transcribe entire human genome Has mapped more than 38,000 human genes
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  • Karyotyping Determination of individuals complete chromosomal complement
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  • Types of inheritance Aside from simple dominant/recessive Incomplete dominance a dominant allele does not completely mask the recessive (red flower + white flower = pink flower). Codominance both traits are expressed together (red flower + white flower = stripes). Multiple alleles More than one allele for a trait. ABO blood group is an example. Polygene several alleles interact to produce a trait. Results are a continuous or quantitative phenotype, as in skin color.
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  • Carriers Individuals who are heterozygous for abnormal allele but do not show effects of mutation
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  • Incomplete dominance: Sickle Cell
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  • Codominance of multiple alleles
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  • Polygenic inheritance
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  • Sex-linked inheritance Males only have one X chromosome. Therefore, if a trait is found only on the X it will be expressed in a male regardless of whether it is dominant or recessive. X inactivation occurs in females. Every normal woman has two Xs but they only need one. Therefore, one X chromosome turns off, forming a Barr body. Because X inactivation is random in most cases, it leads to a fine mosaic of cells in females.
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  • Sex determination in humans
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  • Color- blindness: a sex-linked trait
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  • Environmental influences Phenocopy Developmental influences impact genetic expression in ways that appear to be genetic but are not inheritable. Temperature, nutrition, non-genetic pathologies can have impacts that are expressed in ways that appear genetic.
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  • Genetic defects Aneuploidy a defective set of genes. Triploidy an extra set of chromosomes Trisomy an extra single chromosome Monosomy a missing homolog Trisomy of the 23 rd chromosome XXX = super female XXY = Klinefelters syndrome Trisomy of the 21 st chromosome leads to Downs Syndrome.
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  • Down syndrome
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  • Klinefelters - a type trisomy affecting the sex chromosomes
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  • Turner Syndrome: monosomy of the 23 rd chromosome, X_
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  • Monosomy of the 23rd chromosome Name that condition!
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  • A Peek into the Future: Screening for genetic disorders
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  • Thanks for a great term!


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