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The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. (3.A.3) Big Idea 3: Genetics and Information Transfer Heritable information provides for continuity of life. (3.A.3) a. Rules of probability can be applied to analyze passage of single gene traits from parent to offspring. • The multiplication rule. To determine the probability that two or more independent events will occur together in some specific combination, you multiply the probability of one event by the probability of the other event. • The addition rule. The probability that any one of two or more mutually exclusive events will occur is calculated by adding their individual probabilities. Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Pearson Education, Inc., publishing as Person Benjamin Cummings College Board, AP Biology Curriculum Framework 2012-2013 14.1-14.4, 15.1-15.5 Copyright © Rebecca Rehder Wingerden Segregation of alleles and fertilization as chance events. When a heterozygous (Rr) forms gametes, whether a particular gamete ends up with an R or an r it is like the toss of a coin. We can determine the probability for any genotype among the offspring of two heterozygous by multiplying together the individual probabilities of an egg and sperm having a particulate allele (R or r in this example). Copyright © 2012 Rebecca Rehder Wingerden The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. (3.A.3) The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. (3.A.3) b. Segregation and independent assortment of chromosomes result in genetic variation and can be applied to genes that are on different chromosomes. Each true-breeding plant of the parental generation has identical alleles, PP or pp Gametes (circles) each contain only one allele for the flower-color gene. In this case, every gamete produced by one parent has the same allele. Union of parental gametes produces F1 hybrids having a Pp combination. Because the purple-flower allele is dominant, all these hybrids have purple flowers. When the hybrid plants produce gametes, the two alleles segregate. Half of the gametes receive the P allele and the other half the p allele. The box, a Punnett square, shows all possible combination of alleles in offspring that result from an F1 x F1 (Pp xPp) cross. Each square represents an equally probable product of fertilization. For example, the bottom left box show the genetic combination resulting form a egg fertilized by a sperm. Alleles, alternative versions of a gene. A somatic cell has two copies of each chromosome (forming a homologous pair) and thus two alleles of each gene, which may be identical (homozygous) or different (heterozygous). This figure depicts a homologous pair of chromosomes in an F1 hybrid pea plant. The chromosome with an allele for purple flowers was inherited from one parent, and that with an allele for white flowers from the other parent. Random combination of gametes results in the 3:1 ratio that Mendel observed in the F2 generation Mendel’s law of segregation. Mendel’s model for inheritance of the alleles of a single gene. Copyright © 2012 Rebecca Rehder Wingerden Copyright © 2012 Rebecca Rehder Wingerden P Generation Starting with two true-breeding pea plants (YYRR x yyrr). F1 Generation All plants produce yellow-round seeds (YyRy). F2 Generation Produce phenotypic ration of 9:3:3:1 The chromosomal basis of Mendel’s laws. Here we correlate the results of one of Mendel’s dihybrid crosses with the behavior of chromosomes during meiosis. The arrangement of chromosome at metaphase I of meiosis and their movement during anaphase I account for the segregation and independent assortment of the alleles for see color and shape. Each cell that undergoes meiosis in an F1 plant produces two kinds of gametes. If we count the results for all cells, however, each F1 plant produces equal numbers of all four kinds of gametes because the alternative chromosome arrangements at metaphase I are equally likely. Copyright © 2012 Rebecca Rehder Wingerden The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. (3.A.3) 1. Genes that are adjacent and close to each other on the same chromosome tend to move as a unit (linked) and they do NOT follow Mendel’s law of independent assortment. How linkage affects inheritance. A test crosses that Morgan preformed produced a much higher proportion of parental phenotypes than would be expected if the two genes assorted independently. Based on these result, he concluded that body color and wing size are usually inherited together in specific combination (the parental combinations) because the genes for these characters are on the same chromosome. Copyright © 2012 Rebecca Rehder Wingerden The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. (3.A.3) How does linkage between two genes affect inheritance of characters? Morgan wanted to know whether the genes for body color and wing size were on the same chromosome, and if so, how this affected their inheritance. The alleles of body color are b+ (gray) and b (black), and those for wing size are vg+ (normal) and vg (vestigial). 2. The recombination (crossing over) of linked genes is a function of the distance between them. Design. P Generation was a cross between true-breeding wild-type (b+ b+ vg + vg+) flies with black, vestigial-winged (b b vg vg) flies to produce heterozygous F1 dihybrids (b+ b vg+ vg) all of which are wild-type in appearance. Then crossed the wild-type F1 (b+ b vg+ vg) with the vestigial-winged (b b vg vg) to produce the F2 results. Conclusion. Since most offspring had a parental phenotype, Morgan concluded that the genes for body color and wing size are located on the same chromosome. However, the production of a relatively small number of offspring with non-prenatal phenotypes (recombinants) indicated that some mechanism occasionally breaks the linkage between specific alleles of genes on the same chromosome. A partial genetic (linkage) map of a Drosophila chromosome. The simplified map shows just a few of the genes that have been mapped on Drosophila chromosome II. The number at each gene locus indicates the number of map units between that locus and the locus for arista length (left). Copyright © 2012 Rebecca Rehder Wingerden Copyright © 2012 Rebecca Rehder Wingerden The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. (3.A.3) 3. The pattern of inheritance can often be predicted from data that gives the parent genotype/phenotype and/or the offspring phenotypes/genotypes. • monohybrid: The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. (3.A.3) • dihybrid: YyRr x YyRr Pp x Pp Copyright © 2012 Rebecca Rehder Wingerden Copyright © 2012 Rebecca Rehder Wingerden The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. (3.A.3) • sex-linked The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. (3.A.3) c. Certain human genetic disorders can be attributed to the inheritance of single gene traits or specific chromosomal changes, such as nondisjunction. Huntington’s disease- lethal dominant allele caused by a genetic mutation in a gene on chromosome 4. The defect causes a part of DNA, called a CAG repeat, to occur many more times than it is supposed to. Normally, this section of DNA is repeated 10 to 28 times. But in persons with Huntington’s disease, it is repeated 36 to 120 times. A color-blind father will transmit the mutant allele to all daughters but to no sons. when the mother is a dominant homozygote, the daughters will have the normal phenotype by will be carriers of the mutation. If a carrier mates with a male who has normal color vision, there is a 50% chance that each daughter will be a carrier like her mother and a 50% chance that each sone will have the disorder. In a carrier mates with a color-blind male, there is a 50% chance that each child born to them will have the disorder, regardless of sex. Daughters who have normal color vision will be carriers whereas males who have normal color vision will be free of the recessive allele. The transmission of sex-linked recessive traits. In this diagram, color blindness is used as an example. The superscript N represents the dominant allele for normal color vision carried on the X chromosome, and the superscript n represents the recessive allele, which has a mutation causing color blindness. Copyright © 2012 Rebecca Rehder Wingerden As the gene is passed down through families, the number of repeats tend to get larger. The larger the number of repeats, the greater your chance of developing symptoms at an earlier age. Therefore, as the disease is passed along in families, symptoms develop at younger and younger ages. The disease destroys cells in the basal ganglia, the part of the brain that controls movement, emotion, and cognitive ability. Copyright © 2012 Rebecca Rehder Wingerden The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. (3.A.3) The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. (3.A.3) c. Certain human genetic disorders can be attributed to the inheritance of single gene traits or specific chromosomal changes, such as nondisjunction. d. Many ethical, social and medical issues surround human genetic disorders. • Reproduction issues • Privacy issues • Civic issues such as ownership of genetic information Trisomy 21/ Down syndrome- is a developmental disorder caused by an extra copy of chromosome 21. Having and extra copy of this chromosome means that each gene may be producing more protein product than normal. Down syndrome is typically caused by what is called nondisjunction. If a pair of number 21 chromosomes fails to separate during the formation of an egg (or sperm), then this is referred to as nondisjunction. When that egg unites with a normal sperm to form an embryo, that embryo ends up with three copies of chromosome 21 instead of the normal two. The extra chromosome is then copied in every cell of the baby's body. - HeLa cells have been used extensively in medicine and heath research. For example, they were used to test the first polio vaccine in the 1950s, used for research into cancer, AIDS, the effects of radiation and toxic substances, gene mapping, and many other scientific pursuits. More than 60,000 scientific articles have been published about research done on HeLa, and that number is increasing at a rate of more than 300 papers each month. BBC - The Undead Henrietta Lacks And Her Immortal Dynasty (58:00 min.) http://www.bbc.co.uk/blogs/adamcurtis/2010/06/the_undead_henrietta_lacks_and.html Book - The Immortal Life of Henrietta Lacks (3:00 min.) http://rebeccaskloot.com/the-immortal-life/ Copyright © 2012 Rebecca Rehder Wingerden Copyright © 2012 Rebecca Rehder Wingerden The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. (3.A.3) Bozeman Biology: Mendelian Genetics (15:00 min.) http://www.bozemanscience.com/029-mendelian-genetics Bozeman Biology: Probability in Genetics (11:00 min.) http://www.bozemanscience.com/probability-in-genetics Bozeman Biology: A Beginner’s Guide to Punnett Squares (13:00 min.) http://www.bozemanscience.com/beginners-guide-to-punnett-squares Bozeman Biology: Chromosomal Genetics (15:00 min.) http://www.bozemanscience.com/chromosomal-genetics Bozeman Biology: Advanced Genetics (13:00 min.) http://www.youtube.com/watch?v=YoEgUqHOcbc Bozeman Biology: Linked Genes (18:00 min.) https://paul-andersen.squarespace.com/linked-genes Bozeman Biology: AP Genetics Review (20:00 min.) http://www.bozemanscience.com/ap-genetics-review Copyright © 2012 Rebecca Rehder Wingerden Henrietta Lacks (August 1, 1920 - October 4, 1951) Unwitting source of cells from her cancerous tumor which were cultured by Goerge Otto Gey to create an immortal cell line for medical research known as the HeLa cell line.