+ + =?? Blending of Traits. Mendel. History of Genetics. Mendel, a guy WAY ahead of his time. History of Genetics

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1 History of Genetics In ancient times, eole understood some basic rules of heredity and used this knowledge to breed domestic animals and cros. By about 5000 BC, for examle, eole in different arts of the world had begun alying selective breeding techniques to grow new lant varieties, including tyes of wheat, maize, rice, and date alms, that had never existed in the wild. Ancient eole understood that the rules of inheritance also alied to humans. The ancient Greeks were articularly interested in human heredity and evolution. Greek scientists and hilosohers hotly debated whether a male or female arent contributed more to an offsring. In the 4th century BC, Aristotle seculated that acquired characteristics, such as a scar that was incurred during life, could be assed on to offsring. When it comes to science, its been said that I never let my ignorance stand in the way of my theories. Hey, wait!! History of Genetics Most of the mechanisms of heredity, however, were shrouded in mystery until early in the 20th century + + =?? Blending of Traits It was commonly thought that traits of an individual might be a blend of the arental traits aint analogy Evidence for? Evidence against? + = Mendel Good at math, atient, rigorous lenty of free time & lucky! In 1865, Gregor Mendel first traced inheritance atterns of certain traits in ea lants and showed that they obeyed simle statistical rules. From his statistical analysis Mendel defined a concet of a fundamental unit of heredity This fundamental unit is now called a gene. Mendel, a guy WAY ahead of his time Just to ut Mendel s work into ersective While he was carrying out his exeriments, in the 1860 s, Chromosomes and the genes that lie along them had not been discovered. Little, if any knowledge existed of mitosis or meiosis DNA and its discovery were ~90 years away In the 1860 s, Gregor Mendel deduced the fundamental rinciles of genetics Was the first erson to analyze atterns of inheritance Deduced that arents ass on to their offsring discrete heritable factors (genes) that are resonsible for inherited traits Genes retain their individuality generation after generation Genes are not like aint, but are more like cards in a deck 1

2 arents ass on to their offsring discrete heritable factors (genes) that are resonsible for inherited traits Another way of saying this.. Genes genotye traits henotye DNA RNA rotein Why ea lants? -Mendel discovered the rules of genetics in a series of rigorous studies involving garden eas Why do ea lants make a good model system? What do you think makes a good model system for genetics? Why eas? --In nature, these lants can selffertilize, meaning that the ea flower has both male and female arts, and these are enclosed in the flower itself --But in addition, these lant are easily maniulated. Mendel could closely control crossings of lants, using simle tools. Stamen Carel Remember that ollen ~ serm and in the carel is an egg!! These are lant gametes. They are haloid cells. Anatomy and life-cycle of the ea lant 1. Self ollination occurs as ollen from the anthers falls on the stigma (carel) 2. Fertilization of the lant s eggs, which are housed in the lant s ovary. These eggs develo into seeds in the ovary (eas in a od), which reresent a new lant generation. Each seed is fertilized searately. 3. After being lanted, each seed has the otential to grow into a searate lant. isum sativum FYI: sativum means garden variety, as oosed to silvestris Cross-fertilization (laying God or matchmaker) Mendel carried out some cross-fertilizations Removing ollen (stamens) from one lant and then adding ollen from a different lant to fertilize In both the cross-fertilized and self-fertilized lants, Mendel could know the arents of each lant Carel arents () Offsring (F 1 ) 1 Removed stamens from urle flower White Stamens 2 Transferred ollen from stamens of urle white flower to carel of urle flower 3 ollinated carel matured into od 4 lanted seeds from od Why eas? The ea lants in Mendel s garden had numerous characters (heritable features) Many of these characters only had 2 variants urle flowers OR white flowers Green seeds OR yellow seeds OR (not greenish-yellow) (not ale urle) Characters were either or not more or less, nothing in-between Figure 9.6 2

3 ea lants have characters that are easily observed and that come in two varieties Flower color urle Flower osition Axial White Terminal od shae Inflated Constricted od Color Green Yellow True Breeder All of Mendel s exeriments START with true breeding lants (arental generation, ) --Self-ollinating lants that ONLY give rise to one variety of a character Hybridization: crossing of two true breeders (roduces hybrids, called the F generation) Seed color Yellow Green Seed shae Round Wrinkled Stem length Tall Dwarf Monohybrid cross: crossing of two true breeders that differ only in one character arental lants are called the generation Their offsring are the F 1 generation When F 1 lants self fertilize or fertilize each other, their offsring are the F 2 generation F 1 x (crossed with) F 1 = F 2 generation F 1 x A monohybrid cross is a cross between arent lants that differ in only one characteristic Monohybrid Crosses Generation (true-breeding arents) urle flowers F 1 Generation (monohybrid) White flowers F 2 generation Mendel s First Exeriment Mendel s First Exeriment Cross-fertilize two true breeding lants and analyze hybrid offsring If you were a scientist working with Mendel, and you believed in the hyothesis that the traits of offsring are a BLEND of arental hereditary information. What would be your REDICTION for this exeriment? IF, then. what can you redict about the offsring? Cross-fertilize two true breeding lants and analyze hybrid offsring Does the data suort or not suort your hyothesis? (arental) F (filial, son) Is the white information lost??? = data 3

4 Mendel s Second Exeriment Allow F1 offsring to selffertilize and analyze traits of offsring Mendel s Second Exeriment Allow F 1 offsring to selffertilize and analyze traits of offsring F 1 X F 1 = F 2 F 1 X F 1 = F 2 What will the F2 flowers look like?? Has the white information been lost? Mendel s quantitative analysis of NUMEROUS F 2 lants gave the most imortant information 705 urle 224 white 3 : 1 Mendel s Hyothesis Good at math, atient, rigorous lenty of free time & lucky! Mendel s hyothesis-art 1 Different versions of genes account for variations in inherited characters Now called alleles Heritable factor (card, gene) did not disaear in F 1 lants, but that only the urle flower factor was affecting flower color in these F 1 hybrids. Mendel s hyothesis-art 2 For each character, an organism inherits 2 alleles, one from each arent 1 2 Mendel s hyothesis-art 3 If two alleles at a locus differ, one determines the organism s aearance (the dominant allele), while the other has no noticeable effect (the recessive allele) In this examle, which variety of the character is dominant? Recessive? 4

5 Mendel s hyothesis-art 3 If two alleles at a locus differ, one determines the organism s aearance (the dominant allele), while the other has no noticeable effect (the recessive allele) Mendel s notation labels the dominant allele with a caital letter, for urle. The recessive allele at that locus/site, is labeled with the lower case of the same letter,, for white. 1 2 Mendel s hyothesis-art 3 Mendel s hyothesis-art 4 Segregation occurs at anahase I The 2 alleles searate (segregate) during gamete formation Meaning, egg or serm get only one of 2 alleles At what stage of meiosis does this segregation actually occur?? Baby ****Mendel s law of segregation**** Homologous chromosomes searate (maternal goes one way, aternal goes the other) Mendel develoed four hyotheses from the monohybrid cross 1. There are alternative forms of genes, now called alleles 2. For each characteristic, each organism has two genes, one from each arent 3. Alleles can be dominant or recessive 4. Serm or egg carry only one allele (one version) for each inherited characteristic What are the ossible gametes that could form from each of these three different cells? What alleles could gametes get? 5

6 Testing the Law of Segregation using a unnett square If a lant self-fertilizes arents: X ossible eggs ossible serm ossible offsring The robability of the different genotyes of offsring is shown here. Same thing, just tilted unnett Squares for Mendel s Exeriments What will the F 1 generation look like? What will their genes (alleles) be? Gametes: Do the unnett square!!!! unnett Squares for Mendel s Exeriments unnett Squares for Mendel s Exeriments All F 1 lants had urle flowers. All F 1 lants are. All F1 lants had urle flowers. All F1 lants are. What gametes can an F 1 lant roduce? ossible serm What gametes can an F 1 lant roduce? ossible serm ossible eggs What will the F 2 generation look like? What will their genes be? ossible eggs 3 : 1 6

7 henotye Genotye henotye An organism s hysical traits (ie. urle or white flowers) Genotye An organism s genetic makeu (either,, or ) DNA RNA rotein Homozygous When an organism has identical alleles for a gene Heterozygous When an organism has different alleles for a gene Genetic Alleles and Homologous Chromosomes Homologous chromosomes Have genes at secific loci Have alleles of a gene at the same locus Loci (locations) Test Cross What is my genotye? Test Cross If we saw a urle-flowered ea lant, what are the ossible gentoyes of the lant? How could we determine the genotye? Use a test cross: an imortant genetic tool (not suitable for humans) :) Crossing the organism of interest to a homozygous recessive (in this case, a whiteflowered lant) and analyzing the offsring. urle (mystery genotye) x white () What offsring result if the urle-flowered lant is: Homozygous dominant ()?? Heterozygous ()?? 7

8 Do the two different unnett Squares!! DO THE UNNET SQUARES!!!!!! 8