BIOL 180 Week 2
BIOL 180 Week 2 BIOL 180
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Date Created: 10/12/15
10115 1047 Darwin s 4 Postulates broke nat selection into 4 criteria 1 Individual organisms vary in the traits they possess 2 Some traits are heritable 3 In each generation more offspring are produced than can possibly survive 4 Those that survive the best are not random it is because they have traits that are most likely to survive and reproduce Often reduced to 1 heritable variation leads to 2 differential reproductive success Natural Selection individuals with certain characteristics produce more offspring than those without these traits Fitness ability to produce surviving fertile offspring relative to other individuals in the population Measurable quantity Adaptation heritable trait that increases fitness Evolution by natural selection is testable For example in the 19005 TB was not a big deal since nutrition and antibiotics were better But in the late 19805 it came back and the old antibiotics didn t work anymore Patient with TB came in to get treated for 33 weeks seemingly got better Then 10 weeks later came back with same symptoms but now resistant and then later died Only difference between the TB was a mutation in gene called rpoB What happened 1 By chance one of the cells had the mutation 2 When therapy started many cells died so his symptoms went away and he seemed cured 3 There were still bacteria with the mutation and regained its former abundance 4 Patient went to get treated again but now they are resistant Testing Darwin s postulates 1 Did variation exist Yeah there was mutation and some were resistant and some weren t 2 Heritable HELL YEAH the variation were due to genotypes 3 Variation in reproductive success Yeah only the mutant ones survived and reproduced 4 Selection YEAH when rifampin was present the drug resistant cells had a higher reproductive rate Natural selection acts on individuals because they experience differential reproductive success but only populations evolve Scientists studied birds on Daphne Major an island In 77 there was a major drought 38 birds died and none of the missing birds 84 or 660 birds were found on the island or nearby islands even once everything was back to normal this is called a Natural experiment comparing treatment groups created by unplanned changes in conditions Found out that in only 1 generation natural selection led to change in traits of the birds larger deep beaks were an adaption for cracking large fruits and seeds They continue to notice the affect of the environment on these traits INDIVIDUALS don t change as a part of natural selection POPULATION does Sorts out existing variants it doesn t change them Phoenotypic changes due to acclimatization aren t passed on to offspring since no alleles have changed Acclimatization change in an individuals phenotype that occurs in response to a change in natural environmental conditions SUM MARY TABLE 252 Common Misconceptions Corrected sconceptlon Extnote Evolutionary cllmge occurs In organlsnrsquot comecnon 0 Natural selection just sorts existing variants in organisms it doesn39t change them 0 Evolutionary change occurs only in populations 0 Acclimatization an adaptation Selection does not cause neck length to increase in individual girafies only in populations 0 Maptatlons occur because a be organisms want or need them A 7 0 Mutation the source of new alleles occurs by chance 0 Evolution is not goal directed or progressive 0 Thereisno suchthingasa higher or lower organism Tapeworms are not lower than their human hosts just adapted to a diifterent environment Organisms sacrifice themselves lor the good of the specles I CORRECTION 0 Individuals with alleles that cause selfsacrificing behavior die and do not produce offspring so these alleles are eliminated from the population Lemmings do not iump cit cliffs into the sea to save the species Evolutionperlectsorgalsms CORRECTION 0 Some traits are nonadaptive 0 Some traits cannot be optimized due to tness tradeoffs 0 Some traits are limited by genetic or historical constraints Finch beaks cannot be both deep and narrow due to genetic constraints 10115 1047 genetics branch of biology that focuses on the inheritance of traits heredity inheritance transmission of traits from parents to offspring trait any characteristic Mendel set out to answer the question what are the basic patterns in the transmission of traits from parents to offspring Two hypotheses 1 Blending inheritance claimed that traits observed in parents blend together to form traits in offspring So traits are intermediate between the parents black sheep white grey sheep 2 Inheritance of acquired characters traits in parents modified through use and passed on to offspring in modified form giraffes stretching necks model organism species used for research because it is practical and conclusions drawn from it can apply to other species Mendel used peas To prevent self pollination he removed male reproductive organs before pollen formed and collected pollen from 1 plant and brushed it onto the other plant Self fertilize flower s pollen falls on the femal organ of the same flower Phenotype show type Pure line consists of individuals that produce offspring identical to them For example they have produced pure line for wrinkled and smooth seeds summer TABLE 141 Vocabulary Used in Mendelian Genetics Term Definition Exenmle or Comment Gene A hereditary factor that influences a particular trait This definition will become more precise in later chapters Allele A particular form of a gene The two alleles in a diploid may be the same or different Genotype A listing of the alleles in an individual In diploids the genotype lists two alleles of each gene in haploids the genotype lists one allele of each gene Phenotype An individual39s observable traits Can be observed at levels from molecules to the whole organism influenced not dictated by the genotype homozygous Having two of the same allele Refers to a particular gene Heterozygous Having two different alleles Refers to a particular gene Dominant allele An allele that produces its phenotype in heterozygous and Dominance does not imply high frequency or high fitness Recessive allele homozygous form An allele that produces its phenotype only in homozygous form Phenotype quotrecedesquot or disappears in heterozygous individuals Pure line Individuals of the same phenotype that when crossed Pureline individuals are homozygous for the gene in always produce offspring with the same phenotype question liybrld Offspring from crosses between homozygous parents with Hybrids are heterozygous Reciprocal cross different genotypes A cross in which the phenotypes of the male and female are reversed compared with a prior cross If reciprocal crosses give identical results the sex of the parent does not influence transmission of the trait Testcross A cross between a homozygous recessive individual and Usually used to determine whether a parent with a an individual with the dominant phenotype but an unknown dominant phenotype is homozygous or heterozygous genotype Xllnlted Referring to a gene located on the X chromosome Xlinked genes and traits show different patterns of inheritance in males and females Yllnlted Referring to a gene located on the Y chromosome In humans Ylinked genes determine malespecific development Autonomel Referring to a gene located on any nonsex chromosome Mendel studied only autosomal genes and traits an autosome or a trait determined by an autosomal gene hybrid offspring from matings between true breading parents that differ in traits Mendel crossed pure line round seeds and pure line wrinkled seeds Got round seeds to wrinkled in a 31 ratio Important because 1 Traits didn t blend together 2 Genetic determinant for wrinkled seeds disappeared Whaaa monohybrid cross mating between parents that carry two different genetic determinates for same trait Recessive trait that appeared to reced or temporarily become latent or hidden Dominant dominate over recessive traits Dominant traits do not necessarily have higher fitness Not necessarily more common for example Huntington s disease In genetics terms dominant and recessive only identify which phenotype is observed in individuals carrying two different genetic determinants for give trait Mendel wanted to test reciprocal cross male with female and female with male Turns out for the 6 traits he tested there were no differences in the traits RESEARCH QUTION Is the Inheritance of seed shape In pee effected by whether the genetic determinant Is In a mete or female gamete HYPOTHESIS The type of gamete does affect the inheritance of seed shape NULL HYPOTHESIS The type of garnets does not affect the inheritance of seed shape EXPERIMENTAL SETUP A cross The reciprocal cross to female organ of Roundseeded parent from wrinkled wrinkledseeded parent receives pollen seeded parent 39 r 5 e a 0 v a Male parent Female parent Female parent Male parent PREDICTION OF quotSEX MATTERSquot HYPOTHESIS Offspring phenotypes will be different in the two crosses J Pollen from round seeded parent PREDICTION OF NULL HYPOTHESIS Offspring phenotypes will be identical in the two crosses 1 Illl lll II lI39llTII ll First cross All progeny have round seeds Reciprocal cross All progeny have round seeds RESULTS CONCLUSION It makes no difference whether the genetic determinant for seed shape comes from the male gamete or from the female gamete J So he came up with particulate inheritance do not blend together or become modified over use Traits maintain their integrity Instead of blending they act as discrete entities Gene indicate hereditary determinant for a trait Alleles different version of the same gene Responsible for the variation in the traits Mendel studied Genotype alleles found in a particular individual Mendel proposed that some alleles are dominant and other recessive Dominance and recessiveness determine which phenotype appears when 2 different alleles are present To get that 31 ratio Mendel reasoned that two members of each gene must segregate separate into different gamete cells during formation of eggs and sperm This is called principle of segregation Homozygous RR or rr Heterozygous Rr Punnett squares yeah 10115 1047 Working with 1 trait at a time allowed Mendel to support that blending inheritance does not occur Infer that each pea plant had 2 copies of each gene and see the principle of segregation Dihybrid cross mating between two heterozygous 1 Independent assortment allele for seed shape and allele for color originally present in each parent would separate from each other and be transmitted independently 9331 n uommam allele for seed shape round Y Dominant allele for seed color yellow 8 N Male gametes av o o quot31 x g ti IIIquotu F2 female parent RrYy G M RY RRYY By C RRYy lt O RrYY W O RrYy V4 Ry Wt r Y RRYy RIYY RRyy RrYy C RrYy ITYY 0 C Rryy rrYy quot43 y RrYy RWY rrYy quotW F2 offspring genotypes 9l6FfY 2 3Ms R yy 2 316ITY I Vlsnyy F 2 offspring phenotypes 91ts 316 316 Vie 2 Dependent assortment Allele for seed shape and color would be transmitted to gametes together 31 F female parent RrYy Female gametes Q RY ry F male rent a o o Rryy g RRYY RrYy 3 l g ry Q RrYy nyy Fyollspring genotypes MI HRYY V2RrYy I Arryy Fyollspring phenotypes VI 2 V4 0 testcross uses a parent that has only recessive to find the unknown genotype of the 2nd parent Useful because the genetic contribution of the homozygous recessive parent is known M phase has 1 division of nucleus and 2 division of cytoplasm Chromatin chromosomes that consist of DNA wrapped around globular histone proteins Each chromatid contains one long DNA double helix and sister chromatids represent exact copies of the same genetic info At start of mitosis each chromosome consists of the 2 sister chromatids that are attached to each other at the centromere INTERPHASE M PHASE Daughter cells a P Ase s PliASE 52 P ASE Parent cell Parent cell Parent cell Sister chromatids 4 unrepiicated chromosomes 4 replicated chromosomes At start of mitosis chromosomes are shown each consisting of two sister replicated chromosomes partially condensed to make chromatids condense them visible During mitosis sister chromatids separate FIGURE 124 An Overview of the Cell Cycle Chromosomes are replicated during 8 phase to produce the G cell TWO daughlef 08quot3 8390 During M phase the replicated chromosomes are partitioned to the two daughter cells Each daughter cell contains med by CV quoti 3is the same complement ol chromosomes as the parent cell Mitosis begins when chromatin condenses to form a compact structure 2 sister chromatids separate to form independent daughter chromosomes One copy of each chromosome goes to each daughter cells Interphase9Prophase9prometaphase9metaphase anaphase9teophase Prophase before phase Spindle apparatus structure that produces mechanical forces that 1 move chromosomes and 2 pull chromatids apart Polar microtubules microtubules that extend from each pole and overlap Centrosome structure that contains the pair of centrioles Prometaphase before middle phase Once chromosomes condense nuclear envelope disintegrates Then microtubules attach to chromosomes at structures called kinetochores The microtubules attached to these structures are called kinetochore microtubules Metaphase middle phase Here chromosomes line up at imaginary plane between two spindle poles called metaphase plate Formation of spindle complete Held partly in place by astral microtubules that extend from MTOCs Anaphase against phase Daughter chromosomes move to opposite poles and pushed farther apart Telophase end phase Nuclear envelope is reformed SUMMARY TABLE 121 Structures Involved In Mitosis Stream De nition Chromosome A structure composed ot a DNA molecule and associated proteins Chromatin The material that makes up eukaryotic chromosomes consists ot a DNA molecule complexed with histone proteins see Chapter 19 Chromatid One strand ot a replicated chromosome with its associated proteins Slater chromatids The two strands of a replicated chromosome When chromosomes are replicated they consist of two sister chromatids The genetic material In sister chromatids is identical When sister chromatids separate during mitosis they become independent chromosomes Centromere The structure that joins sister chromatids Klnetochores The structures on sister chromatids where microtubules attach Microtubuie Any structure that organizes organizing center mlcrotubules see Chapter 7 Centroaoma The microtubule organizing center in animals and some plants Centriolea Cylindrical structures that comprise mlcrotubuies located inside animal centrosomes Chromosomes come in distinct sizes and shapes X and Y chromosomes are sex chromosomes males have XY females XX Autosomes do not have a sex Homologous chromosomes Homologs chromosomes of the same size and shape a pair is called homologous pair They carry the same gene Gene is a section of DNA that influences some hereditary trait Homologous chromosomes may differ called alleles which denote different versions of the same gene For example gene for eye color have different alleles for each eye color Karotype number and types of chromosomes present Majority of organisms have more than one of each type of chromosomes Two versions of each chromosomes are called diploid double form 2 alleles of each gene Haploid contain 1 type of each chromosomes usually bacteria algae fungL Haploid number the letter n tells you the number of distinct type of chromosomes If sex chromosomes are present they re counted as a single type of haploid For humans it is 23 To indicate the number of complete chromosome sets number is before n A cell can be n 2n 3n etc Combo of the number of sets and n is called a cell s ploidy Diploid cells are called 2n because they have 2 Maternal chromosome and paternal chromosome comes from the mom and dad Polyploid have multiple homologous chromosomes per cell Cells replicate each of their chromosomes before undergoing meiosis When chromosome replication is complete each chromosome will have 2 identical sister chromatids which contain copies of DNA present Unreplicated and replicated chromosomes are both considered singe chromosomes even though they consist of 2 sister chromatids Replicated Centromele chromome Sister chromatids H Homologous pair of teplicated chromosomes nuns 133 Each Chromosome Replicates before Undergth Meiosis Term Definition Exrlnple or Comment Chromosome Structure made up of DNA and proteins carries the Eukaryotes have linear chromosomes most bacteria cell s hereditary information genes and archaea have just one circular chromosome 0 Sex chromosome Chromosome associated with an individual39s sex X and Y chromosomes of humans males are XY females 00 Z and W chromosomes of birds and butterflies males are 22 females 2W 0 Autosome A nonsex chromosome Chromosomes 122 in humans Unrepllted chromosome A chromosome that consists of one doublehelical molecule of DNA packaged with proteins Beplcated chomosome A chromosome that has been copied consists of two identical Chromatids each containing one double Centromere helical DNA molecule Sister diromatfds The two Identical chromatrd copies In a replicated i Sister chroma ds chromosome Homologous chromosomes In a diploid organism chromosomes that are similar in You have a chromosome 22 from each parent homoIOQS size shape and gene content I v Homologous chromosomes I Nonsister cluomatids Chromatids belonging to homologous chromosomes A v V 394quot Non sister Chromatids Divalent or bind Homologous replicated chromosomes that are joined together during prophase and metaphase I of Bivalem meiosis flaploid number The number of different types of chromosomes in a Humans have 23 different types of chromosomes cell symbolized n n 23 Diplold number The number of chromosomes present in a diploid cell In humans all cells except gametes are diploid and see below symbolized 2n contain 46 chromosomes 2n 46 Ploidy The number of each type of chromosome present The number of haploid chromosome sets present 0 Haplold Having one of each type of chromosome n Bacteria and archaea are haploid as are many algae plant and animal gametes are haploid o Dhlold Having two of each type of chromosome 2n Most familiar plants and animals are diploid o Polyplold Having more than two of each type of chromosome Seedless bananas are triploid many ferns are cells may be triploid 3n tetraploid 4n hexaploid 6n and so on tetraploid bread wheat is hexaploid 1 In meiosis I homologs in each chromosome pair separate from each other They go to the 2 daughter cells At the end of meiosis 1 each daughter cell has 1 of each type instead of 2 2 During meiosis 1 diploid 2n parent cell produces 2 haploid daughter cells Each chromosome has 2 sister Chromatids 2 During meiosis II the sister Chromatids separate Now they have 1 type of chromosome but no longer replicated P Parent cell is diploid 2n and contains 3 a homologous Q 4 pair of III replicated 5 chromosomes Homologs separate Daughter cells are haploid inland Sister contain 9 chromatids 39 8 separate a S Four daughter cells contain one chromosome each n In animals these cells become gametes FIGURE 134 The Major Events in Meiosis Before undergoing meiosis chromosomes are replicated so there are two chromatids per chromosome Meiosis reduces chromosome number by half In diploid organisms the products of meiosis are haploid Maternal chromosomes are shown in red paternal chromosomes blue Note that in this cell 2n 2 Outcome of meiosis I is to reduce chromosome number In the end they have 4 haploid cells Eventually go on to form egg or sperm cells in a process called gametogenesis gameteorigin When 2 haploid gametes fuse during fertilization full complement of chromosomes is restored The cell that results is a zygote Each diploid individual receives a haploid chromosome set from the mom and dad PROCESS MEiOSlSI Homologous chromosomes separate Bivalent 4 Chromatids from 2 homologous chromosomes Nuclear Replicated Nomsister Spindle envelope chromosomes 3th apparatus O Maternal chromosomes n 3 so 2 6 O Paternal chromosomes In this example o I 4 1 g quotl I quot W I 39 1 Interphase 2 Early prophase I 3 Late prophase I 4 Metaphase I 5 Anaph I Uncondensed Chromosomes condense Chiasmata crossover Migration of bivalents Homologs separate chromosomes spindle apparatus forms points visible nuclear to metaphase plate and begin moving to replicate in nuclear envelope begins envelope broken down is complete opposite poles of parent cell to break down Synapsis Often multiple chiasmata the spindle apparatus pairing of homologous between nonsister chromosomes chromatids FIGURE 13 The Phases of Meiosis The micrographs of each phase are from a species of salamander Phases of Meiosis I Early Prophase I nuclear envelope breaks down chromosomes condense spindle apparatus forms Homologous chromosome pairs come together End result is called synapsis Requires breaking and reconnecting of DNA Structure that forms from synapsis is called bivalent or tetrad Chromatids from different homologs are called non sister Chromatids Late Prophase I Microtubules of spindle apparatus attach to kinetochores Chromatids for X shaped structure called chiasma Usually at least 1 chiasma forms in every pair They mark where the DNA was broken and rejoined between homologs in prophase 1 Reciprocal exchanges between different homologs create chromatids that have both paternal and maternal segments Called crossing over Metaphase I Microtubules move the pair of chromosomes to the metaphase plate in the middle of the spindle apparatus Imaginary place They move independently The alignment on one side or the other of the plate is random Basis of genetics Anaphase and telophase I 0 Sister chromatids of each chromosome remain together 0 In anaphase I chromosomes in each bivalent separate and move to opposite poles In telophase I homologs finish moving to the opposite sides Meiosis I is done when division of cytoplasm occurs and two haploid daughter cells form called cytokinesis Recap random assortment of maternal and paternal chromosome called crossing over and random distribution of homologs during metaphase Meiosis II Prophase II spindle apparatus forms Metaphase II Replicated chromosomes consisting of 2 chromatids lined up at metaphase plate Anaphase II Chromatids separate Move to opposite poles of spindle Telophase II Finish moving nuclear envelope forms around each haploid set to opposite poles of the spindle apparatus spindle apparatus disassembles MEIOSIS 7 Prophase ll Spindle apparatus forms Sister chromatids separate Chromosomes line up at middle of the spindle apparatus metaphase plate Sister chromatids separate begin moving to opposite poles of the spindle apparatus 10 Telophase ll md Cytokinesis Chromosomes move to opposite poles of the spindle apparatus spindle apparatus disassembles Diploid parent cell Diploid parent cell Chromosome replication Chromosome replication Prophase I Chromosomes condense bivalents form Nuclear envelope breaks down Chiasrnata mark sites of crossmg over Prophase Chromosomes condense Nuclear envelope breaks down Metaphase I Homologous pairs align at the metaphase plate Metaphase Individual chromosomes align at the metaphase plate Anaphase and Telophase Sister chromatids separate nuclear envelope reforms Anaphase I and Telophase I Homologous chromosomes separate two haploid cells result Two diploid daughter cells of mitosis that contain the same number of Meiosis ll chromosomes as parent cell Sister chromatids separate nuclear envelope reforms Four haploid daughter cells of meiosis that contain half the number of chromosomes as parent cell FIGURE 138 A Comparison of Mitosis and Meiosis Mitosis produces two daughter cells with chromosomal complements identical to the parent cell Meiosis produces four haploid cells with chromosomal complements unlike one another and unlike the diploid parent cell Svnapsis sand Crossing Over 1 Sister chromatids held together along their length by cohesin proteins 2 Homologs pair 3 Network of proteins form synaptonemal complex which hold the homologs tightly together 4 Synaptonemal complex disassembles Homologs partial separate held together only at chiasmata At chiasma chromatids from each homolog have been physically broken at the same point and attached to each other Corresponding segments of maternal and paternal chromosomes exchanged PROCESS KEY EVENTS 0F PHOPHASE I 8mm Crossover between nonSister chromatlds Break in chromatid Cohesin DNA Chm proteins Kinetochore microtubule Kinetochores Homologs Synaptonemal complex Sister chromatids 1 Condensation 2 Pairing 3 Synapsis bivalent 4 Pattial separation tormation of homologs FIGURE133 A Closer Look at Key Events in Prophase of Meiosis I 10115 1047 Chromosome Theory of Inheritance Gene for seed shape is shown at particular position along a certain chromosome This location is called the locus The physical separation of alleles during anaphase of meiosis I Mendel s principle of segregation Independent assortment if alleles for different genes are located on different chromosomes they assort independently on each other eg Yellow peas not related to smooth seed Chromosome theory of inheritance states that Mendel s rules can be explained by independent alignment and separation of homologous chromosomes at meiosis I Determined by Sutton and Boveri Br parent Recessive allele for seed shape Dominant allele for seed shape Alleles segregate Meiosis II PRINCIPLE OF SEGREGATION Pairs of alleles are separated during meiosis in the formation of gametes FIGUIE 147 Meiosis Explains the Principle of Segregation The two members of a parent s gene pair segregate into different gametes because homologous chromosomes separate during meiosis I Testing chromosome theorv Fruit fly as model organism Wasn t domesticated so had to identify wild type red eyes from mutant type white eyes Mutation heritable change in a gene Did reciprocal crosses white female and red male red female and white male but yielded different results Discovered sex linkage with chromosome theory Half the gametes produced by males would contain an X chromosome and half a Y chromosome Gene for eye color located on X chromosome This is called xlinkage YIinkage for y chromosome Sexlinkage in general Females have 2 copies of this gene because they have 2 X chromosomes 1 from mom and from dad Males only have 1 copy of this eye color gene inherited from the mom Autosomal inheritance Genes on non sex chromosomes Linkage tendency of particular alleles of different genes to be inherited together Seen when genes are on the same chromosome If genes are linked means they re on the same chromosome NOTE Sex linked just means they re on the sex chromosome nothing about location Two linked genes one tor quot eye color one for bod r color on the X chromosome Meiosis II Female gametes J L Two rather than tour types of gametes FIGURE 1412 Linked Genes Are Often Inherited Together If the eyecolor and bodycolor genes were found on different chromosomes then this female would generate four different types of gametes instead of just two types as shown here J EXERCISE List the four genotypes that would be generated if the whiteeye and yellowbody genes were not linked Linked genes are NOT independent In fly experiement most males had XAWy or XAwY Small percentage had XAWY or XAwy These are called recombinant because combo of alleles on their X chromosome was different than the ones present in the mother In females they have 1111 ratio RESEARCH QUESTION Will genes undergo independent assortment if they are on the same chromosome LINKAGE HYPOTHESIS Linked genes wil violate the principle of 39ndependent assortment NULL HYPOTHESIS Linked genes will adhere to the principle of ndependent assortment EXPERIMENTAL SETUP Redeyed Whiteeyed gray lebodied R grglybodied em 7 m e wa x 39539 quot39 39 lequot Y PREDICTION Because th two genes are Xlinked male offspring wil have only one copy of each gene from their mother the two possible male offspr39ng genotypes are XWYY and XW Y PREDICTION OF NULL HYPOTHESIS Four male genotypes are possible xwYY xWN xWY xmvi and will occur with equal frequency RESULTS Male offspring Phenotype Genome Number Four maie I xwa 4292 1 genotypes were observed x FyY rather than MO t but not the equal xwa 86 frequencies Recombmant 139 predicted by genotypes xvva 44 independent assortment CONCLUSION Neither hypothesis is fully supported Independent assortment does not apply to I39nked genes linked genes segregate together except when crossing over and genetic recombina on have occurred To explain phenomenon Morgan concluded that alleles on same chromosome don t always stay together crossing over genetic map diagram showing relative positions of genes along particular chromosome Recombinant chromosomes FIGURE 1414 Genetic Recombination Results from Crossing Over To explain the results in Figure 1413 Morgan proposed that crossing over occurred between the body color y and eye color w genes in a small percentage of meiotic divisions in the female parent The recombinant chromosomes that resulted would produce the recombinant phenotypes observed in the male offspring Linked genes are inherited together unless crossing over takes place Crossing over genetic combinations 10115 1047 Multiple allelism more than 2 alleles of the same gene For example the ABO blood group types have 3 common alleles Increase alleles increase options of genotypes Polymorphic having more than 2 distinct phenotypes Codominance both phenotypes expressed simultaneously eg blood types Incomplete dominance phenotypes inbetween Genes influence more than 1 trait Genes that do this are called pleiotropic Mutation in FBNl cause Marfan syndrome but also tall really long arms and legs weird chest and heart problems Environment affects Dhenotvpes Phenotype is as much a productive of environment as genotype Interactions between genes affect DhenotVDes Different genes work together to control a single trait When gene by gene interactions occur 1 trait is influenced by alleles of 2 different genes discrete traits traits that are very different from each other Many traits are not like this like height eye color etc These would be quantitative traits Also greatly influenced by environment If may genes contribute small amount to qualitative trait then there s normal distribution 60019 50002 400111 30002 20002 Number of ch lid ran 39 00m Cquot r V 90 3900 39 39U 3920 3930 3940 Height an FIGURE 14 Quantitative Traits Have a Normal Distribution A histogram showing the heights of firstgrade schoolchildren in Guatemala in 2001 Jl l 146 Mendel s Rules amp Human Inheritance To understand human traits must analyze human genotypes and phenotypes that already exist Mode of transmission describes trait as autosomnal or sex linked and gives type of dominance of the allele Must construct pedigree or family tree First the assume that it is a simple dominantrecessive relationship the easiest one
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