Why Mendel Succeeded. Why Mendel Succeeded. Mendel chose his subject carefully. Mendel chose his subject carefully. Mendel chose his subject carefully

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Why Mendel Succeeded I was no unil he mid-nineeenh cenury ha Gregor Mendel, an Ausrian monk, carried ou imporan sudies of herediy he passing on of characerisics from parens o offspring.

A complee explanaion requires he careful sudy of geneics he branch of biology ha sudies herediy. Mendel chose o use he garden pea in his experimens for several reasons.

1 Why Mendel Succeeded I was no unil he mid-nineeenh cenury ha Gregor Mendel, an Ausrian monk, carried ou imporan sudies of herediy he passing on of characerisics from parens o offspring. Characerisics ha are inheried are called rais. Why Mendel Succeeded Mendel was he firs person o succeed in predicing how rais are ransferred from one generaion o he nex. A complee explanaion requires he careful sudy of geneics he branch of biology ha sudies herediy. Mendel chose o use he garden pea in his experimens for several reasons. Garden pea plans reproduce sexually, which means ha hey produce male and female sex cells, called gamees. he male gamee forms in he pollen grain, which is produced in he male reproducive organ. he female gamee forms in he female reproducive organ. In a process called ferilizaion, he male gamee unies wih he female gamee. he resuling ferilized cell, called a zygoe (ZI goh), hen develops ino a seed. he ransfer of pollen grains from a male reproducive organ o a female reproducive organ in a plan is called pollinaion. Remove male pars When he waned o breed, or cross, one plan wih anoher, Mendel opened he peals of a flower and removed he male organs. 1

2 He hen dused he female organ wih pollen from he plan he wished o cross i wih. Pollen grains his process is called cross-pollinaion. By using his echnique, Mendel could be sure of he parens in his cross. ransfer pollen Female par Male pars Cross-pollinaion Mendel was a careful researcher He sudied only one rai a a ime o conrol variables, and he analyzed his daa mahemaically. he all pea plans he worked wih were from populaions of plans ha had been all for many generaions and had always produced all offspring. Mendel was a careful researcher Such plans are said o be rue breeding for allness. Likewise, he shor plans he worked wih were rue breeding for shorness. Mendel s Monohybrid Crosses A hybrid is he offspring of parens ha have differen forms of a rai, such as all and shor heigh. Mendel s firs experimens are called monohybrid crosses because mono means one and he wo paren plans differed from each oher by a single rai heigh. he firs generaion Mendel seleced a six-foo-all pea plan ha came from a populaion of pea plans, all of which were over six fee all. He cross-pollinaed his all pea plan wih pollen from a shor pea plan. All of he offspring grew o be as all as he aller paren. 2

Mendel allowed he all plans in his firs generaion o self-pollinae. Afer he seeds formed, he planed hem and couned more han 1000 plans in his second generaion.

In he second generaion, all and shor plans occurred in a raio of abou hree all plans o one shor plan.

3 Mendel allowed he all plans in his firs generaion o self-pollinae. Afer he seeds formed, he planed hem and couned more han 1000 plans in his second generaion. hree-fourhs of he plans were as all as he all plans in he paren and firs generaions. One-fourh of he offspring were as shor as he shor plans in he paren generaion. In he second generaion, all and shor plans occurred in a raio of abou hree all plans o one shor plan. P 1 Shor pea plan F 2 All all pea plans 3 all: 1 shor all pea plan he original parens, he rue-breeding plans, are known as he P 1 generaion. he offspring of he paren plans are known as he generaion. When you cross wo plans wih each oher, heir offspring are he F 2 generaion. Dominan rai Recessive rai Seed Seed shape color Flower color round yellow purple Flower posiion Pod color Pod shape Plan heigh axial (side) green inflaed all wrinkled green whie erminal (ips) yellow consriced shor In every case, he found ha one rai of a pair seemed o disappear in he generaion, only o reappear unchanged in one-fourh of he F 2 plans. he rule of uni facors Mendel concluded ha each organism has wo facors ha conrol each of is rais. We now know ha hese facors are genes and ha hey are locaed on chromosomes. Genes exis in alernaive forms. We call hese differen gene forms alleles. 3

he rule of uni facors An organism s wo alleles are locaed on differen copies of a chromosome one inheried from he female paren and one from he male paren.

4 he rule of uni facors An organism s wo alleles are locaed on differen copies of a chromosome one inheried from he female paren and one from he male paren. he rule of dominance Mendel called he observed rai dominan and he rai ha disappeared recessive. Mendel concluded ha he allele for all plans is dominan o he allele for shor plans. he rule of dominance he rule of dominance When recording he resuls of crosses, i is cusomary o use he same leer for differen alleles of he same gene. all plan Shor plan An uppercase leer is used for he dominan allele and a lowercase leer for he recessive allele. all plan Shor plan All all plans he dominan allele is always wrien firs. All all plans he law of segregaion he law of segregaion saes ha every individual has wo alleles of each gene and when gamees are produced, each gamee receives one of hese alleles. During ferilizaion, hese gamees randomly pair o produce four combinaions of alleles. F 2 Phenoypes and Genoypes Law of segregaion cross wo organisms can look alike bu have differen all plan all plan underlying allele combinaions. all all all Shor 3 1 4

Phenoypes and Genoypes he way an organism looks and behaves is called is phenoype. he allele combinaion an organism conains is known as is genoype.

5 Phenoypes and Genoypes he way an organism looks and behaves is called is phenoype. he allele combinaion an organism conains is known as is genoype. An organism s genoype can always be known by is phenoype. Phenoypes and Genoypes An organism is homozygous for a rai if is wo alleles for he rai are he same. he rue-breeding all plan ha had wo alleles for allness () would be homozygous for he rai of heigh. Phenoypes and Genoypes An organism is heerozygous for a rai if is wo alleles for he rai differ from each oher. herefore, he all plan ha had one allele for allness and one allele for shorness () is heerozygous for he rai of heigh. Mendel s Dihybrid Crosses Mendel performed anoher se of crosses in which he used peas ha differed from each oher in wo rais raher han only one. Such a cross involving wo differen rais is called a dihybrid cross. he firs generaion Mendel ook rue-breeding pea plans ha had round yellow seeds (RRYY) and crossed hem wih rue-breeding pea plans ha had wrinkled green seeds (rryy). He already knew he round-seeded rai was dominan o he wrinkled-seeded rai. He also knew ha yellow was dominan o green. P 1 F 2 he firs generaion Dihybrid Cross Round yellow round yellow x wrinkled green Wrinkled green All round yellow Round yellow Round green Wrinkled yellow Wrinkled green 5

6 Mendel hen le he plans pollinae hemselves. He found some plans ha produced round yellow seeds and ohers ha produced wrinkled green seeds. He found hey appeared in a definie raio of phenoypes 9 round yellow: 3 round green: 3 wrinkled yellow: 1 wrinkled green. He also found some plans wih round green seeds and ohers wih wrinkled yellow seeds. he law of independen assormen Mendel s second law saes ha genes for differen rais for example, seed shape and seed color are inheried independenly of each oher. his conclusion is known as he law of independen assormen. Punne Squares In 1905, Reginald Punne, an English biologis, devised a shorhand way of finding he expeced proporions of possible genoypes in he offspring of a cross. his mehod is called a Punne square. Punne Squares If you know he genoypes of he parens, you can use a Punne square o predic he possible genoypes of heir offspring. Monohybrid crosses Heerozygous all paren Heerozygous all paren A Punne square for his cross is wo boxes all and wo boxes wide because each paren can produce wo kinds of gamees for his rai. 6

Gamees from RrYy paren Gamees from RrYy paren Monohybrid crosses Heerozygous all paren Heerozygous all paren he wo kinds of gamees from one paren are lised on op of he square, and he wo kinds of

7 Gamees from RrYy paren Gamees from RrYy paren Monohybrid crosses Heerozygous all paren Heerozygous all paren he wo kinds of gamees from one paren are lised on op of he square, and he wo kinds of gamees from he oher paren are lised on he lef side. Monohybrid crosses I doesn maer which se of gamees is on op and which is on he side. Each box is filled in wih he gamees above and o he lef side of ha box. You can see ha each box hen conains wo alleles one possible genoype. Afer he genoypes have been deermined, you can deermine he phenoypes. RY Ry ry ry Punne Square of Dihybrid Cross Gamees from RrYy paren RY Ry ry ry RRYY RRYy RrYY RrYy RRYy RRYy RrYy Rryy RrYY RrYy rryy rryy RrYy Rryy rryy rryy Dihybrid crosses A Punne square for a dihybrid cross will need o be four boxes on each side for a oal of 16 boxes. RY Ry ry ry Punne Square of Dihybrid Cross Gamees from RrYy paren RY Ry ry ry RRYY RRYy RrYY RrYy RRYy RRYy RrYy Rryy RrYY RrYy rryy rryy RrYy Rryy rryy rryy Dihybrid crosses cross: RrYy RrYy round yellow round green wrinkled yellow wrinkled green Probabiliy In realiy you don ge he exac raio of resuls shown in he square. ha s because, in some ways, geneics is like flipping a coin i follows he rules of chance. he probabiliy or chance ha an even will occur can be deermined by dividing he number of desired oucomes by he oal number of possible oucomes. Probabiliy A Punne square can be used o deermine he probabiliy of geing a pea plan ha produces round seeds when wo plans ha are heerozygous (Rr) are crossed. 7

8 Probabiliy Probabiliy R r RR Rr R Rr rr r he Punne square shows hree plans wih round seeds ou of four oal plans, so he probabiliy is 3 / 4. R r RR Rr R Rr rr r I is imporan o remember ha he resuls prediced by probabiliy are more likely o be seen when here is a large number of offspring. Punne Square Click image o view movie. 8

Trait: characteristics to be passed from parent to offspring. Passed on from parent to offspring by the blood, in bloodlines.

Inheritance Theory Prior to Mendel Trait: characteristics to be passed from parent to offspring Passed on from parent to offspring by the blood, in bloodlines. Gregor Mendel Father of Genetics Mendel s