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GENETIKA DASAR

GENETIKA DASAR. POKOK BAHASAN 3 Pautan Gen Pindah Silang Pemetaan Kromosom. HUKUM MENDEL I : “ The Law of Segregation of Allelic Genes” atau Hukum Pemisahan Bebas HUKUM MENDEL II : “ The law of Independent Assortment of Genes” a tau Hukum Pengelompokkan Gen secara Bebas.

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GENETIKA DASAR

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  1. GENETIKA DASAR

  2. POKOK BAHASAN 3 • Pautan Gen • Pindah Silang • Pemetaan Kromosom

  3. HUKUM MENDEL I : “The Law of Segregation of Allelic Genes” atau Hukum Pemisahan Bebas HUKUM MENDEL II : “The law of Independent Assortment of Genes” atau Hukum Pengelompokkan Gen secara Bebas

  4. Pautan Gen (Linkage gene) • Deviation From Independent Assortment Ratios • Pautan/Berangkai/Linkage gene : Peristiwa beberapa gen bukan alel terdapat pada satu kromosom yang sama

  5. Pautan/Berangkai/Linkage gene : • - RANGKAI/PAUTAN SEMPURNA •  Gen-gen yang terangkailetaknya amat • berdekatan, maka selama meiosis gen-gen itu • tidak mengalami perubahan letak. Sehingga • gen-gen itu bersama-sama menuju ke gamet • - RANGKAI/PAUTAN TIDAK SEMPURNA •  Gen-gen yang terangkai pada satu kromosom • letaknya tidak berdekatan satu sama lainnya, • sehingga gen-gen itu dapat mengalami • perubahan letak yang disebabkan karena ada • penukaran segmen dari kromatid-kromatid pada • sepasang kromosom homolog

  6. Bateson and Punnett crossed a purple, long snapdragon with one that was red and round • The F1 snapdragon was selfed • Observed deviation from a 9:3:3:1 ratio

  7. Because the parental genes seemed to assort together more then they were expected, Bateson and Punnett said they were coupled

  8. Creating a Linkage Hypothesis • Morgan used Drosophila as an experimental organism to prove linkage

  9. Morgan crossed Drosophila red eye, normal wing (pr+pr+ vg+vg+) and purple eye vestigal wing (prpr vgvg) • The F1 flies were test crossed • Observed deviation from the 1:1:1:1 ratio

  10. Coupling Cross Chi-Square Test

  11. Proof That Linked Genes Exist • Morgan hypothesized that alleles of two genes close together may not assort indepentently into gametes • Parental arrangements may appear together in gametes

  12. Morgan performed a second cross to prove the hypothesis • He crossed red eye, vestigal wing (pr+pr+ vgvg) and purple eye, normal wing flies (prpr vg+vg+) • The F1 flies were testcrossed

  13. Parent : pr+pr+ vgvg x prpr vg+vg+ (red eye, vestigal wing) (purple eye, normal wing) F1 : pr+pr vgvg+ x testcross

  14. Repulsion Cross Chi-Square Test

  15. Terms Used in Linkage Analysis Coupling – the F1 configuration where both dominant alleles reside on the same chromosome; also called CIS  gen-gen dominan terangkai pada satu kromosom, sedangkan alel-alel resesifnya terangkai pada kromosom homolognya Penulisannya : AB/ab atau AB ab Repulsion - the F1 configuration where one dominant and one recessive allele reside on the same chromosome; also calledTRANS  Gen dominan terangkai dengan alel resesifnya pada satu kromosom, sedangkan alel-alel resesifnya terangkai pada kromosom homolognya Penulisannya : Ab/aB atau Ab aB

  16. Coupling – the F1 configuration where both dominant alleles reside on the same chromosome; also called CIS The Development Of The Coupling Chromosome

  17. Repulsion - the F1 configuration where one dominant and one recessive allele reside on the same chromosome; also calledTRANS The Development Of The Repulsion Chromosome

  18. Recombination Occurs Less Frequently Between Closely Linked Genes • Physical crossing over is a normal meiosis event • Crossing-over  pertukaran segmen dari kromatid-kromatid bukan non-sister kromatid dari sepasang kromosom homolog • The term used to describe crossing over is recombination • Recombination can occur between any two genes on a chromosome • The farther apart the two genes the more crossing over

  19. Cross over

  20. A B A B meiosis I a b a b A B A B gamet parental A b gamet rekombinasi a B gamet rekombinasi a b a b gamet parental

  21. Faktor-faktor yang mempengaruhi pindah silang • TEMPERATUR, temperatur kurang atau melebiji temperatur biasa dapat memperbesar kemungkinan pindah silang • UMUR, makin tua suatu individu makin kurang mengalami pindah silang • ZAT KIMIA tertentu dapat memperbesar kemungkinan terjadinya pindah silang • PENYINARAN SINAR X dapat memperbesar kemungkinan pindah silang • JARAK ANTAR GEN YANG TERANGKAI, makin jauh letak satu gen dengan gen lainnya, makin besar kemungkinan pindah silang • JENIS KELAMIN, umumnya jantan atau betina dapat mengalami pindah silang. Namun pada ulat sutera betina dan Drosophila jantan tidak pernah terjadi pindah silang

  22. Determining Linkage Distances • By definition, one map unit is equal to one percent recombinant gametesor phenotypes • In honor of Morgan, one map unit is also called one centimorgan (cM) 1 mu = 1% = 1 cM

  23. To determine the distance between two genes,divide the number of recombinant gametes by the total number of gametes Formula : Number of recombinants x 100% Total Number

  24. Coupling Data prvg distance = ((151 +154)/2839)*100% = 10.7 m.u = 10.7 cM

  25. Repulsion Data prvgdistance = ((157 + 146)/2335)*100% = 13.0 cM

  26. Jarak Gen Coupling : pr vg 10,7 cM Repulsion : pr vg 13,0 cM

  27. Remember these are estimates; the differences between the two estimates reflect random deviation • Neither estimate is incorrect; repeated experimentation would give a more accurate estimate

  28. Deriving Linkage Distance And Gene Order From Three-Point Crosses • Analyzing three genes allows us to determine gene order as well as linkage distance • Need to create a F1 and follow deviation from a 1:1:1:1:1:1:1:1 ratio • What are the expected gametes when three linked genes are considered?

  29. Analyzing Three-Point Test Cross Data

  30. What are the parental genotypes? What is the gene order? What are the linkage distances?

  31. What are the parental genotypes? • The genotypes most frequently found are the parental genotypes • ABC and abc are the parental genotypes

  32. What is the gene order? * Menentukan susunan gen dengan memperhatikan Tipe Parental dan Tipe DCO • Pada Tipe Parental di-DCO-kan dan dibandingkan dengan hasil DCO pengamatan • The double crossover moves a non-parental allele of the central gene between two parental alleles • Gene Cis between genes Aand B(gene order = A C B)

  33. Analyzing Three-Point Test Cross Data

  34. What are the linkage distances? • Linkage distance equals the sum of the appropriate single cross plus all double crosses divided by total number of gametes Formula : • Jarak = SCO + DCO x 100% Jumlah Total

  35. *JarakA - C = ((81+85+5+8)/1000)*100 = 17.9 cM *JarakC - B = ((27+30+5+8)/1000)*100 = 7.0 cM A C B 17,9 cM 7,0 cM

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