{"id":1432,"date":"2020-08-06T23:54:27","date_gmt":"2020-08-06T23:54:27","guid":{"rendered":"https:\/\/meddists.com\/learn\/pre-clinical\/medical-genetics\/transmission-genetics\/mendelian-genetics-the-dihybrid-cross-and-mendels-second-law\/"},"modified":"2021-01-31T23:17:26","modified_gmt":"2021-01-31T22:17:26","slug":"mendelian-genetics-the-dihybrid-cross-and-mendels-second-law","status":"publish","type":"page","link":"https:\/\/meddists.com\/learn\/pre-clinical\/medical-genetics\/transmission-genetics\/mendelian-genetics-the-dihybrid-cross-and-mendels-second-law\/","title":{"rendered":"Mendelian Genetics: The dihybrid cross and Mendel’s second law"},"content":{"rendered":"\n

Dihybrid cross<\/h4>\n<\/span>\n\n\n

This is when the parents differ in two traits.<\/div><\/p>\n\n\n\n

When Mendel made his dihybrid cross<\/strong>, he crossed plants with Round and Yellow seeds with those with Wrinkled and Green seeds.<\/p>\n\n\n\n

  • The round was the dominant seed shape and the yellow was the dominant seed colour. We will make the dihybrid cross below;<\/li><\/ul>\n\n\n\n

    Parental Phenotypes:            Round and Yellow\u00d7Green and Wrinkled<\/p>\n\n\n\n

    Parental Genotypes:              RRYY\u00d7rryy<\/p>\n\n\n\n

    Parental Gametes:                 (RY)(RY)\u00d7(ry)(ry)<\/p>\n\n\n\n

     <\/td>(RY)<\/td>(RY)<\/td><\/tr>
    (ry)<\/td>RrYy<\/td>RrYy<\/td><\/tr>
    (ry)<\/td>RrYy<\/td>RrYy<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    F1 Genotype:       RrYy<\/p>\n\n\n\n

    F1 phenotype:    Round and Yellow<\/p>\n\n\n\n

    As seen above, in gamete formation, each gamete gets a copy of the gene for seed shape(R or r) and a copy of the gene for seed colour (Y or y). This is in accordance with the Law of Segregation<\/strong> that was discussed in the previous lesson.<\/p>\n\n\n\n

    Now we will cross the F1 organisms with each other<\/p>\n\n\n\n

    Parental(F1) genotype:         Round and Yellow\u00d7Round and Yellow<\/p>\n\n\n\n

    F1 genotype:                            RrYy\u00d7RrYy<\/p>\n\n\n\n

    F1 gametes:                              (RY)(Ry)(rY)(ry) \u00d7 (RY)(Ry)(rY)(ry)<\/p>\n\n\n\n

     <\/td>(RY)<\/td>(Ry)<\/td>(rY)<\/td>(ry)<\/td><\/tr>
    (RY)<\/td>RRYY<\/td>RRYy<\/td>RrYY<\/td>RrYy<\/td><\/tr>
    (Ry)<\/td>RRYy<\/td>RRyy<\/td>RrYy<\/td>Rryy<\/td><\/tr>
    (rY)<\/td>RrYY<\/td>RrYy<\/td>rrYY<\/td>rrYy<\/td><\/tr>
    (ry)<\/td>RrYy<\/td>Rryy<\/td>rrYy<\/td>rryy<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

    F2 phenotypes: Round and Yellow\u00d7Round and Green\u00d7Wrinkled and Yellow\u00d7Wrinkled and Green<\/p>\n\n\n\n

    Phenotypic ratio: 9:3:3:1<\/p>\n\n\n\n

    If you are wondering why the first cross produced 2 gametes per parent but the second produced four gametes per parent, wonder no more :). The first cross produces four as well, you can write only two because all the four will be the same; either all RY (for the first parent) or all ry (for the second parent). But in the second cross, each parent produces four unique and different gametes so this is why we write them all.<\/p>\n\n\n\n

    This ‘9:3:3:1’ ratio is characteristic for dihybrid crosses for genes that follow Mendelian Genetics. The ‘9:3:3:1’ ratio also shows that the genes are not linked( details on linked genes are discussed in detail in the Transmission Genetics: Linked and Recombinant Genes course)<\/em> but are inherited independently of each other. This brings us to Mendel’s second law<\/strong> or The Law of Independent Assortment.<\/strong><\/p>\n\n\n<\/span>\n

    Law of Independent Assortment<\/h4>\n<\/span>\n\n\n

    It that states that genes are inherited independently of each other i.e the different alleles of the different genes will be passed down to the offspring independently from each other and there is no interaction between the two genes.<\/p>\n\n\n\n

    • This is the reason why the ‘9:3:3:1’ ratio is just two ‘3:1’ ratios that are randomly combined because the two traits act separately and are inherited independently as if it was a monohybrid cross<\/strong>.<\/li>
    • An exception to the Law of Independent Assortment are linked genes ( details on linked genes are discussed in detail in the Transmission Genetics: Linked and Recombinant Genes course)<\/em><\/li><\/ul>\n<\/span>

      Dihybrid cross<\/h4>

      Law of Independent Assortment<\/h4><\/div>","protected":false},"excerpt":{"rendered":"

      Dihybrid cross When Mendel made his dihybrid cross, he crossed plants with Round and Yellow seeds with those with Wrinkled and Green seeds. The round was the dominant seed shape and the yellow was the dominant seed colour. We will make the dihybrid cross below; Parental Phenotypes:            Round and Yellow\u00d7Green […]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":1346,"menu_order":1,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-1432","page","type-page","status-publish","hentry"],"yoast_head":"\nMendelian Genetics: The dihybrid cross and Mendel's second law – Meddists<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/meddists.com\/learn\/pre-clinical\/medical-genetics\/transmission-genetics\/mendelian-genetics-the-dihybrid-cross-and-mendels-second-law\/\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"3 minutes\" \/>\n<script type=\"application\/ld+json\" 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