{"id":28585,"date":"2025-06-20T13:49:53","date_gmt":"2025-06-20T13:49:53","guid":{"rendered":"https:\/\/gaviki.com\/blog\/?p=28585"},"modified":"2025-06-20T13:49:59","modified_gmt":"2025-06-20T13:49:59","slug":"if-two-genes-m-and-n-were-so-close-that-crossing-over-never-occurred-between-them","status":"publish","type":"post","link":"https:\/\/gaviki.com\/blog\/if-two-genes-m-and-n-were-so-close-that-crossing-over-never-occurred-between-them\/","title":{"rendered":"If two genes (M and N) were so close that crossing over never occurred between them"},"content":{"rendered":"\n<p>If two genes (M and N) were so close that crossing over never occurred between them, and we performed a test cross between MMNN and mmnn parents, what is the expected ratio of the F2 offspring?<\/p>\n\n\n\n<p><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-vivid-cyan-blue-color\"><strong>The correct answer and explanation is:<\/strong><\/mark><\/p>\n\n\n\n<p><strong>Correct Answer: 1:1<\/strong><\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Explanation (Approx. 300 Words)<\/strong><\/h3>\n\n\n\n<p>To understand the outcome of this genetic cross, we must examine the scenario step by step using the principles of <strong>Mendelian genetics<\/strong> and <strong>linkage<\/strong>.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Step 1: Understanding the Parental Genotypes<\/strong><\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Parent 1 (MMNN):<\/strong> Homozygous dominant for both genes M and N.<\/li>\n\n\n\n<li><strong>Parent 2 (mmnn):<\/strong> Homozygous recessive for both genes.<\/li>\n<\/ul>\n\n\n\n<p>These two genes are said to be <strong>so close<\/strong> on the same chromosome that <strong>crossing over never occurs<\/strong> between them. This implies <strong>complete linkage<\/strong>, meaning the alleles on the same chromosome are inherited together.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Step 2: F1 Generation (from MMNN \u00d7 mmnn)<\/strong><\/h3>\n\n\n\n<p>Each F1 offspring receives:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>One chromosome with <strong>M and N<\/strong> from MMNN parent.<\/li>\n\n\n\n<li>One chromosome with <strong>m and n<\/strong> from mmnn parent.<\/li>\n<\/ul>\n\n\n\n<p>So, <strong>all F1 offspring have the genotype: Mn\/mn<\/strong> (or more precisely, <strong>[MN]\/[mn]<\/strong> to indicate the allele pairs are linked on their respective chromosomes).<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Step 3: Test Cross<\/strong><\/h3>\n\n\n\n<p>The F1 individual <strong>(MN\/mn)<\/strong> is test-crossed with a <strong>double recessive individual (mn\/mn)<\/strong>.<\/p>\n\n\n\n<p>The possible <strong>gametes<\/strong> from each parent are:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>F1 can produce <strong>only MN<\/strong> and <strong>mn<\/strong> gametes (since no crossing over occurs).<\/li>\n\n\n\n<li>The test cross parent can produce only <strong>mn<\/strong> gametes.<\/li>\n<\/ul>\n\n\n\n<p>So, the offspring genotypes will be:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li><strong>MN\/mn<\/strong> \u2013 receives MN from F1 and mn from tester.<\/li>\n\n\n\n<li><strong>mn\/mn<\/strong> \u2013 receives mn from both parents.<\/li>\n<\/ol>\n\n\n\n<p>Since both types of gametes are produced equally (50% MN, 50% mn), the resulting <strong>offspring ratio<\/strong> is:<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p><strong>1 MN\/mn : 1 mn\/mn<\/strong>, or <strong>1:1 phenotypic ratio<\/strong><\/p>\n<\/blockquote>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Conclusion<\/strong><\/h3>\n\n\n\n<p>When two genes are completely linked and a test cross is performed, <strong>no recombinants<\/strong> appear, and offspring only reflect the <strong>parental types<\/strong>. Therefore, the expected <strong>F2 ratio is 1:1<\/strong>.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>If two genes (M and N) were so close that crossing over never occurred between them, and we performed a test cross between MMNN and mmnn parents, what is the expected ratio of the F2 offspring? The correct answer and explanation is: Correct Answer: 1:1 Explanation (Approx. 300 Words) To understand the outcome of this [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-28585","post","type-post","status-publish","format-standard","hentry","category-quiz-questions"],"_links":{"self":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/28585","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/comments?post=28585"}],"version-history":[{"count":1,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/28585\/revisions"}],"predecessor-version":[{"id":28587,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/posts\/28585\/revisions\/28587"}],"wp:attachment":[{"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/media?parent=28585"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/categories?post=28585"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/gaviki.com\/blog\/wp-json\/wp\/v2\/tags?post=28585"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}