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10.4 Genes of Different Chromosomes Are Inherited Independently A. Dihybrid Crosses Track the Inheritance of Two Genes at Once P generation true-breeding.

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Presentation on theme: "10.4 Genes of Different Chromosomes Are Inherited Independently A. Dihybrid Crosses Track the Inheritance of Two Genes at Once P generation true-breeding."— Presentation transcript:

1 10.4 Genes of Different Chromosomes Are Inherited Independently A. Dihybrid Crosses Track the Inheritance of Two Genes at Once P generation true-breeding for 2 traits F 1 crossed to yield F 2 Four phenotypes in ratio 9:3:3:1 – All possible combinations found rryyRRYY Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2 RY RY ry ry Male gametes F 1 generation rryy Female gametes RRYY Yy Rr Yy RrYyRr Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

3 YY RYRyrYry RY Ry rY ry F 2 generation Female gametes Male gametes Phenotypic ratio 9:3:3:1 Smooth, yellow Smooth, green Wrinkled, yellow Wrinkled, green RR Rr Yy RrYYRrYyRR YyRRyyRrYyyyRr YY RrYy rrYYrrYy RryyrrYyrryy YyRr

4 10.4 Genes of Different Chromosomes Are Inherited Independently B. Meiosis Explains Mendel’s Law of Independent Assortment During gamete formation, segregation of alleles for one gene does not influence alleles for another gene Provided genes are on different chromosomes

5 Figure 10.9 Mendel’s Law of Independent Assortment. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Y Y Y Y Y Y Y Y R R R R R R R R r r r r r r r r y y y y y y y Y Y R R r r y y y R r R r Y R Y y r y y R y Y r Y Diploid cell Alternative 1 Alternative 2 Metaphase I MEIOSIS I MEIOSIS II Haploid gametes Metaphase II

6 10.4 Genes of Different Chromosomes Are Inherited Independently B. Meiosis Explains Mendel’s Law of Independent Assortment Punnet squares for more than 2 genes cumbersome Product rule – Chance that two independent events will both occur equals the product of the individual chances that each event will occur

7 Figure The Product Rule. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. R Rr r ×× Y Yy y T Tt t RRRr rr 1/2 Rr Tt ttTt TTYy yyYy YY 1/2 Tt Probability that off spring is Rr Yy Tt = 1/8 1/2 Yy

8 10.4 Mastering Concepts Explain how meiosis contributes to independent assortment of alleles.

9 10.5 Genes on the Same Chromosome Many Be Inherited Together A. Genes on the Same Chromosome Are Linked Unlike genes on different chromosomes, they do not assort independently during meiosis First noticed in early 1900s

10 Figure Gene Linkage Changes the Results of a Dihybrid Cross. Male gametes 3 1 P L p l P L p l × b. Pp Ll self-cross, genes linked FemaleMale Crimson flowers, long pollen Crimson flowers, long pollen Crimson flowers, long pollen Red flowers, round pollen p l P L Pp Llpp ll PP LL Pp Ll P L p l Female gametes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Male gametes PpPp LlLl × a. Pp Ll self-cross, genes not linked Male Crimson flowers, long pollen Crimson flowers, Long pollen Female P LP lP LP l Red flowers, round pollen Red flowers, long pollen Crimson flowers, round pollen Crimson flowers, long pollen p l p L P l P L Pp Ll Pp LL PP Ll PP LL Pp ll Pp Ll PP ll PP Ll pp Ll pp LL Pp LL Pp Ll pp ll pp Ll Pp ll Pp Ll Female gametes

11 10.5 Genes on the Same Chromosome May Be Inherited Together A. Genes on the Same Chromosome Are Linked Thomas Hunt Morgan Drosophila melanogaster – fruit fly Linkage groups are on the same chromosome

12 10.5 Genes on the Same Chromosome Many Be Inherited Together A. Genes on the Same Chromosome Are Linked Sometimes did see combinations not found in parents – Due to crossing over Parental chromatid- no crossing over Recombinant chromatid

13 Figure Crossing Over. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. p p l l L P L p l P l P P L p P LL P p l p L Homologous chromosomes cross over in prophase I MEIOSIS I MEIOSIS II Homologs part Recombinant Gametes Parental

14 10.5 Genes on the Same Chromosome Many Be Inherited Together B. Studies of Linked Genes Have Yielded Chromosome Maps Some crosses had a higher proportion of recombinant offspring Alfred Sturtevant, Morgan’s undergraduate assistant, proposed linkage maps Genetic markers used now

15 Figure Breaking Linkage. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A Genes A and B are far apart; crossing over is more likely to separate these alleles. Genes B and C are close together; crossing over is less likely to separate these alleles. B C a b c ywvmr a. b.

16 Clicker Question What is the order of genes on a chromosome if g and m are 4 units apart, k and h are 6 units apart and m and h are 2 units apart? A.ghmk B.gmkh C.hkmg


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