Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Predicting Results of Crosses Punnett square Grid to predict the outcome of genetic crosses Place the alleles of one parent across the top and the alleles of the other parent on the left side Fill each of the 4 inside boxes with 1 allele from on top and 1 allele from the left.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Box 1 : Rr Box 2 : Rr Box 3 : rr Box 4 : rr

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Monohybrid Cross A cross in which one characteristic (one specific trait) is tracked

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Punnett Square with Cross

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Monohybrid Cross of Heterozygous Plants

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Predicting Results of Monohybrid Crosses Testcross an individual of unknown genotype is crossed with a homozygous recessive individual determines if unknown individual is homozygous dominant or heterozygous

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Testcross

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Predicting Results of Monohybrid Crosses Complete Dominance occurs when heterozygous individuals and dominant homozygous individuals are indistinguishable in phenotype (they look the same)

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Predicting Results of Monohybrid Crosses Incomplete Dominance occurs when two or more alleles influence the phenotype results in a phenotype intermediate between the dominant trait and the recessive trait Example: RR = a red flower rr = a white flower Rr = a pink flower

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Predicting Results of Monohybrid Crosses Codominance occurs when both alleles for a gene are expressed in a heterozygous offspring Example BB = black feathers WW = white feathers BW = feathers that are black and white

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu BBWW BW

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Dihybrid Cross A cross in which two characteristics (two specific traits) are tracked Use a Punnett Square with 16 boxes Outside alleles, Inside alleles, First alleles, Last alleles Example: RrYy (two traits are shape and color – R is for round and Y is for yellow) Outside = Ry Inside = rY First = RY Last = ry

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Dihybrid Crosses

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Mendel’s Results The Law of Independent Assortment –states that factors for individual characteristics are distributed to gametes independent of one another –observed only for genes that are located on separate chromosomes or are far apart on the same chromosome –Example: Dihybrid Cross of Heterozygous parents results in 9:3:3:1 ratio.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Probability the likelihood that a specific event will occur. may be expressed as a decimal, a percentage, or a fraction

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Calculating Probability