Genotypic and Phenotypic Ratios Law of Segregation and the Law of Independent Assortment

What were the genotype and phenotype ratios of crossing a homozygous dominant green pea pod colour with a homozygous recessive yellow pea pod colour? Genotypic and Phenotypic Ratios Cross GG x gg? 1 The F 1 genotype ratio for the offspring is 0 GG: 4Gg : 0 gg 1The F 1 phenotype ratio is 4 green: 0 yellow

Genotypic and Phenotypic Ratios Vocabulary: G = dominant allele is green g = recessive allele is yellow GG = homozygous dominant genotype gg = homozygous recessive genotype Now what happens when the heterozygous F1 generation is crossed with itself?

Genotypic and Phenotypic Ratios The genotypic ratio is 1GG : 2Gg : 1ggThe genotypic ratio is 1GG : 2Gg : 1gg The phenotypic ratio is 3 green : 1 yellowThe phenotypic ratio is 3 green : 1 yellow Cross F 1 x F 1

Law of Segregation States that inherited traits are determined by pairs of genes and that each of the genes separates into separate gametes Law of Independent Assortment States that inheritance of one trait does not effect the inheritance of alleles for another trait Mendelian Laws

Dihybrid crosses Dihybrid crosses are made when phenotypes and genotypes with 2 independent alleles are analyzed.Dihybrid crosses are made when phenotypes and genotypes with 2 independent alleles are analyzed. Process is similar to monohybrid crosses.Process is similar to monohybrid crosses. The Punnett square now has 16 boxes to represent the 16 possible genotypes in the offspringThe Punnett square now has 16 boxes to represent the 16 possible genotypes in the offspring

Step 1: Figure out the genotypes of the parents. Step 2: Figure out what kinds of gametes the parents can produce. Step 3: Set up a Punnett Square for your cross. One set of gametes go across the top and the other, down the column. Step 4: Fill in the offspring inside the table. Step 5: Figure out the genotypic ratios for your predicted offspring. Step 5: Figure out the phenotypic ratios for your predicted offspring. Steps for solving dihybrid cross problems

Free earlobes are controlled by the dominant allele E and attached earlobes are controlled by the recessive allele, e. A widow’s peak is controlled by the dominant allele H, while a straight hair line is determined by the recessive allele h. What would be the genotypes and phenotypes of the offspring of a free earlobed, widow’s peak male and a free earlobed, widow’s peak female ? Example 1

What would be the genotypes and phenotypes of the offspring of a heterozygous free earlobed, widow’s peak male and a heterozygous free earlobed, widow’s peak female ? Genotypes: –Male – EeHh –Female – EeHh Step 1: Figuring out the genotypes

Need to use the FOIL rule Genotype: EeHh Possible gametes: EH, Eh, eH, eh Step 2: Figuring out the Gametes

Step 3-4: Do Punnett’s Square EEHHEEHhEeHHEeHh EEHhEEhhEeHhEehh EeHHEeHheeHHeeHh EeHhEehheeHheehh P1 P2 EH Eh eH eh EH EheH eh

Genotypic ratios EEHH 1:16EEHH 1:16 EEHh2:16EEHh2:16 EeHH2:16EeHH2:16 EeHh4:16EeHh4:16 Eehh2:16Eehh2:16 eeHH1:16eeHH1:16 eeHh2:16eeHh2:16 eehh1:16eehh1:16 EEhh1:16EEhh1:16 Step 5: Figuring out the Genotypic ratios

Step 6: Figuring out the Phenotypic ratios Red= free earlobes, widow’s peak,9/16 Black= free earlobes, straight hair line 3/16 Black = free earlobes, straight hair line 3/16 Brown= attached earlobes, widow’s peak 3/16 Brown = attached earlobes, widow’s peak 3/16 Blue= attached earlobes, straight hair line 1/16 Note that there is a 9:3:3:1 phenotypic ratio. 9/16 showing both dominant traits 3/16 & 3/16 showing one of the recessive traits 1/16 showing both recessive traits.