heterozygouswidow’s peakbrown hairheterozygous widow’s peakbrown hair. Steps to execute a dihybrid cross Step 1: Determine the genotypes of the parents given the following information: A male who is heterozygous for widow’s peak and brown hair has an offspring with a female who is heterozygous for widow’s peak and brown hair. Genotypes: Father- WwBb Mother- WwBb

Step 2: Set up the cross using the genotypes determined for each parent.  WwBb x WwBb

Step 3: Set up the Punnett square using the genotypes of each parent. WwBb x WwBb Remember that the genes for each trait consist of two alleles. The alleles for each trait must be separated from each other when the Punnett square is set up. WB WbwB wb WB Wb wB wb

WWBBWWBbWWBbWwBBWwBBWwBbWwBb WWBbWWBbWWbbWwBbWwBbWwbbWwbb WwBBWwBBWwBbWwBbwwBBwwBbwwBb WwBbWwBbWwbbWwbbwwBbwwBbwwbb WBWb wB wb WBWbwBwbWBWbwBwb Possible allelic combinations of sperm Possible allelic combinations of egg

WWBBWWBbWWBbWwBBWwBBWwBbWwBb WWBbWWBbWWbbWwBbWwBbWwbbWwbb WwBBWwBBWwBbWwBbwwBBwwBbwwBb WwBbWwBbWwbbWwbbwwBbwwBbwwbb WBWb wB wb WBWbwBwbWBWbwBwb Step 4: Determine the genotypic ratios

Genotypic ratios  WWBB= 1/16  WWBb= 2/16  WWbb= 1/16  WwBB= 2/16  WwBb= 4/16  Wwbb= 2/16  wwBB=1/16  wwBb= 2/16  wwbb= 1/16  1:2:1:2:4:2:1:2:1

WWBBWWBbWWBbWwBBWwBBWwBbWwBb WWBbWWBbWWbbWwBbWwBbWwbbWwbb WwBBWwBBWwBbWwBbwwBBwwBbwwBb WwBbWwBbWwbbWwbbwwBbwwBbwwbb WBWb wB wb WBWbwBwbWBWbwBwb Step 5: Determine the phenotypic ratios

Phenotypic Ratios  Widow’s peak and Brown hair= 9/16  Widow’s peak and blonde hair= 3/16  No widow’s peak and brown hair= 3/16  No widow’s peak and blonde hair= 1/16  9:3:3:1

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