Turner College & Career High School  2017 Dihybrid Crosses Turner College & Career High School  2017

Law of Independent Assortment The inheritance patterns of one trait will not affect the inheritance patterns of another trait. Independent assortment occurs during meiosis. The alleles for a trait separate when gametes are formed. These allele pairs are then randomly united at fertilization. For a single human gamete, the possible combinations is an astounding … 223 or 8,388,608 combinations.

Review of Monohybrid Crosses Remember, monohybrid crosses involve only ONE trait Practice… In fruit flies, red eyes are dominant to white eyes. Cross a white-eyed fly with a homozygous dominant red-eyed fly. Cross two heterozygous red-eyed flies. Draw a Punnett square for each cross, and determine the genotypic and phenotypic ratios.

Dihybrid Cross Dihybrid Cross: a cross that shows the possible offspring for two traits. In this example, we will cross a heterozygous guinea pig with another heterozygous guinea pig. Their phenotypes will be: black, rough x black, rough Their genotypes will be: BbRr x BbRr Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

BbRr BR Br bR br Dihybrid Cross First, you must find ALL possible gametes that can be made from each parent. Use the FOIL method … Remember, each gamete must have one B and one R. BbRr BR Br bR br

Dihybrid Cross BbRr x BbRr Next, arrange all possible gametes for one parent along the top of your Punnett Square, and all possible gametes for the other parent down the side of your Punnett Square… BbRr x BbRr BR Br bR br Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

Dihybrid Cross BbRr x BbRr Then, find the possible genotypes of the offspring. BbRr x BbRr BR Br bR br BBRR BBRr BbRR BbRr BBrr Bbrr bbRR bbRr bbrr BR Br bR br Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

Dihybrid Cross BbRr x BbRr How many of the offspring would have a black, rough coat? What is the genotype? BBRR, BbRr, BBRr, BbRR 9 How many of the offspring would have a black, smooth coat? BBrr, Bbrr 3 BbRr x BbRr BR Br bR br BBRR BBRr BbRR BbRr BBrr Bbrr bbRR bbRr bbrr BR Br bR br BBRR BBRr BbRR BbRr BBrr Bbrr bbRR bbRr bbrr BR Br bR br BBRR BBRr BbRR BbRr BBrr Bbrr bbRR bbRr bbrr Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

Dihybrid Cross BbRr x BbRr How many of the offspring would have a white, rough coat? What is the genotype? bbRR, bbRr 3 How many of the offspring would have a white, smooth coat? bbrr 1 BbRr x BbRr BR Br bR br BBRR BBRr BbRR BbRr BBrr Bbrr bbRR bbRr bbrr BR Br bR br BBRR BBRr BbRR BbRr BBrr Bbrr bbRR bbRr bbrr BR Br bR br BBRR BBRr BbRR BbRr BBrr Bbrr bbRR bbRr bbrr Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

9:3:3:1 Dihybrid Cross BbRr x BbRr Sooo… the phenotypic ratio is … BR Fur Color: B: Black b: White Coat Texture: R: Rough r: Smooth

More Practice… In your notes, write this problem and solve… In pea plants, yellow seeds (Y) are dominant over green seeds (y), and rounded peas (R) are dominant over wrinkled peas (r). Cross a plant that is heterozygous for both traits with a plant that is homozygous recessive for both traits. Draw a Punnett square to show all possible offspring, and determine the genotypic and phenotypic ratios. First, determine the parents …

More Practice… AND … the parents are … YyRr x yyrr

More Practice… YyRr Now create your dihybrid Punnett Square using YyRr x yyrr. YR yR yr Yr yyrr

More Practice… 4:4:4:4 YyRr Now fill in the squares. What is the genotypic ratio? 4:4:4:4 YR yR yr Yr YyRr yyRr yyrr Yyrr yyrr

Endangered Species: The SeaWorld Project

1 Black Rhino PE Pe PPEe PPEe PPee PpEe Ppee pe Pe Ppee

1 Black Rhino PPEe PPee PpEe Ppee PE Pe PPEe pe Pe Ppee PPEe Normal Lip/Normal Ears: 4/16 PpEe PPee Normal Lip/Long Ears: 4/16 Ppee Genotypic Ratio: 4:4:4:4 Phenotypic Ratio: 8:8 None will produce both traits. PPEe PPee PpEe Ppee pe Pe Ppee

2 Burmese Python SSPP SSPp SsPP SsPp SSpp Sspp ssPP ssPp sspp SP sP sp

2 Burmese Python SSPP SSPp SsPP SsPp SSpp Sspp ssPP ssPp sspp SP sP sp Normal Scales/Normal: 9/16 SSpp, Sspp Normal Scales/Albino: 3/16 ssPP, ssPp Large Scales/Normal: 3/16 sspp Large Scales/Albino: 1/16 Phenotypic Ratio: 9:3:3:1 3/16 will produce both traits. SSPP SSPp SsPP SsPp SSpp Sspp ssPP ssPp sspp sp sP Sp SP SsPp

Prehensile-tailed Porcupine 3 Prehensile-tailed Porcupine TW tW tw Tw TtWw TTWW TTWw TtWW TtWw TTww Ttww ttWW ttWw ttww tw tW Tw TW TtWw

Prehensile-tailed Porcupine 3 Prehensile-tailed Porcupine TW tW tw Tw TtWw TTWW, TTWw, TtWW, TtWw Normal/Normal: 9/16 TTww, Ttww Normal/Long: 3/16 ttWW, ttTw Long/Normal: 3/16 ttww Long/Long: 1/16 Phenotypic Ratio: 9:3:3:1 1/16 will produce both traits. TTWW TTWw TtWW TtWw TTww Ttww ttWW ttWw ttww tw tW Tw TW TtWw

4 Leaf-Nosed Bat Nt nt Nntt Nntt nntt nt nntt

4 Leaf-Nosed Bat Nt nt Nntt Nntt nntt nt nntt Nntt Normal/Strong: 8/16 Large/Strong: 8/16 Phenotypic Ratio: 8:8 8/16 will produce both traits. Nntt nntt nt nntt

5 Osprey Ps ps Ppss PpSs ppSs Ppss ppss ps pS ppSs

5 Osprey Ps ps Ppss PpSs ppSs Ppss ppss ps pS ppSs PpSs Normal/Normal: 4/16 Ppss Normal/Long: 4/16 ppSs Dark/Normal: 4/16 ppss Dark/Long: 4/16 Phenotypic Ratio: 4:4:4:4 4/16 will produce both traits. PpSs ppSs Ppss ppss ps pS ppSs

6 Bongo Antelope HL hL hl Hl HhLl HHLL HHLl HhLL HhLl HHll Hhll hhLl

6 Bongo Antelope HL hL hl Hl HhLl HHLL HHLl HhLL HhLl HHll Hhll hhLl Normal/Normal: 9/16 HHll, Hhll Normal/Long: 3/16 hhLL, hhLl Thick/Normal: 3/16 hhll Thick/Long: 1/16 Phenotypic Ratio: 9:3:3:1 1/16 will produce both traits. HHLL HHLl HhLL HhLl HHll Hhll hhLl hhll hl hL Hl HL HhLl