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8.3 Continued… Studying Heredity
Objectives Predict the results of dihybrid genetic crosses by using Punnett squares. Predict the results of dihybrid genetic crosses by using probabilities.
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New Vocabulary Dihybrid Cross
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Suppose a horticulturist has _______ characters to consider when crossing plants
A cross that involves ________ pairs of contrasting traits is called a _______________ cross For example, a cross may be made between two pea plants that are heterozygous for seed __________ and seed ____________ two two dihybrid shape color
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Pea plant seeds may be… round (R) or wrinkled (r) Yellow (Y) or green (y) So heterozygous parents will have the genotype __________ RrYy
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RrYy The four possible gametes formed are… _____ _____ _____ _____
When forming gametes for a dihybrid cross, we must consider how the ______ alleles from either parent may ____________ and _____________ Example…so for an individual with the genotype RrYy, only ____ allele for each trait will be passed on in a gamete RrYy The four possible gametes formed are… _____ _____ _____ _____ four segregate combine one RY Ry rY ry
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Imagine that a student incorrectly determined that one of the gametes contained the alleles Rr…why is this incorrect? The alleles for the same trait separate.. so you may only inherit one of each trait and not two!
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Practice! Create the four possible gametes that an individual with each genotype may create… RrYY = _____ ______ _____ _____ Rryy = _____ _____ _____ ______ rrYY = _____ ______ ______ ______ RY RY rY rY Ry Ry ry ry rY rY rY rY
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RY Ry rY ry RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy
When two heterozygous pea plants (RrYy) are crossed, their gametes are written along the top and side of the Punnett square Then, the gametes ______________ in the individual boxes Phenotype ratio? RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy fuse ry RrYy Rryy rrYy rryy 9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green
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Short cut! 9:3:3:1 dominant second recessive-dominant recessive
When individuals heterozygous for two traits are crossed, a Punnett square will always predict a __________ ratio in the offspring The numbers in the ratio are always listed in the following order… Both ________________ traits are listed first The dominant-recessive combo is listed ____________ The ________________________ combo is written third Both ________________ traits are written last 9:3:3:1 dominant second recessive-dominant recessive
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Probability According to your ratio, what is the probability that an offspring from the cross will inherit round and yellow seeds? …round and green seeds? …wrinkled and yellow seeds? …wrinkled and green seeds? 9/16 3/16 3/16 1/16
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Objective 1 Predict the results of dihybrid genetic crosses by using Punnett squares. Cross a pea plant that is homozygous dominant for seed shape but heterozygous for color ________ with one that is recessive for seed shape and color _________ Phenotype ratio? RY Ry RY Ry ry RrYy Rryy RrYy Rryy RRYy ry RrYy Rryy RrYy Rryy ry RrYy Rryy Rryy rryy RrYy ry RrYy Rryy RrYy Rryy 8 Round Yellow : 8 Round Green
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Objective 2 Predict the results of dihybrid genetic crosses by using probabilities. In the previous cross what was the probability that an offspring will inherit round and yellow seeds? ….round and green seeds? …wrinkled and yellow seeds? 8/16 = 1/2 8/16 = 1/2 0/16
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