Transcript Learning Target: 1/30 Traits and Probability

Learning Target:
Traits and Probability
Ch. 6.5 pp. 183-187
I Can…Create a Punnett square predicting
possible geno- and phenotypes of offspring and
analyze the results
I Will…
• Determine potential gametes of
parents
• Complete a Punnett square of the
cross
• Analyze the geno- and phenotype
ratio and percentage for the offspring
Now that we know about how the parents donate
their genetic traits to their offspring, let’s predict
the offspring characteristics:
R.C. Punnett developed a method to keep track of
the various possible genetic combinations of
offspring
Punnett square: grid system for
predicting all possible genotypes
from a cross (mating of two
parents)
• Axes – potential gametes
• Boxes – possible offspring
Parent
gamete
Punnett
square
Haploid
Possible
Offspring
Diploid
Parent
gamete
Haploid
Possible
Offspring
Diploid
Punnett square steps:
1. Determine parents’ genotype for desired
trait and write the cross.
Trait: Eye color
Dominant: Brown color (B) Recessive: Blue (b)
Parent Phenotype
Genotype Description
Symbol
♂ Brown eyes
Bb
Heterozygous
♀ Blue eyes
Homozygous Recessive
bb
Cross: Bb x bb
Punnett square steps:
2. Split parents’ genotype to represent their
gametes and fill-in the axes of the Punnett
square.
Bb
B
bb
b
b
b
Punnett square steps:
3. Place the alleles into the offspring boxes
• Drop the top axis letters down the column
into each box below it
• Bring the side axis letters across to each
box in the same row
• Each box should have
B
b
• two letters in it
Customary to write
the Dominant
letter first within
the box
b
B b b b
b
B b
bb
Punnett square steps:
4. Analyze the possible offspring:
• Write down all the genotype
combinations
2Bb : 2bb = 1:1 ratio
Offspring
Percentage
Genotype
Genotype
Description
Combination
2/4 = 50% Heterozygous
Bb
2/4 = 50%
Homozygous
bb
recessive
Bb
bb
Bb
bb
Trait
Phenotype
Eye color
Brown
Blue
Probability – predicts the likelihood of a
particular genotype or phenotype occurring.
Probability =
Number of ways a specific event can occur
Number of total outcomes
Common Probabilities – Monohybrid
• Homozygous dominant x Homozygous recessive
• Genotype – 100% Heterozygous Phenotype 100% dominant
• Heterozygous x Heterozygous
• Genotype – 1:2:1 Phenotype 25% Homozygous dominant, 50%
Heterozygous, 25% Homozygous recessive
• Homozygous dominant x Heterozygous
• Genotype – 1:1 Phenotype – 50% Homozygous dominant, 50% heterozygous
• Homozygous recessive x Heterozygous
• Genotype – 1:1 Phenotype – 50% Heterozygous, 50% Homozygous recessive
Learning Check √:
Traits and Probability
Create and complete a Punnett square of the
following cross for eye color:
Homozygous Brown x Homozygous blue
Key:
Dominant: Brown (B)
Recessive: Blue (b)
What are the chances of having a
blue-eyed offspring?