Punnett squares day 2 im
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DO NOWGRAB YOUR GREEN FOLDER. •In golden retrievers, the allele for brown hair is dominant to the allele for yellow hair. If a yellow-haired golden retriever mated with a heterozygous brown-haired retriever, what is the probability that their puppies will be brown haired?
You have 5 minutes.
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PUNNETT SQUARES DAY 2NOTES
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I CAN…•I CAN make and interpret a Punnett square to predict the genotypes and phenotypes of offspring for sex linked, incomplete, and co-dominant traits
•I CAN interpret a dihybrid cross Punnett square
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Can you predict the outcome of 2 traits at the same time?•YES! This is called a dihybrid cross. Just
follow the same Punnett square rules. •On the EOC, you will NOT have to make a
dihybrid cross Punnett Square; you will only have to interpret it correctly.
1.Just figure out who wins the battle in each square, as usual, to determine phenotype
IT’S SO
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Dihybrid Punnett Square Cross• Cross between
2 guinea pigs heterozygous for hair color and length
•B=black
•b=white
•S=short
•s=long
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Dihybrid Punnett Square Cross
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Q: What fraction of the offspring are black and long tailed?
• Cross between 2 guinea pigs heterozygous for hair color and length
•B=black
•b=white
•S=short
•s=long
A:
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Q: What fraction of the offspring are white and short tailed?
• Cross between 2 guinea pigs heterozygous for hair color and length
•B=black
•b=white
•S=short
•s=long
A:
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Mr. Im lied to me…•There are exceptions to the dominant allele
always winning the battle against the recessive allele that might show up on the EOC1. Incomplete dominance: when two alleles
mix to create a new phenotype2. Co-dominance: when alleles are both
dominant and will both express their phenotypes
•The EOC will always let you know in the question if the trait is incomplete or co-dominant.
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Incomplete Dominance: •The alleles for red flower and white flower
petals show incomplete dominance (two alleles mix to create a new phenotype)▫What is the new phenotype? PINK!
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Check for UnderstandingQ: In roses the allele for red flowers shows
incomplete dominance with the allele for white flowers. One pink rose and one white rose are crossed. What is the probability of producing a white rose?
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Co-dominance•The alleles for white petals and red petals
show co-dominance (alleles are both dominant and will both express their phenotypes)▫Both capital letters.
•What is the phenotype of the flower? Spotted red & white!
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Check for UnderstandingQ: A homozygous brown-coated dog is crossed with a brown-and-white-coated dog. Brown and white coats are co-dominant. What is the probability of producing a brown-and-white coated puppy?
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Sex Chromosomes
FEMALE: XX MALE: XY
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Why are more males colorblind?•Some genes are carried on sex
chromosomes. ▫Sex chromosomes are the X and Y
chromosomesExample: The allele for colorblindness
is recessive and carried on the X chromosome▫XEXE: healthy female▫XeXe: colorblind female▫XEXe: female carrier▫XeY: color blind male▫XEY: healthy male
•It is easier for males to be colorblind, because they only have one X chromosome. One shot and you're done!
E=normal eyese=color blind
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Q: Hemophilia (not being able to clot your blood) is a sex-linked recessive disease. A heterozygous female and a male who has hemophilia are worried about having a baby with the disease. What is the probability that they will have a child with hemophilia?
Check for Understanding