Do Now Do the dihybrid cross on your
Do Now: Do the dihybrid cross on your notes sheet.
� Phenotype 9: 3: 3: 1 RW Rw r. W rw RW RR Ww Rr WW Rr Ww Rw RR Ww RR ww Rr Ww Rr ww r. W rw Rr WW Rr Ww rr WW rr Ww Rr ww Rr Ww Rr ww Ratio:
� The dihybrid cross is one of the 5 types of genetic crosses we have studied. �In a dihybrid cross, the inheritance of 2 traits is predicted at the same time �Since each parent has 4 possible combinations of alleles, dihybrid crosses are 4 x 4 squares.
� Complete dominance is the first type we looked at. � One allele hides the effect of the other. �AA = dominant phenotype �Aa = dominant phenotype �aa = recessive phenotype � Possible crosses include: �Heterozygous 3: 1 phenotype ratio, 1: 2: 1 genotype ratio �Homozygous x heterozygous (Aa x Aa) x heterozygous (aa x Aa and AA x aa) 1: 1 phenotype and genotype ratios �Homozygous x homozygous (AA x AA, aa x aa, and AA x aa) 100% have the same genotype and phenotype
� In humans, albinism (a) is recessive to normal pigmentation (A). If an albino man has a child with a woman who is heterozygous for the trait, what is the probability their child will be an albino?
� For codominant traits, BOTH alleles show up in the phenotype �AA = dominant phenotype �Aa = both phenotypes (i. e. red + white fur) �aa = recessive phenotype � Possible crosses include: �Heterozygous 1: 2: 1 phenotype ratio, 1: 2: 1 genotype ratio �Homozygous x heterozygous (Aa x Aa) x heterozygous (aa x Aa and AA x aa) 1: 1 phenotype and genotype ratios �Homozygous x homozygous (AA x AA, aa x aa, and AA x aa) 100% have the same genotype and phenotype
� In a species of tropical frog, there are frogs that have blue skin, frogs that have black skin, and frogs that have both black and blue skin. � If two black and blue frogs mate, what will the phenotype ratio of their offspring be?
� Traits with incomplete dominance produce a heterozygous phenotype that is a blend of the two allele’s effect �AA = dominant phenotype �Aa = blended phenotype (pink flowers �aa = recessive phenotype � Possible crosses include: �Heterozygous 1: 2: 1 phenotype ratio, 1: 2: 1 genotype ratio �Homozygous x heterozygous (aa x Aa and AA x aa) 1: 1 phenotype and genotype ratios �Homozygous aa) x heterozygous (Aa x Aa) x homozygous (AA x AA, aa x aa, and AA x 100% have the same genotype and phenotype
�A type of pepper comes in three colors, red, orange, and yellow. If a gardener crosses two orange pepper plants, what will the phenotype ratio of the offspring be?
� The alleles for sex linked traits are located on the sex chromosomes (X chromosome in humans) � Recessive sex-linked traits are much more common in males than females, since they have only 1 copy
� In a Punnett square for a sex-linked trait, the sex chromosomes are used instead of letters. normal f � X+Xo carrier f � Xo. Xo color-blind f � X+Y normal m � Xo. Y color-blind m + X o X + + XX + o XX Y + XY o XY � X +X +
� Because she has a brother with hemophilia, a biology student wanted to figure out the probability that she was a carrier for the X-linked disorder. Neither of her parents has hemophila. What is the probability she is a carrier of the trait?
� There will be a quiz on genetic crosses this Monday! Each of the 5 types will show up on it. � Do your homework for practice!
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