Mendelian Genetic Problems

Genetics as it applies to evolution, molecular biology, and medical aspects.

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Mendelian Genetic Problems

Post by DRJ » Sun Jan 25, 2009 4:41 am

My teacher gave me a few questions to practice before the test and I'm not understanding the questions as far as how to set them up.
#1. In human beings brown eyes are usually dominant over blue eyes. Suppose a blue-eyed man mates with a brown-eyed woman whose father was blue-eyed. What are the possible genotypes off their offspring with reference to this character? What is the probability of their offspring being blue-eyed? brown-eyed?

#2. In squash, a gene for white color (W) is dominant over its allele for yellow color (w). What are the genotypic and phenotypic ratios of a cross between two heterozygous plants (Ww)? What is the probability of obtaining a white-colored squash? a yellow-colored squash? a Ww (heterozygous) genotype? a WW (homozygous dominant) genotype? and a ww (homozygous recessive) genotype?

#3. If a man with blood type B, one of whose parents had blood type O, mates with a woman with blood type AB, what is the probability of their kid having blood type B? blood type O? blood type AB?

#4. In peas, a gene for tall plant (T) is dominant over its allele for short plants (t) and the gene for smooth peas (S) is dominant over its allele for wrinkled pease (s). What are the phenotypic ratios and genotypic ratios for a cross between TTSS and ttss? between TtSs and TtSs?

#5. Red-green color-blindness is inherited as a sex-linked recessive. If a color-blind woman mates with a man who has normal vision, what would be the expected phenotypes and genotypes of their children with reference to this character? What is the probability of having a color-blind child? a color-blind son? a color-blind daughter?

I'm so confused.

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Inland Taipan
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Post by mith » Sun Jan 25, 2009 8:57 pm

Start by writing out the genotypes of each cross.
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Inland Taipan
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Post by canalon » Sun Jan 25, 2009 9:01 pm

In short you are supposed to draw some Punnet squares after finding the probable genotype (when not stated in the question) of the subject. For example if the gene for eye color is B for brown and b for blue the man is bb and the woman is likely Bb (because her father had blue eyes) then Punnet square and probability and count the total number of boxes, and how many would be blue, how many brown. The probability of each phenotype (blue or brown) is P(%)=100xN(color of your choice)/N(total)

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