1) See Question of the Day for "Mendel's Crap Shoot of Genetics" lecture (9/18/01).  For powerpoint lecture slides go to Artemis->FACBOX->KimSnipes->PwPt->NS11 on any on campus Macintosh computer with Microsoft Office 2001.

2) If person has recessive phenotype (e.g., non-tongue rolling), then they have to have both recessive alleles (e.g., rr).  This is the definition of a recessive trait (see genetics vocabulary handout).

3) If person has dominant phenotype (e.g., tongue rolling), then they only have to have one dominant allele (e.g., RR or Rr).  This is the definition of a dominant trait (see genetics vocabulary handout).

Answers to genetics handout problems:

1) Bob is recessive non-roller.  His genotype = rr.  All is sperm have non-rolling allele (only choice).  Alex had to receive a "r" from his dad.  Alex rolls his tongue, therefore, he has one dominant allele ("R") that ahd to come from his mom.  Alex's genotype is Rr (heterozygous tongue roller).

2) Alex (Rr) marries Gwen, a non-roller (rr).  Possible combinations of gametes for Rr x rr = Rr and rr.  50% (1/2) probablity that child will be a non-roller.

3) Red-green color-blindness is carried on X chromosome (sex-linked).  Martha has normal color vision, so she has at least one normal vision allele (X^NX^-).  Since she has no color-blind relatives, one may guess that both her X chromosomes have normal alleles (X^NX^N).  Felix is color-blind; his one X chromosome carries the color-blond allele (XⁿY).
A) Felix can only give his daughters an X chromosome with a color-blind allele.  All of his daughters will carry the trait.  The odds of their first child being a girl are 50% (1/2).  Ergo, odds of first child being a girl carrying the allele are 50%.
B) Felix cannot give any son his color-blind allele (son gets dad's Y chromosome).  All his sons will get their color vision alleles from their mother with normal color vision.  The odds of a color-blind boy are 0% (0/2).

4) Becky and Roger have type A blood.  To have type A blood phenotype one's genotype is either AA or AO (type O blood is the absence of either the A or B allele -- it's recessive to both A and B allele).  Their son, Will, has type O blood (genotype = OO).
A) If both parents are heterozygous for A and O allele, then type O blood is possible (Roger's sperm with O allele fertilizes egg with O allele from Becky).  This used to be the common way to establish paternity before DNA fingerprinting.
B) Becky and Roger are both AO, and Will is OO.

5) Sudan has a malaria problem and individuals with sickled-cell anemia.  For the parents to be healthy (without drugs) one can assume they have partially sickled red blood cells.  Their genotypes are both Hb^AHb^S.  There are three possible combinations of gametes = Hb^AHb^A, Hb^AHb^S, and Hb^SHb^S (see probability square below).   The odds that a child will have normal hemoglobin and die of malaria are 25% (1/4).  The odds that a child will have both alleles for sickled-cell hemoglobin and die of anemia are 25% (1/4).
 

	HbA	HbS
HbA	HbAHbA	HbAHbS
HbS	HbAHbS	HbSHbS