Testcross - One Locus let A = red a = white Is a red flower AA or Aa? Solution: cross it with aa P 1 A? X aa The A? individual can produce these kinds of gametes: "A" and "?" gametes: A, ? and a F 1 Aa and ?a If the ?a individual is red, then ? = A. If it is white, then ? = a. Should There Be Fewer Recessive Alleles? The population model described above predicts that gene frequencies will not change from one generation to the next even if there are more recessive alleles. There is sometimes a misconception among students beginning to study genetics that dominant traits are more common than recessive traits. Sometimes this is true, sometimes it is not. For some traits, the dominant is more common; for other traits, the recessive is more common. For example, blood type O is recessive and is the most common type of blood. Huntington's disease (a disease of the nervous system) is caused by a dominant gene and the normal gene is recessive. Fortunately, most people are recessive; the dominant is uncommon.
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