BIOL 112 Lecture Notes - Lecture 4: Thomas Hunt Morgan, Homologous Chromosome, Y Chromosome

• School: McGill University
• Department: Biology
• Course: BIOL 112
• Professor: Joseph Dent

Document Summary

To review, mendel proposed a simple theory of exquisite predictive power that explains the rules governing heredity in terms of chromosomes and genes. The problem is, mendel still has some explaining to do. First of all, our theory has explained the exception, discrete traits, not the rule, continuous traits. Second, in order for all genes to segregate, they must all be on different chromosomes. But there are only 23 pairs of human homologs. Turns out there are several traits that run in families but predominantly affect males. Let"s look closely at one example: color blindness. Consider; a normal woman and a normal man who produce some color blind children. Colorblindness must be recessive since it turns up in children of unaffected parents (think f1 x f1 cross). Both parents must be heterozygous or you wouldn"t see it at all (think test cross).