In the 19th Century, monk called Gregor Mendel lived in a monastery in what is now the Czech Republic. His work in the monastery gardens led him to observe how characteristics were passed from one generation of plants to another. In 1867 he published his observations, and called them his First Law--of Segregation and Characteristics.

Mendel said that each characteristic had severl forms of Alleles. When 2 different alleles occured in the same individual, only one, the dominant one whould be expressed and the other would remain hidden, or recessive.

Thus the first generations offspring (F1) of pure breeding parents for different alleles would be hybrids, looking like the dominant allele if these then bred together. Half their offspring will be hybrids, but the other half will be like the grandparents. In other words, the original parental characteristics segregate out in the second generations (F2).


Example: yellow seeds vs. green

Let green = G and yellow = g
(Green is dominant)

Green plant can be GG or Gg and yellow only gg

First generation
Parents (p): GG x gg
Gametes (g): G, g
F1: Gg

Second generation
p: Gg, Gg
g: G1, g1:   G2, g2
F2: G1G2, G1g2, G2g1, g1g2

This shows that there is the probability for at least one pure Green (GG), some Green hybrids (Gg, looking Green), and one Yellow (gg).

We did an experiement of a random selection of seeds, and got the ratio of 2:57:1 for Green vs. Hybrids vs. Yellows. We found that if one kills the recessive pairs, by the fifth generation, F2 all the double recessives will be dead, but that one hybrid will remain, proving that recessive characteristics can never be completely removed


Example 2: Tongue Rolling

Tongue rolling in humans is controlled by 2 alleles, the dominant Rolling (R) and recessive, non-rolling (r).

Parents (p): pRR (pure breeding roller) x prr (pure breeding non-roller)
Spermatozoa & Ova (g): gR x gr
F1: pRr x pRr
Gametes (g2): ;gr, gr
F2: G1G2 (pure roller), G1g2 (hybrid roller), G2g1 (hybrid roller), g1g2 (pure non-roller)


Question: Two blue eyed girls have a brown eyed mother and a blue-eyed father. What percentage chance is there of their expected sibling of having brown eyes? (Brown is dominant)

Answer: 50%.

m(Bb) x f(bb) yields Bb (hybrid brown), Bb (do.), bb (pure blue), bb (do.).

Node your homework: 14.5.96: 15 yrs: Anthropolgy

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