Gregor Mendel”s principles of inheritance form the cornerstone of modern genetics. So just what are they?
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Ever wonder why you are the only one in your family with your grandfather”s nose? The way in which traits are passed from one generation to the next-and sometimes skip generations-was first explained by Gregor Mendel. By experimenting with pea plant breeding, Mendel developed three principles of inheritance that described the transmission of genetic traits, before anyone knew genes existed. Mendel”s insight greatly expanded the understanding of genetic inheritance, and led to the development of new experimental methods.
rd generation individual #3 (a female) mates with a male that is not affected with WS. The couple has one female offspring, who is not affected with WS. 2nd generation female individual #2 has a second mate in her lifetime, and he is unaffected by WS. The couple has a single male offspring (generation 3) who is not affected with the disease. This male offspring mates with a female unaffected with WS, and the couple has a single male offspring (generation 4), unaffected with the disease. 2nd generation male individual #4 mates with a female that is not affected with WS. The couple has five children (generation 3), identified as individuals #8, #9, #11, #13, and #14. Three of the offspring are male, and two are female. Individual #8 (a male) is affected with WS and mates with a female that is not affected with WS. The couple has three offspring: two females that are affected with WS and one male that is not affected by the disease. Individual #9 (a male) is not affected with WS and mates with a female that is also not affected with WS. The couple has two female offspring, neither of whom are affected with WS. Individual #11 (a female) is not affected with WS and mates with a male that is also not affected with WS. The couple has three male offspring, none of whom are affected with the disease. Individual #13 (a male) is affected with WS and does not reproduce. Individual #14 (a female) is not affected with WS and mates with a male that is also not affected with WS. The couple has two female offspring, both of whom are not affected with the disease.”)” class=”inlineLinks”> Figure Detail
Traits are passed down in families in different patterns. Pedigrees can illustrate these patterns by following the history of specific characteristics, or phenotypes, as they appear in a family. For example, the pedigree in Figure 1 shows a family in which a grandmother (generation I) has passed down a characteristic (shown in solid red) through the family tree. The inheritance pattern of this characteristic is considered dominant, because it is observable in every generation. Thus, every individual who carries the genetic code for this characteristic will show evidence of the characteristic. In contrast, Figure 2 shows a different pattern of inheritance, in which a characteristic disappears in one generation, only to reappear in a subsequent one. This pattern of inheritance, in which the parents do not show the phenotype but some of the children do, is considered recessive. But where did our knowledge of dominance and recessivity first come from?