Laws Of Mendelian Genetics

There are several basic laws or principles of genetics first described by Gregory Mendel (1822-1884) that form the foundation for interpretation of DNA evidence. One of Mendel's laws is that the two members of a gene pair segregate (separate) from each other during sex-cell formation (meiosis), so that one-half of the sex cells carry one member of the pair and the other one half of the sex cells carry the other member of the gene pair. In other words, chromosome pairs separate during meiosis so that the sex cells (gametes) become haploid and possess only a single copy of a chromosome. Another of Mendel's laws is that different segregating gene pairs behave independently. This is sometimes called the law of independent assortment and is due to recombination (see Chapter 2). The law of segregation and the law of independent assortment are the basis for linkage equilibrium and Hardy-Weinberg equilibrium that are tested for when examining DNA population databases (see Chapter 20).

For a genetic marker with two alleles A and a in a random-mating population, the expected genotype frequencies of AA, Aa, and aa are given by p2, 2pq, and q2, where p and q are the allele frequencies of A and a, respectively, with p + q = 1 (Hartl and Clark 1997). Figure 19.3 illustrates these principles, which constitute Hardy-Weinberg equilibrium (HWE). This graphical representation of the

Mother gametes (egg) Resulting genotype combinations and frequencies

Punnett square

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A

AA

aA

p

p2

qp

______

_________>

a

Aa

-------

—-

aa

q

pq

q2

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Stammering Its Cause and Its Cure

Stammering Its Cause and Its Cure

This book discusses the futility of curing stammering by common means. It traces various attempts at curing stammering in the past and how wasteful these attempt were, until he discovered a simple program to cure it. The book presents the life of Benjamin Nathaniel Bogue and his struggles with the handicap. Bogue devotes a great deal of text to explain the handicap of stammering, its effects on the body and psychology of the sufferer, and its cure.

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