Basic Genetics.2009 slk

Basic Genetics.2009 slk - BASIC GENETICS FOR BIS...

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BASIC GENETICS FOR BIS 2B (slightly modified by Grosberg from Keen) BIS 2B Spring 2009 B ACKGROUND : One of the main problems in evolutionary biology and ecology, the subjects of BIS 2B, concerns understanding how the physical characteristics of an organism (its phenotype ) are determined by the genetic characteristics of the organism (its genotype ) and the environment in which the organism lives. We also want to understand how the parental genotype and phenotype are passed to the offspring. Long before Mendel, biologists (and nervous fathers) knew that offspring resemble their parents, but offspring are neither identical to their parents, nor are progeny a simple average of the mother and father's phenotypes. To understand the resemblance between parents and offspring, we need to understand genetic inheritance. And, to understand genetic inheritance, we need to thank: Gregor Mendel (1866) for developing and testing the particulate theory of inheritance. Van Beneden and Boveri, who in 1887 described the behavior of chromosomes (replication and separation) during meiosis. Sutton and Boveri, who in 1902 recognized that the transmission patterns of chromosomes during meiosis and fertilization closely parallel Mendelian patterns of inheritance. William Bateson, who in 1905 coined the terms genetics, allele, and chromosome. Thomas Hunt Morgan (1915), who first used experimental crosses to show that genes on chromosomes are the mechanical basis of inheritance. He also documented the cause of many deviations from independent assortment, especially linkage on the same chromosome. Morgan is considered the father of classical ( vs . molecular) genetics. T HE B ASICS OF THE C HROMOSOMAL T HEORY OF I NHERITANCE : Mendel described patterns of inheritance in terms of the frequency distributions of offspring phenotypes (F 1 ’s) in crosses between true- breeding parental stalks (P 1 ), and in crosses between F 1 ’s to generate F 2 ’s. He did not know that the particles of inheritance that he inferred existed resided on chromosomes, and that chromosomes segregate and assort during meiosis. We now know that genetic inheritance depends on the genetic information that parents give their offspring in the form of chromosomes inside an egg or a sperm. If we start with an egg or a sperm (each one is a haploid gamete), we find copies of half of the mother's chromosomes in the egg and copies of half of the father's chromosomes in the sperm. When the egg and sperm fuse to make a zygote , the two haploid (1N) gametes form a diploid (2N) cell. This zygote is the first cell in a new organism and it has all the genetic information needed to create a new individual. This cell will be copied many times to produce a multicellular organism, each cell carrying an identical set of genetic information.
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