Gregor Mendel, Alfred Day Hershey, Barbara McClintock
- The genetic properties or features of an organism, characteristics, etc.
Heredity- The passing of traits from parents to child is the basis of heredity.
Our genes encode the instruction that define our traits. Each of us has thousands of genes, which are made of DNA and reside in our chromosomes. The environment we grow up and live in also helps define our traits. Humans have two complete sets of 23 chromosomes. When parents conceive a child, they each contribute one complete set to the child. In this way, parents pass genes to the child. As a result, every child will have a unique combination of traits. Some will resemble the mother, and some will resemble the father. Still others will be unique, a product of the new combination of chromosomes.
Traits- A trait is a notable feature or quality in a person. Each of us has a different combination of traits that make us unique. Traits are passed from generation to generation. We inherit traits from our parents, and we pass them to our children. Physical Traits are characteristics of one's physical makeup, including hair color, eye color, and height. Behavioral Traits are characteristics of the way one acts. An increased risk of getting a certain disease is also a trait that can be passed from parent to child. Environmental influences can also give us certain traits.
DNA- DNA stands for DeoxyriboNucleic Acid. Encodes a detailed set of plans, like a blueprint, for building different parts of the cell. The DNA molecule comes in the form of a twisted ladder shape scientists call a "double helix". The ladder's rungs are built with the four letter DNA alphabet: A, C, T, and G. These alphabet pieces join together according to special rules, A always pairs with T, and C always pairs with G. The DNA strand is made of letters, the letters make words, and the words make sentences. The "sentences" are called genes. Genes tell the cell to make other molecules called proteins. Proteins enable a cell to perform special functions, such as working with other groups of cells to make hearing possible.
Genes- They are instruction manuals for our bodies. They are the directions for building all the proteins that make our bodies function. Genes are made of DNA. One strand of our DNA contains many genes. All of these genes are needed to give instructions for how to make and operate all parts of our body.
Proteins- They are the things that make all living things function. Every cell contains thousands of different proteins, which work together as tiny machines to run the cell. For proteins, each part looks different and has its own job in helping run things. Receptor proteins are responsible for picking up the signal and passing it to the next cell. Proteins are very very small, even with the most powerful electron microscope, you would have trouble seeing them.
Chromosomes- DNA is packaged into compact units called chromosomes. The packaging of DNA into a chromosome is done in several steps, starting with the double helix of DNA. Then the DNA is wrapped around some proteins. These proteins are packed tightly together until they form a chromosome. Chromosomes are efficient storage units for DNA. Each human cell has 46 chromosomes. They are organized into two sets of 23 chromosomes. Each set of living things has a different number of chromosomes.
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Alfred Day Hershey
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Of course, these discoveries were preceded by extensive breeding experimentation. It was known at the time from previous work by Rollins A. Emerson, another American maize geneticist and the "rediscoverer" of Mendel's laws of inheritance that maize had genes encoding variegated, or multicolored, kernels; these kernels were described as colorless (although they were actually white or yellow), except for spots or streaks of purple or brown (Figure 2). Emerson had proposed that the variegated streaking was due to an "unstable mutation," or a mutation for the colorless phenotype that would sometimes revert back to its wild-type variant and result in an area of color. However, he couldn't explain why or how this occurred. As McClintock discovered, the unstable mutation Emerson puzzled over was actually a four-gene system. In her experiments, McClintock bred females that were homozygous for C and bz and that lacked Ds (denoted CCbzbz--, where the dashes indicate the absence of Ds alleles) with males that were homozygous for C', Bz, and Ds (denoted C'C'BzBzDsDs) to yield heterozygotes with an aleurone layer that had the genotype C'CCBzbzbz--Ds. (Remember, in double fertilization, the sperm provides one set of alleles, and the egg provides two.) Because of the presence of the dominant inhibitor allele C', the offspring kernels were expected to be colorless, no matter what their genetic makeup at the Bz/bz locus. In fact, upon crossbreeding, many of these kernels were indeed colorless. However, McClintock also observed many kernels with colorless backgrounds and varying amounts of dark brown spots or streaks, and she concluded that individual cells in those kernels had lost their C' and Bz alleles because of a chromosomal break at the Ds locus. Without either the C' allele (to prevent color expression) or the Bz (purple) allele, the cells that had experienced a breakage at the Ds locus ended up with some brown coloring.
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