Genes and Mendel - Writers Writing - http://phatbowling.com/fanficsnstuff/Genes

Gene Structure- two types of nucleic acid.
1. Deoxyribonucleic Acid (DNA)
2. Ribonucleic Acid (RNA)
Nucleotides- the components of nucleic acids. Nucleotides are made of three subunits:
a. Sugar
b. Phosphate
c. Nitrogenous Base (there are five possible bases)

B. In DNA, the nucleic acid of chromosomes, four nitrogenous bases are found: adenine (A), gaunine (G), cytosine (C), and thymine (T). RNA consists of similar bases, except that uracil (U) replaces thymine (T).

C. DNA is a double helix molecule with the sides formed by repeating sugar-phosphate groups from each nucleotide, and the horizontal portions formed by hydrogen bonds involving A with T or C with G.

D. Heridetary information (ie. genes) is found along the linear sequence of nucleotides in the DNA molecule.

Genetics- the study of traits and their inheritance.

Law of Segregation of Alternate Factors

A. Single-Trait crossbreeding:
1. Two true-breeding parents (p1) (who always yield the same form when crossed with eachother), but different strains were crossed.
2. The offspring (f1) from this cross all showed only one trait and this was called the dominant trait. The traits from the parents did not blend.
3. The f1 individuals were crossed with each other to produce f2 individuals.
4. 3/4 of the f2 expressed the dominant trait. 1/4 expressed the trait of the other p1 parent.

B. Conclusions: Discrete factors (genes) were responsible for the traits and these factors were paired, seperated (during meosis), and then recombined (during fertalization). Alternate forms of the factors or genes exist called alleles. The f1 individuals had two alleles, their genotype consisted of a dominant and recessant allele. Thus, the f1's were hybrids.

C. Genes are found on chromosomes, and thus multiple traits assort independantly as long as they are located on different chromosomes. Mendel studied traits in peas that were each on seperate chromosomes. Genes on the same chromosome are linked and thus will not normally assort independantly.

D. Interactions between alleles:
1. Complete Dominance- one allele dominates another allele.
2. Incomplete Dominance- neither allele is expressed fully.
3. Codominance- both alleles expressed fully.
4. Multiple Alleles- more than two alleles for a gene within a population.
5. Epistasis- one gene alters the effect of another gene.
6. Polygenic inheritance- many genes contribute to a phenotype.
7. Pleiotropy- one gene can affect several phenotypes.
8. Environmental influences- where the genotype and environment interact to form a phenotype.

Law of Independant Assortment

A. Two true breeding parents of different strains for two traits were crossed. The f1's were than crossed, producing f2 individuals.

B. Mendel concluded statistically that these results occured because alleles for one trait or gene did not affect the inheritance of alleles for another trait.

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