Excelsior Biology Unit 4

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Mendel's law of segregation
Mendel realized through his experiments that during gamete formation, the alleles for each gene segregate from each other during meiosis, so that each gamete carries only one allele for each gene.
Gregor Mendel
Founded the modern science of Genetics who did work in the monastery garden where he lived and changed biology forever. He study the pea pods of the plants to discover how traits are inherited from parents to offspring.
Genetics
The scientific study of heredity and the key to understanding what makes each organism unique.
Traits
A specific characteristic, such as seed color or plant height, of an individual. Many traits vary from one individual to another.
Principles of Probability
The likelihood that a particular event will occur. In genetics, you can use probability to predict the traits of offspring from the combinations of genetic crosses in the parents.
Punnett Squares
Punnett squares use mathematical probability to help predict the genotype and phenotype combinations in genetic crosses. You should be familiar with the process of using Punnett squares and the what kind of results can be expected from them.
Incomplete Dominance
Cases in which one allele is not completely dominant over another where the heterozygous phenotype lies somewhere between the two homozygous phenotypes. This occurs when red roses and white roses combine to make pink roses.
Gametes
The process of producing gamete cells from diploid cells by cutting the number of homologous chromosomes per cell in half.
Tetrads and Crossing-over
During Meiosis I, in Prophase I, each replicated chromosome pairs with its corresponding homologous chromosome which creates a tetrad which then undergo a process call crossing-over. During this process, the chromatids cross over and exchange with each other and recombine in a new and different way producing new combinations of alleles in the cell.
Bacteriophage
A kind of virus that infects bacteria.
DNA
The DNA that makes up genes must be capable of storing, copying, and transmitting the genetic information in a cell.
Chargaff's Rule
Erwin Chargaff discovered that the percentages of certain nucleotides are equal in DNA. This rule occurs because the bases pair with each other so that Adenine and Thymine are equal to each other as well as Guanine and Cytosine.
The Double-Helix Model
DNA forms a double helix (a spiral staircase) with antiparallel strands so that the nitrogenous bases come together in the center through base pairing (A = T and G= C) and bond with hydrogen bonding. This type of bond is quite weak which explains why the DNA can be broken down the center for replication.
Components of DNA
DNA is a nucleic acid made up of nucleotides joined into long strands or chains by covalent bonds. The nucleotides are made up of three basic components: a 5-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base.
DNA Replication
Before a cell divides, it duplicates its DNA in a copying process called replication. This occurs during late interphase, and in it, the DNA molecule separates into two strands (unzipping itself) by breaking the hydrogen bonds connecting the two sides, and then produces two new complementary strands following the rules of base pairing. Adenine is always paired to Thymine and Guanine to Cytosine. So, if the unzipped portion is sequenced TACGTT, the new base sequence is the opposite or ATGCAA.
Introns and Exons
Like a writer's first draft, RNA molecules sometimes require editing to be ready. The pre- mRNA molecules have bits and pieces cut out of them before they are ready. The portions that are cut out and discarded do not code for a specific amino acid and are called introns. The remaining pieces, known as exons, are then spliced back together to form the final mRNA.
Comparing RNA and DNA
There are three important differences between RNA and DNA:
1). The sugar in RNA is ribose instead of deoxyribose
2). RNA is generally single stranded and not double-stranded
3). RNA contains uracil in place of thymine.
RNA Nucleotides
When RNA is copied from DNA, it contains uracil in place of thymine. So Thymine still matches with Adenine, and Cytosine with Guanine and Guanine with Cytosine, but Adenine matches up with Uracil instead of Thymine.
Transfer RNA
The type of RNA molecule that transfers each amino acid to the the correct codon on the ribosome as it is specified by the coded messages in the mRNA.
Reading Codons
Using a genetic code table like the one attached makes decoding codons a simple task. Just start at the beginning of the circle with the first letter of the codon, then move outward.
Mutation
Mutations are heritable changes in genetic information. They occur when mistakes are made in copying the DNA, a wrong base may be substituted, inserted or even skipped. The effect of mutations on genes vary widely. Some have little or no effect; and some produce beneficial variations such as polyploidy, or the ability to adapt to different environmental stimuli. Some negatively disrupt gene function such as sickle cell disease or cancer.
Polygenic Traits
Many traits are produced by the interaction of several genes. Traits that are controlled by two or more genes are said to be polygenic traits.