Modes of Inheritance        1. review basic genetics and protein synthesis         2. Experimentally analyze the inheritance of one trait in a selected organism such as the fruit fly

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Gregor Mendel - the father of genetics    - Mendel's experiments with pea plants marked the beginning of genetics, the scientific study of heredity.          P - the parent generation; F1 - the offspring of P; F2 - the offspring of the F1 generation     - Mendel's model for determining traits in offspring is the Punnett Square     - Mendel found that factors (genes) transmit information about traits from parents to their offspring. The different forms of genes are called alleles.     - In Mendel's theory, an offspring has two factors for each trait ... one from mom and one from dad.     - Note: we will work on constructing and interpreting Punnett Squares in classroom activities.

sample Punnett Square

Basic Genetics Terms (there will be more on  the worksheets):
   Recessive:  A gene that when paired with a normal gene at the same location on the chromosome, will be dominated by the normal gene, and will not influence the appearance of the animal.
   Dominant: A gene that when paired with either a recessive or another dominant gene at the same location on the chromosome, will dominate and will influence the appearance of the animal.
   Heterozygous: Genes are inherited in pairs, one from each parent. When an animal receives genes from each parent at the same site on the chromosome that are different, the animal is Heterozygous.
   Homozygous:  When an animal receives genes from each parent at the same site on the chromosome that are the same, the animal is Homozygous. When an animal receives two recessive genes at the same site on the chromosome, they will influence the appearance of the animal.
   Phenotype: The appearance of an animal as a result of the genes inherited.
   Genotype: The genetic makeup of an animal, including recessive genes that do not affect the appearance of the animal.

All the instructions needed to direct cell activities are contained within the chemical DNA(deoxyribonucleic acid). 

     DNA from all organisms is made up of the same chemical and physical components. The DNA sequence is the particular side-by-side arrangement of bases along the DNA strand (e.g., ATTCCGGA). This order spells out the exact instructions required to create a particular organism with its own unique traits. 
     The genome is an organism’s complete set of DNA. Genomes vary widely in size: the smallest known genome for a free-living organism (a bacterium) contains about 600,000 DNA base pairs, while human and mouse genomes have some 3 billion. Except for mature red blood cells, all human cells contain a complete genome. 
     DNA in the human genome is arranged into 24 distinct chromosomes--physically separate molecules that range in length from about 50 million to 250 million base pairs. (note: though there are 23 pairs, the last pair of sex chromosomes may be different (X,Y) ... so there are 24 different types). 
   A few types of major chromosomal abnormalities, including missing or extra copies or gross breaks and rejoinings (translocations), can be detected by microscopic examination. Most changes in DNA, however, are more subtle and require a closer analysis of the DNA molecule to find perhaps single-base differences. 
     Each chromosome contains many genes, the basic physical and functional units of heredity. Genes are specific sequences of bases that encode instructions on how to make proteins. Genes comprise only about 2% of the human genome; the remainder consists of noncoding regions, whose functions may include providing chromosomal structural integrity and regulating where, when, and in what quantity proteins are made. The human genome is estimated to contain 30,000 to 40,000 genes. 
     Although genes get a lot of attention, it’s the proteins that perform most life functions and even make up the majority of cellular structures. Proteins are large, complex molecules made up of smaller subunits called amino acids. Chemical properties that distinguish the 20 different amino acids cause the protein chains to fold up into specific three-dimensional structures that define their particular functions in the cell. 

     Each time a cell divides, its full genome is duplicated so that each daugher cell has a complete set of the original DNA.  For humans and other complex organisms, this duplication occurs in the nucleus. During cell division the DNA molecule unwinds and the weak bonds between the base pairs break, allowing the strands to separate. Each strand directs the synthesis of a complementary new strand, with free nucleotides matching up with their complementary bases on each of the separated strands. Strict base-pairing rules are adhered to adenine will pair only with thymine (an A-T pair) and cytosine with guanine (a C-G pair). Each daughter cell receives one old and one new DNA strand. The cells adherence to these base-pairing rules ensures that the new strand is an exact copy of the old one. This minimizes the incidence of errors (mutations) that may greatly affect the resulting organism or its offspring. 

Step 1: Transcription: RNA is made, using DNA as a template
   - In the first step of protein synthesis, the 2 DNA strands in a gene that codes for a protein unzip from each other. 
   - Similar to the way DNA replicates itself, a single strand of messenger RNA (mRNA) is then made by pairing up mRNA bases with the exposed DNA nucleotide bases. 
   - After the mRNA is manufactured, it travels to the ribosomes. 

Step 2: Translation: mRNA controls the synthesis of a polypeptide
   - In the ribosomes, the mRNA code is translated into a transfer RNA (tRNA) code which, in turn, is transfered into a sequence of amino acids (a polypeptide, or protein sequence). 
   - In this process, each codon will pair with an anticodon 
   - codon - a 3 nucleotide sequence in mRNA that specifies a certain amino acid 
   - anticodon - complimentary tRNA base triplet to a codon 
   - Each tRNA is specific to an amino acid
   - As tRNA's are added to the sequence, amino acids are linked together by peptide bonds
   - This eventually forms a protein that is later released by the tRNA. 

Protein synthesis is done in different ways for prokaryotes and eukaryotes.
   - Prokaryotic protein synthesis occurs rapidly, since the DNA is not separated from the ribosomes.  Also, repressor proteins regulate transcription.
   - Eukaryotes' DNA is held within the nucleus.  So the mRNA has to be modified in order to leave the nucleus and enter the cytoplasm (where translation occurs).  The genes, which are fragmented, contain a series of sequences called exons and introns.  Exons are portions of a gene that are translated into proteins, while introns are the noncoding areas of DNA. 

Something to think about ... (critical thinking question on the test?)
    Why would the cell want to have an intermediate between DNA and the proteins it encodes? 
1. The DNA can then stay in its original condition ... protected from the harsh chemistry of the cytoplasm. 
2. Gene information can be amplified by having many copies of an RNA made from one copy of DNA. 
3. Regulation of gene expression can be effected by having specific controls at each element of the pathway between DNA and proteins. The more elements there are in the pathway, the more opportunities there are to control it in different circumstances.