Midterm 2

• Expressed genes- free to produce the proteins needed to build a particular type of cell
• We have the same DNA in all of our cells, except red blood cells, sperm & egg
• cell specialisation occurs because the different expressions of genes, make a different type of cell- how all cells have the same DNA yet are different
• Each cell may contain the instructions for an entire human
• Only 10 to 20% of genes in a human cell are active
• The rate of gene expression in the brain is one of the factors that distinguishes humans from other creatures- many more genes expressed than a chimp for example
• Genes turn off and on at precise points in time during development
• Interactions with the environment affect gene expression
• Each cell of the body contains 2 complete copies of the human genome
• Genotype- genetic composition of an individual 
• Phenotype- observable characteristics
• Genotype expression affects phenotype
• DNA- deoxyribonucleic acid
• We have 23 matched pairs of chromosomes- one chromosome of each pair was donated to us by our mother, and the other our father
• Smaller segments of chromosomal DNA are genes- constructed from the different nucleotide bases
• Nucleotide bases- Adenine & Thymine- Cytosine & Guanine
• Each gene contains instructions for making a particular type of protein
• Gene expressions- what genes are actually used- translation of genotype to phenotype
• DNA to proteins- DNA copies itself via RNA- Codon is read & an amino acid is made- ribosome continues reading the DNA and attaching a new amino acid for each codon- creates a chain- polypeptide is formed & released where it folds into a specific shape- protein!
• DNA copies itself on RNA
• RNA is ribonucleic acid
• Codons- triplet of nucleic acid- provides instructions for one of the 20 amino acids
• Chromosomes are made of DNA
• Different phenotype traits results from interactions between alleles
• Alleles- variants of a specific gene
• With 2 sets of chromosomes, we can have 2 version of a gene
• Transcription -> Translation -> completed protein
• Transcription- DNA partially unwinds- a strand of complementary RNA is made
• Translation- RNA instructs ribosomes to create a certain sequence of amino acids
• 2 Identical alleles at a given site- Homozygous gene
• Heterozygous- 2 different alleles at a site
• Recessive alleles will only be expressed when it occurs in a homozygous pair with itself
• No freckles are recessive
• Dominant allele- expressed in phenotype regardless if its pair is homozygous or heterozygous
• Some genes show partial dominance- phenotype is intermediate between the alleles given
• Complete dominance- phenotype of a heterozygous & Homozygous pairing for the dominant gene will be identical
• Some genes have a large amount of alleles- BRCA1 gene- only a small number of these alleles is associated with breast cancer
• Codominance- phenotype represents both of its alleles
• 3 different alleles for blood type- A, B & O- A and B code for proteins on the surface on red blood cells- O does not code for such protein
• 4 blood types- type A, B, AB, O