1/24/12- Gene – portion of DNA tha codes for a protein or part of a protein- Allele – Alternate forms of a gene. Ex: eye color- Locus – position on the chromosome where we find the gene or allele- Point mutation – change in one base of DNAo ATTCGG  ATTGGG – point mutationo Silent mutation – where amino acid isn’t changed Sickle Cell Anemia is a result of point mutation- 2 alpha chains- 2 beta chains – 146 amino acids in these, 3x146 bases in the DNA- 1 change can cause a much larger change o Variation comes from this- Chromosomes - Your DNAo In humans, it is packaged into 46 chromosomes (23 pairs)o Half from each parent Chromosome #1 is longest They all have the same length, same banding, same centromere position, same information (aside from variation of alleles) Centromere – Constriction that divides chromosome- P arm – shorter arm- Q arm – longer arm Each chromosome carries the same information for its position as everyone else’s- Ex: #1 has eye color for everyone #22 is shortest Autosomes – chromosomes 1-22 Sex chromosomes – 23rd pair, either XX (female) or XY (male)- Mother always gives X, male has chance to give X or Yo Apes have 48 chromosomes This is because our chromosomes are the same ones with some stuck togethero Fruit flies have 8 – easy to studyo Minnow – 100 o Fern – 250o Shows that number of chromosomes does NOT show complexity of specieso Our autosomes are Homologous chromosomes – they are always the sameo There is hardly any information on the Y chromosome Determines if you’ll have hairy ears Also has coding for SRY gene- SRY gene codes for TDF proteino TDF – Testus determining Factoro In the embryo, there is a bi-potential gonad that can become testicles or ovaries. o When TDF is introduced to this, they form testicleso Androgens are produced, which causes rest of body to be male (testosterone is one)- Cell Divisiono Mitosis – simple cell division for somatic cells First step is DNA replication- DNA is normally in a loose unwound state called Chromatin - It only condenses to where you can see it before cell division- DNA splits, attracts bases again and forms new DNA, and chromosomes are doubled Cell splits and doubled DNA and chromosomes go into new cell, and both are now identicalo Miosis – complex replication responsible for making eggs and sperm, and only occurs in ovaries/testes DNA replication still occurs for 46 double stranded chromosomes Homologous chromosomes find each other - They share information and change- This is called crossing over or Recombination- This means that none of the chromosomes you make are like the ones you were given from your parents - This adds variation to genetics because there is a 1 in 8 million chance that two eggs/sperm are genetically similar Reduction Division – where 46 double stranded chromosomes split into 2 cells with 23 double stranded chromosomes (1-23) These two cells split again into 4 genetically unique cells with 23 single stranded chromosomes - In females, this only happens in the embryonic stage- In males, once this happens, testosterone gives the cells tails, making them sperm- Females put all the cytoplasm and nutrients and “good stuff” into one cell (the egg), and the other three become Polar Bodies they aren’t usedfor anything Nondisjunction – chromosomes fail to replicate and you get eggs/sperm with the incorrect number of chromosomes- Responsible for 50% of miscarriages Aneuploids – incorrect pairing of chromosomes- Most autosomal aneuploids aren’t compatible with life- Some are, extra 21st chromosome = Down’s Syndroe- Lots of sex chromosome