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Introduction We can use DNA and genetics to reconstruct relationships with living and fossil ancestors It will show how we are related to other primates It will help us understand diseases and how they are transmitted The Cell Prokaryotes are one-celled organisms Eukaryotes are multi-celled organisms Also have a nucleus and cytoplasm Types of cells (important!!): Somatic cells: body cells, use mitosis Gametes: sex cells, sperm/egg, use meiosis DNA Molecule Think of a cell Zoom into the middle, in the nucleus In the nucleus are chromosomes Inside the chromosomes are bundles of DNA DNA forms sequences or codes that give the body instructions The complete set of genes in an individual is a genome DNA and Chromosomes Chromosome number is species-specific! Examples: Camel: 70 Salamander: 24 Apple: 34 Algae: 148 Colobus Monkey: 44 Orangutan: 48 Human 46 Chromosomes A healthy human has 46 chromosomes, in 23 pairs. Why are they in pairs? DNA is homoplasmic: every cell in the body has the exact same, complete set of DNA Mitochrondrial DNA is different and used to trace ancestry. Inherited 100% through mother’s line Heteroplasmic: it can differ within in body Chromosome Types Chromosomes are homologous, meaning they are in pairs, with the same information on the same locations The first 22 (pairs of) chromosomes are autosomes The 23rd pair are sex chromosomes (XX or XY) All chromosomes lined up in order is a karyotype DNA: Blueprint for Life DNA is the instruction manual for the body What shape does DNA have? The sides are made of sugar (deoxyribose) and phosphate The “rungs” are made of 4 bases: adenine, thymine, cytosine, guanine or A, T, C, G Complementary bases Specific pairing: A ALWAYS BONDS WITH T C ALWAYS BONDS WITH G DNA Replication Cells must make more of themselves Makes identical copies if it is a somatic cell In order to do this, the FIRST STEP IN CELL DIVISION IS ALWAYS DNA REPLICATION The bonds between A/T and C/G are broken and the ladder unzips The lonely letters look for their complementary partner: A for T and C for G When they attach to free floating letters, they have made two identical ladders and have replicated Hmmm… Now, if a cell has 46 chromosomes in it And we have done DNA replication, Then that cell will have double the number of chromosomes…it will have 92 Is this normal? How do we get it back to 46? Mitosis Somatic cells have all 46 chromosomes. They are diploid in number To make more, we use mitosis: After DNA replication, when the cell has 92 chromosomes, it pinches apart and becomes 2 cells, each identical, each with 46 chromosomes Gametes Gametes are different How much genetic information can you pass down to your offspring? Therefore, gametes have HALF the number of chromosomes: 23. They are haploid in number Meiosis Gametes make new cells by meiosis The first step is still____________________!!! They now have 92 chromosomes They divide once (just like mitosis) and have 46 But they MUST DIVIDE A SECOND TIME to end up with 23 chromosomes in each cell (sperm or egg) created Variation During meiosis the body can try to add variation Crossing over and recombination are reshuffling of the genetic material just before division Sometimes there can be errors Translocations rearrange chromosome information but can insert or delete information Nondisjunction means that an even number of chromosomes does not get divided into each cell Trisomy 21 Nondisjunction can create Trisomy 21, in which 3 chromosomes are created at the 21st spot This is known as Down Syndrome Protein Synthesis DNA is also used in creating proteins, which help in growth, function, and repair of tissues They are made of amino acids, half of which are made in the body and half of which come from food Proteins can be structural: responsible for physical features (hair, eye color, bone shape) or regulatory (hormones, enzymes, antibodies) Protein Synthesis Has two parts: I. Part I is Transcription II. Part II is Translation Transcription Begins just like DNA replication Enzyme splits the bonds of A, T, C, G BUT, instead of bonding and replicating, one strand bonds in a different way: C bonds with G but A bonds with U (uracil) If a U is involved, it is protein synthesis The U creates RNA, which is smaller than DNA mRNA (messenger) is the product formed in this stage Transcription The mRNA is small enough to leave the nucleus and go to the ribosome It carries the message in the form of 3 letter codons Examples: AUG, GCC, AUA, UAC Translation In the ribosome, the mRNA codons are met by tRNA (transfer RNA) anticodons that match letters Example: mRNA codons tRNA anticodons CCG, UAG, CUG GGC, AUC, GAC These matchings “translate” the code until an stop codon makes them stop (like a period in a sentence). These form amino acids in long chains The chains keep winding and coiling to form proteins, which have unique 3D shapes Regulation Other than Replication and Protein Synthesis, DNA’s function is regulation These codons start or stop certain functions DNA has a high degree of stability Mutations do occur, but the error rate in replication is 1 in 10 billion! A lot of our DNA is inactive: about 98% of our DNA is not actively doing anything Blood Type Blood is unique: it has 4 phenotypes but 6 genotypes: Phenotype Genotype Type A AA or AO Type B BB or BO Type AB AB Type O OO Blood Type You get your blood type from antigens Antibodies will attack foreign particles, so the letters must match in blood donation or agglutination occurs A and B are dominant and share dominance: they are codominant O is recessive (it is neutral and has no antigens) Blood Type To donate, letters must match! Type A can give/receive if it has an A (AA, AO), or O (it is neutral) Type B can give/receive if it has a B (BB, BO), or O (it is neutral) Type AB can receive from anyone (AA, BB, AB AB, O is neutral) but can only give to itself Type O can give to anyone (O is neutral), but can only receive itself Blood Type Who is the universal donor? Who is the universal recipient? Punnett Square Review For the trait for ‘handedness’ (right-handed or lefthanded), right-handed is dominant Mother is left-handed and father is homozygous for right-handed. What is the chance their offspring will be left-handed? Punnett Square A regular punnett square has the same letter, just uppercase or lowercase; for blood type, this is the only time the square will have different letters Let’s do a problem with blood type Sharon just had a baby and doesn’t know who the father is. Sharon: Type A Guy 1: Type AB Baby: Type O Guy 2: Type B Can we say who IS NOT the father? First, write out the possible genotypes: Sharon: AA or AO Guy 1: AB Guy 2: BB or BO Baby: OO Is there anyone who could not be the father? Yes, Guy 1 because both the mother and the father would have to give the baby an “O” Using this, what is Sharon’s genotype? It has to be AO, to give the baby an “O” Now let’s see if Guy 2 could be the father: Punnett Square: Put Sharon’s alleles across the top and Guy 2’s down the side: A O B AB BO O AO OO The last box show that there is a chance (1/4 or 25%) that Sharon and Guy 2 gave the baby O alleles, so Guy 2 could be the father More Practice The Punnett Square and the letters you fill in are the genotypes The end result that we can describe is the phenotype Example 2: Red is dominant in rose color A red rose (homozygous dominant) and a white rose have what chance of producing white roses? Answer Homozygous dominant (red) = RR Homozygous recessive (white) = rr R R Rr Rr Rr Rr r r There is a 0% chance of making white (recessive) roses because each box has at least one dominant (red) R Questions Why are there two types of cell divisions (mitosis and meiosis)? Why does mitosis use DNA and protein synthesis use RNA? How are they different? What is the difference between a genotype and phenotype? Who is the universal donor and recipient?