Genetics: Reproducing Life and Producing Variation

1. Genetics: Reproducing Life and Producing Variation Chapter 3

2. 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

3. 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

4. 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

7. DNA and Chromosomes • Chromosome number is species-specific! • Examples: • Camel: 70 • Salamander: 24 • Apple: 34 • Algae: 148 • Colobus Monkey: 44 • Orangutan: 48 • Human 46

8. 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

9. 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

11. 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

13. 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

15. 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?

16. 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

18. 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

19. 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

21. 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

24. Trisomy 21 • Nondisjunction can create Trisomy 21, in which 3 chromosomes are created at the 21st spot • This is known as Down Syndrome

26. 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)

27. Protein Synthesis • Has two parts: • I. Part I is Transcription • II. Part II is Translation

28. 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

29. 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

31. Translation • In the ribosome, the mRNA codons are met by tRNA (transfer RNA) anticodons that match letters • Example: mRNA codons CCG, UAG, CUG • tRNA anticodons 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

33. 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

34. Blood Type • Blood is unique: it has 4 phenotypes but 6 genotypes: • PhenotypeGenotype • Type A AA or AO • Type B BB or BO • Type AB AB • Type O OO

35. 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)

36. 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 (AA, BB, 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

37. Blood Type • Who is the universal donor? • Who is the universal recipient?

39. Punnett Square Review • For the trait for ‘handedness’ (right-handed or left-handed), 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?

40. 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?

41. 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”

42. 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 O • 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

43. 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?

44. Answer • Homozygous dominant (red) = RR • Homozygous recessive (white) = rr R R r r There is a 0% chance of making white (recessive) roses because each box has at least one dominant (red) R

45. 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?