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Genetics Exam 1 September 16nd Assignment 1 due Sept. 16nd Sections of chapters 8, 9, 10 Chapters 8 and 9 • Gregor Mendel – Was the first person to analyze patterns of inheritance – Deduced the fundamental principles of genetics Figure 9.4 Mendel’s Peas The garden of the Augustinian Convent in Brno, Moravia (Czech Republic) Mendel’s Experiments with Peas • He created what he called true-breeding varieties of the plants: -All purple plants, when self-fertilized, will have purple offspring -All white plants, when self-fertilized, will have white offspring • Mendel then cross-fertilized the two different true-breeding varieties, creating hybrids Monohybrid Crosses • A monohybrid cross is a cross between parent plants that differ in only one characteristic (in this case, flower color) P Generation (true-breeding parents) Purple flowers White flowers All plants have purple flowers F1 Generation Fertilization among F1 plants (F1 F1) F2 Generation 3/ of plants have purple flowers 4 (a) Mendel’s crosses tracking one characteristic (flower color) 1/ of plants have white flowers 4 Figure 9.8a Mendel’s Discoveries • Define alleles. • What are dominant and recessive alleles? Alleles • In Mendel’s peas and other examples: – For each trait there is 1 gene – Gene exists in 2 forms called alleles – Each parent can only give one allele to their offspring. – Some alleles mask others Genetic makeup (alleles) pp PP P plants • An explanation of Mendel’s results, including a Punnett square Gametes All P All p F1 plants: (hybrids) Gametes All Pp 1/ 2 F2 plants: Phenotypic ratio 3 purple : 1 white P Eggs 1/ P P PP p 2 p Sperm p Pp Pp pp Genotypic ratio 1 PP : 2 Pp : 1 pp (b) Explanation of the results in part (a) Figure 9.8b An Example Gene: Seed shape Dominant allele: R (round) Recessive allele: r (wrinkled) 3 Genotypes: RR, Rr, rr 2 Phenotypes: Round & Wrinkled Some definitions • Define Homozygous. • Define Heterozygous. • Homozygous – When an organism has identical alleles for a gene • Heterozygous – When an organism has different alleles for a gene • Gamete: sexual reproduction cell carrying 1 of each chromosome pair and therefore 1 allele • What do gametes have to do with the first two definitions? • Mendel’s principle of segregation – Pairs of alleles (one from mom, other from dad) segregate (separate) during gamete formation – The likelihood that a gamete (sperm or egg) will receive one or the other allele from the allele pair in a gene is 50:50 (like a coin toss) – The fusion of gametes at fertilization creates allele pairs again You try it r r r R Mother’s alleles • Finish the following cross: Rr x rr Father’s alleles • What are the father’s phenotype and genotype? • How many different genotypes could result from this cross? How many different phenotypes? Using a Testcross to Determine an Unknown Genotype • A testcross is a mating between – An individual of unknown genotype and –A homozygous recessive individual Testcross: Genotypes P_ pp Two possibilities for the purple flower: PP Gametes P P Offspring Pp Pp All purple P p Pp p pp 1 purple : 1 white Figure 9.12 Now try this Alleles for flower color: P (dominant, purple flower), p (recessive, white flower) Genetics in humans • Study humans using pedigrees pedigrees Recessive Recessive or ?? Dominant What are genes? • The search was on to find where in the cell the alleles were located. • With the invention of microscopes and microscopic techniques scientists discovered the chromosomes. Chromosomes • Found in every cell (a few exceptions) • Come in pairs • Chromosomes are visible during cell division Chromosomes are visible during cell division Onion root tip Cell division in sex organs is different Sex cells (gametes) are made so they only carry half the chromosomes Early observations about Chromosomes • How do chromosomes behave like Mendel’s alleles? Human Chromosomes • 23 pairs = 46 total • 1 pair is not like the others, sex chromosomes determine your gender – XX = female – XY = male • Pairs called homologous pairs, each member of the pair carries one of the two alleles • Chromosome numbers vary in other species We can use cell division to look at our chromosomes Making a karyotype obtain sample cells culture cells burst cells and place on slides add stain photograph cut out and sort chromosomes Genetics Part 2 More from chapters 8 and 9 Not all traits are Mendelian Exceptions to Mendelian Genetics • What phenotypic ratio would you expect in the offspring of the following cross? Rr x Rr (R = red flowers, r = white flowers) • What if the offspring were ¼ red, ¼ white and ½ pink, what does that indicate? Incomplete Dominance in Plants P Generation Red RR • In incomplete dominance, F1 hybrids have an appearance in between the phenotypes of the two parents White rr Gametes F1 Generation Pink! Rr 1/ Gametes 1/ Eggs With INCOMPLETE dominanceF2 Phenotypic ratio: 1 purple : 2 pink : 1 white r R 1/ F2 Generation 2 2 2 R 1/ 2 1/ R r r 2 Sperm R Red RR 1/ 2 r Pink rR Pink Rr White rr Figure 9.18 Exceptions to Mendelian Genetics Codominance Example: human blood types Phenotypes = A, B, AB and O blood types There are 3 alleles: A and B are dominant Codominance – Multiple alleles in blood type • The ABO blood groups in humans are examples of multiple dominant alleles • Two of the human blood type alleles exhibit codominance • Both alleles are expressed in the phenotype Exceptions to Mendelian Genetics • Polygenic traits: traits determined by multiple genes. – Eye color, height, blood type including Rh factor. Ex: Human Blood types Phenotypes = A+, A-, B+, B-, AB+, AB-, O+ and O2 genes, 1. Rh factor has 2 alleles, + and – (+ is dominant) 2. Type has 3 alleles, A, B and O (A and B are dominant) Polygenic Inheritance P Generation • Polygenic inheritance is the additive effects of two or more genes on a single phenotype aabbcc (very light skin) AABBCC (very dark skin) F1 Generation AaBbCc AaBbCc F2 Generation Possible Eggs Possible Sperm • In the example to the right, what is the dominant phenotype? • How many genes are responsible for skin color in this example? Figure 9.22 Pleiotropy • Pleiotropy is the impact of a single gene on more than one characteristic. These characteristics are thus usually expressed together. Examples: Red hair and freckles or sickle-cell disease Human Chromosomes • 23 pairs = 46 total • 1 pair is not like the others, sex chromosomes determine your gender – XX = female – XY = male • Pairs called homologous pairs, each member of the pair carries one of the two alleles • Chromosome numbers different in other species – This is part of the reason why you can’t breed different species Genes on Chromosomes • There are many more traits than there are chromosomes • There must be more than one trait on each chromosome P S T E P s T e Chromosome pair 1 A b R V A b R v Chromosome pair 2 Homologous chromosomes: Gene loci Dominant allele a P P Genotype: PP Homozygous for the dominant allele a aa Homozygous for the recessive allele B b Recessive allele Bb Heterozygous Figure 9.9 Sex Determination in Humans Male 44 + XY • Sex chromosomes – Are designated X and Y – Determine an individual’s sex (boy or girl) 22 + X Female Somatic cells 22 + Y 44 + XX 22 + X Sperm 44 + XX Female Egg 44 + XY Male Figure 9.27 SEX CHROMOSOMES AND SEX-LINKED GENES • Sex chromosomes – Determine gender – Influence the inheritance of certain traits Sex-Linked Genes • Sex-linked genes – Are any genes located on a sex chromosome – Were discovered during studies on fruit flies (a) (b) Figure 9.28 Sex-Linked Genes • Red-green color blindness – Is characterized by a malfunction of light-sensitive cells in the eyes Figure 9.30 Sex-Linked Genes • Hemophilia – Is a bloodclotting disease Queen Victoria Albert Alice Louis Alexandra Czar Nicholas II of Russia Alexis Figure 9.31 DNA, Replication, and Mitosis Chapter 10 DNA Structure: the double helix C A G T DNA base pairs A–T C–G DNA is “supercoiled” around proteins called Histones to form Chromosomes This is an actual microscopic photograph of DNA supercoiled into a chromosome. Chromosomes • Chromosomes as seen with a light microscope Onion root tip Above is what is sometimes called the “central dogma” of cell biology. In the cell nucleus, DNA is involved with two major processes: (1) DNA replicates itself, making more double stranded DNA (2) One strand of DNA is: A. transcribed to make RNA B. that RNA copy leaves the nucleus, and is then translated at the ribosome to make proteins Cell Cycle Chapter 8 • Life cycle of a cell. – – – – – Cell is “born” from another cell Cell grows Cell gets ready to reproduce Cell reproduces (it splits) Or, the cell dies • When cells reproduce, they pass on their genes • Cell reproduction is called mitosis Cell Cycle • Cell Cycle – What happens at each stage? • Interphase • Mitosis Cell Cycle • The most well understood parts of the cell cycle are replication and mitosis • Replication is the process of copying genes before splitting the cell • Mitosis is the process by which one cell becomes two identical daughter cells Cell Cycle • The stages of mitosis can be seen with a microscope Onion root tip Genes Chapter 10 • DNA carries genetic information • What does DNA look like? • What is it’s chemical structure? • How is that represented? DNA Replication • Now that we know what DNA looks like and how that can be represented, • We can learn how it copies itself. • Replication occurs before mitosis and meiosis DNA Replication • Animation of replication • www.youtube.com/watch?v=4jtmOZaIvS0 Genetics 3 How do genes determine physical traits? DNA to proteins Genes and mutations Chapter 10 The Genetics Story: How does DNA act as instructions for a trait? DNA RNA Protein Genotype Phenotype DNA “Book of instructions” Transcription RNA “Page of instructions” Translation Protein Gene Expression (trait) Overview Ribosomes RNA Protein DNA Transcription 5` Copy from DNA to RNA Messenger RNA (mRNA) 3` A A G G T C G T C C A G 3` T C C A G C 3` A G C T 5` U 5` RNA Polymerase Translation mRNA goes out of the cell nucleus and to the ribosomes. Ribosomes are made of ribsomal RNA (rRNA) and proteins. Translation = RNA to protein Ribosomes “read” the mRNA. mRNA RNA language Three nucleotides of RNA correspond to one amino acid = Codon GCUGUCCCCAGCUUAGCG Alanine Leucine Serine Proline Valine Alanine Table 7.2 Transcription Translation Ribosomes mRNA DNA Protein Summary 1. DNA is transcribed into mRNA. - RNA is slightly different from DNA. 2. mRNA is translated into amino acids. - ribosomes match the codons of the mRNA to the anticodons of the tRNAs. 3. Certain codons are translated into amino acids. Start…………Stop. 4. Amino acids linked together = protein. Example DNA: TAC CCA GTG GAG GTA CCT GAT ACT RNA: AUG GGU CAC CUC CAU GGA CUA UGA Amino Acids: Start Gly His Leu His Gly Leu Stop DNA to protein • Animation of gene expression • www.youtube.com/watch?v=NJxobgkPEAo Mistakes can happen DNA and RNA polymerase can make a mistake in copying = mutation. DNA: TAC CCA GTG GAG GTA CCT GAT ACT Should be A RNA: AUG GGU CAC CUC CAU GGG CUA UGA Amino Acids: Start Gly His Leu His Gly Leu Stop DNA mutations can occur from exposure to x-rays, ultraviolet radiation, human papillomavirus (HPV), and many other mutagens. DNA mutations result in a change in RNA, which then can result in a change in the amino acid sequence of a protein. An effective or missense mutation is one where the mutation actually causes a change in the amino acid sequence. GCA codes for the amino acid Alanine, instead of Glycine (GGA) A non-effective, or silent mutation is one where the mutation caused no change in the amino acid sequence, due to redundancy in amino acid codons (GGG and GGA both code for Glycine) Fig. 7.9 Sickle cell anemia: This is the result of only ONE base pair mutation to DNA, which results in the changing of only ONE amino acid in an amino acid sequence.