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Cell Division and Genetics

Cell Division and Genetics

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Cell Division and Genetics

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  1. Cell Division and Genetics Chapters: 12-15

  2. Why do we need cell division? 2 REASONS: Growth and maintenance Reproduction

  3. Cell Cycle Overview

  4. The Cell Cycle Control System A cyclically operating set of molecules in the cellthat both triggers and coordinates key events in the cell cycle • regulated at certain checkpoints by both internal and external signals

  5. The Checkpoints A control point where stop and go-ahead signals can regulate the cycle • animal cells have built-in stop signals that halt the cell cycle at checkpoints until overridden by go ahead signals • signals come from cellular surveillance mechanisms inside the cell • determine if the major processes of the cell cycle have been completed • Three major check points: G1, G2, M

  6. G1 Checkpoint “Restriction Point" • if a cell receives the go ahead at G1 checkpoint, then the cell will continue with the cell cycle. • If the cell DOES NOT get the go ahead it will enter G0 • the nondividing state of a cell • most cells in body are in G0 (nerves and muscle cells) • liver cells can be taken out of G0 phase if necessary (growth factors released during injury)

  7. The Cell Cycle Clock The cell cycle is controlled by fluctuations of cycle control molecules that occur in intervals • these rhythmic abundances pace the events of the cell cycle Regulatory molecules are two proteins • cyclins • protein kinase • enzymes that will activate or inactivate other proteins by phosphorylating them • give the go ahead signal at the G1 and G2 checkpoints

  8. Cell Division in Prokaryotes Called Binary Fission • means "division in half" (asexual reproduction) • starts at the origin of replication where the circular DNA begins replicating • once the DNA is fully replicated, the cell begins to stretch toward the poles of the cell • the membrane begins pinching off in the middle • you now have two new daughter cells

  9. Interphase • the longest phase of the cell cycle • accounts for 90% of the cell's life • the cell is producing proteins and cytoplasmic organelles • The chromatin is not condensed during interphase because it is needed for protein synthesis • Divided into 3 subphases: • G1 Phase => first gap • S Phase => synthesis (chromosome duplication) • G2 Phase => second gap

  10. Mitosis The part of the cell cycle where the cell is actually undergoing cell division • Consists of 5 stages • prophase • metaphase • anaphase • telophase • Timing and rate of cell division are crucial to normal growth, development and maitenance • varies with type of cell Cytokinesis is part of the Mitotic (M) phase, but not apart of mitosis itself. Different in plants and animals

  11. Prophase 1st stage of mitosis • the chromatin condenses into two identical chromosomes and the nuclear envelope begins to disappear

  12. Metaphase 2nd stage of mitosis • the chromosomes line up on the equatorial plate • spindle fibers are attached to the kinetochore of each chromosome pair • "tug of war"

  13. Anaphase 4th stage of mitosis • shortest • cohesion proteins are cut and the sister chromatids are now separated • the cell beings elongating

  14. Telophase Final stage of mitosis • daughter cells begin to form • nuclear envelope is visible again • nucleoli reappear • spindle fibers disappear

  15. Comparing Cytokinesis Animals: Plants: • There is NO cleavage furrow • because plant cells have cell walls in addition to cell membranes, they need to build a new cell wall • vesicles will form in the middle of the original parent cell from the golgi apparatus (starts during telophase) • merge and become the cell plate • enlarges until the membranes fuse • In animals: • occurs by cleavage • a cleavage furrow will form in what was the middle of the parent cell • the furrow is a contractile ring of actin filaments that contract • eventually splits the cell into two daughter cells

  16. Cyclins and Protein Kinases Timing of the cell cycle is initiated by growth factors and controlled by two kinds of molecules: cyclins and protein kinases • protein kinases (cell signal transduction) catalyze the phosphorylation of target proteins that regulate the cell cycle • Cyclin-dependent kinases (CDKs)

  17. Cyclin-dependent Kinase • Activated by binding to the protein cyclin • exposes the active site to the CDK and activates the molecule • allosteric regulation • Several CDKs regulate the cell cycle at specific stages called cell cycle checkpoints • each cyclin is manufactured at a precise time during the cell cycle and therefore each CDK is activated at a precise time • The activity of CDKs rises and falls with changes in the concentration of its cyclin partner MPF

  18. The Chain Reaction that Controls the Cell Cycle Cell Cycle events CDK activation growth factor cyclin synthesis

  19. Meiosis **this video made us laugh, if you get the gist of it, move on**

  20. Meiosis: Different than Mitosis Meiosis generates the genetic diversity taht is the raw material for natural selection and evolution • produces gametes (egg and sperm) or sex cells • that are haploid the chromosome number (n) of the parent cell • the chromosome number will return to diploid (2n) during sexual fusion • NOT MITOSIS TWICE

  21. Meiosis I: The Source of Genetic Variation Known as reduction division • Meiosis I is characterized by: • homologous chromosomes pairing up • crossing over genetic information • the nonsister chromatids exchange genetic information • results in recombination of genetic material • CROSSING OVER ENSURES GREATER VARIATION AMONG GAMETES

  22. Meiosis: Prophase I Synapsis: the pairing of homologous chromosomes occur crossing over occurs Chiasmata: the point where the crossing over occurs

  23. Prophase vs. Prophase I chiasmata • Prophase: Mitosis • the chromosomes condense and sister chromatids meet at the kinetochore • Prophase I: Meiosis • homologous chromosomes pair up • non-sister chromatids exchange genetic information (crossing over) at the chiasmata

  24. Meiosis I: Overview

  25. Meiosis II Meiosis II is exactly like mitosis in the sense that the sister chromatids are separating and forming two new cells • remember that after Meiosis I, there are two haploid cells (half of the number of chromosomes) that are genetically different • meiosis II continues as cell division, separating the sister chromatids • In the end, each gamete should have half the chromosomes of the parent cell and no sister chromatids

  26. Egg sex cells vs. Sperm cells Male sex cells (sperm) • undergo meiosis where each sperm is equal • like you think a normal cell would undergo meiosis • quantity over quality Female sex cells (eggs) • specialized meiosis • an egg will undergo meiosis to "get rid of" half of genetic material, but will keep the rest of the cells resources • leftover cells are called polar bodies • quality over quantity

  27. Egg cells vs sperm cells

  28. Ch. 14 Mendel and the Gene Idea

  29. Law of Dominance • Mendel’s first law is the law of dominance • Law of dominance: states that when two organisms, each homozygous (pure) for two opposing traits are crossed, the offspring will be hybrid (carry two different alleles) but will exhibit only the dominant trait • The trait that remains hidden is known as the recessive trait Parent (P): TT X tt (pure tall) (pure dwarf) Offspring (F1): Tt All hybrid T T t t Law of dominance All offspring are tall

  30. Law of Segregation • The law of segregation states that during the formation of gametes, the two traits carried by each parent separate Gametes • The cross that best exemplifies this law the monohybrid cross, Tt X Tt. In the monohybrid cross, a trait that was not evident in either parent appears in the F1 generation Tt T t

  31. Law of Independent Assortment • The only factor that determines how these alleles segregate or assort is how the homologous pairs line up in metaphase of meiosis I, which is random.

  32. Law of Independent Assortment • The law of independent assortment applies when a cross is carried out between two individuals hybrids for two or more traits that are noton the same chromosome. • This cross is called the dihybrid cross. • This law states that during gamete formation, the alleles of a gene for one trait segregate independently from the allele of a gene for another trait.

  33. Multiplication Rule • Multiply the chance of one happening by the chance that the other will happen • For example: • The chance of a couple having two boys depends on two independent events. The chance of the first child being a boy is ½ ; and the chance of the next child being a boy is ½ • Therefore, the chance that the couple will have two boy is ½ x ½ = ¼ • The chance of having three boys is ½ x ½ x ½ = 1/8

  34. Addition Rule • When more than one arrangement of events producing the specified outcome is possible, the probabilities for each outcome are added together. • For example: if a couple is planning on having two children, what is the chance that they will have one boy and one girl • The probability of having a girl and then a boy is ½ x ½ = ½ • The probability of having one boy and one girl is ¼ + ¼ = ½

  35. Monohybrid cross • The monohybrid cross (Tt XTt) is a cross between two organisms that are each hybrid for one trait. • The phenotype (appearance) ration from this cross is 3 tall to 1 dwarf plant. • The genotype (type of genes) ratio, 1 to 2 to 1, given as percentages: 25% homozygous dominant, 50% heterozygous, and 25% homozygous recessive. These results are always the same for any monohybrid cross. T t T F1: Tt X Tt F2: TT, Tt, or tt t Monohybrid cross

  36. Testcross • The testcross is way to determine the genotype of an individual plant or animal showing only the dominant trait. If the parent of unknown genotype is BB, there can be no white offspring B= black b= white If the parent of the unknown genotype is hybrid, there is a 50% chance that any offspring will be white. B B b b B b b b

  37. The Dihybrid Cross • A dihybrid cross is a cross between two F1 plants because it is a cross between individual that are hybrid fro two different traits • This cross can produce 4 different types of gametes, such as: TY, Ty, tY, and ty. tY ty TY Ty TY Ty tY Phenotype ratio: 9:3:3:1 ty

  38. Incomplete dominance • Incomplete dominance is characterized by blending. • For example: A red flower (RR) crossed with a white flower (WW) produces all pink offspring (RW) R R W W W R • If 2 pink flowers are crossed, there is a 25% chance that the offspring will be red, a 25% chance the offspring will be white, and a 50% chance the offspring will be pink R W

  39. Codominance • In codominance, both traits show. • For example: Different blood groups: M, N, and MN MM NN MN

  40. Multiple alleles • Occurs when there are are more than two allelic forms of a gene • For example: Human blood types- A, B, AB and O The 3 alleles= A, B, and O determine 4 different blood types

  41. Gene Interactions:Pleiotropy • Pleiotropy is the ability of one single gene to affect an organism in several or many ways. • For example: autosomal recessive disease cystic fibrosisabnormal thickening to mucus that coats certain cells  thick mucus builds up in the pancreas, lungs, digestive tract and other organs • leads to multiple pleiotropic effects including poor absorption of nutrients in the intestine and chronic bronchitis

  42. Gene Interactions: Epistasis • Where two separate genes control one trait, but one gene masks the expression of the other gene • The gene that masks the expression of the other gene is epistatic to the gene it masks • For example: agouti coat color in mice 2 genes control different enzymes in 2 different pathways that both contribute to coat color • Both genes A and B must be present in order to produce that agouti color AaBb X AaBb In the absence of B, even if A is present, the coat is colorless (albino) Therefore gene B is epistasis to gene A

  43. Polygenic Inheritance • Polygenic traits: many characteristics such as skin color, hair color, and height result from blending of several separate genes that vary along a continuum • The wide variation in genotypes always results in a bell-shaped curve in an entire population

  44. The Pedigree • A pedigree is a family tree that indicates the phenotype of one trait being studied for every member of a family • It can determine how a particular trait is inherited • Females are represented by a and males by a • A shape is completely shaded in if a person exhibits the trait

  45. Ch. 15The Chromosomal Basis of Inheritance

  46. The Chromosomal Basis of Inheritance Chromosome theory of inheritance: • Genes have specific loci along chromosomes • Chromosomes undergo segregation and independent assortment

  47. Thomas Hunt Morgan's Experiment: • Fruit fly (drosophila melanogaster) • Bred flies for 2 years with no conclusion • Finally, 1 male had white eyes instead of the usual red (red is the wild type--characteristic most commonly observed) • White eyes were a mutant phenotype • Continued mating females with white-eyed male • Discovered the gene for eye color is gender related and on the X chromosome • Supported chromosome theory of inheritance that a specific gene is on a specific chromosome

  48. Sex-linked genes • X and Y chromosomes • XX-- female; XY-- male (sex determination is 50-50 chance) • Sex-linked gene- gene located on either X chromosome • Very few Y-linked genes, passed from father to son • About 1,100 X-linked genes • Males more likely to have disorders from X-linked gene (have disease if either recessive or dominant because only one X chromosome) • ex. color blindness, Duchenne muscular dystrophy, hemophilia

  49. Sex-linked Genes • X inactivation in Females • Most of one X chromosome becomes inactivated when embryo is developing • If did not become inactivated, chromosomes would make 2x the amount of proteins for X-linked genes as males • Inactive X condenses into compact object called a Barr Body • Selection for which X chromosome is inactivated occurs randomly

  50. Linked Genes • Linked genes- genes located near each other on the same chromosome tend to be inherited together in a genetic cross • Genetic recombination- the production of offspring with combinations of traits that differ from those found in either parent • Parental type- the half of the offspring that inherit a phenotype that matches either parent's phenotype • Recombinant types (recombinants)- offspring that have non parental phenotypes