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NICE GENES!

NICE GENES!. UNIT 3 INTRODUCTION. Homunculus (late 17 th century). Think about this…. We share 99% of our DNA with this chimpanzee… And 60% of the DNA in the banana he is eating!!. HOW DID YOU…. BECOME YOU?!?!. Nature Theory.

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NICE GENES!

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  1. NICE GENES! UNIT 3 INTRODUCTION

  2. Homunculus (late 17th century)

  3. Think about this… • We share 99% of our DNA with this chimpanzee… • And 60% of the DNA in the banana he is eating!!

  4. HOW DID YOU… BECOME YOU?!?!

  5. Nature Theory • Scientists have known for years that traits such as eye color and hair color are determined by specific genes encoded in each human cell. • The Nature Theory takes things a step further to say that more abstract traits such as intelligence, personality, aggression, and sexual orientation are also encoded in an individual's DNA.

  6. Nature Theory • The search for "behavioral" genes is the source of constant debate. Many fear that genetic arguments might be used to excuse criminal acts or justify divorce. • Twin studies have (to some extent) supported this theory…twins raised apart have shown same interests and behaviour. • Savants

  7. Nurture Theory • While not discounting that genetic tendencies may exist, supporters of the nurture theory believe they ultimately don't matter - that our behavioral aspects originate only from the environmental factors of our upbringing

  8. Nurture Theory “Give me a dozen healthy infants, well-formed, and my own specified world to bring them up in and I'll guarantee to take any one at random and train him to become any type of specialist I might select...regardless of his talents, penchants, tendencies, abilities, vocations and race of his ancestors.” -Behavioural Psychologist John Watson-

  9. Nature Vs. Nurture • Researchers on all sides of the Nature Vs Nurture debate agree that the link between a gene and a behavior is not the same as cause and effect. • While a gene may increase the likelihood that you'll behave in a particular way, it does not make people do things. Which means that we still get to choose who we'll be when we grow up.

  10. What is a Chromosome? • A human somatic (body) cell contains 46 chromosomes which are paired up to make 23 Homologous Pairs. • These cells are Diploid. • 1 of each pair comes from mom, 1 from dad!

  11. What is a Gene? • Each chromosome is one molecule of DNA. • The smaller sections of DNA, which code for certain features, are called Genes. • Each gene is responsible for the production of mRNA, which makes a protien • Eg. Blue eye pigment, hemoglobin etc.

  12. Homologous Chromosomes • Both chromosomes contain the same genes, BUT they are not identical. • For example: EYE COLOUR The mother’s chromosome could have the coding for blue pigment and the father’s could have coding for brown.

  13. Homologous Chromosomes

  14. B

  15. MITOSIS

  16. The Role of Mitosis • Two Stages -Divide nucleus & DNA -Divide cell (cytokinesis) • Purpose: to produce 2 identical cells for… -Growth -Repair of tissue -Replace dead cells -Asexual Reproduction

  17. Terms to know! • DIPLOID (2n): Full complement of chromosomes. • In humans 2n = 46 • HAPLOID (n): Number of unique chromosomes • In humans n = 23

  18. Diploid or Haploid? In a cabbage cell the Diploid number is 2n = 18 What is the Haploid number? n = 9 How many homologous pairs? 9

  19. Centrioles Uncondensed DNA – “Plate of Spagetti” Spindle Fibres

  20. Sister Chromatids • A condensed molecule of DNA (chromosome) is called a Chromatid. • A sister Chromatid is an exact replica of the original! • The pair is called a DYAD • Chromatids are held together by a centromere

  21. The Cell Cycle • See page 122 • Most of the cell’s time is spent in Interphase!

  22. Stages of Mitosis - Interphase • This is the parent cell • Rapid growth • Cell doing its job • DNA replication (chromatin) • Prepares for division

  23. Stages of Mitosis - Prophase • DNA condenses into chromatids – Dyads form. • Nuclear membrane disappears • Spindle fibers form from centrioles and attach to centromeres.

  24. Stages of Mitosis - Metaphase • Dyads line up down the middle. • Pulled into place by spindle fibres.

  25. Stages of Mitosis - Anaphase • Dyads are pulled apart (by s.f.’s) to form monads

  26. Stages of Mitosis - Telophase • Nuclear membrane reforms • Cytokinesis occurs (cell divides) • 2 identical daughter cells (DIPLOID – 2n)

  27. Mitosis in Plant Cells • No centrioles • A cell plate forms, then cell wall.

  28. Meiosis and Variation • Recall…Variation is key for species survival, allows organisms to adapt! • During Meiosis, two events occur which increase variation…

  29. Independent (Random) Assortment • When tetrads line up at Metaphase I, the paternal and maternal chromosomes line up randomly on the left and right. • 223 = 8 388 608 different combinations!

  30. Crossing Over • While the dyads are in the tetrad, pieces of homologous chromatids can change places, creating different chromosomes. • This is desirable and occurs frequently • If one piece gets misplaced, a mutation occurs (genes are missing)

  31. Errors during Meiosis • Errors usually occur during Anaphase I, due to NONDISJUNCTION. • The homologous dyads in a tetrad do not separate. • The resulting gametes can have too many or too few chromosomes.

  32. Chromosomal Abnormalities Down Syndrome-Trisomy 21 -1 in 700 births -An extra chromosome #21 -Abnormal facial features, development -Probability increases with age of mother

  33. Chromosomal Abnormalities Klinefelter Syndrome XXY -1 in 800 -Extra ‘X’ from mother -Sterile ‘male’, long arms

  34. Chromosomal Abnormalities Super male XYY -Extra ‘Y’ from father -Tends to produce violent males

  35. Chromosomal Abnormalities Turner’s Syndrome XO -1 in 10 000 -One missing sex chromosome -Girl is usually short and sterile

  36. Things to do! • Mitosis & Meiosis Colour Code • Page 139 – Chromosome Numbers Activity 3. Page 151 - #13 4. Page 142 – Study Mitosis Vs. Meiosis Chart 5. P.142 (#5,6), P. 146 (#2), P.150 (#2-4, 8, 9, 16)

  37. Some Interesting Facts… • The human genome contains 3164.7 million chemical nucleotide bases (A, C, T, and G). • The average gene consists of 3000 bases, but sizes vary greatly, with the largest known human gene being dystrophin at 2.4 million bases. • The total number of genes is estimated at 30,000 —much lower than previous estimates of 80,000 to 140,000 that had been based on extrapolations from gene-rich areas as opposed to a composite of gene-rich and gene-poor areas. • Almost all (99.9%) nucleotide bases are exactly the same in all people. • The functions are unknown for over 50% of discovered genes.

  38. Junk DNA The Wheat from the Chaff • Less than 2% of the genome codes for proteins. • Repeated sequences that do not code for proteins ("junk DNA") make up at least 50% of the human genome. • Repetitive sequences are thought to have no direct functions, but they shed light on chromosome structure and dynamics. Over time, these repeats reshape the genome by rearranging it, creating entirely new genes, and modifying and reshuffling existing genes.

  39. How is DNA Arranged? • Genes appear to be concentrated in random areas along the genome, with vast expanses of non-coding DNA between. • Stretches of up to 30,000 C and G bases repeating over and over often occur adjacent to gene-rich areas, forming a barrier between the genes and the "junk DNA." These C-G islands are believed to help regulate gene activity. • Chromosome 1 has the most genes (2968), and the Y chromosome has the fewest (231).

  40. Variations and Mutations • Scientists have identified about 1.4 million locations where single-base DNA differences (SNPs) occur in humans. This information promises to revolutionize the processes of finding chromosomal locations for disease-associated sequences and tracing human history. • The ratio of sperm to egg cell mutations is 2:1 in males vs females. Researchers point to several reasons for the higher mutation rate in the male, including the greater number of cell divisions required for sperm formation than for eggs. http://www.ornl.gov/sci/techresources/Human_Genome/home.shtml

  41. Genetics…A Historical Survey • Let’s take up the History Sheets!

  42. HOMUNCULUS!

  43. Probability and Genetics ANYONE FOR A GAME OF PLINKO?

  44. Predicting Probability • The Punnet Square is used to predict the genotypes and phenotypes of possible offspring! • Expressed as a ratio, % or a fraction • This is not an outcome…just the likelihood of the outcome! • You need a large sample size in order to come close to the predicted outcome. (Eg. In one family – rarely ½ boys and ½ girls, but in all of Canada it is!)

  45. Probability and Genetics~Mendel’s Two Laws~ • Law of Segregation -A pair of alleles for a given trait are separated randomly into gametes. (Flip coins) 2. Law of Independent Assortment -When two or more pairs of alleles are considered at one time, each pair shows dominance and segregation independently of the other.

  46. Monohybrid Cross • In Review… • In a monohybrid cross we observe 1 pair of alleles for 1 gene. • Example: Colour of flower • Alleles: • B = purple • b = white

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