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NICE GENES!

NICE GENES!. UNIT 3 INTRODUCTION. Think about this…. We share 99% of our DNA with this chimpanzee… And 60% of the DNA in the banana he is eating!!. Nature Theory. Search for "behavioral" genes - source of debate arguments used to excuse criminal acts

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NICE GENES!

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  1. NICE GENES! UNIT 3 INTRODUCTION

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

  3. Nature Theory • Search for "behavioral" genes - source of debate • arguments used to excuse criminal acts • Twin studies - twins raised apart have shown same interests and behaviour

  4. Nurture Theory • Nurture theorists believe genetics ultimately don't matter - our behaviours originate from our upbringing

  5. 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-

  6. Nature Vs. Nurture • Researchers agree that the link between a gene and a behavior is not the same as cause and effect. • A gene may increase the likelihood that you'll behave in a particular way, it does not make your actions

  7. What is a Chromosome? • A human body cell contains 46 chromosomes which are paired up to make 23 pairs. • These cells are Diploid. • 1 of the pair comes from mom, 1 from dad!

  8. What is a Gene? • Each chromosome is one molecule of DNA. • The smaller sections of DNA, which code for certain features, are called Genes. • Eg. Blue eye pigment, height, chin shape, etc.

  9. 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.

  10. MITOSIS

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

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

  13. 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

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

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

  16. Stages of Mitosis - Prophase • P = PREPARING • DNA condenses into chromatids • Nuclear membrane disappears • Spindle fibers form from centrioles and attach to centromeres.

  17. Stages of Mitosis - Metaphase • M = MIDDLE • Chromatids line up down the middle. • Pulled into place by spindle fibres.

  18. Stages of Mitosis - Anaphase • A = APART • Chromatids are pulled apart (by spindle fibres)

  19. Stages of Mitosis - Telophase • T = TEARING • Nuclear membrane reforms • cell divides • 2 identical daughter cells (DIPLOID – 2n)

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

  21. MEIOSIS Mitosis for our sex cells

  22. Meiosis and Variation • Meiosis will not produce clones each time! • Variation is key for species survival, allows organisms to adapt! • During Meiosis, two events occur which increase variation…

  23. 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!

  24. Crossing Over • 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)

  25. 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.

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

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

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

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

  30. 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.

  31. 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).

  32. 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

  33. Genetics…A Little History

  34. Gregor Mendel • Austrian monk • Grew and tested pea plants • Started with two pure plants (tall plants which bore smooth yellow seeds) • Saw that first generation (F1) was all the same, but F2 had some short plants with green, wrinkled seeds….what’s up?

  35. Mendel (cont) • Came up with Law of Heredity (how traits are passed on through generations) • Mendel rap!

  36. Predicting Probability • The Punnett 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!

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

  38. Monohybrid Cross Results: 75% chance of purple flowers 25% chance of white flowers

  39. Example 1 • Brown eye colour (E) is dominant to blue eyes (e). What would be the eye colour of offspring of a heterozygous mother and homozygous recessive father?

  40. Example 1

  41. Example 1

  42. Example 2 • Long tails (T) in rats is dominant to short-tailed rats (t). What is the ratio of phenotypes between 2 heterozygous rat parents?

  43. Example 2

  44. Example 2

  45. Dihybrid Cross • We observe 2 pair of alleles for 2 different genes. • Note:The 2 genes are not linked…they must be on 2 separate chromosomes! • Example…Mendel’s Peas • Gene 1 (on chromosome A): Colour of seed Alleles: Y = Yellow, y = Green • Gene 2 (on chromosome B): Shape of seed Alleles: R = Round, r = wrinkled

  46. Parental Generation RRYY rryy Plant with round, X Plant with Yellow seeds wrinkled, green seeds Alleles: RY ry

  47. F1 Generation • All plants produce round, yellow seeds

  48. Cross the F1 Generation • RrYy X RrYy • Gametes: • RY, Ry, ry, rY RY, Ry, ry, rY

  49. The Results! • 9 Yellow Round • 3 Yellow Wrinkled • 3 Green Round • 1 Green Wrinkled • Try These: Practice Problem • Pg. 166 a-c

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