NICE GENES!

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NICE GENES!

• UNIT 3 INTRODUCTION

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Homunculus (late 17th century)
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Think about this

• We share 99 of our DNA with this chimpanzee
• And 60 of the DNA in the banana he is eating!!

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• HOW DID YOU

BECOME YOU?!?!
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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.

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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
  theorytwins raised apart have shown same
  interests and behaviour.
• Savants

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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

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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-

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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.

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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!

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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.

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Homologous Chromosomes

• Both chromosomes contain the same genes, BUT they
  are not identical.
• For example EYE COLOUR
• The mothers chromosome could have the coding
  for blue pigment and the fathers could have
  coding for brown.

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Homologous Chromosomes
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B
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MITOSIS
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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

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Terms to know!

• DIPLOID (2n) Full complement of
  chromosomes.
• In humans 2n 46
• HAPLOID (n) Number of unique chromosomes
• In humans n 23

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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

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Centrioles
Uncondensed DNA Plate of Spagetti
Spindle Fibres
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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

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The Cell Cycle

• See page 122
• Most of the cells time is spent in Interphase!

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Stages of Mitosis - Interphase

• This is the parent cell
• Rapid growth
• Cell doing its job
• DNA replication (chromatin)
• Prepares for division

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Stages of Mitosis - Prophase

• DNA condenses into chromatids Dyads form.
• Nuclear membrane disappears
• Spindle fibers form from centrioles and attach to
  centromeres.

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Stages of Mitosis - Metaphase

• Dyads line up down the middle.
• Pulled into place by spindle fibres.

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Stages of Mitosis - Anaphase

• Dyads are pulled apart (by s.f.s) to form monads

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Stages of Mitosis - Telophase

• Nuclear membrane reforms
• Cytokinesis occurs (cell divides)
• 2 identical daughter cells (DIPLOID 2n)

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Mitosis in Plant Cells

• No centrioles
• A cell plate forms,
• then cell wall.

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Meiosis and Variation

• RecallVariation is key for species survival,
  allows organisms to adapt!
• During Meiosis, two events occur which increase
  variation

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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!

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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)

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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.

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Chromosomal Abnormalities

• Down Syndrome-Trisomy 21
• -1 in 700 births
• -An extra chromosome 21
• -Abnormal facial features, development
• -Probability increases with age of mother

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Chromosomal Abnormalities

• Klinefelter Syndrome XXY
• -1 in 800
• -Extra X from mother
• -Sterile male, long arms

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Chromosomal Abnormalities

• Super male XYY
• -Extra Y from father
• -Tends to produce violent males

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Chromosomal Abnormalities

• Turners Syndrome XO
• -1 in 10 000
• -One missing sex chromosome
• -Girl is usually short and sterile

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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)

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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.

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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.

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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).

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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 21
  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
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GeneticsA Historical Survey

• Lets take up the History Sheets!

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HOMUNCULUS!
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Probability and Genetics
ANYONE FOR A GAME OF PLINKO?
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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 outcomejust 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!)

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Probability and GeneticsMendels 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.

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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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Monohybrid Cross
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Dihybrid Cross

• We observe 2 pair of alleles for 2 different
  genes.
• Note The 2 genes are not linkedthey must be on
  2 separate chromosomes!
• ExampleMendels 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

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Parental Generation

• RRYY
  rryy
• Plant with round, X Plant
  with
• Yellow seeds
  wrinkled, green
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  seeds
• Gametes
• RY ry

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F1 Generation

• All plants produce round, yellow seeds

RY
ry RrYy 100
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Cross the F1 Generation

• RrYy X
  RrYy
• Gametes
• RY, Ry, ry, rY RY, Ry, ry, rY

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The Results!

• 9 Yellow Round
• 3 Yellow Wrinkled
• 3 Green Round
• 1 Green Wrinkled
• Try These P 166 a-c

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The Test Cross

• Also called a back cross
• Purpose To determine the genotype of an
  individual showing the dominant phenotype!
• Question Is the genotype Tt or TT?
• Answer Cross the individual with a homozygous
  recessive individual

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Possible Outcomes of the Test Cross

• If the genotype of the parent in question is TT
• Then 100 of the offspring from the test cross
  will show the dominant trait!

T T
t Tt Tt
t Tt Tt
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Possible Outcomes of the Test Cross

• If the genotype is of the parent in question is
  Tt
• Then 50 of the offspring from the test cross
  will be recessive for the trait!
• The appearance of only one recessive individual
  means the parent must be heterozygous for the
  trait!

T t
t Tt tt
t Tt tt
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Try These!

• P.167 2 (a-e),8
• P. 233 22
• P. 184 2,3,4,11