NICE GENES!

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NICE GENES!

• UNIT 3 INTRODUCTION

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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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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

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Nurture Theory

• Nurture theorists believe genetics ultimately
  don't matter - our behaviours originate from 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 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

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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!

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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.
• Eg. Blue eye pigment, height, chin shape, 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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MITOSIS
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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

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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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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

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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

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

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Stages of Mitosis - Metaphase

• M MIDDLE
• Chromatids line up down the middle.
• Pulled into place by spindle fibres.

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Stages of Mitosis - Anaphase

• A APART
• Chromatids are pulled apart (by spindle fibres)

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Stages of Mitosis - Telophase

• T TEARING
• Nuclear membrane reforms
• 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

• Mitosis for our sex cells

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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

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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

• 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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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 Little History
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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.whats up?

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Mendel (cont)

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

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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 outcomejust the likelihood of the
  outcome!

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Monohybrid Cross

• 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
Results 75 chance of purple flowers 25 chance
of white flowers
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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?

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Example 1
Mom ? ? Dad B b
b
b
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Example 1
Mom ? ? Dad B b
b Bb (Brown) bb (Blue)
b Bb (Brown) bb (Blue)
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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?

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Example 2
Momma rat ? ? Rat Daddy T t
T
t
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Example 2
Momma rat ? ? Rat Daddy T t
T TT (Long) Tt (Long)
t Tt (Long) tt (short)
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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
• 
  seeds
• Alleles
• 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 Practice Problem
• Pg. 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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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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Outcomes of the Test Cross

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

T t
t Tt tt
t Tt tt
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Try These!

• P.167 2,8,9
• P. 233 22
• P. 184 2,3,4,11