What we know so far

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What we know so far

• DNA is the instructions for your cells
• DNA is like a cookbook the recipes are GENES
• Each GENE provides instructions for making a
  specific protein
• Specific proteins have specific shapes mutations
  in the instructions (DNA) can result in changes
  in the protein.

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Blonde hairBlue eyesHitchhikers
thumbdetattached / attached earlobeswidows
peak
How are these traits passed from one generation
to the next?
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MEIOSIS!!
A VERY SPECIAL TYPE OF CELL DIVISION.
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Words you need to know

• Mitosis
• Diploid
• Haploid
• Homologous Chromosome
• Meiosis
• Sperm

• Egg
• Sexual Reproduction
• Crossing Over
• Genetic Recombination
• Nondisjunction
• Allele

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You have 46 Chromosomes

• Each of your body cells has 46 chromosomes, or 23
  pairs.
• Each pair is made of HOMOLOGOUS CHROMOSOMES

Homo same These chromosomes contain the same
genes in the same order
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You have 46 Chromosomes

• Half of your chromosomes (23) came from your mom
• Half of your chromosomes (23) came from your dad

Each parent gave you one chromosome from a
homologous pair.
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Homologous Pairs
From Mom From Dad
gene
From Mom From Dad
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MITOSIS Review

• When your BODY cells (autosomal) divide, they
  make exact copies
• Results two cells with the same type and number
  of chromosomes as the parent cell.
• Many animals reproduce ASEXUALLY through
  mitosis
• ex flatworms, sponges, jellyfish

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This is a problem for most other animals.

• If humans were created through mitosis
• 1st generation
• 46 from mom 46 from dad 92 chromosomes for
  baby
• then
• 2nd generation
• 92 from mom 92 from dad 184 chromosomes for
  baby
• And so on, and so on, and so on

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MEIOSIS

• A second type of cell division that occurs in the
  SEX CELLS (gametes sperm and egg)
• Division creates four cells with half the number
  of chromosomes as the parent cell.

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Haploid vs Diploid

• Body cells (autosomal cells) are DIPLOID
• DI 2 Each cell has 2 copies of each chromosome
• These are considered 2n
• n is the chromosome number

• Sex cells are HAPLOID
• Each sex cell has HALF the normal number of
  chromosomes
• These are considered n

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Sperm and Egg

• Sperm are the sex cells in males
• Eggs are the sex cells in females
• Both are produced through MEIOSIS

Any reproduction that involves SPERM and EGGS is
considered SEXUAL REPRODUCTION.
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Steps of MEIOSIS

• Prophase I
• Metaphase I
• Anaphase I
• Telophase I
• Prophase II
• Metaphase II
• Anaphase II
• Telophase II

• Looks a lot like Mitosis, huh?
• Meiosis has 2 DIVISIONS
• How does this result in unique individuals?

Division 1
Division 2
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Crossing Over

• Prophase 1 Homologous Chromosomes line up next
  to each other
• CROSSING OVER

Homologous chromosomes exchange sections
Genetic Recombination
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Crossing Over

• Crossing over creates new genetic combinations
• This results in new and unique individuals
• This is why you look similar to, but not
  identical to, your brothers and sisters!

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Mendels Laws of Heredity

• Gregor Mendel worked with pea plants in the mid
  nineteenth century
• When he crossed tall pea plants and short pea
  plants, all offspring were tall.
• These were F1 generation

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Mendels Laws of Heredity

• When he crossed the F1 generation, the offspring
  were mixed Tall and Short.
• hmmmmmmmmmm.
• These were the F2 generation

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Mendels Laws of Heredity

• The rule of unit factors
• each organism has two factors that control the
  traits
• Now, we call those factors GENES.
• A homologous pair can have two variations of the
  same genes.

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Mendels Laws of Heredity
Identical ALLELES
Different ALLELES
TALL GENE
TALL GENE
TALL GENE
SHORT GENE
mom
mom
dad
dad
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Mendels Laws of Heredity

• 2. The Rule of Dominance
• Alleles (variations of a gene) can be DOMINANT
  or RECESSIVE
• Dominant genes contain instructions for a
  functional protein
• Recessive genes contain instructions for a
  non-functioning protein

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Mendels Laws of Heredity

• For Example
• Cystic Fibrosis is caused by a non-functional
  protein (recessive gene)
• To have Cystic Fibrosis you must have 2 recessive
  alleles one from each parent.
• This is called HOMOZYGOUS recessive.
• HOMO same

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Mendels Laws of Heredity

• It is possible to have one dominant allele (a
  functional protein) and one recessive allele
  (non-functioning protein).
• This is called HETEROZYGOUS.
• HETERO different
• These individuals are carriers.

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Mendels Laws of Heredity

• 3. The Law of Segregation
• During meiosis, homologous chromosomes separate
  and each sex cell receives one of the homologues.

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Long chromosomes are HOMOLOGUES
Short chromosomes are HOMOLOGUES
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Errors in MEIOSIS

• Nondisjunction homologous chromosomes do not
  separate during meiosis results in gametes with
  too many chromosomes
• EX. Down Syndrome
• Individuals with an unusual number of chromosomes
  are POLYPLOID.

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Polyploidy

• Some chromosome abnormalities do not cause
  disease, however abnormal numbers of chromosomes
  can be lethal or give rise to genetic disorders.
• Cri-du-chat
• Down Syndrome
• Edwards Syndrome
• Patau Syndrome

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Punnett Squares

• Allow you to make predictions of offspring
  GENOTYPE and PHENOTYPE
• Genotype the actual genes an individual has
• Phenotype the physical appearance of an
  individual

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Punnett Squares

• Genotype can be HOMOZYGOUS or HETEROZYGOUS
• Homozygous both alleles (copies of the gene)
  are the same both genes for eye color are
  blue
• Heterozygous both alleles are different one
  gene for blue, one gene for brown

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Punnett Squares

• Genotypes are written using letters. Each letter
  represents one allele
• All genotypes will have 2 letters
• Dominant genes (functional protein) are
  CAPITALIZED
• Recessive genes (non-functional protein) are
  lowercase.

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Punnett Squares

• Example Brown eyes are dominant, blue eyes are
  recessive.
• Genotype of an individual with brown eyes
• BB (homozygous) or Bb (heterozygous)
• Genotype of an individual with blue eyes
• bb (only homozygous)

To have a recessive trait, you need to have both
recessive alleles one from mom, one from
dad. Recessive traits are always HOMOZYGOUS.
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Punnett Squares

• Phenotypes are written as descriptions blonde
  hair, brown hair, brown eyes, blue eyes, etc.

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Punnett Squares

• Example Black fur is dominant to white fur in
  rabbits.
• What are the possible genotypes for a black
  rabbit?
• What are the possible genotypes for a white
  rabbit?

BB, Bb
bb
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Cross 2 white rabbits
b
b
b
bb
bb
bb
bb
b
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Punnett Squares

• Monohybrid cross only work with ONE gene/trait
• Determine what gametes are formed
• Homologous pairs are split up, one goes to each
  gamete
• Gametes from male and female are combined