Genetics

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Genetics

• A basis for understanding our genes

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Mitosis (a quick review!)

• Interphase intermittent stage before
  mitosis, DNA replication, chromosome pairing
• Prophase chromatin coils and begins to form
  chromosome
• Metaphase chromosomes move to equator
• Anaphase centromeres split and sister
  chromatids are pulled to opposite poles
• Telophase cytokinesis produces 2 daughter
  cells

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Vocabulary

• Chromatin long, tangled portions of DNA in the
  eukaryotic cell nucleus before Interphase
• Chromosome threadlike structure within the
  nucleus containing the genetic information that
  is passed through generations
• Chromatid one of two identical sister parts
  of a duplicated chromosome

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Vocabulary

• Centromere cellular structure that holds
  sister chromatids together
• Homologous chromosome the paired chromosome,
  which has the same genes for the same trait

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Vocabulary

• Gene sequence of DNA that codes for a protein
  and determines a trait
• DNA substance inside genes that holds the
  information about an organisms traits
• Allele alternate forms of a gene for each
  variation of a trait within an organism
• Ex. TT tall, Tt tall, tt short

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Vocabulary

• Haploid a cell with one kind of chromosome
  (N)
• Diploid a cell with two of each chromosome
  which are in pairs (2N)

MALE
FEMALE
(Karyotype Map of chromosomes within an
organism)
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So what is Meiosis?

• Definition a type of cell division where one
  cell produces 4 gametes, each containing ½ the
  number of chromosomes as parental cell.
• 2 Distinct Stages Meiosis 1 Meiosis 2
• No Interphase in Meiosis 2

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Meiosis 1

• Interphase I DNA replication, pairing of
  duplicate chromosomes

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Meiosis 1

• Prophase I pairs of similar chromosomes come
  together to form tetrad, spindle fibers form

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Meiosis 1

• Metaphase I chromosomes move to equator and
  line up with their opposite pair, spindle fiber
  attaches to centromere

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Meiosis I

• Anaphase I spindle fibers pull homologous
  chromosomes toward opposite ends of the cell

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Meiosis I

• Telophase I spindle fibers break down,
  chromosomes uncoil, and cytoplasm divides
  creating 2 new daughter cells

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Meiosis I

• Meiosis I results in 2 DIPLOID CELLS, each
  with the same number of chromosomes as the
  original cell (2N)

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Meiosis 2

• Prophase II chromatin coils and begins to
  form chromosome, spindle fibers form
• Metaphase II chromosomes move to equator,
  spindle fibers attach centromere
• Anaphase II sister chromatids are pulled to
  opposite poles
• Telophase II spindle fibers break down,
  chromosomes uncoil, cytoplasm divides

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Meiosis 2

• Because of the first meiotic division, the end
  products of Meiosis II result in 4 HAPLOID CELLS,
  daughter cells (N)

End of Meiosis 1
End of Meiosis 2
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Question.

• What are some of the sources of variation that
  can occur as a result of meiosis?
• (hint think about the different phases?)

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Genetic Recombination MAJOR SOURCE of genetic
variation among organisms caused by re-assortment
- Phenotypes 2n - Genotypes 3n (n
number of pairs)
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Example How many different kinds of sperm can
a male frog produce? They have a diploid number
of 26 (13 pairs) so 2¹³ 8,192 different
phenotypes 3¹³ 1,594,323 different genotypes
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Looking at human reproduction(we have 23 pairs
of chromosomes!) so 2²³ (egg) X 2²³
(sperm)Over 70 trillion different phenotypes
within a zygote!
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Vocabulary

• Crossing Over exchange of genetic material
  between non-sister chromatids from homologous
  chromosomes during PROPHASE I of meiosis.
  Results in new allele combination. (Pg. 277)
• Non-Disjunction the failure of homologous
  chromosomes to separate during meiosis. Common
  example is Down Syndrome.

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Down Syndrome

• Epicanthic fold in eye corner
• IQ seldom above 70
• Life expectancy shorter, few survive to 50
• Have simian crease
• May have heart defects
• May have small heads
• May have furrowed tongues

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Down Syndrome
Typical Karyotype
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Basis for Segregation
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Independent Assortment
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Types of Reproduction

• Asexual type of reproduction where one
  parent produces one or more identical offspring
  without the fusion of gametes.
• Sexual pattern of reproduction that involves
  the production and subsequent fusion of two
  haploid sex cells.

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Spermatogenesis
Formation of sperm cells that results in 4
genetically different haploid cells.
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Oogenesis
Formation of egg cells that results in 1
genetically unique egg cell and 3 polar bodies
that are not involved in reproduction.
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So why is meiosis important to an organism that
reproduces sexually? (hint over-crowding)
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It is also important that each female have 2 Xs
and a male to have an X and a Y!
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Turners Syndrome

• 45, XO female
• 1/3000 female live births
• Ovaries rudimentary, sterile
• Short stature, shield-like chest, webbed neck
• Normal intelligence

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Klienfelters Syndrome

• 47, XXY male
• 1/500 male live births
• Male genitalia, testes undeveloped, fail to
  produce sperm
• Female secondary-sex characteristics

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XXX Condition

• 47, XXX female
• 1/1200 female live births
• Variable phenotype, frequently normal, may be
  sterile, may show mental retardation
• Under-developed secondary sex characteristics
• Many institutionalized

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XYY Condition

• 47, XYY male
• 1/1000 male live births
• Above-average height, 2 in maximum security
  prisons are XYY, personality disorders,
  subnormal intelligence
• Fertile
• Many XYY males socially normal

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Gregor Mendel

• He began to breed garden peas so that he could
  study the inheritance of their characteristics.
• Mendel carried out the 1st important studies of
  heredity. (The passing on of characteristics
  from parents to offspring.)

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• Genetics The branch of biology that studies
  heredity.
• Characteristics that are inherited are called
  traits.
• Gametes are Sex cells.

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Mendels Experiment

• In peas, both male and female gametes are in the
  same flower.
• The transfer of the male pollen grains to the
  pistil of a flower is called pollination

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• Uniting male and female gametes is called
  fertilization.
• Monohybrid cross - Cross involving parents
  differing in only one trait.
• F1 generation - Offspring of a cross between true
  breeding plants.

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Monohybrid cross

• Mendel crossed a true breeding yellow seed (YY)
  with a true breeding green seed (yy).
• Results All Yellow seeds Yy

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• In the F1, Mendel cross-pollinated 2 of the pea
  plants from the first generation.
• Results ¾ - tall ¼ - short
• Or a ratio of 31

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Definitions

• Genes are located on chromosomes.
• They exist in alternative forms
• The different gene forms are called alleles

• An organisms two alleles are located on
  different copies of a chromosomes.
• 1 from the male parent
• 1 from the female parent

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Rule of Dominance

• Dominant trait - A trait expressed preferentially
  over another trait. Ex. Hh (H is dominant)
• Recessive trait - The opposite of dominant. A
  trait that is preferentially masked. Ex. Hh
  (h is recessive)
• A dominant allele always takes charge in
  expressing a trait.

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Mendels Laws of Heredity

• 1 Law of Segregation
• During cell division, each allele of a gene pair
  will randomly move to different gametes.
• This produces 4 combinations of genes.

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• 2 Law of Independent Assortment
• This law states that each trait or
  characteristics is found on separate factors
  (genes) that each factor comes in pairs, and that
  each pair separates on its own.
• Members of different pairs of alleles will sort
  independently,if they are on a separate pairs of
  chromosomes.

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Phenotypes and Genotypes

• Genotype
• The Type of gene
• The genetic makeup. Yellow seeds are dominant,
  but yellow seeded plants could have a genotype of
  either YY or Yy.

• Phenotype
• The physical appearance of an organism with
  respect to a trait, i.e. yellow (Y) or green (y)
  seeds.

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Homozygous and Heterozygous

• Homozygous
• Both alleles for a trait are the same. They can
  be homozygous dominant (YY), or homozygous
  recessive (yy).

• Heterozygous
• Differing alleles for a trait, such as Yy.

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• 16 possible combinations of gametes are possible.
  
• We will see that there are 9 possible genotypes
  and 4 possible phenotypes.
• PHENOTYPIC Ratio is 9331
• 4 Phenotypes Round/yellow,
  Round /green
• Wrinkled/yellow,
  Wrinkled/green

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Dihybrid cross

• Crosses 2 traits
• P1 generation Pure breed Smooth and Yellow seed
  (SSYY) X a Dented and green seed (ssyy)
• F1 generation - all smooth and yellow seeds (SsYy)

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Tracing our Traits

• When looking at traits within our family we must
  look at a geneticists rendition of a family tree

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A Pedigree

• Definition A map of the inheritance of genetic
  traits from generation to generation within a
  family
• Used by geneticists to track all types of traits
  throughout family history.

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Pedigree Symbols
AFFECTED MALE
MALE
AFFECTED FEMALE
FEMALE
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Symbols (cont.)
MATING
PARENTS
DEATH
SIBLINGS
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Symbols (cont.)
Heterozygote or Carrier
FEMALE
MALE
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Analysis
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Recessive Traits

• Cystic Fibrosis
• Recessive disorder
• Most common in white Americans
• Caused by a defective protein in plasma membrane
• Results in formation of thick, white mucus in
  lungs and digestive track

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• Tay Sachs
• Recessive disorder of Central Nervous System
• Caused by absence of an enzyme which breaks down
  the lipids produced and stored in the CNS
• Lipids build up in CNS
• Common in Amish people and in Jewish descendants
  of Eastern Europe

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• Phenylketonuria (PKU)
• Recessive disorder
• Caused by absence of an enzyme that converts the
  amino acid Phenylalanine to Tyrosine
• Build-up of Phenylalanine in body damages the
  CNS
• Fatalities among young drink milk which is high
  in Phenylalanine

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Dominant Traits

• Simple Dominant Traits
• Tongue rolling
• Free hanging earlobes
• Hapsburg jaw
• Hitchhikers thumb
• Almond-shaped eyes
• Thick lips
• Mid-digital hair

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• Huntingtons Disease
• Caused by rare dominant allele
• Onset of the disease is between 30 and 50 years
  old
• Genetic test has been made available, burden on
  parents
• Offspring of the affected individual leads to
• 50 chance of being affected too
• 50 chance of passing it to their offspring

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Different Rules of Heredity

• Mendel dealt with simple inheritance dominance
  vs. recessive
• We are going to start looking at other types of
  inheritance..

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Incomplete Dominance

• Definition pattern of inheritance where the
  phenotype is intermediate between the two
  homozygotes.
• Common example is in flowers
• Snapdragons
• Parental
• Red Flowered (FRFR) X White Flowered (FWFW)

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• When you do an incomplete dominance question,
  since neither is recessive or dominant you use
  the same base letter but different descriptive
  letters.
• F is base letter (flower)
• W R descriptive letters (white and red)

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• F1 Generation

FW
FW
FWFR FWFR
FWFR FWFR
FR
FR
All F1 offspring are FWFR or pink
When the flowers are crossed to F2 generation the
ratio is 1 red 2 pink 1 white
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Codominance

• Definition when both the phenotypes caused by
  the homozygotes are expressed equally.
• Common example is in chickens
• Parental
• Black Feathers (BB) X White Feathers (WW)

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• When you do a co-dominance question, since
  neither is recessive or dominant and they both
  affect the phenotype you use different base
  letters.
• B W are base letters (black and white)

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• F1 Generation

B
B
W
BW BW
BW BW
W
All F1 offspring are BW or checkered
When the chickens are crossed to F2 generation
the ratio is 1 black 2 checkered 1 white
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Is it possible for more than two alleles to
control a trait in a population?

• YES
• A new allele can be formed anytime a nucleotide
  is mutated within a gene

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Multiple Alleles

• Definition when traits are controlled by more
  than two different alleles.
• Examples pigments of bird feathers blood
  groups (A,B,O)

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Sex Determination

• Human diploid number is 46, or 23 pairs
• 22 pairs are known as autosomes, or pairs of
  matching chromosomes. They control all traits
  not associated with gender.
• 1 pair is known as your sex chromosomes.
  Control the inheritance of sex characteristics.
• Females XX Males XY

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Sex Linked Traits

• Base letters are X Y
• Descriptives are only used on Xs because Ys
  are different
• Because they are different, any trait on an X
  within a male will not be masked by the Y.
• White eyed flies example in book

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Polygenic Inheritance

• Definition inheritance pattern in which there
  is a trait controlled by one or more genes.
• Can be on the same or different chromosome
• Each allele is represented by uppercase letters
  but neither is dominant
• Each allele contributes to a small, yet equal,
  portion of expression

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So we understand dominant vs. recessive traits
and we know about inheritance patterns, but can
we predict every trait that the organism will
have?

• NO
• As an organism develops and matures many
  factors can influence expression

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External Environmental Influences

1. Temperature
2. Nutrition
3. Light
4. Chemicals
5. Infectious agents

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Internal Environmental Influences

• Things that are controlled by hormones
• Male pattern baldness
• Peacock feathers
• Age

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Complex Inheritance of Traits

• Sickle Cell Anemia
• Major health problem in the U.S. and in Africa
• Most common among African Americans, whose
  ancestors originated in Africa
• Caused by oxygen rich protein, hemoglobin, to be
  defective
• Forms a crystal-like structure, shaped like a
  half moon

Normal red blood cell
Sickled Red Blood Cell
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Multiple Alleles

• Blood Types (Pg. 331)
• Types A, B, AB, O
• Phenotype A carries surface protein A
• Genotypes IAIA, IAi
• Phenotype B carries surface protein B
• Genotypes IBIB, IBi
• Phenotype AB carries surface proteins A B
• Genotype IAIB
• Phenotype O carries no surface proteins
• Genotype ii

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Sex Linked

• X-Linked If mother or father carry a recessive
  alleles on their X
• In a female there is a chance for it to be
  covered by the other X, but in a male it would
  not be covered.
• This means that in a male, a single recessive
  allele for the disorder found on the X would
  cause them to have the disorder.

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• Color Blindness
• More common in males
• One type is allows for the inability to
  differentiate between green and red
• Recessive disorder, b
• XBXB, XBXb, XBY normal colored vision
• XbXb, XbY color blindness

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• Hemophilia
• More common in males
• 1 in 10,000 males
• 1 in 100 million females
• Disorder that does not allow the blood to clot
  normally
• Recessive disorder, h
• XHXH, XHXh, XHY normal blood clotting
• XhXh, XhY Hemophilia

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• Polygenic Inheritance
• Some examples
• Hair color
• Eye color
• Skin color

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What if you had changes in your chromosome
number? Too many? Too little?
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Unusual Autosomal Numbers

• Normally have 22 pairs, but can have extra or
  less if caused by a non- disjunction or failure
  to separate correctly during meiosis.
• Usually called trisomy.
• Most famous is Trisomy 21 or Down Syndrome

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Unusual Sex Chromosome Numbers

• Normally have 1 pair, but can have extra or less
  if caused by a non- disjunction failure to
  separate correctly during meiosis.
• Turners Syndrome XO
• Kleinfleters Male XXY

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Turners Syndrome

• 45, XO female
• 1/3000 female live births
• Ovaries rudimentary, sterile
• Short stature, shield-like chest, webbed neck
• Normal intelligence

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Kleinfelters Syndrome

• 47, XXY male
• 1/500 male live births
• Male genitalia, testes undeveloped, fail to
  produce sperm
• Female secondary-sex characteristics

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Selective Breeding

• Definition breeding or crossing of organisms
  with favorable traits
• Allows the favorable allele to remain in the
  population
• Cats
• Food
• Cows

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Inbreeding

• Definition mating of closely related organisms
• Ensures that offspring are homozygous for favored
  traits
• Greater chance of harmful recessive traits to
  appear
• Horses
• Dogs

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Hybrid

• Definition the offspring of parents that have
  different forms of a trait
• Closely related species are crossed
• Wheat
• Corn
• Rice
• Garden flowers roses dahlias

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• When good breeders want to cross plants or
  animals they look for those that have the best
  chance of passing the trait on
• However, choosing the best
• parents may be difficult

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So how can a breeder determine which genotype
should be used for breeding?

• Homozygous recessive is obvious because it shows
  the recessive trait

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Test Cross

• Definition a cross of an individual of unknown
  genotype with an individual of a known genotype
• Usually homozygous recessive

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• If known parent is homozygous recessive (rr)
  and the unknown is homozygous dominant (RR)

R
R
Rr Rr
Rr Rr
r
r
All offspring are Rr and show dominant trait
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• If known parent is homozygous recessive (rr)
  and the unknown is heterozygous (Rr)

R
r
Rr rr
Rr rr
r
r
50 of the offspring will be heterozygous and
show dominant trait and 50 will be recessive and
show recessive
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Genetic Engineering

• Much faster and more valuable method for
  increasing allele frequency in a population.
• Must cut or cleave the DNA and insert it into
  host organism.
• Also called Recombinant DNA Technology

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Recombinant DNA Technology

• Made by connecting or recombining fragments of
  DNA from different sources.
• Transgenic organism organism that contains
  foreign DNA.
• In order to do this you must isolate a fragment
  or small part of the DNA. You do this by using
  

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Restriction Enzymes

• Definition bacterial proteins that have the
  ability to cut both strands of the DNA molecule
  at specific nucleotide sequences.
• There are hundreds of restrictions enzymes, each
  different in length and specification.

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Vector

• Definition a means by which DNA from another
  species can be carried into the host cell.
• Can be mechanical or biological.

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Types of Vectors

• Biological
• Viruses
• Plasmid small circular vector
• Mechanical
• Micropipette inserts DNA into host cell
• Bullet coated with DNA and shot into nucleus
  with gene gun

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• Gene Splicing the rejoining of DNA fragments.
• join at the sticky ends of fragmented DNA
• Clone genetically identical copy of an
  organism.
• multiple copies of desired recombinant DNA made
  by replication and division

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Applications of DNA Technology

• Industry
• Bacteria to degrade oil
• Bacteria to extract minerals from ore
• Medicine
• Production of growth hormone
• Creation of insulin
• Making of Aspartame artificial sweetner

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Applications of DNA Technology

• Animals
• Mice
• Roundworms
• Fruit fly
• Agriculture
• Strawberries built-in frost protection
• Resistance to herbicides, produce internal
  pesticides, and increase protein production

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The Human Genome Project

• Organized in 1990, projected to be a 30 year
  project, rough completion in 2001.
• International effort
• Wanted to map and sequence the HUMAN GENOME
  80,000 genes on our 46 chromosomes

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• Made possible by the use of linkage maps
• Linkage maps genetic map that shows the
  location of genes on a chromosome
• Helps to also evaluate the rate of crossing-over

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Why the Human Genome Project?

• Better understanding of the human body and
  condition
• Diagnosis of genetic disorders
• Identification of suspects in a criminal case

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• Gene Therapy insertion of normal genes into
  human cells to correct genetic disorders.
• DNA Fingerprinting
• Used by law enforcement to determine if suspect
  was at the crime scene
• Uses the PCR method
• Especially helpful because no two people are
  genetically identical