Early thoughts on genetics

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Early thoughts on genetics

• 1. heredity occurs within species ( prior to
  this it was thought that there was intra species
  origins- example Giraffa camelopartisda
  meaning camel and leopard
• 2. traits are transmitted directly or blending of
  traits. Problem is this would lead to loss of
  individual characteristics.

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• Genetics is part of topic 3 pages 23-26 as well
  as topic 8 pages 83-89 where you will also find
  meiosis on page 89

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Mendelian Genetics

• The man
• DNA From The Beginning
• Go to page 23 of study guide

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Mendel and his peas. Why peas?

• 1. early investigations produced hybrids
  (segregation of traits)
• 2. Large number of true breeding varieties
  available (he worked with 32)

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• 3. choose lines with easily selected traits.

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• 4. both male and female sex organs enclosed
  within flower
• due to ability to self fertilize Mendel removed
  male parts
• introduced pollen from different strain resulting
  in cross fertilization.

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Mendels experimental design

• 1. provide true or pure breeding plants (
  allow self fertilization for several
  generations.)
• 2. perform crosses
• 3. allow hybrids to self fertilize.
• 4. count of young
• 5. manipulate data using statistics.
• Workbook page 185 get out calculators

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Notation

• Homozygous Dominant upper case letter
• Homozygous Recessive lower case
• Heterozygous One upper case, one lower The
  dominant trait is expressed but the recessive
  trait may be passed on
• Phenotype what it looks like
• Genotype the genetic makeup of offspring

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More notations

• P parents
• F1 offspring of P
• F2 off spring of F1

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Monohybrid cross page 23 sg

• Cross between pure lines differing in a single
  character of interest
• Monohybrid Cross page 188 workbook
• Test cross the cross of any individual to a
  homozygous recessive parent used to determine if
  the individual is homozygous dominant or
  heterozygous .
• T_ X tt ( do this your self and determine
  genotype of first parent)

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Punnet square 

• 1. Provides a simple method to calculate probable
  results of a genetic cross
• 2. All possible types of sperm alleles are lined
  up vertically, all possible egg alleles are lined
  up horizontally every possible combination is
  placed in squares

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Mendels model

• 1. parents transmit information
• 2. each individual receives 2 alternative traits
  (alleles) , only one per gamete.
• 3. Factors are not identical- when two identical
  alleles fuse at fertilization homozygous. If
  different heterozygous.

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• 4. Two alleles ( mom and dad) are independent of
  each other
• 5. Presence of trait does not mean it will be
  expressed.
• While looking at next slide study the diagram
  on page 184 of workbook

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Mendel's First LawThe Law of Segregation

• "The alleles of a gene exist in pairs but when
  gametes are formed, the members of each pair pass
  into different gametes. Thus each gamete contains
  only one allele of each gene. The Chromosomes
  have randomly been divided. ( remember meiosis)

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Meaning

• Alignment of chromosomes on metaphase plate
  during meiosis I and disjunction at anaphase II
  mean each gamete may be unique and random.

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Monohybrid /Dihybrid Cross reminder of the steps

• Step 1 Figure out the genotypes of the parents.
• Step 2 Figure out what kinds of gametes the
  parents can produce.
• Step 3 Set up a Punnett Square for your mating.
• Step 4 Fill in the babies inside the table by
  matching the egg allele at the top of the column
  with the sperm allele at the head of the row.
• Step 5 Figure out the genotypic ratio for your
  predicted babies.
• Step 6 Figure out the phenotypic ratio for your
  predicted babies.

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A closer look

• Pages 188 workbook
  Gregor
  Mendel's Legacy ( go to Monohybrid/ scroll up)
• Teachers' Domain Some Genes Are Dominant

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Dihybrid Cross sg 83-84

• A cross between two organisms where the
  inheritance patterns of two genes are studied is
  called a dihybrid cross.

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Mendels 2nd Lawthe Law of Independent
Assortment

• During gamete formation the segregation of the
  alleles of one allelic pair is independent of the
  segregation of the alleles of another allelic
  pair
• Page 194/195 of workbook. Sg 83
• Independent Assortment and Gamete Diversity
• Gregor Mendel's Legacy go to dihybrid cross.

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But. The expression of genotype is not straight
forward. Polygenic sg 85

• Continuous variation
• When multiple genes act jointly to influence a
  character such as height and weight. Showing a
  range of differences

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• Continuous variationIn continuous variation
  there is a complete range of measurements from
  one extreme to the other .
• Height
• Weight
• Hand span
• Length of feet
• Milk yield in cows

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Pleiotropic effect page 204 workbook

• An individual allele will have more than one
  effect on the phenotype one gene affects many
  traits.

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Examples

• Cystic fibrosis clogged blood vessels, overly
  sticky mucous, salty sweat, liver and pancreas
  failure. (mutation on gene that codes for the Cl
  ion transmembrane channel. Teachers' Domain
  Finding Cures Is Hard

• Sickle Cell Anemia anemia, heart failure,
  increased susceptibility to pneumonia, kidney
  failure, enlargement of spleen, painful joints.

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Incomplete Dominance. Polygenic inheritance sg 85

• A form of intermediate inheritance in which
  heterozygous alleles are both expressed,
  resulting in a combined phenotype.For example,
  in cross-pollination experiments between red and
  white snapdragon plants the resulting offspring
  are pink.

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Codominance workbook 190-191sg 24

• An inheritance pattern when both alleles in a
  heterozygous organism contribute to the
  phenotype. Both alleles are independently and
  equally expressed.

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Blood Types multiple alleles pages 192 -93
workbook sg 24

• Both A and B are dominant.
• Type O is recessive
• Four phenotypes
• Six genotypes

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• blood types are caused by the presence of a
  protein cell-surface marker. An antigen on the
  surface of the RBC plasma membrane. mixed with
  the wrong blood type, antigens are bound by
  antibodies clumping

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There are four basic Blood types

• Type A with A antigens on the red cells and anti
  B antibodies in the plasma.
• Type B with B antigens on the red cells and anti
  A antibodies in the plasma.
• Type AB with both A and B antigens on the red
  cells and no blood type antibodies in the plasma.
  
• Type O with no antigens on the red cells and both
  anti A and anti B antibodies in the plasma

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• . Group O blood cannot be clumped by any human
  blood, and therefore persons with Group O are
  called universal donors

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of
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• The Rh (for the rhesus monkey in which it was
  discovered) blood group is made up of those Rh
  positive (Rh) individuals who can make the Rh
  antigen and those Rh negative (Rh-) who cannot.

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• Hemolytic disease of the newborn (HDN) results
  from Rh incompatibility between an Rh- mother and
  Rh fetus.
• Rh blood from the fetus enters the mother's
  system during birth, causing her to produce Rh
  antibodies. The first child is usually not
  affected, however subsequent Rh fetuses will
  cause a massive secondary reaction of the
  maternal immune system. To prevent HDN, Rh-
  mothers are given an Rh antibody during the first
  pregnancy with an Rh fetus and all subsequent
  Rh fetuses.

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Distribution of blood types

• Modern Human Variation Distribution of Blood
  Types

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Environmental Effects

• Some alleles are heat sensitive. Example The
  artic fox . Makes pigment only when temperatures
  rise

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Epitasis - page 204 05

• interactions among products of 2 or more gene
  pairs (the hair color in mammals for example)
• Labrador retrievers can be black, brown, or
  yellow. Two genes control this
• One gene influences melanin production
• B (black) is dominant to b (brown)
• One gene influences melanin deposition
• E (full deposition) is dominant to e (reduced
  deposition)

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• The black Labs have the allele to produce black
  color AND the allele to allow deposition of color
  into the hair. 
• B_/E_  (black)

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• Chocolate Labs are homozygous for the
  nonfunctional b protein (cannot produce black)
  and have the allele for color deposition, so that
  their coat hair is brown instead of black.  bb/E_
  (chocolate)

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• The yellow Labs, are homozygous for the
  nonfunctional e allele, meaning they do not
  deposit dark color into their coats. 
• bb/ee (yellow) or
• B_/ee (yellow)