Chapter 11 Introduction to Genetics - PowerPoint by 5CKbcvya

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									Introduction to
Genetics
Chapter 11
The Work of Gregor Mendel
A. Gregor Mendel’s peas
  1. Genetics – study of heredity
  2. Mendel studied pea plants
   in the monastery gardens
  3. Fertilization – male and
   female reproductive cells join
  Work of Mendel
  4. True-breeding – produce
   offspring identical to
   themselves.
B. Genes and Dominance
  1. Trait – specific characteristic,
   such as seed color, or plant
   height, that varies from one
   individual to another.
Work of Mendel

 2. Mendel crossed plants with
   different traits
   a. Example: yellow seed with
        a green seed
 3. Original pair of plants – P
   generation
Work of Mendel

 4. F1 – Offspring to the P
   generation
 5. Hybrids – cross between
   parents with different traits
 6. Genes – chemical factors
   that determine traits.
Work of Mendel

 7. Alleles – different forms of
   a gene
   a. Example: Gene is hair
       color, the different alleles
       are red, blond, brown,
       black, etc.
Work of Mendel

 8. Principle of dominance –
   some alleles are dominant
   and others are recessive
 9. Dominant allele for a trait will
   always show up.
Work of Mendel

  10. Recessive allele will only
   show up if the dominant is
   not present.
C. Segregation
Work of Mendel

 1. Mendel took 2 plants, each
   with a different trait and
   crossed them
   a. Example: tall x short
 2. F1 generation had all tall
   plants
Work of Mendel

 3. Allowed F1 to self-pollinate
 4. F2 generation had ¾ tall
   and ¼ short
 5. Segregation – separation of
   alleles
Work of Mendel

 6. Gametes – sex cells
 7. Capital letter represents a
   dominant allele
 8. Lower case letter represents
   a recessive allele
Probability and Punnett Squares

A. Genetics and Probability
  1. Probability – likelihood that
   a certain event will occur
   a. Example: chances of
       flipping heads on a coin is
       50%
Probability and Punnett Squares

   b. Chance of tails three
       times in a row?
       ½ x ½ x ½ = 1/8
 2. Past outcomes do not
   affect future ones.
Probability and Punnett Squares

B. Punnett Squares – diagram
  that shows gene combinations
  1. Types of gametes produced
   by the parent are on the top
   and left side.
  2. Possible gene combinations
   appear in the squares.
Probability and Punnett Squares

 3. Punnett squares are used
   to predict and compare the
   genetic variations that will
   result from a cross.
 4. Homozygous – organism that
   has 2 identical alleles for a
   particular trait
Probability and Punnett Squares

   a. Example: TT or tt
 5. Heterozygous – organism
   that has two different alleles
   for the same trait
   a. Example: Tt
 Probability and Punnett Squares
  6. Phenotype – Physical
   characteristic
  7. Genotype – genetic makeup
C. Probabilities predict averages
  1. More likely to get the expected
   ratio the more times the test is
   done.
Mendelian Genetics

A. Independent Assortment
  1. Two-Factor cross (F1)
   a. Crossed true breeding
       round yellow peas (RRYY)
       with wrinkled green (rryy)
Mendelian Genetics

   b. All offspring were round
      and yellow (RrYy)
 2. Two-Factor Cross (F2)
   a. Mendel wanted to know
      what these heterozygous
      F1 plants would produce.
Mendelian Genetics

   b. Crossed RrYy x RrYy
   c. Independent assortment –
       alleles for one trait are not
       influenced by the other
       alleles.
Mendelian Genetics

B. Summary of Mendel’s
  Principles
  1. The inheritance of
   characteristics is determined
   by genes. Genes are passed
   from parent to offspring.
Mendelian Genetics
2. Some forms of the gene are
  dominant and others recessive.
3. Organism has 2 copies of each
  gene – one from each parent.
  Genes are segregated during
  gamete production.
Mendelian Genetics

  4. Alleles for different genes
   usually segregate
   independently of one
   another.
C. Beyond Dominant and
  Recessive Alleles
Mendelian Genetics

 1. Some alleles are neither
   dominant or recessive.
   Many traits are controlled by
   multiple alleles or multiple
   genes.
Mendelian Genetics
2. Incomplete Dominance – one
  allele is not completely
  dominant over another,
  heterozygous shows a blending
  a. Example: four o’clock flowers
  b. RR (red) x rr (white)
Mendelian Genetics
3. Codominance – both alleles
  contribute to the phenotype,
  heterozygous shows both
  phenotypes
  a. Example: chicken feathers
  b. BB (black feathers) x bb
  (white feathers)
Mendelian Genetics
4. Multiple Alleles – more than 2
  alleles exist to form several
  different combinations of genes
  a. Example: coat color in
       rabbits, blood types
  b. Each organism only has 2
       alleles, but more than 2
       alleles exist in a population.
Mendelian Genetics
 c.   I       – Type A
        AIA, IAi

    IBIB, IBi – Type B
    IAIB – Type AB
     ii – Type O
 d. Heterozygous type A x type
     AB
Mendelian Genetics

 5. Polygenic Traits – traits
   controlled by 2 ore more
   genes
   a. Example: more than 4
      different genes control
      skin color
Mendelian Genetics

D. Genetics and The
  Environment
  1. Genes provide a plan, but
   how it unfolds depends on the
   environment.
Meiosis

A. Chromosome Number
  1. Homologous – 2 sets of
   chromosomes (one set from
   mom, a set from dad)
   a. Humans – 23 mom, 23 dad
Meiosis

 2. Diploid – a cell that
   contains both sets of
   homologous chromosomes
   a. Humans 2N = 46
Meiosis

 3. Haploid – a cell that
   contains only a single set of
   chromosomes
   a. Humans N = 23
   b. Sperm and egg cells
Meiosis

B. Phases of Meiosis
  1. Meiosis – process of
   reduction division in which
   the number of chromosomes
   per cell is cut in half.
Meiosis

   a. Has 2 divisions – Meiosis
      I, Meiosis II
   b. Start with 2N and at the
      end each cell has N
Meiosis

 2. Meiosis I
   a. Chromosomes have been
      doubled
   b. Homologous chromosomes
      pair up and form a tetrad
Meiosis

   c. Crossing over – parts of
      homologous
      chromosomes are
      exchanged
      i. Crossing over increases
          genetic variety
Meiosis

   d. Homologous
      chromosomes separate
      and from two cells
   e. Each cell only has half
      the genetic information
Meiosis

 3. Meiosis II
   a. The chromosomes have
      sister chromatids
   b. The chromosomes line up
      down the middle
   c. Sister chromatids break
      apart
Meiosis

   d. Produces 4 cells with the
      haploid number of
      chromosomes
C. Gamete Formation
  1. Male animals – produce
   sperm cells
Meiosis

 2. Plants – pollen contains
   sperm cells
 3. Female plant and animal –
   egg cells
Meiosis

   a. In female animals the cell
       divisions are uneven in
       Meiosis, producing one
       egg and three polar
       bodies (not used in
       reproduction)
Meiosis

D. Comparing Mitosis and
  Meiosis
  1. Mitosis – 2 cells – identical
   Meiosis – 4 cells – different
  2. Mitosis – 2N (diploid)
   Meiosis – N (haploid)
Meiosis

 3. Mitosis – Cells used in
   asexual reproduction
   Meiosis – cells used in
   sexual reproduction
Linkage and Gene Maps

A. Gene Linkage
  1. In flies for example:
   reddish-orange eyes and
   miniature wings are almost
   always found together.
Linkage and Gene Maps

 2. Chromosome is a group of
   linked genes
 3. Chromosomes are
   associated independently,
   not individual genes
Linkage and Gene Maps
4. Gene Map – relative locations
  of known genes on the
  chromosome
  a. Farther apart 2 genes are,
      the more likely they are of
      being separated by crossing
      over.

								
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