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Chapter 5 Heredity _ Genetics

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Chapter 5 Heredity _ Genetics Powered By Docstoc
					Heredity & Genetics
PART ONE
  I: Mendel and Genetics :
  A. What are dominant & Recessive
     traits?
  B. What is a Punnett Square?
  C. What is incomplete dominance?
A- Genetics: Similarities and differences
     among parents and offspring. It studies
     how offspring inherit characteristics from
     their parents and how DNA is involved.
B- Mendel: in 1866, this Austrian monk
   studied traits of pea plants.
  1. Mendel studied 7 traits one at a time. Each
     trait had two forms.
     Height Tall Vs. Short.
  2. Mendel grew short and tall pea plants.
  3. Mendel let these plants self-pollinate for
     several generations to get pure breed
     seeds.
     Self-pollinate = Pollination within one plant
4. Mendel cross-pollinates the pure tall with
   the pure short pea plants.
   Cross-pollination = Take pollen from one plant
    and put it on another plant.
  5. The seeds Mendel collects are Hybrids.
           Hybrid = combination of two varieties of
            organisms.
  6. Mendel plants the hybrid seeds to see if
     they will grow tall, short, or medium.
     They all grow tall.
7.   Mendel self-pollinates the hybrid for
     several generations, and plants the seeds
     from the hybrids. 3:1 ratio some grew tall
     some grew short.
8. Conclusion the trait for tallness
   was visible and the trait for
   shortness was hidden.
   Visible trait = dominant, prevents
    the expression of recessive trait in
    organism.
   Hidden trait = recessive.
C-What we learned from Mendel.
1.Traits (characteristics) are
  determined by Genes.
2.Genes = a section of chromosomes
  that determines a trait. { eye color,
  hair color, etc..}
3. Two genes for every trait. Example tallness
   in pea plants if pure tall two tall genes, if
   short two short genes, if a hybrid one tall
   gene and one short gene.
4. The different forms of a gene are ALLELES
   {recessive & dominant}
D- Punnett Squares.
 1. Genotype = the genetic make-up of an
    organism.
  Homozygous: alleles of a gene are the
    same.
  Heterozygous: alleles of a gene are
    different; one allele for tall one for short.
    Hybrids are heterozygous.
 2. Phenotype = What the organism looks
    like.
3.Punnett Squares: predict the
  genotypes & phenotypes of
  offspring.
 Symbols for different alleles of a gene.
 Dominant is capital and recessive is
  lower case letter.
 Height = T for dominant & t for
  recessive.
       TT or tt= homozygous
       Tt = heterozygous or hybrid.
4. Offspring receive one allele for each trait from each
   parent.
5. Heterozygous pass on either T or t.
D- Incomplete Dominance: Condition in
 which the two alleles of a gene are
 both dominant.
 1-It produces a blended phenotype.
  Blended phenotype = hybrid.
  Example: cross a pure red snapdragon with a
   pure white snapdragon, and you get a pink
   snapdragon. RW is the hybrid note both are
   dominant.
Part Two Genes and Traits:
A.In the nuclei of a human cell you find two
  sets of chromosomes 23 pairs. This is a
  diploid number of chromosomes.
1. One pair of the chromosomes comes
   from the father the other set comes
   from the mother.
2. Genes are sections of DNA, each
   human chromosome may contain
   1,000’s of genes.
3. The way chromosomes pair up results
   in different genetic make-ups in the
   offspring.
B. Meiosis: is the formation of sex cells
  or gametes.
  1. Eggs are produced in the female sex
     organ the ovaries, sperm is produced in
     the male sex organ the testes.
  2. Meiosis produces sex cells with only
     one set of chromosomes these cells
     are monoploid.
  3. In meiosis the chromosomes separate
     twice as do the cells.
4. Steps of Meiosis:
a. 1st everything that occurs in Mitosis
   happens with Meiosis. Except the 2nd time
   the chromosomes DO NOT DOUBLE.
b. Sometimes the twin chromosomes that
   are similar pair with each other. If they
   exchange DNA this is known as crossing
   over this increases the differences in the
   offspring compared to the parent.
3. At the end of meiosis we have 4 cells with
   a monoploid number of chromosomes.
   {HALF THAT OF PARENT CELL}

4. When the egg and sperm cells unite the
   two monoploid cells combine their DNA
   forming a diploid zygote.
                  2n Diploid   n Monoploid


             4n

2n Diploid
PART THREE
I. How Sex is Inherited: Sex of an
   offspring is determined by a pair
   of chromosomes.
 A. The male body cell has XY
    The female body cell has XX
B. Twins:
 1. IDENTICAL TWINS: ONE EGG IS
    FERTILIZED BY ONE SPERM. THE
    ZYGOTE SPLITS. ALWAYS THE
    SAME SEX.
    Sperm              Egg



                       Zygote



            Same Sex
             Always
2. FRATERNAL TWINS: TWO EGGS AND
   TWO SPERM CELLS. THEY DO NOT
   CONTAIN THE SAME DNA. CAN BE
   DIFFERENT SEX.
              2 Sperms

              2 Egg

              2 Zygote
C. X-Linked Traits: are traits
 determined by genes on the
 x-chromosome.
1. Several diseases are more common
   in males then in females.
       • Women may not be affected by
          the disease, but pass it on to
          their sons. These women are
          known as carriers.

      • X-chromosomes are larger so
        they carry more genes. The
        ability to see color is on the
        x-chromosome.
2) X-chromosomes have genes that tell
   whether or not you see color. (Red, Green)
  • Women are seldom color-blind because
    the gene is a recessive gene on the
    X-chromosome and they have
    two x-chromosomes.

X’=recessive
gene for color-
blindness
3)Hemophilia: is another x-linked
  disease it is a blood disorder that
  prevents the blood from clotting
  properly.
X’ = recessive
trait for
hemophilia
IV. Source of Gene Variations: When cells divide each
    DNA molecule in the cell makes exact copies of
    itself. But sometimes the cell makes a mistake;
    bases may pair up incorrectly. The codon are
    changed the altered gene is passed on to the new
    cell.
A- Mutation is any permanent change in the
  DNA of a cell.

  1. Mutation increases with the exposure of DNA
     to some chemicals ands radiation that damage
     the DNA molecule.
B. Chromosome Mutation: When a piece of
  chromosome breaks and are rearranged or lost.
  During meiosis chromosomes mutation may occur
  when chromosomes do not separate evenly.
1. Muscular Dystrophy= Weak muscles.
2. Down Syndrome or Trisomy 21= is caused as a result
   of a sex cell having too many 21st chromosomes. The
   fertilized egg, contains three 21st chromosomes instead
   of two.
3. Importance of Mutations= are a source of new traits
   or new forms of traits.

				
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