Genetics --- introduction - Download as PowerPoint by mp7okJd

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									             Biology 2250
         Principles of Genetics
                 Announcements

   Lab 3 Information: B2250 (Innes) webpage
      download and print before lab.

    Virtual fly: log in and practice
http://biologylab.awlonline.com/
      Weekly Online Quizzes

                              Marks
Oct. 14 - Oct. 22 Example Quiz 2** for logging in
Oct. 21- Oct. 24 Quiz 1         2
Oct. 28            Quiz 2       2
Nov. 4             Quiz 3       2
Nov. 10            Quiz 4       2
              B2250
       Readings and Problems


Ch. 4 p. 100 – 112   Prob: 10, 11, 12, 18, 19
Ch. 5 p. 118 – 129   Prob: 1 – 3, 5, 6, 7, 8, 9
Ch. 6 p. 148 – 165   Prob: 1, 2, 3, 10
                  Mendelian Genetics
    Topics:
    -Transmission of DNA during cell division
        Mitosis and Meiosis
   - Segregation
   - Sex linkage (problem: how to get a white-eyed female)


    - Inheritance and probability
                                                 - Tetrad Analysis (mapping in fungi)
    - Independent Assortment                     - Extensions to Mendelian Genetics
    - Mendelian genetics in humans               - Gene mutation
    - Linkage                                    - Chromosome mutation
    - Gene mapping                               - Quantitative and population genetics
  Sex-linked Inheritance


Correlation between inheritance
         of genes and sex
          Drosophila melanogaster
              (T. H. Morgan)
                               White eye
                               (mutant)
Red eye
(wild)

                    X
          Drosophila
Red Eye                White eye
                 Cross A
red female          X         white male

   F1            all red

  F2           red : white
                3 : 1
                     white all male
No white-
eyed females         red 2 : 1 female : male
How to obtain a white-eyed female?
                          Cross B
  white female                 X              red male

      F1          females            males



     F2           females             males

              1      :1        : 1           :1
                 Cross A
 Xw+Xw+                            Xw Y
          w+w+     X       wY

 F1        ww+             w+Y

ww+   X   wY



                       w         Y
                  w    ww        wY
                  w+   ww+       w+Y
       Mendelian Inheritance
Determining mode of inheritance:
    - single gene or more complicated
    - recessive    or dominant
    - sex linked or autosomal

Approach:       cross parents
                observed progeny
                compare with expected
        Principle of Segregation
              Implications
Answer questions on inheritance:
    - mode of inheritance (dominant, recessive
                                 sex-linked)
    - paternity
    - hybridization
               Mendel’s First Law
 Equal segregation of two members of a gene pair

                                ½ A gametes
Meiosis:                   Aa
 diploid nucleus divides        ½ a gametes
 produces haploid nuclei
                                P(a) = ½
                                P(A) = ½
          Rules of Probability
1. Product rule (AND):
    probability of 2 independent events occurring
   simultaneously

2. Sum Rule (OR):
     probability of either one of two mutually
     exclusive events
           Probability
1. **Coin toss: P (T) = P(H) = 1/2

     P(T, T, T) = P(T) and P(T) and P(T)
                = (½)3 = ½ x ½ x ½

2. One die: P (6) or P (5) = 1/6 + 1/6

            **http://shazam.econ.ubc.ca/flip/
                                       equal
                                       Segregation
Self F1      Aa        X     Aa        P(A) = ½
                                       P(a) = ½
                     sperm
  F2             1/2 A    1/2 a
          1/2 A 1/4 AA 1/4 Aa                 P(AA) = ½ * ½
   eggs
          1/2 a 1/4 Aa 1/4 aa

           Prob. (AA or Aa) = 1/4 + 2/4 = ¾
           Prob. (aa) = ¼
          Two Characters

Monohybrid Cross
  parents differ for a single character
    (single gene ); seed shape

Dihybrid Cross
   parents differ for two characteristics
     (two genes)
          Dihybrid
Two Characters:
1. Seed colour yellow green
                 Y      y
2. Seed shape Round wrinkled
                 R      r



    4 phenotypes
                  Dihybrid
P     RRyy         X          rrYY

Gametes      Ry          rY


 F1               RrYy        DIHYBRID
       F1 Dihybrid ----->F2
F1                 RrYy

        RrYy        X     RrYy

F2   9       315   round, yellow
     3       108   round, green
     3       101   wrinkled, yellow
     1        32   wrinkled, green
     Total   556
       Individual Characters
1. Seed shape    round : wrinkled
                  423 : 133
                     3: 1      (¾ : ¼)

2. Seed colour   yellow : green
                  416 : 140
                     3 : 1
              Conclusion


* 3 : 1 monohybrid ratio for each character

* 9 : 3 : 3 : 1 phenotypic ratio a random
   combination of 2 independent 3:1 ratios
          Two Independent Genes
     F2               seed shape
                    3/4         1/4
colour           round        wrinkled
   yellow 3/4     9/16         3/16

  green    1/4   3/16         1/16

                 F2     Phenotypes
       Applying Probability to
             Genetics

Dihybrid: RrYy
Hypothesis:

  mechanism for putting R or r into a gamete is
 independent of the mechanism for putting Y or
 y into a gamete
         Gametes from Dihybrid
Dihybrid: RrYy    (F1)

Principle of segregation during gamete
  formation:
       Yy -------> P(Y) = P(y) = 1/2

       Rr ------->P(R) = P(r) = 1/2
   Gametes from dihybrid
RrYy :
             probability   4 gamete types

   Y and R 1/2 * 1/2 = ¼      YR
   Y and r 1/2 * 1/2 = ¼      Yr
   y and R 1/2 * 1/2 = ¼      yR
   y and r 1/2 * 1/2 = ¼      yr
      F1 gametes produce F2

F1   YyRr       X         YyRr
                            gametes
              ¼ YR        Yr yR     yr
       ¼ YR   1/16 RRYY

gametes Yr
         yR                F2
         yr
            Sperm
F2                  Fig. 6-7
     Eggs
                       F2
                    4 Gametes
                    9 Genotypes
                    4 Phenotypes
        Mendel’s Second Law

Independent assortment:

 during gamete formation, the segregation of
 one gene pair is independent of other gene
 pairs.
(Genes)
                     Meiosis I



          A       Correlation of genes and
                  Chromosomes during
                  Meiosis I
          a


              B        A          b
          A
                  OR
          a             a
              b                   B
          Producing the
               F2
F1   YyRr      X        YyRr

            1. F1 Gametes produce F2
     F2     2. Genotypes
            3. Phenotypes
      Independent Assortment
Two gene systems:
1. Gametes from dihybrid 4 x 4 = 16
         YyRr:
                      Male gametes
                 ¼ YR     Yr yR yr
          ¼ YR 1/16YYRR
  Female     Yr
  gametes                 F2
             yR
             yr
     Independent Assortment
2.    F2 Genotypes 3 x 3 = 9
                                  YyRr X YyRr


        ¼ RR        ½ Rr   ¼ rr
 ¼ YY   1/16 YYRR

 ½ Yy               F2
 ¼ yy
  Independent Assortment
3. F2 Phenotypes 2 x 2 = 4
                             YyRr X YyRr

         ¾ R- ¼ rr
  ¾ Y- 9/16 R-Y-
  ¼ yy
  F1           YyRr   x   YyRr




       YY RR
       YY Rr                                    Y-R-
       Yy RR
       Yy Rr

       YY rr
                                                Y-rr
       Yy rr

       yy RR                                    yyR-
       yy Rr

       yy rr                                     yyrr

9 Genotypes                      4 phenotypes
     Independent Assortment
F1      AaBb   X      AaBb



F2         9   A-B-
           3   A-bb
                       4 phenotypes
           3   aaB-
           1   aabb
   Independent Assortment
            Test Cross

    AaBb      X        aabb

gametes           ab
      1/4 AB AaBb
                              4 phenotypes
      1/4 Ab Aabb
                              4 genotypes
      1/4 aB aaBb
      1/4 ab aabb
   Independent Assortment




                                 Inferred F1
                                 gamete types

                                 AB
 Fig 6-6
                                 ab

                                 Ab

                                 aB

Interchromosomal Recombination
     Independent Assortment
Any number of independent genes:

Genes         Phenotypes      Genotypes
  1               2               3
  2               4               9
  3               8              27
  n               2n              3n
          Mendelian Genetics
             in Humans
Determining mode of inheritance
Problems:
          1. long generation time
          2. can not control mating
Alternative:
         * information from matings that have
  already occurred “Pedigree”
        Human Pedigrees

Pedigree analysis:

•    trace inheritance of disease or condition
•    provide clues for mode of inheritance
         (dominant vs. recessive)
         (autosomal vs. sex linked)
•    however, some pedigrees ambiguous
           Human Pedigrees
1. Ambiguous:       2. Unambiguous:




           Normal    Normal
Affected             female
           male
female
     Clues (non sex-linked)

Recessive:
   1. individual expressing trait has two
      normal parents

   2. two affected parents can not have an
     unaffected child.
               Rare Recessive
             Rare = AA
    A-
(AA or Aa)




                                Cousins
                                (inbreeding)
                   Clues
Dominant:

  1. every affected person has at least one
     affected parent

  2. each generation will have affected
    individuals
                 Dominant
                            Not AA
All genotypes known
               Examples
Recessive:
       - phenylketonuria (PKU)
       - hemophilia (sex linked)
       - cystic fibrosis
       - albinism
Dominant:
       - huntingtons chorea
       - brachydactyly (short fingers)
       - polydactyly (extra fingers)
       - achondroblasia (dwarf)
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=OMIM
 Brachydactyly




Bb   bb

             Bb short fingers
             bb normal
Online Tutorial:




http://www.biology.arizona.edu/mendelian_genetics/mende
lian_genetics.html
Solving Genetics Problems
1. Don’t panic!
2. Carefully read the problem
3. What information is given? Know
   the terms used.
4. What aspect of genetics does the
   problem address?
       Sex Linked Inheritance
X-linked Dominant

1. affected male ---> all daughters affected
                       no sons
        aa x AY ----> Aa, aY

2. affected female ----> ½ sons, ½ daughters
                               affected
   Aa x aY ----> AY, aY, aa, Aa
                     *            *
     X-Linked Dominant
1.
                         All daughters
                         affected, no
                         sons



2.
                         1/2 daughters
                         affected, 1/2
                         sons affected
       X-linked Inheritance

X-linked recessive:
1. more males than females show
          recessive phenotype

2. affected female ------> both mother
       and father have recessive allele
       A a x a Y --------> a a
          X-linked Inheritance

X-linked recessive:
3. affected male ----> mother carries allele
      A a x AY -----> a Y
carrier

4. affected male -----> no affected offspring
      AA x a Y ----> AY, Aa
                                      carrier
X-Linked Recessive

              Mother
              carrier
        Sex Linked Inheritance
             (examples)
X linked genes

    Humans: - colour blindness
            - hemophilia

•   More common in males (hemizygous aY)
•   X linked recessives expressed
        Queen
        Victoria
        (carrier)




QE II      Hemophilic male

           Carrier female



  X-linked recessive hemophilia
X – linked disease genes
Mendelian Genetics

Topics:
 -Transmission of DNA during cell division
     Mitosis and Meiosis
 - Segregation (Monohybrid)
 - Sex linkage
- Inheritance and probability
- Independent Assortment (Dihybrid)
 - Mendelian genetics in humans (Pedigree)

								
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