Mendelian Genetics and Inheritance by cuiliqing

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									1.   Tongue rolling
2.   Hair on second knuckle
3.   Widow’s peak
4.   Thumb crossing
5.   Attached \ unattached ear lobes
6.   Crooked finger
A. Genetics is the
     study of heredity
B. Heredity is the
     passing of traits
     from parents to
   C.―Father of
    Genetics‖- Gregor
    Mendel,an Austrian
    monk who studied
    garden pea plants in
    the 1800’s.☺
 Why a pea plant?
   1. True breeding
   2. Reproduce quickly & in large numbers.
   3. Easy to grow
   4. Self-pollinating
D. Mendel chose to cross pollinate
    Pollination-pollen is dispersed and makes its
      way to the female portion of a flower
   Fertilization is when the pollen unites with
            the ovule to form a zygote.☺
Pistil or (Carpel) is the female portion of the
   flower. It consists of:
     1) Stigma
     2) Style
     3) Ovary-contains ovules (eggs)
If fertilized, the ovules
    develop into seeds.
The ovary develops
    into fruit.
The male portion of the flower is called the
     The stamen is composed of:
1.   Anther-where the pollen is produced.
2.   Filament
1.   1st cross: true
     breeding tall plants
     (TT) with short
     plants(tt). (Called
     P1 or parental
2.   Offspring (called F1
     or first generation)
     of this cross were
     all tall.
3.  2nd cross: 2
    plants of the
    and the
4. results were
    ¾ tall and ¼
This crossing of
    one trait is
    called a
A. Mendel thought that
    some ―factor‖
    controlled the
    inheritance of traits
    B. one factor could
    mask or hide the
    expression of
1.  Genes are segments
    of DNA on a
    chromosome that
    code for a trait. Each
    trait is coded for by
    two alleles.
C. Mendel’s ―factors‖ are the alleles. Alleles are
   alternate forms of the same gene.
   Ex-color of flower is a trait
   The alleles for flower color in pea plants are
   purple or white☺
Some alleles are dominant (they are expressed over a
   recessive gene)
Other alleles are recessive (they are not expressed when a
   dominant allele is present)
   a) Recessive alleles are ONLY expressed if the
   organism has 2 recessive alleles
 Capital letters are used for dominant alleles and lower
   case for recessive alleles.
   Ex- B means brown fur
         b means white fur☺
Genotype-   Definition        Phenotype-
combo of                      physical
alleles                       appearance
BB          Homozygous        Brown fur
            dominant (pure)
Bb          Heterozygous     Brown fur
bb          Homozygous       White fur
            recessive (pure)
A.   Organisms inherit one allele from each parent
B.   Each organism has 2 alleles per trait.
C.   The alleles can be the same or different
D.   During meiosis, the paired alleles for each trait
     separate and end up in different gametes
Meiosis and the
Separation of alleles

•What are the alleles
for the flower?
•What is the dominant
•What is the recessive
•What genes would be
present in the
•Are the parents
heterozygous or
•How many alleles are
donated to each gamete?
•How many ways could
the gametes combine?
•How many offspring will
be homozygous
A.   Patterns of only one trait are studied.
B.   One allele from the female gamete is combined
     with one allele from the male gamete.
C.   Pairs can be homozygous (pure) or
D.   Heterozygous (hybrid)
E.   Genotype is the gene combination – BB,Bb,bb
F.   Phenotype is physical appearance
G.   To determine if an organism is pure or hybrid,
     conduct a test cross with a homozygous
Laws of probability can be used to predict
  Probability is the chance that a certain event will occur.
A. Shows all possible genotypes
B. Probability predicts what is most likely to
C. But actual outcome may be different.
D. Each outcome is NOT influenced by previous
The Punnett Square is a
   diagram showing
   all possible gene
   combinations for a
   genetic cross.
   Step 1: Assign letters for the traits
     B= brown b= white
   Step 2: Write the cross
     Brown Bb x White bb
   Step 3: Set up and work the Punnett square
                      B     b
                 b
                 b

   Step 4: State the genotype ratio and the phenotype
1.   Probability is given as a ratio, fraction, or percentage.
2.   Ratio-number of offspring that have a particular gene
     or trait versus the number of offspring that have
     another gene or trait. 3:1
3.   Fraction-shows the predicted number of offspring
     having a particular trait over the total number of
     possible outcomes. ¾ tall to ¼ short
4.   Percentage-calculated from fractions 75% tall to 25%
1.   What do the letters inside the square represent?
2.   What does a correctly completed Punnett square tell
3.   Does the probability predict the actual outcome?
4.   Is the outcome of a cross affected by previous crosses?
5.   Who was Gregor Mendel?
6.   What is a monohybrid cross?
7.   What are alleles?
8.   What does it mean if an organism is heterozygous?
9.   What is the only way a recessive trait will be expressed?
   A heterozygous tall pea plant is crossed with a
    homozygous short pea plant. A Punnett
    square predicts that the probability that the
    offspring of this cross will 50% tall and 50%
    short . In a classroom experiment, student
    tested this prediction with four seeds obtained
    from this cross
   . The first three offspring from this produced
    all tall plants. How is this possible? What is
    the probability that the fourth offspring will be
   Step 1:
   Step2:
   Step3:
   Step 4:
   Two heterozygous tall pea plants are crossed.
    They produced 16 seeds. How many of those
    seeds will likely result in short plants?
   Step 1:
   Step2:
   Step3:
   Step 4:
   Phenylketonuria or PKU, is an inherited
    disease caused by a recessive allele. If baby has
    PKU and is untreated, a certain amino acid
    builds up in the tissues and causes severe
    mental retardation. If treated, the child can
    develop normally.
   A young couple has decided that they want to start
    their family. David is 28 years old and has been
    promised a promotion in his company that will gave
    him a better position and more benefits, as well as a
    larger salary. He has phenylketonuria, or PKU. His
    mother and one sister also have PKU. His wife Trevon
    is 25 years old and has an aunt with PKU. She also had
    two grandparents with phenylketonuria although
    neither of her parents had it. David and Trevon want
    to know what their chances are of having a child with
   David’s genotype:____
   Trevon’s possible phenotypes: _____ or _____
   What are the possible genotypes and
    phenotypes of their future children?
   Step 1:
   Step2:
   Step3:
   Step 4:
   What is the probability that their children will
    NOT have PKU?
A.   Often called blending.
B.   Neither allele is dominant over the other.
C.   Third phenotype is intermediate between the
     dominant and recessive ( Ex-four o’clock
     flowers white X red = pink)
D.   When making a Punnett Square for incomplete
     dominance, use 2 different capital letters (RR
     for red and WW for white, RW is pink)
How to determine if there is incomplete
  dominance? Three different phenotypes, one
  of which is a blend.
When homozygous dominant are crossed with a
  homozygous recessive, all F1 are intermediate,
  while the F2 have a 1:2:1 phenotypic ratio.
A.   Both alleles are expressed equally.
B.   Codominant alleles are designated with
     uppercase letters for each allele and a
     superscript may be used.
Example = white
   chicken X black
   chicken =
   speckled chicken
   ( FWX FB = FWFB)
   This causes the 1. hemoglobin in the red blood
    cells to be the 2. wrong shape. Hemoglobin is
    the protein that carries the oxygen. People who
    are homozygous 3. recessive for the allele have
    very serious health problems.
E. Roan color
   in cattle and
   both 1. red
   and white
   hairs mixed
   together or     Blue
   2. black &      Roan
   1. A trait for snapdragon flower color is
    controlled by incomplete dominance. A
    snapdragon plant with red flowers is crossed
    with a snapdragon plant with white flowers.
    What percent of the offspring will have pink
   2. If two snapdragon plants with pink flowers
    are crossed, what percent of offspring would
    you predict as also having pink flowers?
    3. A pink snapdragon plant is crossed with a
    red snapdragon plant. What percent of the
    offspring can be predicted to have white
   4. Cross a red horse crossed with a roan
    colored horse. List the possible genotypes and
A.   Traits controlled by more than 2 alleles.
B.   Only two alleles for each individual, but there
     are more than 2 alleles for the trait found in a
     general population. (in gene pool)
C.   Example ABO blood type in humans and
D.   coat color in rabbits
   There are three alleles for blood type
   1. Type A ( IA) , 2. Type B (IB ) and 3. Type O (ii)
   4. IA and IB are codominant to each other
   5. Both IA and IB are dominant over i, which is
   6. Blood typing is important because a person would
    die if the wrong type of blood was given. It is also
    used to determine who’s NOT ―Yo’ Daddy!‖
   Pope Innocent VII-
                         attempted the first
                         blood transfusion.
                         He drained the
                         blood of three 10
                         yr old boys into the
                         mouth of Pope
                         Innocent VII. They
                         all died.
   Dr. Jean Baptiste Denys-1667
   1st successful transfusion – poured about 12 oz
    of sheep’s blood into a 15 yr old boy. The boy
    lived probably because so little blood actually
    made it into the boys blood stream
   It was not until the 4 basic blood types were
    identified that transfusions could be done
   WWII blood trans-
   Fusion tool
   Sample problems:
       If a child has type AB blood and the mother has type
        A blood, could a man with type O blood be the
   A mother has type A blood and a father has type B
    blood. Can they have a child with type O blood?
    Why or why not?
   A woman with Type AB blood marries a man with
    homozygous Type O blood . What would the blood
    type of their children be?
   A woman with heterozygous Type A blood (IAI)
    marries a man with homozygous Type B blood (IBIB).
    What blood type could their children NOT have?
A.   Traits are inherited independently.
B.   Law is always true IF genes for traits are located on different
During meiosis, alleles for different traits assort independently from
     one another.
c. For example, seed color has no effect on plant height.
   Each parent will donate half of their alleles to
    the offspring.
   FOIL – F the first letters of the genotype
           O the outside letters of each genotype
     I the inner letters of the genotype
     L the last letters of the genotype
   Example: mother is FfWW
            possible gametes – FW,FW,fW,fW
   Father is FfWw
    possible gametes – FW,Fw,fW,fw
     FW   FW   fW   fW
A. IF genes for a trait are on the same
   chromosome, they may be linked.
   B. Inherited together
   C. Discovered by Thomas Hunt Morgan (early
    D. Studied Drosophila or the fruit fly
• Early studies of crossing over were performed using
  the fruit fly Drosophila

               Wild type             Variant
           (gray body, long    (black body, short
           wings, red eyes)   wings, cinnabar eyes)
                                                      Figure 9.25
 • Inheritance patterns of a sex-linked gene

          Female         Male                       Female         Male             Female          Male
           XRXR          XrY                         XRXr          XRY               XRXr            XrY

All females inherit
two X chromosomes,
one from each parent.

    All males inherit                          Female                           Female
    one X chromosome,
    always from the     R = red-eye allele
    mother.             r = white-eye allele          Male                             Male

(a) Homozygous red-eyed female  white-        (b) Heterozygous female  red-   (c) Heterozygous female white-
eyed male                                      eyed male                        eyed male
                                                                                                     Figure 9.29
A.   Humans have 23 pairs of chromosomes.
     1. Autosomes are 22 matching
         chromosome pairs
     2. Sex chromosomes make up the 23rd
        a. X and Y are the sex chromosomes
       b. XX is a female and XY is a male
E. Traits found on the sex chromosomes
   1. A male with a recessive trait on the X
     chromosome will always ―have it‖ because
     there is only one X.
A.   Hemophilia is an example of a sex-linked trait
     that is passed from mother to son, but not
     necessarily from father to daughter.
B.   X chromosomes are larger and carry more
     genes than Y chromosomes.
C.   Red-green colorblindness is another example
   1. Organisms that have two identical alleles for the
    same trait are called—
   2. Both hemophilia and red-green color blindness are
    examples of disorders that are—
   3. A couple has two children, both girls. What is the
    chance that the parents’ next child will be a boy?
   4. A Punnett square shows---
   5. Where are most the sex-linked genes located?
   6. What is the genotype of a female?
   7. The type of inheritance that produces roan color is
   8. If the recessive trait is expressed as the phenotype,
    what would the genotype be?
A.   Pedigree is a diagram used to show genetic
     inheritance patterns.
B.   Male is represented by a square and a female is
     represented by a circle.
C.   Each horizontal row represents one generation
     labeled with Roman numerals.
D.   Line connecting male & female means they are
     a couple
                                     Figure 14-3 A Pedigree

           Section 14-1

                                   A circle represents   A square represents
                                   a female.             a male.
                                                                           A vertical line and
    A horizontal line connecting                                           a bracket connect
    a male and female                                                      the parents to their
    represents a marriage.                                                 children.
      A half-shaded
      circle or square                                                             A circle or
      indicates that a                                                             square that is
      person is a carrier                                                          not shaded
      of the trait.                                                                indicates that
                                                                                   a person
     A completely                                                                  neither
     shaded circle or                                                              expresses the
     square indicates                                                              trait nor is a
     that a person                                                                 carrier of the
     expresses the                                                                 trait.
Go to
   Samples problems:
       In the pedigree above, determine the
        genotypes of the parents in the P1 generation.
       In the F1 generation, the one affected daughter
        has three children with an unaffected man.
        Their two sons are affected with color
        blindness. What is the chance of another son
        having the disorder?
A.   Type of Mutations
     1. Gene Mutations-Changes in only one
       gene that codes for one protein
       a. Substitution-One nucleotide is
       substituted or replaced by
             1) Point Mutation


This will change only one word or in this case one
  amino acid in the protein chain.
b. Insertion-One nucleotide is added to
   the sequence.
  1) Called a frame-shift mutation.

This throws off the whole message from the point
  of insertion on. This will more than likely
  change the amino acid sequence and the whole
  protein chain.
c. Deletion-A nitrogen base is omitted.
   1) Another type of frame-shift


The words or amino acid sequence is changed
  from the point of deletion.
2. Chromosomal mutation-structure or number of
   chromosome changes.
   a. Duplication-part of chromatid is
   b. Deletion-part of chromatid is missing
   c. Inversion-broken part reattaches backward
   d. Translocation-part of a chromatid attaches
      to a different chromosome
B. Karyotypes-pictures
   of chromosomes
   used to identify
This is a method in which fragments of DNA are
  separated by electric charge and size on a gel
  with the smallest fragments traveling the
  greatest distance.

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