Beyond dominant and Recessive Alleles

1
Beyond dominant and Recessive Alleles

• CP 11.3
• Honors 12.2

2
The tongue rolling muscle allele is completely
dominant

• Complete dominance (or dominance)-
• Most of the time an allele will be dominant or
  recessive
• A dominant gene hides a recessive gene when both
  are present
• Incomplete dominance or codominance occur when
  there is not a complete dominance (we will see
  this later)

3
Dihybrid Cross- A two trait Cross

• RrYy x RrYy cross
• Figure out the possible combinations for each
  parent
• R r Y y

1
2
3
4
Both parents here have the same traits so we need
to figure the combinations only once. Possible
combinations RY Ry rY ry After figuring out the
combinations you will have to do a punnett square
that has 4 rows and columns
4
Incomplete Dominance When neither of the
parents alleles are seen in a heterozygous child.
Instead you see an intermediate trait

• Red allele (R) and White allele ( r) blend to
  make pink flowers heterozygous condition

5
Co-dominance When both of the parents alleles
are seen in a heterozygous child.

• Brown skin color allele (B) and white skin color
  allele (b) both expressed (Bb) in phenotype

6

• Multiple alleles a set of 3 or more different
  alleles controlling a trait ( eye color, skin
  color, blood type)
• Example Blood type
• There are 3 alleles for blood type -- A, B, O
• Possible combinations
• AA, AO -- Type A blood
• BB, BO -- Type B blood
• AB -- Type AB blood
• OO -- Type O blood
• Here, A and B are dominant over O, but if A and B
  are present together, neither dominates!!! This
  is codominance they share the power of
  expression.

7
Examples of Blood type crosses
                                                  
                                                  
                                                  
              
8
Sex linked traits

• 1912 Thomas Hunt Morgan Showed evidence that
  the presence of white eye color in fruit flies
  was associated with a particular gene on a
  particular chromosome.
• Drosophila melanogaster -- scientific name for
  fruit fly

9
Thomas Hunt Morgan

• Normally, fruit flies always have RED eyes, but
  Morgan saw a white eyed one show up, and it was
  MALE!! Thought that this was strange, so he
  conducted an experiment
• P white eyed X red
  eyed
• F1 all red eyed
  offspring
• (thus concluded that red is dominant over white
  for color)
• F1 red eyed X
  red eyed
• F2 ¾ red eyed ¼ white
  eyed
• AND ALL OF THE WHITE EYED ONES WERE MALE!!!
• Determined that this was a sex-linked trait the
  trait for eye color in fruit flies is carried on
  the sex chromosome.
• Examples of other sex-linked traits
  hemophilia
• Color blindness

10
Sex Linked Traits The genes for these traits are
on the X chromosome, because boys only receive
one X chromosome they are more likely to inherit
disorders passed to them from their mother who
would be a carrier. Hemophilia and Colorblindness
are sex linked traits, the punnet square below
shows how a woman who is a carrier passes the
trait to her son, but not her daughters.
                                                  
                              
11
Colorblindness Red-green color blindness is an
X-linked, recessive trait.
Figure 14-13 Colorblindness
Section 14-2
Father (normal vision)
Normal vision
Colorblind
Male Female
Daughter (normal vision)
Son (normal vision)
Mother (carrier)
Daughter (carrier)
Son (colorblind)
Go to Section
12
Hemophilia is also sex linked

• Q What is hemophilia?A Hemophilia is a rare
  disorder in which a person's blood does not clot
  properly because the body does not produce enough
  of, or is missing, the blood clotting proteins,
  Factor VIII or Factor IX. The body depends on
  these clotting factors to stop bleeding after
  injury and to promote healing. When a person with
  hemophilia gets a cut or bleeds internally, he
  bleeds longer than someone without hemophilia.
  Internal bleeding is usually into joints and
  muscles, but can also occur in the brain or other
  organs.
• Hemophilia is a sex linked recessive trait
• A mother is a carrier if she is heterozygous X X
• If her husband has the disorder what would the
  chances be that they would have a male son with
  hemophilia?

H
h