Transcript Degrees of Dominance - Rowan County Schools

Degrees of Dominance
• Complete dominance occurs when
phenotypes of the heterozygote and
dominant homozygote are identical
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Extending Mendelian Genetics for a Single Gene
• Inheritance of characters by a single
gene may deviate from simple Mendelian
patterns in the following situations:
– Sex Linked Traits -When alleles are on the
sex chromosomes . (color blindness)
– Incomplete Dominance -When alleles are not
completely dominant or recessive (pink
flowers from red and white phenotype)
– Multiple Alleles - When a gene has more than
two alleles. (Blood Type)
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Sex linked traits
*Hemophilia
*Muscular dystrophy
*Red/green colorblindness
*Rickets
Discovery of Sex Linkage
Thomas Hunt Morgan
• First to associate a specific gene on a
specific chromosome (early 1900’s)
• Mated flies
Sex linked genes
• Genes located on sex chromosomes
• Most are usually genes on X
chromosomes
• Have unique patterns of inheritance
– Mothers pass sex-linked alleles to daughters
and sons
– Fathers pass sex-linked alleles to daughters,
NOT sons
Muscular Dystrophy
•
•
•
•
Absence of a key protein called dystrophin
Symptoms: weakening of muscles
1 out of 3500 males in US
Rarely live past 20’s
Hemophilia
• Sex linked recessive
• Absence of proteins required for blood clotting
• Sons born to women with a family history of
hemophilia
• Queen Victoria of England
– Introduced to royal family thru a mutation in one of
sex cells: carrier of allele
– The royal families of Prusia, Russia, Spain had
Hemophilia genes that spread thru their families
• In Codominance, phenotypes of both
alleles are exhibited in the heterozygote
Example: Pink/white flower, Roan horse
both colors are being expressed.
How can I make lots of money?
• If I was a horse breeder and I wanted to
sell Roan horses what horse color do I
want for my breeding stock?
RR (red), rr (white), Rr (Roan)?
Draw Punnent Square.
Incomplete Dominance
• Offspring has a phenotype that is
intermediate between the traits of its two
parents.
• Ex. Red flowering Snapdragon is crossed
with a white flowering Snapdragon the
offspring is pink flowers. Neither the red
or the white Allele is dominant. There is
just less pigment.
Fig. 14-10-1
P Generation
Red
CRCR
Gametes
White
CWCW
CR
CW
Fig. 14-10-2
P Generation
Red
CRCR
Gametes
White
CWCW
CR
CW
Pink
CRCW
F1 Generation
In incomplete
dominance, the
phenotype of F1 hybrids
is somewhere between
the phenotypes of the
two parental varieties
Gametes 1/2 CR
1/
2
CW
Fig. 14-10-3
P Generation
Red
CRCR
White
CWCW
CR
Gametes
CW
Pink
CRCW
F1 Generation
Gametes 1/2 CR
1/
CW
2
Sperm
1/
2
CR
1/
2
CW
F2 Generation
1/
2
CR
Eggs
1/
2
CRCR
CRCW
CRCW
CWCW
CW
Incomplete Dominance
What would happen?
• Could a plant breeder produce only pink
flowering snapdragons by crossing pinkflowering snapdragons and white –
flowering snapdragons?
• Why?
Multiple Alleles
• Most genes exist in populations in more than
two allelic forms
• For example, the four phenotypes of the ABO
blood group in humans are determined by
three alleles for the enzyme (I) that attaches A
or B carbohydrates to red blood cells: IA, IB,
and i.
• Multiple alleles control the ABO blood groups.
Different combinations of three alleles result in
four blood phenotypes (A, AB, B, and O)
Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings
Fig. 14-11
Allele
IA
IB
Carbohydrate
A
B
i
none
(a) The three alleles for the ABO blood groups
and their associated carbohydrates
Genotype
Red blood cell
appearance
Phenotype
(blood group)
IAIA or IA i
A
IBIB or IB i
B
IAIB
AB
ii
O
(b) Blood group genotypes and phenotypes
• Antigens – Located in Plasma. “Bad Guy”
• Antibodies – located on surface of red
blood cells. “Anti-A antibodies”
Blood
Group
Antigens
Antibodies
Can give blood
to…
Can receive
blood from…
AB
A, B
NONE
AB
AB, A, B, O
Universal
Receiver
A
A
B
A, AB
A, O
B
B
A
B, AB
B, O
O
NONE
A&B
A,B,AB,O
Universal Donor
O
What Blood Types will be…
• An Universal Donor?
O. Does not contain any A or B
antigens (bad guys) at all.
• An Universal Recipient?
AB. Can receive blood from all other
blood groups.
Did you know?
• Another inheritance pattern demonstrated
by the ABO blood group is
CODOMINANCE.
• Explain why?
Oh No! We need to go the ER!
• You need blood now what?
ABO Blood System
Rh Factor
• Rh is a protein that is attached to a red blood cell.
• Rh- is the absence of the Rh factor on the red blood
cell. (Just like the O blood cell.)
• You can give Rh- blood to a patient with Rh+ blood
but not vice versa.
• Mother has 1st child…the child is Rh+ (from the
father)…baby’s and mother’s blood mix at time of
delivery. Once exposed to Rh+ mother makes Rh
antibodies.
• Mother is pregnant with 2nd child (Rh+, same dad) The
mother has Rh antibodies so her body attacks the
babies blood cells and she miscarries.
Rh factor
• Treatment: Rh Immune Globulin- It
destroys baby cells in mom’s blood and
suppresses mom’s Rh antibody
production.
`
Fig. 14-15b
1st generation
(grandparents)
2nd generation
(parents, aunts,
and uncles)
Ww
ww
ww
Ww ww ww Ww
Ww
Ww
ww
3rd generation
(two sisters)
WW
or
Ww
Widow’s peak
ww
No widow’s peak
(a) Is a widow’s peak a dominant or recessive trait?
Fig. 14-15c
1st generation
(grandparents)
Ff
2nd generation
(parents, aunts,
and uncles)
FF or Ff ff
Ff
ff
ff
Ff
Ff
Ff
ff
ff
FF
or
Ff
3rd generation
(two sisters)
Attached earlobe
Free earlobe
(b) Is an attached earlobe a dominant or recessive trait?