Post on 18-Jan-2016
Complex Inheritance Patterns
1. Incomplete Dominance – phenotype of heterozygous is intermediate of the 2 homozygous phenotypes- results in the blending of traits- example: snap dragons
• Alleles: R = redR’ = white
• Genotypes/PhenotypesRR = __________R’R’ = _________RR’ = __________
red
white
pink
Example Problem:Red snapdragon crossed with a pink snapdragon_______ X _______
Results:___ of 4 red = _____%___ of 4 pink = _____%___ of 4 white = _____%
RR RR’
2
2
0 0
50
50
human example of incomplete dominance: sickle cell anemia (on the clinical level)
• most common in Africans/African Americans• 1 in 12 black people are carriers• causes red blood cells to form sickle shape
• sickled cells block blood flow• symptoms: shortness of breath, pain in joints, anemia,
fatigue• being a carrier is an advantage against malaria
– alleles:
A = normalS = sickle cell
genotypes/phenotypes:AA = _________________ (no sickling)AS = _________________ (few cells will sickle;
extremely mild symptoms)SS = _________________ (distinct sickling;
full-fledged symptoms)
normal
carrier
sickle cell anemia
Problem: 2 carriers have a child. What is the chance that the child will have SCA?_______ X _______
% chance ______
AS AS
25%
2. Codominance – both phenotypes of homozygous individuals show up in heterozygous
- Results in the expression of both traits- Example: chickens
alleles:B = blackW = white
genotypes/phenotypes:BB = __________WW = _________BW = __________
black
white
checkered
Problem: Cross 2 checkered chickens.What % of the offspring will be white?_______ X _______
___ of 4 is white = ______% white
BW BW
1 25
Another Codominance Example
• Roan cow – result of cross between a red cow and a white cow
3. Multiple alleles – there are more than two forms (alleles) for the traitHuman example: ABO blood typing
alleles: IA , IB , i
IA and IB are codominant to each otherIA and IB are dominant to __i__
genotypes/phenotypes:IAIA and IAi = _______________IBIB and IBi = _____________IAIB = ____________ii = ___________
type A blood
type B blood
type AB blood
type O blood
Importance of blood typing:• parentage• blood transfusions
incompatible blood can result in blood clotting, then death
Problem: A woman with blood type O has a baby with blood type O. Her husband has blood type AB. Could the baby be his?
Problem: A woman with blood type A has a baby with blood type O. Her husband has blood type B. Could the baby be his?
• Transfusion compatibility:• A and B are surface proteins on red blood cells• You CANNOT accept blood from someone who has a
protein that you do not have!
Donor
A B AB O
A
B
AB
O
Acceptor
Rh factor – another surface protein_+_ = has Rh protein_-_ = does not have Rh protein (-) can give to (+) (+) cannot give to (-)
So, O- can give blood to anyone = universal donorAB+ can get blood from anyone = universal acceptor
If a woman is Rh - and is pregnant with a baby who is Rh + , her body can attack her next Rh+ child.
Problem for 2nd child!!
Test for Blood Typing
4. Sex DeterminationHumans have 22 pairs of autosomes
(chromosomes shared by males and females) and 1 pair of sex chromosomes (X and Y) = __23__ pairs = __46__ total per cell.
Humans:XX = femaleXY = male
Problem:– A man and a woman have 5 sons. What is the
chance their next child will be a girl?
ALWAYS __50%__ chance!!!• FYI: The man “chooses” the sex of the child.
Women only have X’s to give. Man gives X to daughters and Y to sons.
5. Sex-Linked Traits/Diseases – controlled by genes on the X or Y chromosomes
If trait is on:– X and is dominant – more females have it (ex.
scoliosis)– X and is recessive – more males have it (ex.
baldness, colorblindness, hemophilia)– Y – only males have it
Red-green colorblindness (recessive on X)
N =______________ n = _______________XNXN = ___________ XnXn = ___________XNXn = ___________ XnY = ___________XNY = ___________
normal colorblind
female
female
female
male
male
normal
normal
carrier
colorblind
colorblind
A man who is not colorblind has a son with a woman who is a carrier for colorblindness. What is the chance that the son will be colorblind?
Who did the son inherit the colorblindness from?Can a man that is not colorblind have a daughter that is?
Hemophilia – disease that interferes with blood clotting• Treated with clotting enzymes or transfusion• Recessive on X
Famous People with Hemophilia
Ryan White and momAlbert and Victoria – English royal family
Romanoff Family
N = ____________n = _____________XNXN = ___________ XnXn = ____________XNXn = ___________ XnY = ____________
XNY = ___________
A woman who is a carrier for hemophilia and a man who has hemophilia want to have a child. They want to know the chance of their child having hemophilia.
normal hemophilia
female
female
female
male
male
normal
normal
carrier
hemophilia
hemophilia
Sex-Linked Recessive Pedigrees• Males have it; females are carriers
6. Polygenic Traits – traits controlled by many genes; difficult to predict exact outcome
These traits show broad range of phenotypesEx. hair color, eye color, skin color, human height