Variations on Mendel
1. INCOMPLETE DOMINANCE• Neither trait is completely
dominant over the other• Get a BLEND of the two traits• The new phenotype is
somewhere between the original two
• IW = white IR = Red
• White Carnation x Red Carnation
• Parent Genotypes?
–IWIW x IRIR
–Do the Punnett Square
• What do you get????
IW IW
IR
IR
IW IR IW IR
IW IR IW IR
IWIR = 4 / 4 are pink carnations
•What happens if you cross 2
Pink Carnations?
–IWIR x IWIR
–Do the Punnett Square
–What phenotypes occur?
IW IR
IW
IR
IW IW IW IR
IW IR IR IR
IWIW = 1 / 4 white
IWIR = 2 / 4 pink
IRIR = 1 / 4 red
Another Incomplete Dominance example…..
• White bunny x brown bunny = ??
• IWIW x IBIB = IWIB
• IWIB = tan IWIB IWIB
IWIB IWIB
IW IW
IB
IB
2. CODOMINANCE
• Two traits are dominant at the same time
• Both traits are fully expressed at the same time
• EX: Speckled Chickens•These birds have BOTH black and white feathers
•Both black and white are dominant
• IBIB = black feathers• IWIW = white feathers• IBIW = speckled
• Cross a black with a speckled--what are possible phenotypes?
IB IB
IB
IW
IB IB IB IB
IB IW IB IW
IBIB = 2 / 4 black
IBIW = 2 / 4 speckled
• Blood Type: based on 2 gene groups
(1)ABO: --Two dominant ( IA and IB )--One recessive ( i )
– IA IB makes ______ – IA i or IA IA makes ______– IB i or IB IB makes _______– i i makes _______
• Can a Type A and a Type B have:–Type AB child?
•Yes–Type A child?
•Yes..if Type B parent is IB i–Type B child?
•Yes…. if Type A parent is IA i–Type O child?
•Yes…if both are heterozygous
• Blood Type: based on 2 groups of genes
(2) Rh Factor: -- One dominant gene (I+)
-- One recessive gene (I-)
IA i I+ I- makes _________IB i I+ I- makes __________i i I- I- makes __________
5. Sex-Linked Genes• X & Y = sex chromosomes• X X = female genotype• X Y: male genotype• “X” –carries traits
–Colorblindness, hemophilia
• “Y” --no corresponding traits• Males are more likely to have these recessive traits than females
5. Sex-Linked Genes• XB = normal sight• Xb = colorblindColorblind Female = Xb Xb
Normal Female= XB XB or XB Xb
Colorblind Male= Xb YNormal Male = XB Y