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