Lecture 32 11/15/13
Chapter 12 – Section 12.3, 12.4 Friday
Lecture Objectives:
1. Describe patterns of inheritance in Mendelian and sex-linked loci.
2. Use Punnett Squares or pedigrees to determine modes of inheritance.
3. Explain the role of the environment in patterns of expression.
Some traits are inherited as Mendel predicted…some are not.
- Complete /Incomplete dominance
- Co-dominance – blood type
- Sex-linked – orange vs. black cat
- Epistasis/Pleiotropy – Labrador retriever color
- Gene by environment – temperature-sensitive pigment
- Quantitative traits – height
- Linked genes
Pedigrees are used to observe Mendel’s laws.
-Use Punnett squares to predict the potential outcome and ratios of potential phenotypes of
offspring
-We don’t have enough children usually to show those predicted ratios.
-We use pedigrees to look at the actual observations.
oCircle = female
oSquare = male
oWhite doesn’t have phenotype, solid has phenotype.
-Carrier doesn’t’ show up in phenotype (half-filled)
-Dominant shows up in every generation. Recessive stays masked. Until the carrier mates with
another carrier, you may not see the phenotype show b/c its recessive.
- Huntington’s disease = dominant
- Albinism = recessive
Incomplete dominance may be due to many mechanisms.
-Heterozygote has a different phenotype than both of the parents.
-Copy of a gene that codes for a protein that doesn’t function so well.
-Two little aa’s, enzyme can’t work
oPrecursor – some compound in the flower and enzyme doesn’t work (cant convert into
red pigment) so white flower
-Enzyme used in depositing pigment but doesn’t work completely
In codominance, both alleles are expressed equally.
-Different heterozygote but has both alleles expressed equally
-Blood type examples
oOn cell membrane, you have glycoproteins (have sugars attached to them). You have
different glycoproteins on your blood cells. There are four different common blood
types:
A – has A glycoproteins
Can’t accept B
B – different type of glycoprotein
Can’t accept A
AB – A and B glycoproteins
