Class Notes (834,991)
Canada (508,850)
Biology (6,794)
Biology 1001A (1,727)
Tom Haffie (1,170)
Lecture 13

Biology Lecture 13.docx

3 Pages
Unlock Document

Biology 1001A
Tom Haffie

Biology Lecture 13 Before: Extensions of Mendel’s fundamental principles: In incomplete dominance, dominant alleles do not completely compensate for recessive alleles Incomplete dominance  Occurs when the effects of recessive alleles can be detected to some extent in heterozygotes (Rr)  Example: When a red and white snapdragon plant are crossed they create a pink snapdragon (F1 generation) o When two F1 generations are crossed they create 1 white:2 Pink:1 Red snapdragon plants (F2 Generation) o **When one allele is not completely dominant we use a subscript to indicate the character (C ,C ) o This cross is the same ratio as when two heterozygotes are crossed  Real life Example: Sickle cell disease is an example of incomplete dominance o An alteration in the hemoglobin molecule that changes to shape of red blood cells when low oxygen available o Individuals with homozygous recessive alleles have this defective polypeptide that creates the hemoglobin molecule o Individuals who are heterozygous with the recessive allele and normal allele both have a condition known as sickle cell trait  Milder form of the disease because they create normal and abnormal polypeptides from the allele  Real Life Example 2: Familial hypercholesterolemia o Individuals who are homozygous  They have a defective LDL receptor gene (produces no LDL receptors)  These individuals usually have a heart attack as children due to the build up of cholesterol in ateries o Individuals who are heterozygous  These individuals have half the number of receptors  Although it takes longer these individuals usually have heart attacks by the age of 35  Thus it is seen that many alleles appear to be completely dominant but infact are incomplete dominant o To determine if incomplete or complete it depends on the level at which on is examinging to decide between the two o Eg. A heterozygous may produce enough pigment to look the same as a homozygous. But at the biochemical level the levels could infact be different  Real Life Example 3: Tay-Sachs Disease o Individuals who are homozygous recessive  Do not have a functional version of the enzyme that breaks down gangliosides (membrane lipid) Biology Lecture 13  this leads to mental impairment and death o heterozygotes  have no symptoms of the disease  however when looked at the biochemical level it is seen that there is a reduction in the amount of gangliosides that are broken down Conclusion:  NOT ALL traits are simple or complete dominance as Medel’s law may lead us to believe** In codominance, the
More Less

Related notes for Biology 1001A

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.