Lecture_6_-_Modifications_of_Mendelian_Ratios

Lecture_6_-_Modifications_of_Mendelian_Ratios - Lecture 6...

Info iconThis preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
Lecture 6 Lecture 6 Modifications of Modifications of Mendelian Ratios Mendelian Ratios
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Allelic Variation Allelic Variation Mendel’s work proved that ‘genes’ can exist in alternate forms (alleles) His work also showed that for many traits or characteristics that one allele of a gene can be dominant to others This seemed to suggest that one allele was responsible for determining the phenotype for a trait while the other allele in an individual did nothing We now know that genes can exist in more than two allelic states and each allele can have a different impact on the phenotype
Background image of page 2
Incomplete or Partial Dominance Incomplete or Partial Dominance An allele that is truly dominant has the same phenotypic effect in heterozygous individuals that it does in individuals homozygous for the allele For some traits however, heterozygous individuals have phenotypes that are different from either of their associated homozygotes
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Incomplete or Partial Dominance Incomplete or Partial Dominance One classic example is in flower color of snapdragon plants Flower color is determined by a single gene with two alleles: W and w Plants that are WW have red flowers and plants that are ww have white flowers However, heterozygous individuals (Ww) have pink flowers
Background image of page 4
Incomplete or Partial Dominance Incomplete or Partial Dominance The most logical explanation for this is that the intensity of pigmentation depends on the amount of gene product produced by the W allele. If the W allele creates the pigmentation and the w allele does not, then all the flower cells in individuals with WW will have very intense colors, individuals with ww will have no pigmentation and Ww individuals will have some pigmentation but not as much as WW individuals
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Codominance Codominance Another exception to the principle of simple dominance occurs when the heterozygote has characteristics found in each of the homozygotes An example of this occurs in cellular products called blood antigens in humans Antigens are produced by the human immune system and react with proteins called sera in the serum portion of human blood This causes blood cells to clump together or agglutinate By testing blood cells for agglutination with different known sera, we can determine the type of antigens produced by an individual
Background image of page 6
Codominance Codominance The ability to produce these antigens is determined by a single gene with two alleles designated M and N Individuals that are MM only produce M antigens while those that are NN only produce N antigens However, individuals that are heterozygous (MN) produce both M and N antigens in relatively equal portions
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 05/07/2011 for the course DARY 2072 taught by Professor Hay during the Spring '09 term at LSU.

Page1 / 28

Lecture_6_-_Modifications_of_Mendelian_Ratios - Lecture 6...

This preview shows document pages 1 - 8. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online