Heritable variations among individuals in a population…
“Gene control model”? and How?
II. Abbey Garden: The beginning…
Gregor Mendel…1843 ~ 1857, Augustinian monastery…
temporary teacher… U of Vienna… Brünn Modern School and Abbey Garden…
A. Mendel’s Experiments with garden peas
1. Monohybrid crosses:
2. Mendels’ First Law: Principles of Segregation
Allele: An alternative form of the same
Four Components in Mendel’s First Law:
i. Alternative versions of genes (different alleles) account for variations in inherited characters.
ii. For each character, an organism inherits two alleles, one from each parent.
iii. If the two alleles differ, then the dominant allele is fully expressed, while the recessive allele has no noticeable effect on the organisms’ appearance.
*iv. The two alleles (of the same gene) for each character segregate during gamete production.
3. Modern Explanation of Monohybrid Cross
Some useful genetic vocabulary:
III. Test a Monohybrid Cross
Back cross with the recessive parent…
IV. Dominance allele, Recessive allele and their Relationships:
1. Complete dominance:
Both alleles are separately manifest in the phenotype:
Three different human blood groups: M, N, MN.
MN phenotypes are individually expressed by the presence of two types
of molecules (M, N) on red blood cells.
3. A dominant allele doesn’t always subdue a recessive allele ---- incomplete
The dominant allele codes for a red color pigment. The recessive allele codes for a white color pigment. When the number of the red and white pigments is equal, it gives out a pink color.
4. Dominant allele for a character is not necessarily more common than
the recessive allele for the character:
Human: extra finger is dominant, only 1/400, while 399/400 is recessive with no extra finger.
5. Biochemical explanation of dominance:
A dominant allele coexists with a recessive allele in a heterozygous genotype, and they don’t interact at all. It is in the pathway from genotype to phenotype (gene expression) that dominance and recessiveness come into play.
Smooth round shape seed: dominant allele codes for the synthesis of an enzyme, which convert sugar to starch.
Wrinkled shape seed: controlled by the recessive allele, which
codes for a defective form of this enzyme. Sugar in the seed cannot
be converted into starch, when the seeds dry. They show a wrinkled