3章-孟德尔遗传规律的拓展 上传用 6单元

chapter outline
chapter
3
• 3.1 Extensions to Mendel for single-gene inheritance
• 3.2 Extensions to Mendel for multifactorial inheritance (4)
3.2.1 Two genes can interact to determine one trait 3.2.5 Mendelian principles can also explain
continuous variation 3.2.4 The same genotype does not always
produce the same phenotype 3.2.3 With humans , pedigree analysis replaces
breeding experiments 3.2.2 Breeding studies help decide how a trait is
inherited
3.2 Extensions to Mendel for multifactorial inheritance
gene effect
3.2.5 Mendelian principles can also explain continuous variation
n Dis continuous trait (discrete trait, 不连续性状) or qualitative
trait (质量性状)
Phenotype is clear cut without variation.
n Continuous trait (连续性状) or quantitative trait (数量性状)
Phenotype shows continuous variation.
Height is a continuous trait in humans
Skin color is a continuous trait
Herman Nilsson-Ehle (1873-1949)n 1908 Nilsson -Ehle studied quantitative traits in wheat and demonstrated that they are inherited in the same Mendelian way.X F 1P F 2
A a
B b AABB aabb
A a
B b X # Additive alleles
F 2
# Additive alleles
n The more genes or alleles, the more possible phenotypic classes,
and the greater the similarity to continuous variation.
n 1 gene (A) with 2 alleles
(0, 1) yields 3
phenotypic classes.
n 2 genes (A, B) with 2 alleles (0, 1)
apiece yield 5 phenotypic
classes
*Incomplete dominant alleles have additive effects (累加效应).
n3 genes (A, B, C) with 2 alleles (0, 1) yield 7 phenotypic classes
n 2 genes (A, B) with 3 alleles (0, 1, 2) yield 9 phenotypic classes
Continuous traits result from the action of many genes
n The more genes that contribute to a trait, the greater the
number of possible phenotypic classes and the greater the
similarity to continuous variation.
n Each of these genes has a small effect.
n Incomplete dominant alleles have additive effects.
n Sensitive to the environment.
Continuous traits in humans
Type Trait
Anatomical Height, weight, pigmentation, eye color,
hair color
Physiological Metabolic rates, running speed,
tolerance
Behavioral I.Q., memory, handedness
Diseases Diabetes, hypertension, arthritis, obesity,
Schizophrenia, Manic-depression。