第2章 孟德尔定律

Basic Terminology
纯合体(homozygous): a pair of alleles which are identical. 杂合体(heterozygous): a single pair of alleles which are unlike each other. 真实遗传（true breeding line）: organisms that always pass the same genotype to their offspring. 杂交（hybrid）: offspring resulting from crossbreeding two true breeding lines. 测交（testcross): Breeding a homozygous recessive with a dominant phenotype (unknown genotype). P – True breeding parent generation; F1 – First “filial” generation; F2 – Second “filial” generation.
progeny
RrYy Rryy rrYy rryy
¼ RY yellow, round ¼ Ry green, round ¼ rY yellow, wrinkled ¼ ry green, wrinkled
Monohybrid cross: the interpretation
Pure breeding round (AA) Homozygous
dominant
×
Pure breeding wrinkled (aa) Homozygous
recessive
F1
Hybrids (Aa)
Heterozygous
选材（Chose a good genetic organism）: short life cycle; large progeny; Several variable characters with two discrete traits(许多稳定的、易于区分的性状）, easy to score (yellow or green) Self fertilize(自花受粉), can produce pure lines(纯系) can cross fertilize 量化结果（Quantified results）.
RY
RY
RR YY round, yellow RR Yy round, yellow
Ry
RR yY round, yellow RR yy round, green
rY
rR YY round, yellow rR Yy round, yellow
ry
rR yY round, yellow rR yy round, green
豌豆的性状： 种子：平滑圆形或皱纹 种子内部颜色：黄色或绿色
成熟豆夹的形态：饱满或压缩
未成熟豆夹的颜色：绿色或黄色
花的颜色：紫色或白色
花的位置：枝腋或枝顶
茎的长度：短(9-18英吋) 或长(6-7英呎)
孟德尔推断（Mendel’s Inferences）
1. Alternate traits caused by alternate forms of genes (hereditary factor). Genes were distinct entities that remained unchanged during crosses. 2. Each plant has two alleles of a gene. 3. Each gamete got only one allele. 4. Alleles segregated into gametes in equal proportions. 5. During gamete fusion, the number of alleles was restored to two. Pairs of alleles from different genes behaved independently.
AaBb
AB
Ab
aB
ab
1
:
1
:
1
:
1
测交验证（Dihybrid Test Cross） Test Cross with multiple traits: Same as with one trait!
the test cross is RrYy × rryy
parents gametes RrYy RY, Ry, rY, ry rryy ry
All wrinkled
5,474 round peas Grow 565 into plants allow to self fertilize（自交）
Third Filial Generation (F3)
193 plants produced only round peas
372 plants produced round and wrinkled peas
All allele pairs randomly segregate during gamete formation（配子形成过程中等位基因随机分离）
Paired condition restored with fusion (fertilization) （成对基因在受精后得到恢复） Aa
a 1 :
Peas can self fertilize
柱头
花粉囊
子房
龙骨瓣
胚珠
Peas can cross fertilize.
孟德尔实验及其分析
孟德尔实验及其分离定律的归纳 孟德尔分析的关键性名词概念
Mendel chose seven traits to study.
Trait on the left is dominant（显性）. Trait on the right is recessive（隐性）.
The first experiment: monohybrid cross
Parental Pure breeding round Generation ♀ (P)
×
Pure breeding wrinkled ♂
wrinkled
First Filial Generation (F1)
Hybrids all round (round is dominant; wrinkled is recessive)
测交Test Cross: Breeding a homozygous recessive with a dominant phenotype (unknown genotype) can determine an unknown allele.
Mendel’s First Conclusion: 分离定律（Law of Segregation）
R; Y
r; y
Parental combination
Recombination
Two hypotheses: dependent or independent assortment（自由分离）
9:3:3:1 RATIO
We can use a Punnett Square to show that a self cross of dihybrids producing gametes in a 1:1:1:1 will generate a 9:3:3:1 phenotypic ratio. female gamete
第二章 孟德尔定律
Chapter 2 Mendel’s Laws
This is a review chapter that you need to review on your own.
§1-1 Law of Segregation
Gregor J. Mendel 1822-1884
Why was Mendel successful?
Ratio of F2 plants producing only round : round and wrinkled F3 progeny is 1:2. Therefore 3:1 phenotypic ratio is 1:2:1 ratio based on breeding behavior (pure breeding round:hybrids:pure breeding wrinkled.
F2
Round peas (AA and Aa)
wrinkled peas (aa)
All round
Round and wrinkled
All wrinkled
How did Mendel explain the 3:1and 1:2:1 ratios?
How to test his inferences?
A1Biblioteka 实现孟德尔分离比的条件：1. F1代个体形成的♀♂配子数目相等，生活 力相同； 2. ♀♂配子结合的机会是相等的； 3. 到观察时，F2代 3 种基因型个体的存活率 相等； 4. 显性是完全的； 5. F2应有足够的个体。
Basic Terminology
基因(gene): a part of a chromosome which determines a certain trait. 性状(Character): is a feature that is heritable. 基因座(locus): Location on chromosome of gene 等位基因(allele): An alternative form of a gene; variant. 显性基因(dominant gene): a gene allele which is always expressed when it is present, regardless of whether it is homozygous or heterozygous. 隐性基因(recessive gene): a gene allele which is not expressed if it is in the heterozygous state. 基因型(genotype): the genetic makeup of an organism (combination of genes in its nucleus). 表现型(phenotype): the physical appearance of an organism.