Chapter 6 Chromosome Aberrance

第六章 染色体畸变

6.1 Alteration to chromosome structure 染色体结构变异 6.1.1 Deletion 6.1.2 Duplication 6.1.3 Inversion 6.1.4 Translocation 6.1.4 Factors 6.2 Alteration to chromosome number 染色体数目变异 6.2.1 Euploidy 6.2.2 Aneuploidy

Aberrance Alteration

Deletion Duplication

Inversion Translocation

Euploidy Aneuploidy

Mutation

Autopolyploids Allopolyploids

Haploid Monoploid

Diploid Triploid

Tetraploid Monosome

Disomy Trisomy B1,D6

Genetic material change - 突变（ mutation ）

new gene new trait

Chromosome stru. Chromosome aberrance Mutation Chromosome no. Gene mutation (point mutation)

6.1 Alteration to chromosome structure

Fragment lost and gene lost

Rearrangement

(reconstructed and non-reconstructed)

Types of structural alteration 结构变异类型 :

Chromosome type ( 染色体型 ) - Breaking happened in G1 period,

two chromatids aberrance

Chromatid type ( 染色单体型 ) - Breaking happened in G2 period,

one chromatid aberrance

Four types ：1. Deletion （缺失）：失

去某一片段

2. Duplication / addition（重复）：增加某一相同片段

3. Inversions （倒位） : 染色体片段 180 度颠倒后的重排

4. Translocations （易位） :非同源染色体间相互交换片段的重排 玉米 (2n=20) 、果蝇 (2n=8)

-- 研究染色体畸变好材料

6.1.1 Deletions

Deletions involve loss of genetic material,

which is more or less deleterious, depending on

the number and role of the genes which are lost.

D

Genetic effect ( 遗传效应 )

homozygous deletions – no viability

heterozygous deletions

meiotic pairing / synapsis inhibited 联会受抑 nondisjunction and lower fertility caused

染色体不分离、育性降低 dominant gene lost, recessive gene expressed

- pseudodominance - 拟显性 more than 3% of genome deletion – lethal 致死

• Drosophila

heterozygous deletion on chromosome x

– defective wing in female or lethal in male ones

• Maize

color of plant (purple to green)

• Human

- criduchat syndrome

(cat cry syndrom) (46, 5p-)

6.1.2 Duplications

Duplications give an extra copy of a block of genes.

They are generally less harmful than deletions, and one copy of the duplicated genes can become mutated and evolve a new role.

This is the origin of all new genes throughout most of evolution.

Multiple duplications often visible as a staining region on the chromosome.

Genetic effect

同源染色体配对时出现弧形结构 (loop) ，基因随之重复或增加了，比缺失遗传效应来得缓和，但太大也会影响个体生活力，导致死亡。

Dosage and position effect:

( 剂量效应 – 重复基因的累 加作用位置效应 – 重复区段的位置 对表型的影响）

• Drosophila

棒状复眼

(<779 小眼 ) 果蝇的

X 染色体至少 5 条

横纹