[Chapter II Relationship between genes and chromosomes] summary of biological knowledge - Biology in grade one of senior high school

Chapter two The relationship between genes and chromosomes

The first 1 section Meiosis and fertilization I 、 The concept of meiosis

Meiosis ： The way in which cells divide during the formation of germ cells by sexually reproducing organisms . During meiosis , Chromosomes replicate only once , And cells divide twice in a row , The number of chromosomes in newly produced germ cells is half that in somatic cells .
【 notes 】 Somatic cells are produced mainly by mitosis , During mitosis , Chromosome duplication once , Cell division once , The number of chromosomes in newly produced cells is the same as that in somatic cells .
Two 、 The process of meiosis
1、 The site of sexual germ cell formation ： The testis of an animal 、 ovary ; Anthers of plants 、 Ovules
2、 The formation of sperm and egg cells ：

3、 ... and 、 A comparison of the processes of sperm and egg formation

Four 、 Be careful ：
（1） Homologous chromosomes ：① form 、 It's basically the same size ;② One comes from the parent , One comes from the parent party .
（2） The chromosome numbers of spermatogonia and oogonia are the same as those of somatic cells . therefore , They belong to somatic cells , Proliferate by mitosis , But they can also undergo meiosis to form germ cells .
（3） Staining during meiosis 00000000 Body number halving occurs during the first meiotic division , The reason is that homologous chromosomes separate and enter different daughter cells . Therefore, there is no homologous chromosome during meiotic second division .
（4） Chromosomes and during meiosis DNA The law of change

（5） Meiotic daughter cell type ：
Suppose that the somatic cells of an organism contain n To homologous chromosomes , be ： Its essence （ egg ） Protocells undergo meiosis to form 2n Kind of sperm （ Egg cells ）; its 1 Spermatogonia undergo meiosis to form 2 Kind of sperm . its 1 Oocytes undergo meiosis to form 1 Seed egg cell .
5、 ... and 、 The characteristics and significance of fertilization
characteristic ： Fertilization is the mutual recognition between sperm and egg cells 、 The process of fusing into a fertilized egg . The head of the sperm enters the egg cell , The tail stays outside , Soon the nucleus of the sperm and the nucleus of the egg cell fused , Restore the number of chromosomes in the fertilized egg to the number of somatic cells , Half of them come from sperm , The other half comes from egg cells .
significance ： Meiosis and fertilization are important for maintaining a constant number of chromosomes in the somatic cells of the previous and subsequent generations , It plays an important role in biological inheritance and variation .
6、 ... and 、 Meiosis and mitosis image discrimination steps ：
1、 Whether the cytoplasm divides equally ： Unequal division —— The formation of an egg cell during meiosis
2、 The number of chromosomes in a cell ：
If it's an odd number —— The second meiotic division （ Secondary spermatocytes 、 Secondary oocytes 、 Anaphase of meiotic second division , Look at the pole ）;
If even —— mitosis 、 The first division of meiosis .
3、 The behavior of chromosomes in cells ：
There are homologous chromosomes —— mitosis 、 The first division of meiosis ;
The Federation 、 Tetrad phenomenon 、 Segregation of homologous chromosomes —— The first division of meiosis ;
No homologous chromosomes —— The second meiotic division .
4、 Separation of sister chromatids ：
A polar absence of homologous chromosomes —— Anaphase of meiotic second division ;
One pole has homologous chromosomes —— Anaphase of mitosis .
【 notes 】 If the cytoplasm is divided unevenly , Is the decrease of oocytes Ⅰ Or minus Ⅱ Later stage of .
example ： Determine what division is going on in the following cells , At what time ？

The first 2 section Genes are on chromosomes

Sutton hypothesis ： Genes are carried by chromosomes from parents to the next generation , That is, the gene is on the chromosome . Research methods ： reasoning from analogy .

The first 3 section Sex linked inheritance

One 、 Concept ： The genetic control gene is located on the sex chromosome , Therefore, it is always related to gender .
Two 、XY Type a sex determination mode ：
1、 Chromosome composition （n Yes ）：
Male ：n－1 For autosomes + XY female ：n－1 For autosomes + XX
2、 sex ratio ： commonly 1 : 1
3、 Common creatures ： All mammals 、 Mostly hermaphroditic plants , Most insects 、 Some fish and amphibians .
3、 ... and 、 Three characteristics of sex - related inheritance ：
（1） with X Characteristics of recessive inheritance ：
① male ＞ Woman ② Intergenerational inheritance （ Cross inheritance ） ③ A sick mother and a sick son , If a woman is ill, her father will be ill
（2） with X Characteristics of dominant inheritance ：
① Woman ＞ male ② Continuous onset ③ A sick father makes a sick daughter , A sick son makes a sick mother
（3） with Y Genetic characteristics ：
① Men are ill and women are not ② Father → Son → Grandchildren
【 attach 】 Types of common genetic diseases （ Remember ）：
with X implicit ： Color blindness 、 Hemophilia companion X display ： Anti vitamin D Rickets are often hidden ： Congenital deafness 、 Albinism often appears ： many ( and ) finger

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