(2) The DNA molecular fragments that contain chromosomes and DNA in the nucleus and have specific genetic information and can determine a certain character of an organism are called genes.

(3) All biological traits are controlled by genes. In biological somatic cells, chromosomes exist in pairs, and genes also exist in pairs, which are located on paired chromosomes respectively; In the process of forming germ cells, pairs of chromosomes are separated, one of each pair of chromosomes enters sperm or egg cells, and genes enter different germ cells with chromosome separation. All kinds of biological traits are controlled by genes, and the inheritance of traits is essentially that parents pass genes on to their offspring through germ cells. In the process of sexual reproduction, sperm and egg cells are the bridge of gene transmission between parents and children.

(4) Human cells have 23 pairs of chromosomes, one of which determines the sex of an individual. During reproduction, the number of chromosomes in germ cells is reduced by half. Through fertilization, the nuclei of sperm and eggs fuse together to form fertilized eggs.

(5) Organisms produce new cells through cell division and form tissues through cell differentiation. Cell differentiation makes the shape, structure and function of cells develop in a specific direction, and the result of differentiation is the formation of tissues, such as human epithelial tissue, connective tissue, muscle tissue and nerve tissue.

(6) The structure of sex chromosome in an cell is that women only produce one kind of egg, each egg has 22 autosomes and 1 x chromosome, while men produce one of two kinds of sperm: one kind of sperm contains 22 autosomes and 1 x chromosome; The other sperm contains 22 autosomes and 1 Y chromosome.

(7) The sex chromosome consists of one from the father and one from the mother, so it is XX or XY.

(8) A fertilized egg containing Y chromosome combines with an egg cell, containing 1 X chromosome and 1 Y chromosome, and will develop into a boy in the future.

(9) A fertilized egg with X chromosome will combine with an egg cell, which will contain two X chromosomes and develop into a girl in the future.

So the answer is: ① cell membrane; ② gene; ③ control; ④ Fertilization; ⑤ Cell differentiation; 6 x or y; ⑦XX or xy; ⑧XY； ⑨XX。