The law of interlocking inheritance describes the relationship between the segregation and combination of interlocking genes located on a pair of homologous chromosomes. Due to the interaction of interlocking genetic genes in the process of segregation and combination, resulting in heterozygotes produced by various types of gametes in varying proportions, and the proportion of segregation of their self-crossed and tested offspring phenotypes varies according to the recombination rate, but it is always the recombinant type is less, and the parental type is more. Due to the different positions and distances of genes on the heterochromatin, the strength of the chain between genes is also different.
Operation method
Experiments on genetic analysis of linked genes
Principle
The law of interlocking inheritance describes the relationship between the segregation and combination of interlocking genes located on a pair of homologous chromosomes. Due to the interaction of interlocking genetic genes in the process of segregation and combination, resulting in heterozygotes produced by various types of gametes in varying proportions, and the proportion of segregation of their self-crossed and tested offspring phenotypes varies according to the recombination rate, but it is always the recombinant type is less, and the parental type is more. The strength of the chain between genes varies due to the different positions and distances of the genes on the heterochromatin. The relative distance of genes on chromosomes can be expressed as recombination rate. Certain genes that determine endosperm traits in maize have interlocking inheritance, and segregating cobs can be obtained by using a two- or three-point test, and then the recombination rate can be obtained by analyzing the observations of seed traits to obtain the order of the genes on the chromosomes and their inheritance distances. It is known that genes controlling certain traits in Drosophila are located on the X chromosome, and that the Y chromosome in male Drosophila does not carry genes corresponding to those on the X chromosome. Therefore, complete interlocking inheritance is shown in male Drosophila. The location and distance of the genes can also be determined by crossing wild-type and mutant Drosophila flies and crossing their hybrids with recessive parents, based on the analysis of the offspring of the crosses.
Materials and Instruments
Corn. Drosophila. Move I. Experimental materials and supplies For more product details, please visit Aladdin Scientific website.
Binocular dissecting mirror Magnifying glass Dissecting needle Calculator Rough-tipped brush White porcelain plate Culture bottle Anesthesia bottle
1. Materials: cobs of the hybrid generation (F1) of a purple, full-grain inbred line and a brown, sunken-grain inbred line of maize, as well as cobs of the hybrid generation (F1) crosses with the brown, sunken parent; wild-type and mutant Drosophila melanogaster with white eyes (w), small shaped wings (m), and curly bristles (sn).
2. Supplies: binoculars, magnifying glass, dissecting needles, calculator, thick-tipped brush, white porcelain plate, culture flask, anesthesia bottle, etc.
3. Drugs: ether.
Second, the experimental method and experimental steps
1. Determination of the rate of recombination of maize endosperm traits chain genes: when two pairs of genes for the chain of inheritance, F2 and cross the offspring of the segregation ratio is obviously different from the independent inheritance, manifested in the number of individuals of the pro-type is obviously more than the theoretical value, and the number of individuals of the recombinant type is obviously less than the theoretical value. It can be seen that the generation of recombinant type is not the result of free combination of non-homologous chromosomes, but the generation of exchange recombination between chain genes on homologous chromosomes. In maize, the genes that determine the color of the pasty layer, purple and brown, and the shape of the kernel, full and sunken, are all located on chromosome 9, which shows interlocked inheritance. A purple, full (BzSh/BzSh) individual was crossed to a brown, sunken (bzsh/bzsh) individual and the F1 was purple, full (BzSh/bzsh). Make a cross to the recessive parent and the distance between the two pairs of genes can be determined from the type and proportion of expression in the progeny of the cross.
(1) Observe the tested ears of the heterozygote (BzSh/bzsh) crossed to the recessive parent, differentiate between the different phenotypes, and count the number of seeds in each category.
(2) Calculate the rate of recombination between bz-sh.
(3) Fill in Table 1 with the results of the analysis of linkage inheritance. 
2. A three-point quiz on Drosophila linked genes
(1) Mate white-eyed, curly bristled, small shaped winged mutant virgin flies with wild-type males, 5 pairs per vial. Allow the parental adult flies to be removed after pupation and identify the hybrid flies after feathering.The F1 females should have red eyes, straight bristles, and long wings, while the males exhibit white eyes, curly bristles, and small shaped wings.
(2) Mate F1 females with mutant males and remove the parental flies after 7 to 8 days, start with the emergence of test-crossed offspring adults and observe every two days and fill in the results in Table 2.
(3) Analyze and calculate
① Determine the genetic relationship of the three pairs of genes according to the results of the experiment. That is, whether the three pairs of genes are inherited independently or chained, or one pair is independent and two pairs are chained.
(② Determine the various types of exchange types and pro-types.
③ Determine the order of the three pairs of genes, analyze the double exchange type, if there are two pairs of traits appeared to be reduced to the parental type of combination, the gene that determines the third pair of traits must be in the middle.
(iv) Calculate the rate of recombination: 
⑤ Draw a chain diagram: use 1% as a unit of distance and draw a chain diagram according to the order of the genes.