①In mammalian females (XX), a random X chromosome is inactivated, and in males (XY), a single X chromosome remains active.

②In Drosophila, both X chromosomes in females are active, while the only X chromosome in males, XY or XO, is hyperactive.

③The dosage compensation mechanism of Caenorhabditis elegans, commonly known as nematodes, is that when XX individuals are hermaphrodites, the transcriptional activity of the linked genes of the two X chromosomes is weakened at the same time, leaving them in a low activity state.

① In the somatic cells of normal female mammals, only one of the two X chromosomes is genetically active, and the other X chromosome is genetically inactive, so that the X-linked genes are compensated quantitatively. Female XX and male XY have the same effective gene product

②Deactivation is random

③Heterozygous females are chimeras in the role of sex-linked genes

④Inactivation occurs in the early stages of embryonic development

① Most X-linked genes show stable transcriptional inactivation during early embryonic development, but not all genes on the entire X chromosome are inactivated.

②There is a specific inactivation site on the mammalian X chromosome and the X life center

It means that the frequency of genes located on the same pair of chromosomes being combined together and inherited is greater than the frequency of recombination.

The percentage of the number of recombinant types (or crossover types) in the test cross offspring to the total number in the test cross offspring (number of parental types + number of recombinant types) is defined as the recombination rate

formula

Crossover refers to the local exchange of genetic material, while recombination is the recombination of genes after exchange.

The process of determining only the relative position and order of genes on chromosomes

Also called linkage map or genetic map

The quantitative unit of the relative distance between two linked genes on the chromosome diagram is called the distance

Early people believed that the position of genes on chromosomes was relatively constant, based on the relative constant recombination rate between two genes.

definition

definition

Methods to determine central genes

A single crossover may affect the likelihood of another near it, a phenomenon called interference or chromosomal interference

interfering

negative interference

definition

Calculation formula

Calculation formula

The larger the concurrency coefficient, the smaller the interference effect. When the concurrency coefficient C=1, then I=0, indicating that no chromosome interference occurs; otherwise, the interference is complete, which means that the genes are very close to each other, so that double crossover does not occur.

① When homozygous dominant genes are transmitted by the same sex, both F1 female and male individuals have dominant traits

② When homogamous sex transmits pure and recessive genes, F1 shows cross inheritance

A specific gene occupies its specific location on the chromosome

X-linked inheritance

Y-linked inheritance

Genetic analysis of other sex-linked genes

Most higher plants are monoecious, but a few dioecious plants also have sex chromosome sex determination mechanisms similar to those in animals.