TYPES OF SEX DETERMINATION
Date: 2015-10-07; view: 673.
The development of sex is the genetically determined process, but since the formation of sexual characteristics is for the entire period of the life of an organism, internal and external factors may affect their implementation.
In the animal world, the overwhelming number are separate male and female organisms, hermaphroditism is described only in invertebrates and coelenterates. In plants autogamy (hermaphrodite) and cross-pollination producing species predominate, but are fairly common and dioecious species.
Sexual process associated with the division by sex and the presence of female and male or female and male organs from one organism.
Laboratory work ¹6
Pea with red flowers (dominant) and wrinkled seeds (recessive) with white flowers (recessive) with smooth (dominant) seeds.
Subject: Analysis of F1 in the experiment number 3 and the staging of crosses to produce second generation (experiment number 3). Genetics of sex. Mechanisms ensuring gender balance in nature. Inheritance of sex-linked features.
Objective: Studying of the basic laws of genetics of sex. The solution of genetic problems.
Sexual reproduction is typical for most living organisms. Recombination of genes and chromosomes during meiosis and fertilization is the basis of heredity (combinant) variability. At the same time as a result of natural selection favorable genes and their combinations are accumulated and secured.
Sex determination may occur at different stages of the cycle of reproduction. The following types of sex determination.
• Syngamy is the predominance of male or female trends seen at the time of gamete fusion and zygote formation. Ñèíãàìíûé characteristic of most plants, birds, fish and mammals.
•Progamy is occurring before fertilization type determination before sex division occurs in a few organisms (rotifers - Rotatoria, primary kolchetsov - Dinophilus, aphids - Rhullohera Vastatrix). Their sex is determined during the process of oogenesis, while because of the unequal division of cytoplasm formed large and small eggs, after fertilization of large eggs develop females, and from the small - males.
•Epygamy is occurring after fertilization, it is a rare type of sex determination. As an example, marine worm (Vopellia viridis), which has very small males live in a uterus larger than females. If free-larvae attach to rocks, they develop into females, and if you fall on the female trunk, then turned him in males and migrate to its genitals.