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Sex Determination in Melandrium album (Silene latifolia)

Sex determination in Silene latifolia

The XX -XY Sex Chromosomal Mechanism of Sex Determination in Plants

Majority of the flowering plants are monoecious with male and female reproductive parts are borne on the same flowers or different flowers of same plant. Only about 6% of Angiosperms are dioecious (male and female flowers on separate plants).  The studies of sex determination mechanisms in plants were done only in very few species, such as Coccinia, Asparagus and Melandrium. Melandrium album or Silene latifolia (synonym) is a dioecious model plant in genetics belongs to the Family Caryophyllaceae. The diploid chromosome number of Melandrium album is 24 (n = 12). This post describes the genetic mechanism of sex determination in Melandrium album or Silene latifolia.

Melandrium album shows sex chromosomal sex determination. They have X and Y sex chromosomal constitution similar to Drosophila and Human. However, the mechanism of sex determination is quite different from the usual XX – XY system. In Melandrium album, the AAXX individuals will be females and AAXY individuals will be males. The Y chromosome plays a crucial role in the sex determination of Melandrium album. The Y chromosome contains male determining genes and female suppressing genes, both are necessary for the development and maturation of fertile anthers in the male plants. Since the female individuals are homogametic, (produce only one type of gametes – XX constitution) the segregation of X and Y chromosomes occurs only in the male individuals during meiosis.

Usually plants with AAXY chromosomal constitution are males. Sometimes AAXY individuals will be hermaphrodite (bisexual) or androhermaphrodites (forming both bisexual and male flowers on the same individuals). The formation of bisexual individuals in AAXY individuals may be due to the mutation or deletion of the female suppressing genes on the Y chromosome or due to the change in DNA methylation pattern.

Mechanism of sex determination in Melandrium album:

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Genic Balance Theory of Sex Determination in Drosophila melanogaster

Sex determination mechanism


What is sex determination?

Living organisms, with a very few exceptions, are differentiated into male and female individuals based on their morphological, physiological and behavioral characteristics. Even though the mechanism greatly varies, the sexes of the individuals are genetically determined. The biological system that determines the development of sexual characteristics in an organism is called sex-determination. There are two different types of sex determination systems, they are:

(1). Chromosomal sex determination

(2). Non–genetic sex determination

In chromosomal sex determination, the individuals will process specialized chromosomes called sex chromosomes. In this case, the presence or absence of a particular sex chromosome or the relative ratio of these sex chromosomes determines the sex of the individuals.

Similar to human beings, Drosophila melanogaster (fruit flies) shows XX female and XY male sex chromosomal constitution. However, the mechanism of sex determination is quite different in Drosophila from human. In humans, the Y chromosome is the actual sex determining chromosome. Invariable to the number of X chromosomes, the presence of a single Y chromosome initiates the development of male sex in human embryos. Thus, in human XX and XY individuals will be always female and male respectively. In human XXY and XXXY individuals are also males because of the presence of Y chromosome.

What is Genic Balance System of Sex Determination?

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Hardy Weinberg Equilibrium: Population and Evolutionary Genetics

What is Hardy Weinberg Equilibrium?

What is population?

An ecosystem consists of many species. Species is a group of living organism comprising of similar individuals capable of exchanging genes through interbreeding. The individuals of a same species of a particular region are called population.

Population definition: “A group of individuals of a particular species occupying a definite space, in which the individuals interact, interbreed and exchange genetic materials.”

What is Population Genetics?

Apart from its ecological significance, population has a important role in the process of evolution. We generally have a wrong notion that an individual in a population is evolving during the course of evolution of a species. But in reality, not the individuals but the population only can evolve. Thus population forms the basic unit of evolution, not the species. We also know that for the process of evolution to occur in a system, there should be changes in the genetic constitution. Since the population is undergoing evolution and not the individuals, the changes should be in the genetic constitution of the population. There is considerable difference between the inheritance of genes in the population and that in the individuals. Population genetics is the study of distributions and changes of allele frequency and interaction of alleles in a population. Study of population genetics is very essential for understanding the species adaptation and evolution.

As we mentioned earlier, the process of evolution to occur in a population, the population should face evolutionary forces. A population is usually prone to four main types of evolutionary forces such as:

(1). Natural selection

(2). Genetic drift

(3). Mutation

(4). Gene flow (migration)

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