Sex determination - reproduction, Biology

Sex Determination - Reproduction

Sex, whether an individual will be a male or a female is determined at fertilisation, and this directs and controls all the later processes involved in male-female differentiation of the genital system. The genetic determination however is not final and irrevocable. Many internal and external environmental factors come into operation during the developmental process and modify or completely reverse the sexual constitution of the individual. Sex which is established at fertilisation, depends upon the "sex" chromosomes contributed by the parents. You are aware that cells of multicellular organisms contain two types of chromosomes; autosomes and sex chromosomes. In human for example, there are twenty two pairs of autosomes and one pair of sex chromosomes.

In mammals, most frogs, some fishes, and dipterus insects there are two types of sex chromosomes, X and Y. Y chromosome is strongly "male determining". The zygote bearing XY chromosomes gives rise to male and it is called heterozygote, where as zygote of XX chromosomes develops into a female, and it is homozygote. Since a mammalian male is a heterogamete, containing XY chromosomes, therefore, half of the spermatozoa bear X chromosomes and the other half Y chromosomes. A mammalian female is a homogamete containing XX chromosomes, therefore ova contain only the X chromosomes. The union of the spermatozoon bearing X chromosome with the egg gives rise to a female and union of the spermatozoon bearing Y chromosome with the egg will be the genetic male. In birds, female is the heterogametic sex. The small chromosome, equalent to the Y in mammals, is designated by the letter W, and the X chromosome is designated in this case as , Z. Half of the eggs carry a W chromosome and the other half a Z chromosome. All of the sperms carry a Z chromosome. The homozygous (ZZ) condition produces males, and the heterozygous (ZW) produces females. This is the type of mechanism that operates in birds, most reptiles, salamanders, some fishes and insects. XX-XY type of sex determination is called mammalian type of sex determination and ZZ-ZW type is called avian type of sex determination.

 

Posted Date: 1/16/2013 6:48:08 AM | Location : United States







Related Discussions:- Sex determination - reproduction, Assignment Help, Ask Question on Sex determination - reproduction, Get Answer, Expert's Help, Sex determination - reproduction Discussions

Write discussion on Sex determination - reproduction
Your posts are moderated
Related Questions
Q. Cows swallow their food once and then this food goes back to the mouth to be chewed again. How can this phenomenon be explained? The food ingested by cows and other ruminant

H Y ALURONI C ACID It is formed by alternating unit of D-glucuronic acid and N-acetylglucosamine. Hyaluronic acid acts as animal cement between adjacent animal cells

Define Interaction of Vitamin D with other Nutrients? Vitamin D metabolism is inter-related with calcium, phosphorous, vitamin K and iron.  Let us discuss each of these:

AGA R - AGAR It is cell wall mucopolysaccharide of some red algae (e.g. Gelidium, Gelidiella, Gracillaria). Agar is used as culture medium, thickener, stabilizer and as lax

Define the Growth Charts of Infant? Besides identifying growth faltering, growth charts also provide the following information: 1) The growth is considered normal or satisfa

Explain the Food Applications of Gum Arabic A major use for gum Arabic is in the confectionery industry where it has two important functions; to retard or to prevent crysta

Q. As a result of the DNA replication two DNA molecules come into existence. Why is it not correct to assert that the two "new" DNA molecules are created? What is the name given to

In a population of e-coli, it turns into 4 individuals in 1 day (assuming no deaths). What is it instantaneous per capita birth rate? Assume instantaneous death rate is 0.10. What

Q. How are the three major arthropod classes characterized according to the body division? In arachnids and crustaceans the head is fused with the thorax forming the cephalotho

Briefly explain about the Sit-ups Test? To measure muscular endurance, bent knee sit-ups can be done. Sit-ups begin with the subject lying flat on their backs with their knees