Sex determination - chromosomal theory of sex determination.

A presentation on chromosomal theory of sex determination.

1. Sri bhagavan mahaveer jain college

2. A presentation on chromosome theory of sex determination. Submitted to: Mrs. Levenya Department of life science G enetics

3. SEX DETERMINATION CONTENTS INTRODUCTION 1 discovery of sex chromosomes 2 types of sex chromosomes 3 structure of sex chromosomes Chromosomal theory of sex determination. Heterogametic males ( XX-XY, XX-XO) (b) Heterogamatic females (ZO-ZZ, ZW- ZZ)

4. W hat is sex determination? The method by which distinction between male and female is established in an organism under genetic control. The chromosomes are responsible for determination of separate sexes. the phenomenon of molecular, morphological, physiological, behavioral differentiation between male and female sexes is called sex determination/sexual dimorphism. Traditionally, the symbol ♂ designate male And the symbol ♀ designates females. Sexes is a latin word ‘sexus’ which in english means section or separation INTRODUCTION

5. An animal possessing both male and female reproductive organs is usually referred to as hermaphrodites. in plants where staminate (male) and pistilate (female) flowers occur on the same plant, the term of preference is monoecious. The organisms in which both male and female gametes are produced by different individuals are called as diecious. The sex cells and reproductive organs form the primary sexual characters of male and female sexes. Besides the primary sexual characters, the male and female sexes differ from each other in many somatic characters known as secondary sexual characters.

6. Mechanism of sex determination Most of the mechanisms of the determination of the sex are under genetic control and they may be classified into following categories : Sex chromosome mechanism or heterogamesis; genic balance mechanism; male haploidy or haplodiploidy mechanism; Single gene effects.

7. Sex chromosomal mechanism (heterogamesis) 01. Discovery of sex chromosomes. Clarance McClung (1870-1946) A German biologist, Henking in 1891 while Studying spermatogenesis of the squash bug ,Pyrrhocoris , noted that meiotic nuclie contained 11 pairs of chromosomes and an unpaired element is moved to one of the poles d uring the first meiotic division. Henking called this u npaired element a “ X body” and interpreted it as a nucleolus. The significance of X body was immediately understood, but in 1902 an American geneticist Clarance McClung who had made extensive observations of gametogenesis in grasshoppers, s uggested that the X body was involved in some way with the Determination of sex

8. 02. Types of sex chromosomes In diecious organisms, thus, two types of chromosomes were recognised which are as follows: (ⅰ) Autosomes : The chromosomes which have no relation with the sex and contain the genes which determine the somatic characters of the individuals are known as autosomes . (ⅱ) S ex chromosomes : The chromosomes which are responsible for the determination of sex are known as sex chromosomes, e.g., X and Y chromosomes.

9. DIFFERENCE BETWEEN AUTOSOMES AND ALLOSOMES AUTOSOMES ALLOSOMES OR SEX CHROMOSOMES Refer to other than sex chromosomes/ chromosomes that do not determine the sex of individuals These are sex chromosomes./ chromosomes that determine the sex of individuals Chromosome no. = 2n-1 Chromosome no. = 2 Morphology is similar in male and female. Morphology is different in male and female. Number differs from species to species. Each diploid organism usually has two allosomes . Do not exhibit sex linkage. Exhibit sex linkage.

10. 03. Structure of sex chromosomes: The X and Y chromosomes exhibit structural differences. t he cytological studies have shown that the X chromosomes of most organisms are straight, rod-like and comparatively larger than Y chromosomes. The Y chromosomes is smaller in size with one end slightly Curved or bent to one side in drosophila; in man and Melandrium no such curvature of Y chromosomes occurs. The X chromosomes have large amount of euchromatin and Small amount of heterochromatin. The Y chromosome contains small amount of euchromatin and large amount of heterochromatin.

11. Types of sex chromosomal mechanism of sex determination In diecious diploidic organisms following two system of sex chromosomal determination of sex have been recognized:

12. Sex determination in various organisms. ORGANISMS GENOTYPE OF FEMALE GENOTYPE OF MALE 01. Insects. XX XO 02. Drosophila, humans and other mammals. XX XY 03. Moths, butterflies and insects. ZO ZZ 04. Birds fishes and butterflies. ZW ZZ

13. The heterogametic males: (ⅰ) XX-XO type: In certain plants (e.g., vallisneria spiralis, Dioscorea Sinuate, etc.) and in insects specially those of the orders hemiptera (true bugs) and orthoptera (grasshoppers and roaches)the female having two X chromosomes (XX) and are, thus, homogametic, while the male having only one X chromosome(XO). Female is homogametic and produces all the eggs with X Chromosome. The male is heterogametic, which produces half of which have X chromosome and the other half have none. In this type of sex chromosomal determination of sex, the female sex has two X chromosomes, while the male sex has only one X chromosome.

14. XX-XO type of determination of sex

15. The sex of the offspring depends upon the sperm that fertilizes the egg (each of which carries single X chromosome) Union of egg with sperm having X chromosome will give rise to female sex and union of egg with sperm having none results in development of make sex. Haploid male and diploid female type

16. (ⅱ) XX-XY type: Seen in man, other mammals, certain insects including drosophila and lygaeus turicicus and in certain angiospermic plant such as Melandrium album, humulus lupulus , coccinia indica . In this system, female has two X chromosomes, is homogametic and produces only one type of gamete, i.e., X. The male has one X and one Y chromosome, is Heterogametic and produces two types of gametes, viz., X and Y. Union of X ovum with X sperm leads to development of Female (XX) sex. If X ovum units with Y sperm, it produces male (XY) sex.

17. XX-XY type of sex determination

18. Male and female drosophila melanogaster

19. The Heterogametic females: (ⅰ) ZO-ZZ type: ( in moths and butterflies,very low species of insects like fumea ) In this system, female has only one Z chromosome and hence Is heterogametic. As a result of meiosis, 50% eggs of such female carry an Z Chromosome and remaining 50% have none. On the other hand, male has two Z chromosomes and produces All the sperms with one Z chromosome. Thus, male sex is Homogametic. The union of Z sperm with ovum having Z chromosome gives Rise to male sex and union of Z sperm with ovum having none Leads to development of female.

20. ZO-ZZ type of sex determination

21. ( ⅱ) ZW-ZZ type: (occurs in insects ( gyspy moth), vertebrates such as fishes, reptiles and birds and plants such as fragaris elatior ) Female is heterogametic and produces two types of gametes Z and W types. Male is homogametic and produces all the sperms of same type Carrying one Z chromosome. Union of Z sperm with ovum having Z chromosome gives rise To male and union of Z sperm with ovum carrying W Chromosome leads to the development of female sex.

22. ZW-ZZ type of sex determination

23. CONCLUSION: After the gametes fuse with each other during fertilization, what factors determine whether the resulting zygote developed into male or female? Researchers have studied the process of sex determination in a wide range of species and discovered several mechanism of sex determination. They conclude that the difference in chromosome constitution is a mechanism for determining sex at the time of fertilization.

24. Submitted by: Jennifer joy.I B.Sc BGB Ⅱsem Thank you…