Genic balance theory of bridges gynandromorphs

This theory was proposed by a Drosophilist Calvin Blackman Bridges in 1921.
This theory fully explains
the sex determination in
Drosophila.
This theory shows that the
Maleness - Autosomes
Femaleness -X chromosomes.

1. Genic balance theory of bridges - gynandromorphs Submitted by SHIVASHINI R ID NO.: 2017021065 Course Teacher Dr. M. Kanimoli Mathivathana Assistant Professor Department of Plant Breeding & Genetics COLLEGE OF AGRICULTURAL TECHNOLOGY (Affiliated to Tamil Nadu Agricultural University,Coimbatore-3) (Accredited by Indian Council of Agricultural Research, New Delhi) Kullapuram (Po), Via Vaigai Dam, Theni - 625 562.

2. Introduction: This theory was proposed by a Drosophilist Calvin Blackman Bridges in 1921. This theory fully explains the sex determination in Drosophila . This theory shows that the Maleness Autosomes Femaleness X chromosomes.

3. Sex is determined by the composition of chromosomes in the zygote. If the sex is determined by the SEX chromosome, Chromosomal determination of sex. If the sex is by the AUTOSOMES, Genetic determination of sex Genic Balance theory – Balance between them.

4. Why we are going behind fruit fly ? They have rapid reproductive rate. i.e., many offspring at a time. Contains only 4 pairs of Homologous chromosomes. Easy & inexpensive to maintain. They are tiny. Easily examine the changes (Phenotypically or Genotypically)

5. HISTORY behind THIs balance: In 1916, Bridges discovered XXY females & XO males in Drosophila while studying the inheritance of vermilion eye gene located in the X chromosome. He showed that XX Femaleness XY Maleness Y chromosome didn’t play a role in sex determination. BUT Y chromosome MALE FERTILITY Without Y, males are Sterile.

6. Genic balance theory: It states that sex of an individual is determined by a ratio called sex index . Sex Index = No. of X chromosomes = X Autosomal sets A Autosomal sets diploid or triploid or tetraploid.

7. X/A Ratio Sex of that individual Greater than 1 Super females/Meta females Equal to 1 Normal Females Between 1 & 0.5 Intersex Equal to 0.5 Normal males Less than 0.5 Super males/Meta males

8. Genes involved in the sex determination of drosophila

9. Sex lethal gene: Transformer gene 1&2: Master regulatory gene controlling sex differentiation. X- linked gene. Present in both male & female. Causes Lethality when Loss of function Female Gain of function Male Sxl must be active in FEMALE. Tra 1& 2 are Feminizing genes. Tra 1 is present both in male & female. Tra 1 is active in FEMALES. But Tra 2 is absent in Males.

10. Double sex gene: Dsx gene present in both male & female. Dsx gene suppresses the opposite sex trait in an individual. Dsx(F) gene present in female, suppresses the male character. Dsx(M) gene present in male, suppresses the female character.

11. Intersex gene: Fruitless gene: Ix is the terminally positioned gene. Ix gene functions only with the Dsx(F) gene to implement Female sex differentiation. Fru gene is required for courtship in males. Fru gene is functions only with Dsx (M) gene.

12. IN SHORTCUT:

13. gynandromorphs: These are the organisms that contain both female & male parts in a single individual. Gynandromorphs derived from the Greek words . Gyne = Woman Andro = Man Morph = Form These gynanders are sterile. Have less life period than normal ones.

14. Types of gynandromorphs:

15. Bilateral gynandromorphs : Lobster Bilateral Gynandromorph Butterfly Bilateral Gynandromorph

16. Sex piebalds in Lobster Anterior - Posterior gynanders : [ Anterior portion of the organism contains male parts + Posterior portion contains female parts] or Vise versa. Sex piebalds :

17. Gynandromorphs in drosophila Gynanders in Drosophila are the mosaics (an organism composed of cells of 2 genetically different types) for X chromosome. Part with Female phenotype XX Part with Male phenotype XO Gynandromorphs arise from the XX zygotes .

18. Causes for gynanders in drosophila Mitotic chromosomal loss (X) Female losing one x chromosome during first mitotic division after fertilization

19. WHITE AND RED EYE IN THE SAME DROSOPHILA Bilateral gynandromorph in drosophila

20. References: Singh B.D. 2018. Fundamentals of Genetics. Kalyani Publishers. Ludhiana. P : 266 – 269 Senthil, Kalaiselvi S and Krishnan V. 2018. Principles of Genetics. Thannambikkai Publications. Coimbatore P: 212 – 215 Verma P.S., Agarwal V.K. 2018. Genetics. S Chand and Company Limited. New Delhi. P: 473- 507 Paul Ajoy . 2018. Text book of Genetics. Books and Allied (P) Ltd. Kolkata. P : 229,235-241 Sahu Arun Chandra. 2010. Fundamentals of Genetics and Biotechnology. Kalyani Publishers. Ludhiana. P: 28

21. Yuri P Nekrutenko. ‘Gynandromorphic Effect’ and the Optical Nature of Hidden Wing pattern in Gonepteryx rhamni L. (Lepidoptera, Pieridae ). Nature 205 (4969), 417, 1965. James M Cook .Sex determination in the Hymenoptera: a review of models and evidence . Heredity 71 (4), 421,1993. Christopher S Raymond et.al., Evidence for evolutionary conservation of sex-determining genes . Nature 391 (6668),691,1998 . Monica Steinmann - Zwicky et.al., Genetic control of sex determination in drosophila. Advances in Genetics 27,189-237,1990. H Allen Orr. The Genetic theory of adaptation a brief history. Nature Reviews Genetics 6(2), 119, 2005.

22. Thank u so much!