NON-DISJUCTION AND ITS IMPLICATIONS

BY-POOJA PRAVIN KAMBLEM.SC part-one

PSZO103: GENETICS,EVOLUTION AND DEVELOPMENTAL BIOLOGY

UNIT I: GENETICS-CHROMOSOME THEROY OF INHERITANCE AND MENDELISM-1

1.1:MITOSIS AND MEIOSIS

1.1.3-NON-DISJUCTION AND ITS IMPLICATOON

CONTENTS

• INTRODUCTION• DEFINATION• DISCOVERY OF NON-DISJUCTION• TYPES OF NON-DISJUCTION• DISORDERS DUE TO NON-DISJUCTION• CONCLUSION• REFRENCES

BASICS OF NON-DISJUCTION

• WHAT IS NON-DISJUCTION?• HOW DO INDIVIDUALS GET NON-DISJUCTION?• WHAT HAPPENS DURING NON-DISJUCTION?• WHY NON-DISJUCTION HAPPEN?• WHAT IS THE CAUSE OF NON-DISJUCTION?• WHEN DOES NON-DISJUCTION OCCUR?• AT WHICH PHASE NON-DISJUCTION OCCURS?

INTRODUCTION

Proper disjuction separates the two homologus chromosomes during cell division.

When there is a faliure of two homologus chromosomes or sister chromatids to separate during cell division it is called as NON-DISJUCTION

DEFINATION

• Non-disjuction is the failure of chromosome pairs to separate during meiosis stage 1 or meiosis stage 2 specifically in the anaphase.

DISCOVERY OF NON-DISJUCTION

• Non-disjuction was discovered in crosses between white eyed female drosophilla and red eyed male drosophilla

• All F1 generations should have white eyed males and red eyed females

• In 1913 calvin bridges found that there are rare exceptions to this results,he found few white eyed daughters and red-eyed sons among F1 generations.

• TYPES OF NON-DISJUCTION• • 1)MEIOTIC NON-DISJUCTION• 2)MITOTIC NON-DISJUCTION

TYPES OF NON-DISJUCTION

• MEIOTIC NON-DISJUCTION• Non-disjuction may occur during either the I or

II meiotic division.• If non-disjuction occurs during 1st meiotic

division then all the sperm derived from that primary spermatocyte will be abnormal.

• In humans for example these sperm will end up with a total of 22 or 24 chromosomes rather than the ususal 23.

• If non-disjuction occurs in a secondary spermatocyte undergoing meiosis II,then only two of the four sperm will be abnormal.

• MITOTIC NON-DISJUCTION• Mitotic non-disjuction gives mosaic cells with different number

of chromosome numbers.• This is a caused by a breaking of the spindle fiber during

metaphase or anaphase.• For example, if spindle fibers do not form for one of the

chromosomes, then during anaphase it will not separate into two chromatids and one cell will have an extra chromatid and the other will be lacking one.

• This causes a trisomic and a monosomic daughter cell to be formed, which produces a mosaic of cell types in the individual.

CHROMOSOMAL NON-DISJUCTION

• AUTOSOMES• 1)PATAU SYNDROME• 2)EDWARD SYNDROME• 3)DOWNS SYNDROME• SEX CHROMOSOMES• 1)TURNER SYNDROME• 2)KLINEFELTER SYNDROME• 3)SUPER MALE SYNDROME• 4)SUPER FEMALE SYNDROME

PATAU SYNDROME

EDWARD SYNDROME

DOWN SYNDROME

TURNER SYNDROME

KLINFELTER SYNDROME

SUPER MALE SYNDROME

SUPER FEMALE SYNDROME

PHILADELPHIA SYNDROME

CRI-DU CHAT SYNDROME

D-G TRANSLOCATION SYNDROME

CONCLUSION

• To identify new mutations that are defective at some step in chromosome segregation.

• Use of nondisjunction to prove the chromosome theory of heredity (Bridges 1916).

• The current study provides guidance for researchers designing genetic experiments on nondisjunction and improves several methods for the analysis of genetic data.

• Study of non-disjuction provides a use full model for studying the association of increasing maternal age and recombination.

REFRENCE

• Principles of genetics-Robert H.Tamarin• Concepts of genetics-williams S.Klunge• i-genetics-russell

• THANK YOU