EVOLUTION AND CLASSIFICATION

1)  EVOLUTION AND CLASSIFICATION -                                              

                                   SOME BASIC CHARACTERISTICS WILL BE SHARED BY VARIOUS ORGANISM. THE CELL IS BASIC STRUCTURAL AND FUNCTIONAL UNIT OF LIFE IN ORGANISM. THE CHARACTERISTICS IN THE NEXT LEVEL OF CLASSIFICATION WOULD BE SHARED BY MOST OF THE ORGANISM BUT NOT BY ALL. A BASIC CHARACTERISTICS OF CELL DESIGN THAT  DIFFERS AMONG VARIOUS ORGANISM IN WHETHER THE CELL CONTAIN A NUCLEUS. BACTERIAL CELL DO NOT , WHILE THE CELL OF MOST OTHER ORGANISM DO. AMONG ORGANISM HAVING NUCLEATED CELLS . THAT PROPERTY MARKS A VERY BASIC DIFFERENCE IN BODY ORGANISATION , BECAUSE OF SPECIALISATION OF CELL TYPE AND TISSUES . IN MULTI CELLULAR ORGANISMS , THEY CAN PERFORM PHOTOSYNTHESIS OR NOT WILL PROVIDE THE NEXT LEVEL OF CLASSIFICATION . AMONG THE MULTI CELLULAR ORGANISM CAN NOT PERFORM PHOTOSYNTHESIS , WHETHER SKELETON PRESENT INSIDE THE BODY OR AROUND THE BODY WILL MARK ANOTHER FUNDAMENTAL DESIGN CHANGE . WE CAN SEE THAT , EVEN IN THESE SOME QUESTION THAT WE HAVE ASKED, A HIERARCHY IS DEVELOPING THAT ALLOWS US TO FORM CLASSIFICATION OF GROUPS. 

 THE MORE CHARACTERISTICS TWO SPECIES WILL PRESENT IN COMMON , THE MORE CLOSELY THEY ARE RELATED. AND THE MORE CLOSELY  THEY ARE CO-RELATED , THE MORE RECENTLY THEY WILL HAVE A SAME ANCESTOR. EXAMPLE, A SISTER AND A BROTHER ARE CLOSELY RELATED. THEY HAD COMMON ANCESTORS IN THE FIRST GENERATION NAMELY, THEIR PARENT BEFORE THEM. A GIRL AND HER FIRST COUSIN ARE ALSO RELATED BUT LESS THAN THE GIRL AND HER BROTHER. THIS IS BECAUSE COUSIN COME FROM A COMMON ANCESTORS, THERE GRANDPARENTS,IN THE SECOND GENERATION BEFORE THEM, NOT IN THE FIRST ONE. NOW WE CAN APPRECIATE THAT CLASSIFICATION OF SPECIES IS A REFLECTION OF THEIR EVOLUTIONARY   RELATIONSHIP.  

2)  SEX DETERMINATION -

                                DIFFERENT SPECIES USE VERY SEPARATE STRATEGIES FOR THIS. IN SOME ANIMALS THE TEMPERATURE AT WHICH FERTILISED EGGS ARE PLACED DETERMINED WHETHER THE ANIMALS DEVELOPING IN THE EGGS WILL BE FEMALE OR MALE. IN OTHER ANIMALS SUCH AS SNAILS, INDIVIDUAL CAN CHANGE SEX, SHOWING THAT SEX IS NOT GENETICALLY DETERMINED. IN HUMANS , THE SEX OF THE INDIVIDUAL IS LARGELY  DETERMINED GENETICALLY.  IN OTHER WORDS , THE GENE INHERITED FROM OUR PARENTS DETERMINE WHETHER WE WILL GIRLS OR BOYS. BUT SO FAR, WE HAVE ASSUMED THAT IDENTICAL GENE SETS ARE INHERITED FROM BOTH    PARENTS. THE EXPLANATION LIES IN THE FACT THAT ALL HUMANS CHROMOSOMES ARE NOT PAIRED. MOST HUMAN CHROMOSOMES HAVE A PATERNAL AND MATERNAL COPY, AND WE HAVE 22 SUCH PAIRS.BUT ONE PAIR,KNOWN AS THE CHROMOSOMES,IS ODD IS NOT BEING ALWAYS A PERFECT PAIR.WOMAN HAVE A PERFECT PAIR OF SEX CHROMOSOMES ,BOTH KNOWN AS X. BUT MAN HAVE A MISMATCHED PAIR IN WHICH ONE IS A NORMAL SIZED X WHILE THE OTHER IS SHORT NAMED Y. SO MEN ARE XY , WHILE WOMAN ARE XX. NOW WE CAN WORK OUT THE INHERITANCE PATTERN OF Y AND X WILL BE?

 ALL CHILDREN WILL INHERIT AN X CHROMOSOME FROM THEIR MOTHER REGARDLESS OF WHETHER THEY ARE GIRL AND BOY. THE SEX OF THE CHILDREN WILL BE DECIDED BY WHAT THEY INHERIT FROM THEIR FATHER . A CHILD WHO INHERITS AN Y CHROMOSOMES FROM HIS FATHER WILL BE A BOY , AND ONE WHO INHERITS A X CHROMOSOMES FROM HIM WILL BE A GIRL. C