MEIOSIS Flashcards
Diploid organisms have two versions of each ……………………., also known as …………………
Chromosome
Homologues
Homologues are either …………………. or ………………… and only one is packaged into a gamete.
Maternal
Paternal
Pairing of homologues before segregration (the extra step of meiosis) allows for ……………………………….
Crossing over/ homologous recombination
At which phase do homologues join up
Meiotic prophase 1
What is the purpose(s) of crossing over
- ALIGNS CHROMOSOMES READY FOR ANAPHASE
2. ALLOWS FOR GENETIC RECOMBINATION OF MATERNAL AND PATERNAL DNA
WHAT HELPS PAIRING OF HOMOLOGUES
- DNA BASE PAIRING
2. SYNAPTONEMAL COMPLEX
HOW MANY TIMES CAN CROSSING OVER OCCUR
AT LEAST ONCE BUT NO MORE THAN FOUR TIMES
HOW CLOSE ARE PAIRED HOMOLOGUES
400NM APART
WHAT MAKES UP THE SYNPATONEMAL COMPLEX
THE AXIAL CORE - PROTEINS THAT BIND TO CHROMATIN VIA COHESIN ARE CROSS LINKED BY TRANSVERSE FILAMENTS TO FORM THE SYNAPTONEMAL COMPLEX
WHAT ARE THE PHASES OF CROSSING OVER
INTERPHASE LEPOTENE ZYGOTENE PACHYTENE DIPLOTENE
WHAT IS THE DIFFERENCE BETWEEN MITOSIS AND MEIOSIS
IN MITOSIS: SISTER CHROMATIDS SEPARATE TO FORM A DIPLOID CELL
IN MEIOSIS 1: HOMOLOGUES SEPARATE (BOTH KINETOCHORE ON ONE CHROMOSOME ARE ATTACHED TO THE SAME POLE
END RESULT IS A HAPLOID CELL
WHAT CAN GO WRONG IN MEIOSIS
ABNORMALITIES IN CHROMOSOME NUMBER
CHROMOSOME STRUCTURAL REARRANGEMENTS
WHAT IS MONOSOMY
ONLY HAVING 1 COPY OF A CHROMOSME
EXAMPLE OF MONOSOMY
USUALLY EMBRYONIC LETHAL EG MONOSOMY 45 X - TURNERS SYNDROME COMPLETE OR PARTIAL ABSENCE OF SECOND SEX CHROMOSOME IN PHENOTYPIC FEMALES POOR GROWTH SHORT STATURE DELAYED PUBERTY CONGENITAL HEART DEFECTS
WHAT IS TRISOMY
3 COPIES OF A CHROMOSOME
EXAMPLE OF TRISOMY
USUALLY EMBRYONIC LETHAL
TRISOMY 21 - DOWNS SYNDROME
TRISOMY 22
TRISOMY 18 - EDWARD SYNDROME
USUALLY DIE BEFORE OR SHORTLY AFTER BIRTH
WHAT IS POLYPLOIDY
WHOLE SETS OF CHROMOSOMES DUPLICATED
HOW DOES ANEUPLOIDY OCCUR
THIS OCCURS BY CHROMOSOME NON DYSJUNCTION EITHER IN HOMOLOGOUS CHROMOSOMES OR SISTER CHROMATIDS UPON SEPARATION IN MITOSIS OR MEIOSIS 1 OR MEIOSIS 2
IF OCCURS IN MEIOSIS ONE YOU WILL HAVE NO NORMAL GAMETES PRODUCED
WHAT IS THE IMPACT OF ADDITIONAL SEX CHROMOSOMES
MINOR PROBLEMS , NORMAL LIFE SPAN
WHAT IS THE IMPACT OF LACKING SEX CHROMOSOMES
45Y - NOT VIABLE
45X - TURNERS SYNDROME
ONLY 1% SURVIVE TO TERM
WHAT ARE THE TWO MODELS OF POSSIBILITY WHEN WE SEE LETHALITY
- HAPLOINSUFFICIENCY - IN TERMS OF SEX CHROMOSOMES THE DOSE IS CRITICAL
- IMPRINTED GENES ON X - MONOALLELIC EXPRESSION IS LOST
THIS ASSUMES X INACTIVATION
WHAT IS X INACTIVATION
IN FEMALES ONE OF THE X CHROMOSOMES IS RANDOMLY INACTIVATED (MOST OF THE GENES ARE NOT CONTRIBUTING)
WHY ARE SOME GENES ON X INACTIVATED CHROMOSOMES STILL EXPRESSED
SOME REGIONS OF DNA ON THE SEX CHROMOSMES (PAR) BEHAVE ON A PSEUDOAUTOSOMAL BASIS IE THEY ACT LIKE AUTOSOMAL CHROMOSOMES AND THEREBY REQUIRE EXPRESSION FROM BOTH COPIES OF THE GENE - THEREFORE THE DOSAGE MATTERS
GIVE AN EXAMPLE OF X INACTIVATION AND LETHALITY
USUALLY IN FEMALES AN X IS INACTIVATED - THIS IS RANDOM. IN TURNER SYNDROME, ON ONE FULL X IS PRESENT. IF THE FULL X IS DEEMED TO BE THE X THAT IS INACTIVATED THEN THERE IS NO TRANSCRIPTION.
IF THERE FULL X IS DEEMED ACTIVE THEN IT IS STILL HAPLOINSUFFICIENT SINCE THE PAR GENES REQUIRE TWO COPIES AND SO NOT ENOUGH CAN BE TRANSCRIBED.
BOTH RESULT IN DEATH.
IN MOSAIC TUNERS SYNDROME, SOME OF THE CELLS HAVE BOTH COPIES AND SOME OF THE CELLS DONT THEREFORE 1% CAN SURVIVE.
