Qhov Tseem Ceeb Qhov txawv - Nondisjunction in Meiosis 1 vs 2
Cell division yog txheej txheem tseem ceeb hauv cov kab mob ntau lub cev thiab hauv cov kab mob unicellular. Muaj ob txoj kev faib cell loj hu ua mitosis thiab meiosis. Genetically zoo tib yam diploid hlwb yog tsim los ntawm mitosis thiab gametes (haploid) nrog ib nrab chromosome teeb yog tsim los ntawm meiosis. Thaum cov txheej txheem ntawm tes faib, homologous chromosomes thiab tus muam chromatids tau sib cais yam tsis muaj qhov yuam kev los tsim cov menyuam ntxhais nrog tib tus lej ntawm chromosomes lossis ib nrab ntawm cov chromosomes. Nws yog hu ua chromosomal disjunction. Txawm hais tias kev faib tawm ntawm tes yuav luag yog cov txheej txheem zoo tshaj plaws, kev ua yuam kev tuaj yeem tshwm sim thaum lub sijhawm chromosomal disjunction ntawm qhov yuam kev me me. Cov yuam kev no yog hu ua nondisjunction yuam kev. Nondisjunction yog qhov tsis muaj peev xwm lossis tsis ua tiav ntawm homologous chromosomes lossis tus muam chromatids cais kom raug thaum lub cell faib hauv mitosis thiab meiosis. Nondisjunction tuaj yeem tshwm sim thaum meiosis I thiab meiosis II, ua rau cov chromosomes txawv txav ntawm gametes. Qhov sib txawv tseem ceeb ntawm kev tsis sib haum xeeb hauv meiosis 1 thiab 2 yog tias thaum lub sij hawm meiosis 1, homologous chromosomes tsis sib cais thaum nyob hauv meiosis II tus muam chromatids tsis cais.
Kev tsis sib haum xeeb hauv Meiosis 1 yog dab tsi?
Meiosis yog txheej txheem uas tsim gametes (qe thiab phev) los ntawm cov hlwb diploid rau kev yug me nyuam. Gametes muaj 23 chromosomes (n). Meiosis tshwm sim ntawm ob theem loj hu ua meiosis I thiab meiosis II. Meiosis I muaj tsib theem loj hu ua prophase I, metaphase I, anaphase I, telophase I thiab cytokinesis. Thaum lub sij hawm anaphase I, homologous chromosomes sib cais ntawm ib leeg thiab txav mus rau ob tug ncej. Qee lub sij hawm, homologous chromosomes qhia tias tsis tuaj yeem sib cais kom raug. Yog tias qhov no tshwm sim, gametes yuav raug tsim nrog cov chromosomes ntxiv lossis ploj lawm. Yog li, tag nrho cov chromosomes hauv gametes yuav txawv ntawm tus lej qub. Thaum cov gametes no fertilized, lawv tsim cov lej chromosome txawv txav, uas yog hu ua aneuploidy.
Daim duab 01: Tsis muaj kev cuam tshuam hauv meiosis
Cov lej chromosome txawv txawv no tsim ntau yam mob (mob kab mob) hauv cov xeeb ntxwv. Piv txwv li, trisomy ntawm chromosome 21 ua rau cov menyuam yaus Down syndrome. Down syndrome yog tshwm sim los ntawm gamete uas muaj n + 1 chromosomes. Thaum lub gamete no fertilized, nws tsim ib lub zygote uas muaj 2n + 1 tus naj npawb ntawm chromosomes (tag nrho ntawm 47 chromosomes). Lwm qhov piv txwv yog Turner's syndrome. Nws tshwm sim vim kev tsis sib haum xeeb ntawm kev sib deev chromosome (monosomy XO). Nws ua rau n-1 tus lej chromosomes hauv gametes thiab tom qab fertilization, cov xeeb ntxwv yuav dais 2n-1 tus lej ntawm chromosomes (tag nrho ntawm 45 chromosomes).
Daim duab 02: Trisomy vim tsis muaj kev cuam tshuam hauv meiosis I
Kev tsis sib haum xeeb hauv Meiosis 2 yog dab tsi?
Meiosis II yog qhov thib ob sib law liag ntawm meiosis uas zoo li mitosis. Thaum lub sij hawm meiosis II, plaub gametes yog tsim los ntawm ob lub hlwb. Nws yog ua raws los ntawm ob peb theem sib txawv hu ua prophase II, metaphase II, anaphase II, telophase II thiab cytokinesis. Chromosomes kab nyob rau hauv nruab nrab ntawm lub cell (metaphase phaj) thiab txuas rau spindle fibers los ntawm lawv centromeres thaum lub sij hawm metaphase II. Lawv tau npaj los faib ua ob pawg thiab mus rau hauv anaphase II. Thaum lub sij hawm anaphase II, tus muam chromatids faib sib npaug thiab raug rub mus rau cov ncej los ntawm microtubules. Cov kauj ruam no yuav xyuas kom meej tus naj npawb ntawm chromosomes hauv gametes. Qee lub sij hawm tus muam chromatids tsis cais kom zoo nyob rau theem no vim muaj ntau yam xws li kev sib raug zoo thiab kev sib txuas ntawm cov phaj metaphase thiab lwm yam. Nws yog hu ua nondisjunction hauv meiosis II. Vim qhov ua tsis tiav no, gametes yuav raug tsim nrog cov lej txawv txav ntawm chromosomes (n+1 lossis n-1).
Nondisjunction hauv meiosis I lossis II ua rau gametes nrog cov lej chromosomal txawv txav thiab tsim cov menyuam mos uas muaj ntau yam mob xws li Down's syndrome (trisomy 21), Patau syndrome (trisomy 13), Edward's syndrome (trisomy 18), Klinefelter syndrome (47, XXY txiv neej), Trisomy X (47, XXX poj niam), Monosomy X (Turner's syndrome), thiab lwm yam.
Daim duab 03: Tsis muaj kev cuam tshuam hauv meiosis II
Qhov txawv ntawm Nondisjunction hauv Meiosis 1 thiab 2 yog dab tsi?
Nondisjunction in Meiosis 1 vs 2 |
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| Tsis ua tiav ntawm homologous chromosomes cais ntawm tus ncej thaum lub sijhawm anaphase 1 yog hu ua nondisjunction hauv meiosis 1. | Kev ua tsis tiav ntawm tus viv ncaus chromatids cais ntawm tus ncej thaum anaphase 2 hauv meiosis hu ua nondisjunction hauv meiosis 2. |
| Chromosomes vs Sister Chromatids | |
| Homologous chromosomes tsis cais kom zoo hauv meiosis I. | Muam chromatids tsis cais kom raug hauv meiosis II. |
Summary – Nondisjunction in Meiosis 1 vs 2
Nondisjunction yog txheej txheem uas tsim gametes nrog tus lej ntawm chromosomes txawv txav. Nws tshwm sim vim qhov tsis ua tiav ntawm homologous chromosomes cais thaum lub sij hawm anaphase I lossis tsis ua haujlwm ntawm tus viv ncaus chromatids cais thaum anaphase II hauv meiosis. Yog li, qhov sib txawv tseem ceeb ntawm kev tsis sib haum xeeb hauv meiosis 1 thiab 2 yog nondisjunction hauv meiosis 1 tshwm sim hauv homologous chromosomes thaum nondisjunction hauv meiosis II tshwm sim hauv cov muam chromatids. Thaum cov gametes no tau fertilized, cov neeg aneuploidy yuav ua rau muaj ntau yam mob xws li Down's syndrome, Klinefelter syndrome, Turner's syndrome, thiab lwm yam.
