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level: 3.3 + 10.1 Meiosis

Questions and Answers List

level questions: 3.3 + 10.1 Meiosis

QuestionAnswer
what is non-disjunction? (2)when chromosomes don't separate properly = extra or missing chromosomes aneuploidy
what is meiosis?how sex (haploid cells) are made = germline cell = 4 cells
how many divisions are there in meiosis?2
what happens during the two divisions to create 4 haploid cells? (2)1) separates homologous chromosomes to half the chromosome number (haploid) 2) separates sister chromatids (made from DNA replication in interphase
when is DNA replicated and in which specific phase?interphase - s phase
what does DNA replication in interphase form?2 genetically identical copies = sister chromatids (1 chromosome)
what are the phases of meiosis? (PMAT)prophase metaphase anaphase telephase
What is the second growth phase between meiosis I and meiosis II called?interkinesis
Describe the different stages in meiosis I? (4)P = chromosomes condense, membrane dissolves and crossing over happens with paired chromosomes (bivalents) M= spindle fibres connect to bivalents to align them in the middle A = spindle fibres contract and homologous chromosomes are pulled away to opposite ends T = chromosomes decondense and cell divides to 2 haploid cells through cytokinesis
Describe the stages of meiosis II?P = chromosomes condense, membrane dissolves M = spindle fibres attach to chromosomes and aligns them in the middle A = spindle fibres pulls sister chromatids away seperating them T = chromosomes decondense, membrane reforms and cell divides to form 4 haploid cells
Why can the 4 haploid cells from meiosis be genetically distinct?because of crossing over in prophase 1 can cause recombination
what is the process called whereby chromosomes forms pairs? what are these pairs called?synapsis forms bivalents
how are the pairs of chromosomes held together in prophase 1?by the chiasmata
how and where does crossing over occur?in prophase 1 in meiosis crossing over occurs at the chiasmata which forms recombinant chromatids by exchanging genetic material
how does metaphase 1 lead to more variation?Due to random independent assortment of chromosomes into the gametes when aligning in the middle
what would happen if the chromosome numbers were not halved?the total chromosome numbers would double in each generation = polyploidy
what are the 3 ways genetic variation is achieved?crossing over in prophase 1 random assortment in metaphase 1 random fusion of gametes
what is non-disjunction? (2)when chromosomes don't separate properly = extra or missing chromosomes aneuploidy
when can non-disjunction happen? (2)when chromosomes don't separate in anaphase 1 = affects all 4 when chromosomes dont separate in anaphase 2 = affects 2
how is down syndrome caused?3 copies of chromosome 21 ( trisomy)
what can influence the chances of non-disjunction occuring?maternal age because of developing oocytes being in p1 until ovulation especially after 30 mostly from non disjunction in meiosis 1
what is karyotyping? how is it done?chromosomes are organised to find genetic abnormalities cells are harvested from fetus before cell division so that the chromosomes are visible
what is chorionic villi sampling?removes placental tissue at 11 weeks to find CS abnormalities 1% risk of miscarriage
what is amniocentesisamniotic fluid at 16 weeks to find CS abnormalities with 0.5% chance of miscarriage
what are the differences between mitosis and meiosis? (8)Division – Mit 1 division mei 2 divisions Independent assortment – Homologous pairs are randomly separated into separate cells only in meiosis Synapsis – Homologous pairs form bivalents in meiosis only Crossing over – Non-sister chromatids of homologous pairs may exchange genetic material in meiosis only Outcome – Mitosis forms 2 cells meiosis forms 4 Ploidy – mitosis forms diploid while meiosis forms haploid Use – Mitosis is used to clone body cells, while meiosis is used to generate sex cells (gametes) Genetics – Cells produced by mitosis are genetically identical (clones), while cells produced by meiosis are genetically distinct