Mitosis And Meosis Flashcards
Describe the structure of a chromosome
- has a Omar, ( short)
Has a q arm ( long)
Has a telomere ( present at the end of a chromosome)
What is a telomere?
Repeated structures that are found at the end of a chromosome - they have repeated sequences.
What are the 4 different ways a centromere can be located in sister chromatids ?
- in the middle (metacentric)
- at the top ( telocentric - not found in humans )
- just after the middle ( submetacentric)
- near the top ( Acrocentric)
What occurs during prophase in mitosis ?
- chromosones condense , becoming shorter and fatter in length.
- nucleolus and nuclear membrane disintegrate.
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What occurs in prometaphase ?
- spindle fibres form.
- spindle fibres attach to the kinetochore on the centromeres.
What occurs during metaphase ?
The 46 chromosones ( with 92 chromatids ) line up at the centre of the cell called the metaphase plate.
What occurs during anaphase ?
The sister chromatids separate
With centromeres going first , each chromatid moves to opposite ends of the pole.
What occurs during telophase ?
- nuclear envelope re appears
- chromosomes go back to their original shape.
- cleavage furrow forms
What occurs during cytokinesis ?
- cytoplasm divides
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When do you call chromosomes chromatids ?
ONCE THEY HAVE BEEN REPLICATED
When do you stop calling chromosomes chromatids ?
- when they split during anaphase , you then go back to calling them chromosomes.
Define homologous chromosomes
- maternal and paternal copy
- have the same genes , but could have a different variation of alleles
- centromere on the Same position
What occurs in prophase 1?
Homologous chromosome pairs find eachother eg chromosome 1 from paternal finds chromosome 2 from maternal. They can do this because they have similar sequences so are attracted to eachother.
- this makes a bivalent/tetrad
- crossing over occurs : this is where non-sister chromatids swap sections of themselves over. The chromosomes are now non-identical. A new combination of alleles.
What occurs during metaphase 1?
- homologous pairs of chromosomes line up at the metaphase plate.
- random assortment occurs : it is completely random at which the homologous pairs line up at the equator.
Is there a prometaphase stage in meiosis ?
No
What occurs during anaphase 1?
Homologous pairs of chromosomes separate.
The daughter cells produced after meiosis 1 are haploid or diploid ?
Haploid
What occurs during anaphase 11?
Chromatids separates
What occurs during metaphase 11 ?
Chromosomes line up
Outline the process of spermatogenesis
- spermatogenesis is the process by which mature sperm are produced in the testes.
- it begins with a stem cell called spermatogonium (2n) which divides by MITOSIS into primary spermatocyte (2n).
- primary spermatocyte then undergoes meiosis 1 to form secondary spermatocytes. Meiosis 11 then occurs where the secondary spermatocyte divides into four spermatids (n). These then mature into 4 spermatozoa.
How long does spermatogenesis take ?
60 days
How long does oogenesis take ?
12-50 years. Oogenesis is only completed once egg has been fertilised
Why women after the age of 45 find it difficult to get pregnant ?
- this is because when babies are born - they are born with the maximum number of primary Oocytes. And so across the years , these of course deplete.
When does meiosis 11 of secondary Oocytes begin ?
When fertilisation occurs - this would produce polar bodies and egg cell.
