L9-10: Mitosis, Meiosis and Sex Flashcards
Where does mitosis take place?
In somatic tissue
Why is mitosis necessary in humans?
Embryonic development
Replacement of skin cells
Wound healing
Production of reticulocytes
What are the phases of the cell cycle?
G1, S, G2 and mitosis
What are the key components of mitosis?
Kinetochore, spindle fibres, centriole, centrosome
What is the centriole made up of?
Composed of nine groups of microtubules that serve as foci for the generation of the mitotic spindle fibres
What happens in prophase?
Chromosomes condense
Centrioles divide and move apart
What happens in prometaphase?
Chromosomes are recognisable as double structures
Centrioles reach opposite poles
Spindle fibres form and attach to kinetochore
What happens in metaphase?
Centromeres align on the metaphase plate
What happens in anaphase?
Centromere split and the daughter chromosomes migrate to the opposite poles
What happens in telophase and cytokinesis?
Daughter chromosomes arrive at poles, chromosomes decondense and nuclear envelope reforms, cytokinesis cell division commences
How does genetic exchange occur?
Via crossing over as a chiasma forms
What are the phases of meiosis I & II?
I: Prophase
Metaphase
Anaphase
Telophase
II: Prophase
Metaphase
Anaphase
Telophase
What are the stages in prophase I called?
Leptonema
Zygonema
Pachynema
Diplonema
Diakinesis
What takes place in prophase I?
Duplicated chromosomes start to condense, synapsis begins, synapsis complete and crossing over takes place, synaptonemal complex disappearing and chiasma visible and bivalent ready for metaphase
What is the synaptonemal complex?
A nucleoprotein ‘zipper’ that forms between the paired homologous chromosomes
What takes place in meiosis I?
MI: Alignment of tetrads on metaphase plate
AI: One half of the tetrad migrates to one pole, other half to the opposite pole (disjunction)
TI: Nuclear membranes form around dyads and cells divide
What happens in meiosis II?
PII: each dyad is composed of a pair of sister chromatids
MII: alignment of dyads on metaphase plate
AII: one half of dyad migrates to one pole the other half to the opposite pole
TII&C: four haploid daughter cells
What is non-disjunction?
When the chromosomes do not separate which forms aneuploid gametes (not an exact multiple of the haploid number)
What diseases/syndromes can be caused by human autosomal trisomies?
Warkany syndrome 2
Chronic Lymphocytic Leukemia
Patau Syndrome
Edwards Syndrome
Down Syndrome
Why is sexual reproduction more advantageous than asexual reproduction?
Results in production of recombinant genotypes
Makes population better able to deal with changes in environment
What is the difference of natural selection in sexual and asexual reproduction?
Sexual strains have a faster growth in harsh conditions in comparison to asexual strains
What is heterogametic sex?
When males produce the unlike gametes (not always male)
What is homogametic sex?
Females production of uniform gametes (not always female)
What are Klinefelter and Turner syndromes?
Variation in the number of X chromosomes as a result of nondisjunction which results in aneuploidy
What did the Klinefelter and Turner karyotypes determine?
That the Y chromosome determines male characteristics
What are the features of the Y chromosome?
PARs (pseudoautosomal regions), MSY (male specific region of the Y) and SRY (sex determining region Y) - produces testis determining factor (TDF)
What is dosage compensation?
The mechanism that keeps X-linked gene product doses similar between males and females
What is a Barr body?
It is a method of darkly staining the nucleus of female cells
What is the Lyon hypothesis?
Inactivation is random at an early point in development
Once inactivated all the progeny cells have the same X-chromosome inactivated
What is an example of X- Mosaicism in humans?
Anhidrotic ectodermal dysplasia, males have no sweat glands and females have a mosaic of decors with and without sweat glands around the body
How is the X chromosome inactivated?
At a site called XIC, key products are non-coding RNA transcripts (Xist and Tsix)
Xist coats X chromosome from spreading outwards so its densely packed into heterochromatin
