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reproduction > chromosome and gametes > Flashcards

chromosome and gametes Flashcards

1
Q

What must DNA be able to do for genes to be functional?

A
  1. replicate
  2. separate its 2 copies at mitosis
  3. maintain itself between generation
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2
Q

How does DNA requirements for sexual reproduction differ to somatic cell reproduction?

A

-each parent passes on one allele(one version of a particular gene) to each offspring.
-heterozygous alleles AA, Aa, Aa, aa so can be dominant or recessive trait.

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3
Q

Gene transcription and trasnlation

A
  • promoter and coding sequence transcribed into gene product
    -introns are removed from exon by splicing
  • mRNA exported out of nucleus
    -translated into proteins in ribosomes, i.e complexes of tRNA and proteins
  • proteins then fold into unique 3D structure that determines function
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4
Q

How can the same gene be tissue specific?

A
  • by having alternative promoters.
    -same gene producing same protein but have different promoters depending on where it is makes it tissue specific.
  • eg. CYP19A1 uses different promoters in breast, ovary and brain.
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5
Q

How can same gene give rise to different proteins?

A
  • alternative splicing of exons
    -products are known as isoforms
    -post translational modification eg. phosphorylation
    => eg. AKT used to phosphorylate FSH and LH to make it effective
    -hormones are secreted as pro hormones and must be emzymatically processed to form the active hormone
    => pre-pro GnRH.
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6
Q

What are advantages of sexual reproduction?

A
  • prevents the accumulation of genetic mutaions
    -increase in gentic diversity
    -maintenance ocuurs because of the advantage of genetic variability
  • variation in offspring -> survival of fittest , better adapt to changing environment and evolve.
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7
Q

how did X and Y develop?

A
  • thought to have differentiated from a pair of identical chromosomes … 300 million years ago.
  • mammal developed a variation which made it male.. gradually this chromosome become the Y and the other the X
  • with evolution, genes advantageous to either sex become focussed on X or Y and those maleness close to SRY gene
    -with evolution, genes advantageous to either sex become focused on X or Y and those for ‘maleness’ close to SRY gene.
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8
Q

What to gametes originate from?

A
  • gametes are highly specialised cells formed from germ line cells: primordial germ cells that migrate into gonad and then differentiate to either male or female gametes.
  • the process producing oocytes - oogenesis (incorporated producing sperm- spermatogenesis)
  • undergo cycles of mitosis to increase numbers.
  • then undergo meiosis
    -then combine at fertilisation.
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9
Q

alternative splicing and glycolysylation of FSH and LH

A
  1. Alternative splicing to make different proteins , some protein forms may cause FSH and LH not binding well
  2. different glycosylated FSH and LH have different efficacy (as woman approaches menapause they get more glycolylation)
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9
Q

What happens before mitosis - interphase

A

-interphase
- chromatin - uncondensed form of DNA
-DNA duplicates , not only DNA but centreoles and organelles start to form also duplicate(growth)
-preparation for cell division

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10
Q

what are 4 stages of mitosis

A

1.prophase- duplicated chromosome condenses, centrioles migrate to opposite ends and spindles start to form
2. metaphase - chromosomes line up in the centre
3.anaphase - attachment between sister chromatids breaks and get pulled apart to opposite poles
4. telophase - new nuclei form, each with two complete set of chromosomes , cytokinesis divides cell into two daughter cells.

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11
Q

What happens in prophase 1 in meiosis?

A
  • chromosome condense
  • synapsis occurs : homologous chromosomes pair up and become perfectly aligned with one another
    -crossing over takes place
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12
Q

What happens in metaphase 1?

A
  • homologous pairs of chromosomes line up at the midline of cell
    -spindle fibre from each end attach to the homologue
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13
Q

What happens in anaphase 1?

A
  • homologous pairs of chromosomes separate and move to opposite ends of the cell
  • each homologue still consists of two chromatid
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14
Q

What happens in telophase 1?

A
  • one member of each homologue pair is at each pole
    -cytokinesis occurs and forms two haploid daughter cells.
  • each chromosome still consists of two chromatid
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15
Q

What is synapsis/recombination -in prophase 1?

A
  • pairing of homologous chromosomes to form a tetrad in prophase I
  • genetic material from the homologous chromosomes is randomly swapped
  • this creates 4 unique chromatids hence increasing overall genetic diversity of the gametes
    -each of the affected chromatids has a mixture of maternal and paternal genetic information
16
Q

What are homologous pairs chromosomes?

A
  • in metaphase 1 chromosomes line up in the equator
    -chr1 from mum and chr 1 from dad line up next to each other, chr2 from mum and chr2 from dad etc (homologous pairs)
  • so during anaphase the chromatids dont split at the centromere like they did in mitosis they seperate as a whole , eg chr1 from mum goes to one side and chr1 from dad goes to the opposite pole so each homologue consists of two chromatid still.
17
Q

What is independent assortment - in metaphase 1?

A

-maternal and paternal members of homologous pairs align randomly at the equatorial plate, creating a random assortment of maternal and paternal chromosomes in the daughter cells.
-the orientation of the members of the pair is random with respect to which member is closer to which pole

18
Q

What happens in meiosis II?

A
  1. prophase II - chromosomes condense again , occurs in both daughter cells
  2. metaphase II - chromosomes line up at the midline of the cell
  3. anaphase II - centromeres of sister chromatids separate, chromatids of each pair are now called chromosomes and they move to opposite poles
  4. telophase II - one complete set of chromosomes is located at each pole , cytokines occurs in both daughter cells, forming 4 haploid daughter cells.
19
Q

compare and contrast mitosis and meiosis

A

mitosis :
- involves one cell division not two
- produces two diploids not 4 haploids
-occurs in somatic cells , meoisis occurs only in ovaries and testes during formation of gametes
- results in growth and repair, results in gamete production
- no exchange of genetic material , parts of chromosomes are exchanged in crossing over
- daughter cells are genetically identical , not genetically identical .

20
Q

how is genetic variability achieved?

A
  1. independent assortment
  2. crossing over (recombination)
21
Q

why does crossing over not happen in sex chromosomes?

A
  • X and y chromosomes align but crossing over doesn’t happen bc they are hemizygous (only has one segment of chromosome rather than two) so recombination may be harmful
    -X-inactivation occurs in which one of the copies of the X-chromosomes is inactivated to prevent females from having twice as many gene products
22
Q

What is the only region of the sex chromosome where crossing over happens?

A

-pseudoautosomal regions (PAR)

23
Q

Chromosomal abnormalities: aneuploidies

A
  • gain or loss of chromosomes from the normal 46 is called aneuploidy
  • each chromosome contains hundreds of genes so addition/loss of chromosome dirupts the phenotypes
  • cytogenetics (karyotyping) can be used to identify aneuploidies
    -majority are lethal
24
Q

What are 3 most common aneuploidies in humans?

A

-trisomy 21 (Downs syndrome , 1: 750 births)
-trisomy 18 (edwards syndrome)
-trisomy 13 (platau syndrome)

25
Q

what are sex chromosome aneuploidy?

A

-turner syndrome (45, X monosomy), only 1 X chromosome, short stature , primary amenorrhea, webbed neck.
-Klinefelter syndrome (47, XXY trisomy), variable phenotype taller than average , small testes producing reduced testosterone, infertility.

26
Q

What is the prevalence of trisomies based on maternal age?

A
  • as the woman gets older the presence of trisomies also increases
    -trisomy 16 and 21 occurs in meiosis I whereas trisomy 18 occurs in meiosis II
27
Q

What contributes to the effect of maternal age and risk of trisomy?

A
  • recombination failure
    -premature homologue separation
    -premature sister chromatid separation due to loss of cohesion between sister centromeres
28
Q

What causes polar bodies?

A
  • uneven cytokinesis
  • in mitosis it is equal division but in oocyte first division majority of cytoplasm is retained in secondary oocyte and very little in first polar body and in the second meotic division egg gets most organelles and second polar body is disregarded

reproduction (29 decks)

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