Meiosis Flashcards
Diploid organisms? meaning
have two versions of each chromosome (homologues
homologue meaning ?
Homologues are either paternal or maternal.
Only one homologue for each chromosome is packaged into a gamete
what happens in meiosis 1
• Centrioles + chromosomes are replicated (just like mitosis)
• Maternal + paternal homologs pair up
• Genetic diversity is generated by recombination between homologous chromosomes
One complete chromosome (2 chromatids) pulled to sep. poles
• These cells will be haploid with each homologue represented by two sister chromatids.
difference between meiosis 1 and 2
The main difference is that cells in meiosis II are haploid instead of diploid
what is the synaptonemal complex
Pairing in facilitated by the synaptonemal complex (proteins) as well as DNA base pairing between homologues.
• The axial core (proteins that bind the chromatin via cohesion) are cross-linked by transverse filaments to form the Synaptonemal complex
• This tight bringing together of sister chromatids by the synaptonemal complex
- aligns the two chromosomes
- and helps in homologous recombination
Fundamental difference between meiosis and mitosis and what allows for this difference
Mitosis: Sister chromatids separate
Meiosis: Homologs separate
allows for difference
(i) BOTH kinetochores (on one chromosome) attach to the same spindle pole
(in mitosis you to avoid this) This is done by a protein complex that is removed after meiosis I
(ii) Crossing over = physical linkage between homologs
(iii) Cohesin is only removed from the arms
Fundamental difference between meiosis and mitosis and what allows for this difference
Mitosis: Sister chromatids separate
Meiosis: Homologs separate
allows for difference
(i) BOTH kinetochores (on one chromosome) attach to the same spindle pole
(in mitosis you to avoid this) This is done by a protein complex that is removed after meiosis I
(ii) Crossing over = physical linkage between homologs
(iii) Cohesin is only removed from the arms
who is Crossing over in Meiosis highly regulated
There’s at least one crossing over per bivalent BUT no than 4
Crossover interference – once one forms it inhibits others close by. Thus the number per arm are limited
two ways meiosis can go wrong
(i) abnormalities in chromosome number
(ii) chromosome structural rearrangements.
what is polyploidy and name 2 types
You can get whole extra sets of chromosome, called polyploidy. often lethal, unless sex chromosomes then usually just infertile.
Monosomy – 1 copy of a chromosome
Trisomy – 3 copies of chromosome
Autosomal Trisomy - Trisomy 22 symptoms
¥ Undeveloped midface (midface hypoplasis)
¥ Malformed ears
¥ Wide-spaced eyes (hypertelorism)
¥ Microcephaly
¥ Congenital heart disease
¥ Rare in live born (usually die shortly after birth) is found in miscarried foetuses
Trisomy 18 (Edwards syndrome) symptoms
- Severe intellectual disability
- Low birth weight
- A small, abnormally shaped head
- A small jaw and mouth
- Clenched fists with overlapping fingers
- Congenital heart defects
- Various abnormalities of other organs
- Death before birth or within 1st month of life
- Rare survival to teenage years
Monosomy symptoms
45, X: Turner’s syndrome • Complete or partial absence of a second sex chromosome in phenotypic females ¥ Poor growth ¥ Short stature ¥ Delayed/absent pubertal development ¥ Congenital heart defects ¥ Skeletal abnormalities
what is halpoinsufficiency
Haploinsuficiency – the gene is expressed from both alleles and dose matters. But if you had X-inactivation . Some cells would have their only X inactive – ie null, Some cells would only have 1 copy - ie not enough dose
