Meiosis Flashcards
What is a somatic cell?
Any cell that isn’t a part of the reproductive cells.
What is the role of germ cells?
They are used to produce gametes which contain half the number of chromosomes as a somatic cell. Germ cells undergo meiosis to grow and divide into gametes.
Where are germ cells found in the human body?
In males, the testes.
In females, the ovaries.
What is the difference between sister and nonsister chromatids?
Sister chromatids belong to the same copy of the chromosome.
Nonsister chromatids refers to either of the two chromatids of paired homologous chromosomes,
What is general overview of meiosis?
- DNA replication results in 2 homologous pairs
- First division separates homologous pairs into two cells
- Second division results in 4 haploid cells with 2 chromosomes after separation of sister chromatids
What is the major difference between meiosis in males and females (humans)?
From puberty onwards, meiosis continues throughout the lives of males. A single meiotic divsion results in four haploid cells that are ready tovfertilize an ovum.
The products from a single meiotic division in females only gives a 1/4 as gametes.
What are the two stages in the life cycle of a plant called?
- Gametophyte (gametes are produced)
- Sporophyte (haploid spores produced by meiosis)
What typically happens in meiosis I?
Reductional division
Homologous chromosomes pair, exchange pair, exchange parts and segregate.
What typically happens in meiosis II?
Behaves similar to mitosis. Divides sister chromatids into four daughter cells with just one chromosome. (Haploid)
What is it called when two homologous pairs wind together to exchange genetic material?
Synapsis. This is unique to meiosis.
What typically occurs at Prophase I?
Condensation of chromatin, homologous pairing. Genetic exchange.
In human females what stage is meiosis suspended?
At prophase until ovulation.
Frokm ovulation it proceeds to metaphase 2 until fertilization.
How many stages are involved in prophase 1?
5 stages. This follows as:
- Leptotene
- Zygotene
- Pachytene
- Diplotene
- Diakinesis
What is the mnemonic that helps to remember these stages?
LZPDD
Lonely Zombies Peel Delicious Doughnuts
What is characteristic of zygotene?
- Synapsis occurs
- Chromsomes form a bivalent with a protein called synaptonemal complex
What happens during pachytene?
- Synapsis fully occurs
- Recombination nodules allow genetic exchange between the maternal and paternal homologous pairs
What part of the prophase 1 causes genetic diversity to greatly increase?
Crossing over of genetic information between maternal and paternal chromosomes.
Describe what is seen during diplotene?
- Synaptonemal complex dissolves, However, chromosomes still keep condensing
- Homologous chromosomes start to move apart but remain tightly joined at chiasmata – sites where crossing over occurred
- Meiotic arrest occurs in many species
What allows diakinesis to be distinguished?
All four chromatids can be seen.
Nuclear envelope breaks down
Spindle fibres begin to form
Is there any difference between metaphase 1 and in mitosis?
Only difference is that the homologous chromosomes are still attched at the end as chiasmata
What occurs during anaphase?
Chiasmata dissolve
Homologous chromosomes separate to opposite poles by spindle fibres
What occurs during interkinesis?
Cytokinesis around the chromosomes.
No DNA replication
Difference between metaphase 2 in meiosis and mitosis?
–The number of chromosomes is half that in mitotic metaphase in the same species
–Sister chromatids are no longer identical thanks to crossing over in meiosis I.
What contributes to the level of genetic diversity during meiosis?
Independent assortment of chromosomes during metaphase 1
Different mix of paternal and maternal chromosomes gives different combinations in the final stage (telophase 2)
What happens in the event of non-disjunction?
Zygotes end up with one more or one less chromosome during fertilization.
Non-disjunction in anaphase 2?
Only half the zygotes will be normally fertilized
