Meiosis and Sexual Reproduction Flashcards
1
Q
Sperm/egg = germ cells = sex cells = gametes
A
- Have ½ the number of chromosomes
- Haploid chromosome number (23)
- Regular cells have 46 chromosomes, haploid number is 23, one of each
2
Q
diploid cell
A
- 2 haploid cells come together
- 2 copies of each chromosome
3
Q
zygote
A
- first cell you get after sperm and egg
4
Q
gonads
A
- organ that produces gametes
- ovaries and testes
5
Q
germ line cells
A
- after fertilization–> have zygote
- few cells are put aside
6
Q
Goals of Meiosis (2)
A
- To reduce chromosome number from diploid to haploid
- To generate genetic diversity
A. Random assignment (of chromosomes in metaphase 1)/ independent assortment
B. Crossing over- physical exchange of chromosome sections from one chromosome to the other- breaking/rejoin chromatids
7
Q
cells in meiosis
A
- 2 daughter cells from reduction division- first round of division (still have chromosomes in replicated form)
- 4 haploid cells from mitotic-like division- second round of division
8
Q
reduction division (1)
A
- first round of meiosis
- chromosome pairs at metaphase plate and split up (but not splitting of centromeres, like in mitosis)
- -> 2 daughter cells
9
Q
Mitotic-like division (2)
A
- second rounds of meiosis
- centromeres split during anaphase
- -> 4 haploid cells
10
Q
random assortment
A
- at metaphase I, there is a random assortment of chromosomes from mother and father along the plate
- 8 million combinations in humans
- contributes to genetic diversity
11
Q
Homologues
A
- 2 chromosomes of the same number (don’t have to be together)
- Homologous pairs- both together
12
Q
crossing over
A
- physical exchange of chromosome sections from one chromosome to the other
- contributes to genetic diversity
- When chromosomes are paired up, they are in synapsis (fully paired)
- 2 chromosomes with sister chromatids in each- referred to as bivalent or tetrad
- Synaptonemal complex- structure that forms in between chromosomes–> somehow breaks and rejoins chromatids
13
Q
chiasma
A
- Chiasma = crossover point
- plural chiasmata
14
Q
Substages of Prophase I (5)
A
- chromosomes condense- become visible
- Chromosomes to pair up
- Full synapses (recombination nodules- enzyme activity that breaks and rejoins chromatids)
- Chromosomes separate form each other, pull apart slightly, see crossover points
- More condensed and away from each other
15
Q
meiosis metaphase to anaphase transition (compared to mitosis)
A
- Meiosis 1- paired chromosomes and separate (but do NOT split)
- Physical constraint to block attachment of microtubules (because centromeres are together)–> microtubules attach to only 1 side of centromere
16
Q
Human male gametogenesis
A
- Males produce germ cells throughout life
- Start with some germ line cells in testes, go through meiosis
- 2nds meiotic division–> get 4 round haplitic cells, and then differentiate
- Throw out cytoplasm and everything else
- Keep nucleus and mitochondria
- Chromosomes in head of sperm cell
- Develop flagellum for movement
17
Q
Human female gametogenesis
A
- Females produce germ cells only during reproductive years (13-47)
- Develop and some cells are put aside to be germ line cells
- Meiosis process begins before birth
- Chromosomes condense and pair up before birth
- At birth- around 2 million cells are primary oocytes–> “arrested” in prophase 1–> until puberty
- At puberty- some small number of these primary oocytes will begin to develop
–> As they grow, will continues through process of meiosis until they get to metaphase 1 and will wait
–> At moment of ovulation, usually only 1 egg will be coming out - At ovulation, the first meiotic division completes itself
- Unequal division- take half chromosomes into nucleus (polar body), all cytoplasm will go to other cell
- Then will get ready for second division which ONLY happens if there is fertilization
- IF a sperm enters- will split, and take chromosomes (23), split centromeres, and puts half into 2nd polar body
- NOW HAVE cell with ALL cytoplasm, mitochondria, 23 chromosomes (unreplicated)
ALSO have sperm w/ 23 chromosomes–> have 46 chromosomes = fertilized egg/ ZYGOTE
18
Q
fungus life cycle
A
- Life cycle is reversed
- Mostly always haploid throughout life
- +/- mating types (instead of male and female)
- Zygote goes immediately into meiosis (2-, 2+)
- Grow up into haploid organisms
19
Q
plant life cycle
A
- Plants have diploid stages and haploid stages- do both in life cycle
