Genetics Chapter 1 Pt. 2

meiosis

special type of eukaryotic cell division cycle that occurs during the generation of gametes in animals(sperm and eggs), or spores in plants and single-cell eukaryotes

outcome of meiosis

4 haploid cells

do homologous chromosomes pair up in meiosis

homolgous chromosomes pair to form tetrads during prophase 1

in anaphase 1 the tetrads...

are disjoined and the homologouschromosomes are segregated to daughter cells

in anaphase 2 the chromosomes...

are disjoined and aresegregated to daughter cells

tetrads

the paired chromosomes consisting of four chromatids

reduction division

another name for meiosis I, the division where homologous pairs separate.

equational division

another name for meiosis II because cells in meiosis II have the same number of chromosomes at the beginning and at the end of the process.

in meiosis I, the number of chromosomes in daughter cells is

half the original

dyads

pairs of individuals

synaptonemal complex

an ordered protein structure that forms between homologous chromosomes during meiotic prophase I. It mediates the pairing of the chromosomes and facilitates crossing over; disappears late prophase I

crossing over

Process in which homologous chromosomes exchange portions of their chromatids during meiosis, occurs in prophase I

five substages of meiotic prophase I

leptotene, zygotene, pachytene, diplotene, diakinesis

leptotene

DNA begins to partially condense

zyogotene

homologous chromosomes pair to form tetrads (or bivalents). The synaptonemal complex begins to form

pachytene

condensation continues and the individual chromatids become more visible. Crossing over occurs:the exchange of fragments of DNA between the paired homologous chromosomes

diplotene

the homologous chromosomes begin topartially separate. the chiasmata become visible: pointsat which crossing over already occurred

diakinesis

the homologous chromosomes pull further apart (but they remain together). Further condensation occurs in preparation for metaphase

what substages does crossing over occur in

zygotenem pachytene, diplotene

following pachytene, the sister chromatids...

are no longer identical DNA molecules because crossing over and recombination occurred between non-sister chromatids

middle prophase I

chromosomes begin to condense, the spindle forms

late prophase I

homologous chromosomes pair, crossing over takes place, and the nuclear membrane breaks down

metaphase I

homologous pairs of chromosomes line up along the metaphase plate

anaphase I

Homologous chromosomes separate and move toward opposite poles

telophase I

chromosomes arrive at the spindle poles and the cytoplasm divides

outcome of meiosis I

2 haploid cells

meiosis II

resembles mitosis, chromosomes are disjoined, chromatids are segregated to daughter cells

prophase II

the chromosomes recondense

metaphase II

individual chromosomes line up on the equatorial plate

anaphase II

sister chromatids separate and move toward opposite poles

telophase

chromosomes arrive at the spindle poles and the cytoplasm divides

outcome of meiosis II

4 haploid cells

meiosis gametogensesis

spermatogenesis and oogenesis

spermatogenesis

production of sperm, equal cytokinesis, outcome: 4 gametes (sperm:haploid)

oogenesis

unequal cytokinesis: one cell receives all the cytoplasm, the rest of the cells become polar bodies, outcome: only one gamete (the egg: haploid)

fertilization

produces a zygote (2n)

steps of spermatogenesis

1. Primary Spermatocyte - a diploid cell in testes undergoes Meiosis I to produce

2. Secondary Spermatocyte - a haploid cell with 2 sister chromatids undergoes Meiosis II to produce

3. Spermatids - haploid cell with 1 chromatid that will mature

4. Sperm - mature spermatids

5. sperm fuses with egg to form zygote - diploid cell

6. zygote undergoes mitosis and eventually produces specialized cells, gonads, to start cycle all over again.

steps of oogenesis

1. Primary Oocyte - diploid cells housed in the fetus; 1 undergoes Meiosis at a time.

2. Secondary Oocyte - haploid cell with sister chromatids per chromosome

a.) 1st cell - secondary oocyte

b.) 2nd cell - polar body that eventually disintegrates. (uneven division)

3. Sperm fuses with secondary oocyte

a.) meiosis II occurs

b.) egg develops

c.) 2nd polar body will form and disintegrates

4. Sperm and egg form zygote

5. zygote undergoes mitosis and eventually produces gonads to start cycle all over again.

S. cerevisiae can exist in two forms

diplophase (fuse to form one a/α cell) or haplophase (a or α)

if environmental condition deteriorate, the diplophase S. cerevisiae cells may undergo...

meiosis, (sporulation); to generate four spores inside an ascus that remain dormant

when environmental conditions improve for S. cerevisiae...

the ascus germinates to release four haplophase cells (sexual reproduction)

meiosis fails

organisms that do not contain a chromosome complement consisting of an even multiple of the haploid number.; produce unbalanced gametes

seedless watermelons

tetraploid plant paired with a diploid plant; sterile and no seeds

mules

female horse (2n=64) and male donkey (2n = 62), most are sterile with 63 chromosomes

what would happen if the chinese muntjac and indian muntjac interbred?

embryonic mitotic divisions may generate a viable adult, but the hybrid will be sterile due to meiotic failures

nondisjunction

occurs if chromosomes or chromatids do not separate during anaphase I or anaphase II of meiosis; both chromosomes/chromatids migrate to the same gamete; after fusion with a normal gamete, trisomic and monosomicaneuploidies may occur

trisomy

3 copies of a chromosome

down syndrome

Non-disjunction of chromosome 21, viable, results in trisomy-21 aneuploidy

patau syndrome

trisomy-13, survival beyond neonatal period is uncommon

edward syndrome

trisomy-18, survival beyond neonatal period is uncommon

turner syndrome

Non-disjunction of X chromosome can also result in themonosomy-X aneuploidy

monosomy

only one copy of a chromosome is present

cri-du-chat syndrome

loss of a piece of one of the two copies of a chromosome, as opposed to the entire loss of one of the two copies; results in a partial monosomy