meiosis Flashcards
what are the 2 classes of cells in a human
somatic cells- skin cells, liver cells, ect.
gametes- sperm cells and egg cells
describe homologous chromosomes
Pairs of chromosomes that have the same structure- same size and the same genes (not identical), one chromosome from each parent
When would a tetrad be able to form? with duplicated or unduplicated homologous pairs.
Tetrads form with duplicated homologous pairs
Describe the similarities and differences of the chromosomes that make up a homologous pair.
Homologous pairs have around the same size, shape, and arrangement of genes, a pair consists of 1 chromosome from each parent, info of genes(alleles) may vary making the homologous chromosome pairs NOT identical
What is the difference between a diploid and haploid cell? Give examples of diploid and haploid cells.
diploid= 2 sets of every chromosome, ex- somatic cells, product of mitosis
haploid= 1 set of every chromosome, ex- gametes/sex cells, product of meiosis
What is the n number of a cell? How can you determine the value of that number in different species cells? Does the value of n in a species change if the cell is diploid or haploid?
n= the number of chromosomes in one set or the number of chromosomes in a haploid cell, diploid= 2n, haploid=n
How are haploid cells formed?
Meiosis- when the homologous pairs are split in half in Anaphase 1 and telophase 1, the 2 newly created cells now has 1 type of each homologous pair, making haploid cells. And after the 2nd stage of meiosis, 4 new haploid cells are made.
What is the main purpose of meiosis?
to create genetically unique gametes (sex cells)
What types of cells undergo meiosis?
germ cells
prophase I
Chromosomes condense, nuclear membrane breaks down, duplicated homologous chromosomes pair up forming a tetrad, crossing over occurs
metaphase I
homologous chromosomes line up along equator- 1 duplicated chromosome on either side, mix of chromosomes from each parent on each side
anaphase I
homologous chromosome pairs are separated, sister chromatids still together
telophase I
nuclear membrane forms, cytokinesis occurs resulting in 2 haploid daughter cells with sister chromatids attached
prophase II
chromosomes condense, nuclear membrane breaks down
metaphase II
chromosomes line up along the equator- 1 sister chromatid on each side
anaphase II
sister chromatids are separated
telophase II
nuclear membrane forms, cytokinesis occurs which results in 4 unique haploid daughter cells w/ unduplicated chromosomes
describe the number of daughter cells after meiosis I
2 daughter cells
compare their genetic make-up of the cells after meiosis I
pairs of homologous cells separate, the homologous chromosomes are similar not identical (not genetically identical) due to not being the same at first+crossing over that occurred in prophase 1
diploid or haploid cells after meiosis I
haploid
in a human cell - describe the number of autosomes and sex chromosomes
22 pairs individual autosomes, 1pair sex chromosome (xx or xy)
describe the # of cells after meiosis II
4 daughter cells
genetic make-up of the cells after meiosis II
all are genetically unique to each other (due to the crossing over that occurred and independent assortment in meiosis 1)
number of autosomes and sex chromosomes after meiosis 2
23 total chromosomes- 22 autosomes, 1 sex chromosome
end result of mitosis vs meiosis
mitosis- 2 genetically identical diploid cells, meiosis- 4 genetically unique haploid cells
differences of processes in mitosis and meiosis
mitosis- 1 stage of division, asexual reproduction, 2 daughter cells produced, diploid, no genetic variation
Meiosis- 2 stages of division, sexual reproduction, 4 daughter cells produced, haploid, lots a genetic variation, homologous pairs initially but then separated, crossing over occurs in prophase 1
overall purpose of mitosis
growth and repair, make identical body cells
overall purpose of meiosis
contributes to genetic variation, makes gametes
When does independent assortment happen - what process and what phase. What is necessary for it to happen.
Metaphase and anaphase 1- when the homologous pairs line up in the middle during metaphase, they have a 50/50 chance of moving to either pole during anaphase, making the variation of genes completely random which contributes to genetic variation
What happens and why can it only happen in meiosis and not mitosis for independent assortment
independent assortment requires homologous pairs to randomly separate, and this pairing up only occurs in meiosis (during prophase 1 and metaphase 1) and not in mitosis
how does independent assortment contribute to genetic variation
leads to random combinations of maternal and paternal chromosomes in the resulting gametes
When does it happen - what process and what phase. What is necessary for it to happen for crossing over
Occurs during prophase 1, is the exchanging of genetic material between homologous chromosomes, is necessary for genetic variation (genetic diversity)
What happens and why can it only happen in meiosis and not mitosis for crossing over
happens in meiosis because its whole purpose is to produce genetically diverse gametes, while mitosis has the purpose of producing genetically identical cells for growth and repair
how does crossing over contribute to genetic variation
when the pieces of chromosomes are swapped, the alleles are swapped which creates new combinations of genotypes= new phenotypes
What processes lead to chromosomal abnormalities within a single chromosome?
A mistake in DNA replication,
Deletion: removes a segment of chromosome
Duplication: repeats a segment
Inversion: reverses a segment within a chromosome
Translocation: piece is broken off and added to another chromosome
What process leads to additional chromosomes in a gamete and thus offspring?
Nondisjunction- pairs of homologous chromosomes/sister chromatids don’t separate normally during meiosis, resulting in gametes having extra copies of chromosomes while others receive no copies of chromosomes
