meiosis Flashcards
inheritance/heredity
transmission of traits from one generation to the next
parent —> offspring
traits
variants of a character
heritable feature that may vary among individuals
gene
unit of hereditary information
locus
gene’s specific location along the length of a chromosome
chromosomes consist of dna and associated proteins
somatic cells
body cells
humans have 46 chromosomes in the nuclei of these diploid(2n) cells
two sets of 23 chromosomes from parent 1 and parent 2
gametes
sex cells
egg or sperm haploid (1n) cells that fuse to pass on genes to the next generation
asexual reproduction
less common version
individuals pass on genetically identical copies of its genes to its offspring without fusion of gametes (mitosis only)
produces a clone
sexual reproduction
two individual parents pass on genetically different copies of their genes to its offspring with fusion of gametes
fertilization plus meiosis
synaptonemal complex
join two chromatids together
gametogenesis
diploid (2n) cell in ovary and testis go through meiosis to produce haploid (n=23) gametes (egg or sperm cell)
fertilization
union of gametes leading to a fusion of their nuclei to produce a diploid (2n) zygote
mitosis
zygote and descendent cells generate all the somatic cells of the body (2n=46)
similarity between reproductive cycle in animals, plants/algae, and fungi/protists
meiosis, mitosis, fertilization all happen
zygotes produced in all three
difference between reproductive cycle in animals, plants/algae, and fungi/protists
plants have something called alternation of generations
go from diploid multicellular organism to haploid multicellular organism
sporophytes produce spores
gametophytes produce gametes
fungi haploids can be multicellular or unicellular
can produce both multicellular or unicellular haploids depending on environmental factors/stresses
chromosome sets during meiosis
meiosis reduces the number of chromosome sets from diploid(2n) to haploid(n)
meiosis interphase generally what is accomplished
stage before meiosis where DNA is replicated to produce paired chromatids in diploid cell
go from one chromatid to paired chromatids (2n)
similar to mitosis
meiosis I generally what is accomplished
homologous chromosomes are separated into two haploid cells with duplicated chromosomes
different from mitosis
meiosis II generally what is accomplished
paired chromatids are separated into haploid cells with unduplicated chromosomes
4 haploid cells with unduplicated chromosomes
different from mitosis
meiosis step by step
interphase what is produced
1 diploid cell 2n=4
2 pairs of homologous chromosomes X X
DNA replicated during S phase of cell cycle
DNA and chromosomes doubled
meiosis I
in depth step by step
prophase 1 - homologous chromosomes pair up forming X shapes (bivalent) –> crossign over occurs here –> chromosomes condense
metaphase I – pairs of homologous chromosomes line up along metaphase plate–> spindle poles connect to kinetochores of each paired chromatid (independent assortment happens here)
anaphase I – pairs of homologous chromosomes start separating towards the poles
telophase I and cytokinesis – nuclear envelope reforms, cytoplasm divides, results in 2 haploud cells n=2
meiosis II
in depth step by step
start w 2 haploid cells n=2
prophase II – homologous chromosomes condense and spindles connect
metaphase II – sister chromatids line up along metaphase plate
anaphase II – poles pull one chromatid from each paired chromatid towards it
sister chromatids are separated and pulled as one chromatid
telophase II and cytokinesis – nuclear envelope reforms
cytoplasm divides
4 haploid cells with unduplicated chromosomes that are genetically different
mechanisms that contribute to genetic variation during sexual reproduction
crossing over
independent assortment
random meeting of gametes(fertilization)
dependent on chromosome behavior
crossing over
synapsis during early stages of prophase I
DNA molecules of nonsister chromatids are broken by a protein and physical exchange occurs between a pair of homologous chromosomes
leads to exchange between homologs and generates new combination of alleles
chiasma
point where crossing over occurs
independent assortment
pairs of homologous chromosomes orient randomly at metaphase I
each pair sorting its homologs into cells independently of every other pair
number of possible combinations for resulting gamete is 2^n
n = haploid number of the species
humans (n=23), results in 2^23 or 8.4 million possible combinations of chromosomes
random meeting of gametes (fertilization)
any sperm can fuse randomly with any ovum (unfertilized egg)
fusion of gametes produces a zygote with 70 trillion diploid combinations (2^23 x 2^23)