Module 2—Meiosis & Sexual Life Cycles Flashcards
life cycle
generation to generation sequence of stages in the reproductive history of an organism, from conception to the production of its own offspring
Alternation of ______ and ________ is common to all sexually reproducing organisms
meiosis and fertilization
3 definitions of genetics
study of how traits are inherited
how genotype relates to phenotype
how information is transformed into living systems
homologs
a pair of the same type of chromosome, one from each parent
n
used to designate a set of chromosomes from a single parent
n in humans =
23
Even if DNA has been duplicated, we still call the cell diploid/2n because…
there are 2 sets of unique information
diploid dominant life cycle
fertilization by two haploid gametes yields diploid zygote →
mitosis yields diploid adult →
meiosis yields haploid gametes
alternation of generations life cycle
fertilization by two haploid gametes yields diploid zygote →
mitosis yields diploid sporophyte adult →
meiosis yields haploid spores →
mitosis yields haploid gametophyte adult →
mitosis yields haploid gametes
sporophyte
diploid adult
gametophyte
haploid adult
haploid dominant life cycle
fertilization by two haploid gametes yields diploid zygote →
meiosis yields haploid cells →
mitosis yields haploid adult →
mitosis yields haploid gametes
purpose of meiosis
create novel combinations of novel chromosomes
drawbacks of asexual reproduction
mutation load
↓ genetic diversity means slow response to environmental change
only ______ cells undergo meiosis
diploid
events of prophase I (excluding those found in mitosis)
each chromosome pairs with its homolog, aligned gene by gene
crossing over occurs
microtubles attach to kinetochores of each homolog (the kinetochores of each sister chromatid joined and acting as one kinetochore)
homologs move toward metaphase plate
homologous chromosomes move together & align together during…
meiosis I
independent assortment
each pair of homologs lines up independent of the other pairs - any combination may end up in the daughter cells
meiosis __ reduces the ploidy of the cells
meiosis I
at telophase I, each half of the cell now has a _____ set of chromosomes, each composed of two…
haploid
non-identical sister chromatids
most similar to mitosis
meiosis II
what separates during meiosis II?
non-identical sister chromatids
what separates during meiosis I?
homologs
steps of crossing over
occurs when?
- occurs during prophase I
- homologs associate along their length
- DNA of maternal & paternal chromatids is broken
- synaptonemal complex is formed
- synapsis
- synaptonomal complex disassembles
function of the synaptonemal complex
zipper like structure holding homologs together during crossing over
synapsis
loose ends of DNA at the breaks are joined to the corresponding segments of nonsister DNA
average crossing over events in human chromosomes
3
crossing over produces…
protects cells from…
recombinant chromosomes
deleterious alleles
3 mechanisms that produce genetic diversity
- Crossing over
- Independent assortment
- Random fertilization
possible combinations during independent assortment
2n
>8 million in humans
