meiosis Flashcards
what is asexual reproduction?
a single individual passes all of its genes to its offspring without the fusion of gametes, offspring identical to parents
what is sexual reproduction?
two parents give rise to offspring that have unique combinations of genes inherited from the two parents, not identical
what are the remaining 22 pairs of chromosomes called?
autosomes
what does meiosis do to the chromosomes?
reduces the number of chromosome sets from diploid to haploid
what do the two cell divisions produce?
four daughter cells rather than two in mitosis
how are the chromatids sorted?
four haploid daughter cells
where does crossing over occur?
prophase 1
what are X shaped regions called?
chiasmata where two non homologous sister chromatids exchange
how is crossing over different in sexes?
55x in males and 75x in females
how are the sister chromatids held together?
by proteins called sister chromatid cohesion
what is the synaptonemal complex?
a zipper-like structure in the EM that holds the homologs together, forms between homologous chromosomes during meiosis 1 to mediate synapsis
why is meiosis different than mitosis?
meiosis can only occur in diploid cells while mitosis can occur in both diploid and haploid
what contributes to genetic variation?
crossing over, independent assortment of chromosomes, random fertilization, mutations, natural selection
how many crossover events happen per chromosome?
1 to 3
what is the average co events for each chromosome?
1.2
how many crossing over sites per cell?
55.2
what is independent assortment?
homologous pairs of chromosomes orient randomly at metaphase 1 of meiosis, each pair of chromosomes sorts maternal and parental homologs into daughter cells
how many combinations of chromosomes are possible in humans?
8 million
what is random fertilization?
any sperm can fuse with any ovum, the fusion of two gametes produces a zygote with any diploid
when do mutations occur?
due to instability of purine and pyrimidine bases, errors during DNA replication, exposure to environmental factors
how many mutations are there per generation?
64
what does natural selection do?
results in the accumulation of genetic variations better adapted to the environment
what is nondisjuction?
the members of chromosome pair fail to separate at anaphase, producing gametes with an incorrect number of chromosomes, more frequent in females, loss of cohesion, incorrect kinetochore attachment
