BSC 1010/C - Ch. 13 "Meiosis and Sexual Life Cycles"

what is asexual reproduction?

when a single individual passes genes to its offspring without the fusion of gametes

what is sexual reproduction?

two parents give rise to offspring that have unique combinations of genes inherited from the two parents

are there any organisms that can reproduce both sexually and asexually?

yes; aphids, flatworms, and starfish

what type of cell division is involved in asexual reproduction?

mitosis

what type of cell division is involved in sexual reproduction?

meiosis

what constitutes a pair of homologous chromosomes?

the two chromosomes in each pair are called homologous chromosomes, or homologs; each pair includes one chromosome from each parent and are the same length and shape and carry genes controlling the same inherited characters

in humans, how many individual chromosomes and homologous pairs are autosomes? how many are sex chromosomes?

each set of 23 chromosomes consists of 22 autosomes and a single sex chromosome

describe the types of human sex chromosomes. which would be present in a female? which in a male?

in an unfertilized egg, the sex chromosome is X; in a sperm cell, the sex chromosome may be X or Y

what is the end product of meiosis?

at the end of meiosis 1 and 2, the result is four non-identical daughter cells with only half as many chromosomes as the parent cell; only diploid cells can undergo meiosis because meiosis reduces the number of chromosomes sets from diploid to haploid

describe meiosis 1

reductional division; homologs pair up and separate, resulting in two haploid daughter cells with replicated chromosomes

describe meiosis 2

equational division; sister chromatids separate; the result is four haploid daughter cells with un-replicated chromosomes

describe crossing-over

crossing-over involves non-sister chromatids exchanging DNA segments

when does crossing-over occur in meiosis?

meiosis 1 (prophase 1)

how does crossing-over contribute to genetic recombination in offspring?

it contributes to genetic variation by combining DNA from two parents into a single chromosome

how does the alignment of the chromosomes at the metaphase plate differ between meiosis 1 and meiosis 2?

in metaphase 1, tetrads line up at the metaphase plate, with one chromosome facing each pole; they line up by homologous pairs; in metaphase 2, sister chromatids line up/align individually at the metaphase plate

what is independent assortment? at what point in meiosis does it occur? how does it contribute to genetic recombination in offspring?

when cells divide in meiosis, homologous chromosomes are randomly distributed to daughter cells, and different chromosomes segregate independently of each other; it results in gametes that have unique combinations of chromosomes and it occurs during metaphase 1 and anaphase 1

how does sister chromatid cohesion differ between meiosis and mitosis?

sister chromatid cohesion allows sister chromatids of a single chromosome to stay together through meiosis 1; it is maintained during anaphase of meiosis 1 but not anaphase of mitosis

compare mitosis and meiosis (DNA replication, # of divisions, # and genetic composition of daughter cells, and roles in body)

mitosis conserves the # of chromosome sets, producing cells that are genetically IDENTICAL to the parent cell; meiosis reduces the # of chromosome sets from diploid (2) to haploid (1), producing genetically DIFFERENT cells

what three events are unique to meiosis and that occur all in meiosis 1?

1 - synapsis/crossing-over in prophase 1; homologous chromosomes physically connect and exchange genetic information

2 - homologous chromosome pairs at metaphase plate

3 - separation of homologs during anaphase 1

what is a clone?

one of a group of genetically identical individuals from the same parent

what are genes?

the units of heredity, and are made up of segments of DNA found on a specific location of a certain chromosome

what is a locus?

a specific location of a certain chromosome

what is heredity?

the transmission of traits from one generation to the next

what is variation?

the differences in appearance that offspring show from parents and siblings

what are somatic cells?

non-reproductive cells (non-gametic); they have 2 sets of 23 chromosomes (total of 46)

what are autosomes?

non-sex chromosomes; pairs 1-22 in humans

what are homologous chromosomes?

the 2 chromosomes in each pair, called homologs; same length/shape and carry genes controlling the same inherited characters

what is gametogenesis?

the production of gamete cells

what does diploid (2n) mean?

has two sets of chromosomes; for humans 2n=46

what does haploid (n) mean?

gametes; single set of chromosomes; for humans, n=23

what is fertilization?

the union of gametes, creating a zygote

what is a gonad?

an organ that produces gametes; a testis or ovary

what is synapsis?

homologous chromosomes loosely pair up, aligned gene by gene, and held together by the proteins of the synaptonemal complex

what is chiasmata?

x-shaped regions where crossing-over occurred

what is a zygote?

fertilized egg

what is cohesin?

protein complexes responsible for sister chromatid cohesion