BIOSC-101 Chapter Notes - Chapter 1: Sister Chromatids, Synapsis, Interphase
31 Aug 2020
School
Department
Course
Professor
Leo Ellis
Fundamentals of Biological Science
Biosc-101
● Sexual reproduction by definition is the production of offspring through the union
of male and female gametes – eggs and sperm cells
● Sex reproduction depends on meiosis, a specialized process of cell division that
recombines DNA sequences and products cells with half the number of
chromosomes present in the somatic (body) cells, n = 23 each
● Fertilization is when the nuclei of an egg and sperm cell fuse and produce the
zygote, where the chromosome number typical of the species is restored, in humans
this is 2n = 46
o Without the halving of chromosome number in meiosis, fertilization would
double the number of chromosomes in each next generation
● Meiosis and fertilization both mix genetic info into new combinations, so offspring
of a mating pair are unlikely to be genetically identical to any family
● Haploid number of chromosomes is the stage with one basic set of chromosomes
and diploid is the stage with two
● Animals make gametes by meiosis, but there are many organisms that make
gametes by mitosis
● Animals follow the pattern in which:
o Meiosis halves the chromosome number to gametes and fertilization restores
it to zygotes
● Plants follow the pattern in which:
o Meiosis produces haploid spores which make multicelled gametophytes
o Gametophytes make gametes which fertilize to zygotes and grow into new
sporophytes
● The difference between the two is that mitosis is used throughout the entire plant
life cycle to divide, meiosis is only used to make gametes in animals and mitosis for
the zygotes
● While mitotic cell division is essentially replication, meiosis is recombinant
replication
o Mitosis is used to replicate the exact same cell with the same genes and same
alleles, meiosis creates a daughter cell with the same genes but recombined
info
● Meiosis halves chromosome number and splits a parent cell into two genetically
different daughter cell
o Meiosis separates the members of each homologous pair into different cells,
reducing the diploid number (2n) to the haploid number (n)
Document Summary
Sexual reproduction by definition is the production of offspring through the union of male and female gametes eggs and sperm cells. Sex reproduction depends on meiosis, a specialized process of cell division that recombines dna sequences and products cells with half the number of chromosomes present in the somatic (body) cells, n = 23 each. Meiosis and fertilization both mix genetic info into new combinations, so offspring of a mating pair are unlikely to be genetically identical to any family. Haploid number of chromosomes is the stage with one basic set of chromosomes and diploid is the stage with two. Animals make gametes by meiosis, but there are many organisms that make gametes by mitosis. Animals follow the pattern in which: meiosis halves the chromosome number to gametes and fertilization restores it to zygotes. Plants follow the pattern in which: meiosis produces haploid spores which make multicelled gametophytes, gametophytes make gametes which fertilize to zygotes and grow into new sporophytes.
