MEIOSIS
Key Concepts:
1. Three Parts of Sexual Reproduction: meiosis,
formation of gametes (egg & sperm)
fertilization
2. First step in sexual reproduction
3. Sorts out the chromosomes of a germ cell
into four new nuclei
4. Body cells are diploid, with one set from
their mother and one set from their father
Key Concepts:
5. Meiosis divides the chromosome number in
half, thus diploid cells become haploid
6. Chromosomes may swap segments during
the process thus shuffling hereditary genes
Asexual Reproduction
 One parent pass on a duplicate of all its genes
to each new individual
 Genetically identical offspring
 Includes binary fission (split of the body into
two), budding (a growth that breaks off), and
vegetable propagation (usually underground
vines called runners or rhizomes)
Sexual Reproduction
 Two parents pass on one of each of genes to
an offspring
 Leads to variation in genes and thus
genetically unique offspring
Genes:
 Heritable bits of information that are required
to produce new individuals
Alleles:
 Different forms of the same gene
Gametes
 Another name for sex cells
 Ex: sperm & egg
Germ Cells:
 Diploid cells that are produced by
reproductive structures and organs
 Go through meiosis to form haploid gametes
or sex cells
Homologous Chromosomes:
 Pair of chromosomes for the same genes that
line up with each other at meiosis
Meiosis:
 Nuclear division by which the parental
number of chromosomes is reduced by half
(to haploid) in order to create gametes
 Consists of Interphase, Meiosis I, and Meiosis
II
Interphase:
 Same stage as in mitosis
 DNA is replicated
Prophase I
 Chromosomes condense and pair with
homologue
 Crossing over occurs
 Nuclear Envelope breaks down
Crossing Over:
 Homologous chromosomes break apart
during Prophase I and exchange genes
 This reshuffles alleles and leads to genetic
variation
Metaphase I:
 Chromosomes become positioned at the
equator of the cell
 Separation mixes up the fraternal and
maternal alleles into different cells
Anaphase I:
 Each chromosome is separated from its
homologue and moved to opposite ends
Telophase I:
 Cytoplasm divides to form two cells
 Both cells are haploid
 Each chromosome is still in a duplicated state
Prophase II:
 Chromosomes becomes attached to the
spindles and move towards center
Metaphase II:
 Chromosomes line up in the middle
Anaphase II:
 Sister chromatids of each chromosomes are
now separated from each other
Telophase II:
 Four daughter cells begin to form nuclei
 Each cell is now haploid and chromosome
numbers have been reduced by half
 One or all may become gametes
Fertilization
 Gametes formed during Meiosis can develop
into gametes
 When a male gamete (haploid) and a female
gamete (haploid) come together at
fertilization, they form a diploid zygote,
which develops into a offspring