REV #5 - Introduction To Genetics
REV #5 - Introduction To Genetics
REV #5 - Introduction To Genetics
Garden Peas
● Mendel chose to work with pure strains
of garden peas.
● The plants were self-fertilizing but
subject to experimental
cross-fertilization.
- He studied single characteristics that
displayed sharply contrasting traits.
MEIOSIS: REDUCTION DIVISION Prophase I
- The two members of each pair of
OF GAMETES
homologs make side-by-side contact
(synapsis) to form a bivalent.
● Meiosis is a special pair of cell divisions - Bivalent composed of two pairs of
in which a cell’s genetic material chromatids (each pair termed a dyad) or
replicates once followed by two rounds four future chromosomes and is called a
of cell division. tetrad.
● The result is a set of four daughter - Homologs cross-over and exchange
cells of which has only one member of genetic information.
each homologous chromosome pair.
● The number of chromosomes in a single Metaphase I
set is called haploid (n) number of - Homologs line up side-by-side on the
chromosomes. metaphase plate.
FERTILIZATION Anaphase I
● Gametes combine in fertilization. - Tetrads are separated into dyads and
- Reestablishes the diploid moved to opposite poles of the cell.
chromosome number (2n). - Centromeres do not divide.
- Union of egg and sperm produces a
zygote (single cell). At the end of Meiosis I each daughter cell
● Contains chromosomes of egg contains one chromosome (made of two
and sperm or two sets of chromatids) from each homologous pair.
chromosomes (diploid).
● Each zygote is genetically • Each of these cells (now haploid) enter
unique. Meiosis II
● In humans, the zygotes and all body • No interphase between Meiosis I and Meiosis
cells normally have a diploid number II
(2n) of 46 chromosomes; the gametes
have the haploid number (n), or 23, and MEIOSIS II
meiosis reduces the number of ● Meiosis II resembles mitosis
chromosomes per cell from diploid to - Dyads are split
haploid. - Single-stranded chromosomes move
● Alternative forms of genes for the same toward poles.
trait are allelic forms or alleles. - Results in four daughter cells, each with
- Sometimes only one of the alleles has a one haploid set of chromosomes.
visible effect on the organisms, although
both are present in each cell, and either
may be passed to progeny by meiosis
and subsequent fertilization.
SEX DETERMINATION