Sex Cells: The Biology of Sex
• The Nature vs. Nurture Debate
– Biology supports that this is a complex issue
– Men and Women are more similar than different
• Male and Female are not necessarily
adequate as labels for people
Humans
• Being bodies that learn language
thereby becoming wordlings
humans are
the symbol-making, symbol-using, symbolmisusing animal
inventor of the negative
separated from our natural condition
by instruments of our own making
goaded by the spirit of hierarchy
acquiring foreknowledge of death
and rotten with perfection
Human
• hu·man n.
1.A member of the
genus Homo and
especially of the
species H. sapiens.
2.A person: the
extraordinary
humans who
explored
Antarctica.
--adj.
•
•
•
•
•
Of, relating to, or characteristic
of humans: the course of human
events; the human race.
Having or showing those positive
aspects of nature and character
regarded as distinguishing
humans from other animals: an
act of human kindness.
Subject to or indicative of the
weaknesses, imperfections, and
fragility associated with humans:
a mistake that shows he's only
human; human frailty.
Having the form of a human.
Made up of humans: formed a
human bridge across the ice.
From WebMD
• human
• \Hu"man\, a. [L. humanus; akin to homo man: cf.
F. humain. See Homage, and cf. Humane, Omber.]
Belonging to man or mankind; having the qualities
or attributes of a man; of or pertaining to man or
to the race of man; as, a human voice; human
shape; human nature; human sacrifices.
To err is human; to forgive, divine. --Pope
Human
• Species of sentient being
originating from/on the planet
Earth in the Milky Way galaxy, is
distinguished from other species
in several ways:
– Anthropologically: Differentiation
through evolution
– Biologically: DNA sequence
comprised in 23 chromosomal pairs
– Sociologically: Social, hierarchical,
dominate environment and other
species, use tools and language
DNA
DNA n.
• A nucleic acid that carries the genetic information in the
cell and is capable of self-replication and synthesis of
RNA. DNA consists of two long chains of nucleotides
twisted into a double helix and joined by hydrogen
bonds between the complementary bases adenine and
thymine or cytosine and guanine. The sequence of
nucleotides determines individual hereditary
characteristics.
• d(eoxyribo)n(ucleic) a(cid).
Chromosome
chro·mo·some n.
1. A threadlike linear strand of DNA and
associated proteins in the nucleus of
eukaryotic cells that carries the genes and
functions in the transmission of hereditary
information.
2. A circular strand of DNA in bacteria that
contains the hereditary information necessary
for cell life.
Unraveling DNA to see a chromosome
Gene
gene n.
• A hereditary unit consisting of a sequence of
DNA that occupies a specific location on a
chromosome and determines a particular
characteristic in an organism. Genes undergo
mutation when their DNA sequence changes.
• A self-replicating protein molecule that
occupies a fixed place on a chromosome; a unit
of heredity
Mitosis
• When most cells in the body reproduce,
which they need to do to grow or replace
old cells, they do so through a process
called mitosis.
• In mitosis, the chromosomes pair up and
split, creating two new cells, which are in
theory identical to each other.
Human Cells
• Each cell in the human body contains a set of
chromosomes from a mother (her egg) and a father
(his sperm). When you look at human
chromosomes, they are X-shaped, except for the
male Y chromosome.
– Every human cell, except for the sex cells, contains 46
chromosomes.
• When a body produces sex cells (sperm or egg,
depending on whether one is a male or female),
the body must reduce the number of chromosomes
by half.
– Sex cells contain only 23 chromosomes
Meiosis
• To do this, it randomly sorts chromosomes from
both sets in one cell division and then reduces
them by half in another. Therefore, each sperm or
egg that the body produces is unique and different
-- it contains a different mix of the mother's and
father's genes.
– This is why two brothers in the same family can look
and act totally different from one another even though
they come from the same parents -- it all depends on
which genes (chromosomes) were randomly chosen
when producing the sex cells of the mother and father.
Comparison of Mitosis and Meiosis
Spermatogenesis
Spermatogenesis n: development of spermatozoa
and
Oogenesis n: development of the ova
Types of
Chromosomal
Mutations
Fertilization
• When semen is deposited at the base of the uterus,
the sperm must first cross the barrier of the cervix
and then up the lining of the uterus into the
Fallopian tubes to reach the egg.
– Only one of the Fallopian tubes contains an egg, so
many sperm travel in the wrong direction.
– This process must be completed within 12 to 48 hours,
before the sperm die.
– Fewer than 1,000 sperm out of the millions in the
semen actually reach the Fallopian tubes.