Fundamentals of Human Growth and Development - Alexandria City ...

I. The Impact of Heredity
HEREDITY
A. Like produces like
B. All humans share certain characteristics (2 legs, 2 arms, etc.)
C. Races and ethnic groups share certain characteristics (Why?)
D. Families share certain characteristics
E. Each individual is a unique combination of shared characteristics
F. Some characteristics have positive impact; some have negative; some have no impact or are neutral
G. Characteristics are passed down through the genes
H. Remember: heredity and the environment interact
II. How Heredity Works
A. The human body is made up of billions of cells
B. Each cell nucleus contains 46 chromosomes in 23 pairs
C. Each chromosome carries thousands of genes (like a string of beads)
D. Genes are giant molecules of DNA - information is coded there
E. The genes are all located on the 46 chromosomes
F. Reproductive cells (ova and sperm) each carry only 23 chromosomes (one from each pair) so that
when they combine at fertilization, the being will have 46: 23 from mom and 23 from dad
G. The 23 from ovum and 23 from sperm “find” each other and pair up to make the 46 - so mother and
father contribute to genetic inheritance equally
H. However, some genes are dominant and some genes are recessive
I. Dominant genes tend to be expressed because they overpower the recessive genes
J. Recessive genes will be carried and passed on to the next generation.
III. What Heredity Determines
A. All physical traits (height potential, hair color, eye color, etc.)
B. Sex (the father’s sperm carry one sex chromosome that is either “Y” or “X”; the mother’s ova all
carry an “X” chromosome; if an “X” sperm meets an ovum [XX] = girl; if a “Y” sperm meets an
ovum [XY] = boy
C. Genetic disorders and birth defects
D. Emotional, mental and personality traits (interaction with the environment affects, remember)
E. Genetic “predisposition” to certain diseases (i.e., types of cancer)
Reproduction Unit 6