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Heredity
Chapter 5, Day 4
Child Development
The Basic Rules of Heredity
 Heredity is the passing on, or transmission, of
biological traits from parent to child
 A child’s hair color, eye color, skin color as
well as their height or the way they look are all
determined, in part, from the genetic
information inherited from the parents.
Chromosomes
 Chromosomes are tiny structures found within
cells that contain the genetic information that
is passed on from one generation to the next
 Most of the cells in your body contain 23 pairs
of chromosomes
 A fertilized egg contains 46 chromosomes, 23
from the sperm(dad) and 23 from the ovum
(mom)
Genes
 A gene is a section of a chromosome that
determines or affects a characteristic or trait
 Genes come in pairs
 The 46 chromosomes form the person’s DNA
 DNA is the complex molecule that makes-up
genes.
 DNA contains the genetic code
 DNA molecule has a specific gene for height, another
for weight, another for eye color, etc.
Dominant and Recessive Traits
 Individuals carry two genes for each trait
 When the genes are the same, that characteristic
automatically shows
 Two Dominant genes – characteristic automatically shows
 Two Recessive genes – characteristic automatically shows
 When the genes are different, the characteristic
is controlled, or dominated by the Dominant gene
 One Dominant + one Recessive – Dominant shows
Dominant Hierarchy
 Dominant hierarchy
 Tall dominates short
 Brown eyes dominate blue eyes
 Dark hair dominates blonde hair
Sex Chromosomes
 The gender of the child is determined at
conception
 Each egg carries an X-chromosome
 Each sperm carries either an X- or a Ychromosome
 Sex Determination
 Sperm (X) + Egg (X) = Girl (XX)
 Sperm (Y) + Egg (X) = Boy (XY)
Multiple Births
 The delivery of more than one baby (i.e., twins,
triplets, quadruplets) is called a multiple birth
 Multiple births carry greater risk to the mother
and the fetus’
Identical Twins
 Identical twins develop from a single fertilized
egg or zygote
 Have the same inherited traits
 Are the same sex (because they develop from identical
embryos)
Fraternal Twins
 Fraternal twins develop from two eggs released
at the same time from the ovary and are
fertilized by two sperm
 No more alike than any other siblings
 May or may not be the same sex
Other Multiple Births
 Triplets, quadruplets, and other multiple births
are less common than twins
 Caused by more than one egg being released and
some of those eggs splitting.
 Could result in a combination of Identical and
Fraternal twins
Infertility
 Infertility is the inability to become pregnant.
 Options for Infertile Couples
 Adoption
 Artificial Insemination – the father’s sperm is injected
into the mother’s uterus
 In vitro Fertilization – egg is extracted and egg and
sperm are combined in the lab. The fertilized egg is
then inserted into the mother’s uterus
 Ovum Transfer – donated egg plus in vitro fertilization
 Surrogate Mother – fertilized egg is inserted into
surrogate or artificial insemination process
Individual Activity
 Heredity In the Works – Follow the
instructions on the handout. Will Discuss as a
Class
 Culture Matters Essay – Follow the
instructions on the handout. TURN IN
TODAY!
 HOMEWORK – What Is In My Genes? DUE
NEXT CLASS