Transcript Ch. 5.1 Human Inheritance

Ch. 5.1 Human
Inheritance
Patterns of Human Inheritance
 Some
human traits are controlled by single
genes with two alleles.
 Others are by single genes with multiple
alleles.
 Still other traits are controlled by many
genes that act together.
Single Genes with Two Alleles
 Many
human traits are controlled by a
single gene with one dominant allele and
one recessive allele.
 They will have 2 distinctive phenotypes,
meaning they are very obvious which one
you have.

Can you roll your tongue?
Single Genes with Multiple Alleles
 Some
human genes are controlled by a
single gene with more than 2 alleles.
 This is called multiple alleles (having 3 or
more different options for that trait).
 Human Blood Type is an example of this.
There are 4 different options:

A, B, AB, and O
 When
we talk about these kinds of genes,
they are called Co-dominant.
 This means that EVERY option that you
end up with shows up.
 So if you have a gene for blood type A
from your mom and blood type B from
your dad, you will be AB.
 To write this out we use a superscript.
How to write Blood Types:
 IA
 IB
 IAB
 For
blood type O, O is recessive, so how
do you think we will write it’s allele?
Blood Type O
 So
in order to have blood type O, your
genotype must be: ii
Traits controlled by Many Genes
 Height
is a great example of a trait
controlled by MANY MANY MANY genes!
The Sex Chromosomes
 The
sex chromosomes are one of the 23
PAIRS of chromosomes found in each cell
of the human body.
 The sex chromosomes carry genes that
determine whether a person is male or
female.
 They also carry other genes that
determine other traits.
Girl or Boy?
 The
sex chromosomes are the only
chromosomes that DO NOT ALWAYS
match.
 The two chromosomes are celled X
chromosomes. Here, you do match.
 If you are a boy, your sex chromosomes
do not match. You are XY. They Y is much
smaller than the X chromosome.
X and Y Chromosomes
Sex Chromosomes and
Fertilization
 Since
females have only X’s (XX) they can
only pass on a female gene: X.
 It is then up to the guy to donate the final
chromosome. He has both an X and a Y
(XY).
 So it will be a 50-50 chance that the
offspring will be a girl: XX or a boy XY.
Sex-Linked Genes
that are carried on the 23rd
chromosome pair (the sex chromosomes)
are called Sex-Linked because they are
linked to the sex chromosome.
 Genes
 Remember:


Females = XX
Males = XY
 Genes
found on the X chromosome are
NOT found on the Y chromosome.
 This means if you are XY, but you get a
recessive gene on your X, you will have
that recessive trait because the Y cannot
offer a gene to compete!
 This
means that men are more likely to
inherit rare genes found only on the sex
chromosome.
 Female’s can still inherit these genes, but
it’s just much harder because they have
the 2nd X for a backup.
Colorblindness
 Colorblindness
is a trait controlled by a
recessive allele on the X chromosome.
 Many more males than females have redgreen colorblindness.
 A carrier is a person who has one
recessive allele for a trait and one
dominant allele.
 Meaning: they don’t show that they have
the gene, but they “carry” it in hiding.
 Let’s
cross a Male with Normal Vision: XCY
 And a Mother who is a Carrier: XCXc
Question:
 1.
What is the sex of a person who is a
carrier for colorblindness?
 2. Can a male be a carrier for
colorblindness? Why or Why Not?
The Effect of the Environment
 Many
of a person’s characteristics are
determined by an interaction between
genes and the environment.
 You have learned that several genes work
together to help determine human height.
 However,
the “environment” can also have
a great effect.


Meaning: If you don’t get enough vitamins and
minerals from a healthy diet, you might not be
able to grow as tall as your genes want you
to.
Like trying to grow a giant pumpkin. If you
don’t water it, it can’t grow!