Download Human Inheritance - Conackamack Middle School

Chapter 5
Human
Inheritance
Pages 144-150
So far in science class…
• Chapter 4 discussed
traits controlled by
one, single gene. (Ex.
hair line in humans,
freckles, hair
texture, etc.)
• All of these traits
only ever had TWO
alleles (Ex. W and w,
F and f, HC and HS)
Some traits are controlled
by a SINGLE gene with
MORE THAN TWO alleles.
• Such a gene is said to have multiple
alleles:
– THREE or more forms of a gene (alleles)
that code for a single trait.
– Example: your blood type
Blood type in humans is an
example of a trait where there
are MULTIPLE ALLELES.
• What is blood typing?
• How many different blood
types are there?
• How many different
phenotypes are found in
the human race?
4
• THREE alleles
Blood Typing
– IA – dominant
– IB - dominant
– i – recessive
• A blood can be homozygous or
heterozygous
• B blood can be homozygous or
heterozygous
• AB blood is co-dominant
• O blood is recessive
PHENOTYPE=
GENOTYPE
A
A
I I
A
I i
A blood =
or
B
B
B
B blood = I I or I i
AB blood = IAIB
O blood = ii
6
Example Punnett Square
• I stands for the
two dominant
alleles
– (A and B)
• i stands for the
recessive alleles
– (O)
Try this Punnett Square
• Cross a mother
with AB blood
and a father who
is heterozygous
for his B blood.
Some traits show MANY
different phenotypes.
• There are some human
traits that do not have just
two or three phenotypes,
but show MANY different
phenotypes.
• These traits are controlled
by MANY genes that act
TOGETHER to produce a
single trait.
• Ex. skin color or height in
humans
Male or
Female
• The sex of the baby is
determined by genes on
chromosomes.
• The 23rd pair of
chromosomes are called
the sex chromosomes.
• The sex chromosomes
are the only
chromosomes that do not
always match.
• Male = XY
• Female = XX
• What are the chances of
having a girl? What about
a boy?
Sex-linked Traits
• Traits carried on the
X chromosome.
• How many X
chromosomes do males
have?
• How many X
chromosomes do
females have?
– Why is it more likely
for a male to have an
X-linked trait than a
female?
What is a carrier?
• A person who has ONE
recessive allele for a trait
and one dominant allele.
– If the trait is recessive ,
then a carrier will not have
it.
– It isimportant for a person
to know they are a carrier
because they CAN pass the
trait on to their offspring.
• In sex-linked traits, only
FEMALES can be carriers.
Sex-linked traits - Alleles
Sex-linked traits CAN
have dominant and
recessive alleles.
If the trait is
recessive, like
colorblindness, it must
be on BOTH X
chromosomes for
females, but only ONE
X chromosome of males.
• Males: Normal
– XNY
• Females: Normal
– XNXN
• Males: Colorblind
– XnY
• Females: Carrier
– XNXn
• Females: Colorblind
– XnXn
Practice Problem
XN
XN
Y
XNXN
XNY
Xn
XNXn
XnY
• Cross a mother who
is a carrier for color
blindness with a
father with normal
color vision.
• Report all
Geno/Phenotypes:
COLOR BLIND?
LET’S TAKE THE
TEST!
15
Color blindness
Color Blindness
Color Blindness
Color Blindness
A day in the life
How does the Environment
Effect How an Organism Look?
• Factors like diet,
medical care, and
living conditions
can also effect
the way an
organism looks.
VS.
OUT:
Baldness is a recessive sex-linked
trait. B is not bald, b is bald
Cross a Not Bald male XB Y with a Not Bald carrier
female XBXb . Report all genotypes and phenotypes.
XB
XB
Xb
Y