Download X-Linked traits

Today- Criss Cross Applesauce
worksheet
Tomorrow:
Human Genome notes
Chapter 14
What is this?
Pedigree = Family Tree

Squares represent males

Circles represent females

Shaded shapes represent
the presence of a trait
Pedigree cont.

Horizontal lines show a
marriage.

Vertical lines show a child.
Brackets show a group of
children.

Start with the bottom and move
upward when making a
pedigree. It makes it easier to
space shapes.
Reading a Pedigree
Practice

What is the gender of X?

How are Tom and
Kenzie related?

How are Katie and
Mary related?

Who is married
to Nancy?
What do you notice about the trait?
What do you notice about the trait?
What do you notice about the trait?
Dominant / Recessive Traits

The Principle of Dominance states that
some genes are dominant while others are
recessive.
 Dominant
= strong, overpowering (A)
 Recessive = weak, overpowered (a)

Assume word problems involve dominant / recessive
relationship unless otherwise stated.
Other Genetic Traits

Incomplete dominance =
blending



Sickle cell anemia;
“spiderpig”
Codominance = more
than one dominant allele

Blood type
Multiple alleles = more
than one allele


Rabbit fur color; blood type
Polygenic traits = several
genes


Skin color
Gene linkage = genes are
close to each other

Freckles & red hair
(“Gingers”)
Basic Blood Types
Blood Type
Allele
Genotypes
A
IA
IAIA or IAi
B
IB
IBIB or IBi
AB
IA and IB
IAIB
O
i
ii
Blood Type cont.

Blood type (A, B, AB, O) is actually the phenotype.

Blood can also be positive or negative, but that is based on a
clotting factor.

Since type O is recessive, people with this blood type can ONLY
RECEIVE type O. However, they can donate to anyone.

Since type AB is codominant, people with this blood type can
RECEIVE ANY blood type. However, they can DONATE ONLY to
people with type AB blood.

Solve blood type problems with Punnett Squares.
Blood Type Problem #1

Katie has type O blood. She has a child
with a man who is heterozygous for type B
blood. What is the probability the child is
type O? Type B?
Answer #1

ii x IBi
50% type O (ii)
 50% type B (IBi)

Blood Type Problem #2

Kenzie has type A blood. If we know that
her mother is type O, what is the blood
type of her father?
Answer #2

Kenzie is type A, so her genotype must be either IAIA or
IAi. Since her mother is type O, which is recessive, we
know that Kenzie’s genotype is IAi.

Kenzie must have received the IA allele from her
father, which means that he has AT LEAST ONE
IA allele. Which blood types have this allele?

Type A or Type AB
Human Chromosomes

Humans have 23 pair of chromosomes
 Chromosomes
1-22 are called autosomes.
You have two copies of each autosome in
your diploid cells.
 Chromosome pair 23 are sex chromosomes.
There are two alleles, X and Y. Usually XY =
male and XX = female.
Read the numbers and/or letters
X-Linked Traits

X-Linked traits are usually recessive and
are carried ONLY on the X chromosome.

Affect males more often than females
 Why?

Examples: colorblindness, hemophilia
X-Linked Colorblindness
Karyotypes

A Karyotype is an
enlarged picture
showing
chromosomes.
Karyotypes cont.

How are they used?
 Can
identify some problems in fetuses. For
example, normal karyotypes have two copies
of each chromosomes. Monosomies (1 copy)
and trisomies (3 copies) can cause a disorder.
 Can identify the genetic gender by looking at
the X and Y chromosomes.
What do you know about this
person based on their karyotype?
Chromosomal Disorders

Everyone needs at least one X
chromosome. Since females have two
copies, sometimes one copy is turned
off in part of the body while the other is
turned off somewhere else. This XChromosome Inactivation causes
different phenotypes in different parts of
the body.


Example: multicolored cats
Sometimes the body misreads
chromosomes and produces a different
phenotype.

Example: pseudohermaphrodites
Chromosomal Disorders cont.

In normal meiosis, gametes (sex cells)
divide chromosomes equally. However,
sometimes chromosomes are divided up
unequally. This is called
Nondisjunction and causes resulting
offspring to have too many or too few
chromosomes.


Examples: Down Syndrome
Sex Chromosome Disorders are
caused by nondisjunction of the sex
chromosomes. Sometimes this can
affect fertility among other things.

Examples: Klinefelter’s Syndrome, Turner
Syndrome, Jacob’s Syndrome
Application of Human Genetics

The Human Genome Project is trying to identify the location of all
genes in the human genome.

Genome: entire sequence of genes

Since everyone’s DNA is unique (except for identical twins etc),
scientists can now use DNA Fingerprinting to identify individuals.

Gene therapy tries to add, remove, or modify genes from a person’s
genome. In some cases this creates a temporary cure, but it is still
a highly experimental field of research.