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Chapter 14: The Human Genome (14-1)
A picture of chromosomes arranged in order is
called a karyotype.
 2 of the 46 chromosomes are sex chromosomes
 Females (46XX) and males (46XY)
 The other 22 pairs (44 chromosomes) are called
autosomes.
 All egg cells carry a single X chromosome
(23X). However, half of all the sperm carry an X
chromosome (23X) and half carry a Y… ½ girls
and ½ boys.
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A pedigree chart shows the relationships within a
family and is used to study inheritance patterns of
genes.
Many obvious human traits are polygenic and
controlled by many genes.
Also, many traits are only partially governed by
genetics—many traits are strongly influenced by
environment (nutrition, exercise, disease, etc.)
Remember genes are inherited and not gene
expression.
Chapter 14: The Human Genome (14-1)
Genes that are denied a proper environment in
which to reach full expression in one generation
can, in a proper environment, achieve full potential
in a later generation.
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Rh blood group is controlled by a single gene—2
alleles (+, -) + is dominant over –
ABO blood group is more complicated:
o Three alleles (IA, IB, and i)
o IA and IB are codominant (these alleles
produce antigens that are recognized by the
immune system)
o i (no antigens are produced)
A
B
AB
O
I AI A
IBIB
I AI B
ii
I Ai
IBi
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Chapter 14: The Human Genome (14-1)
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PKU (phenylketonuria)—
 Lack the enzyme that is needed to break down
phenylalanine, a common amino acid found in
many foods.
 Causes build up of phenylalanine—leads to
severe brain damage/mental retardation
Tay-Sachs—
 Affects Jewish families with central/eastern
European ancestry.
 Causes fats to build up in the brain
 NO CURE! Early childhood death
Achondroplasia (most common from of dwarfism)
Huntington’s disease (progressive loss of muscle
control/mental function until death)
Sickle cell disease (1 in 500 African Americans)
Why??? A combination of genetics, history and
human biology
Chapter 14: The Human Genome (14-1)
How do the actual DNA sequences in genes affect
the phenotype?
 In both cystic fibrosis and sickle cell disease, a
small change in the DNA of a single gene affects
the structure of a protein, causing a serious genetic
disorder.
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Cystic Fibrosis
 Common fatal genetic disease
 Recessive allele
 Digestive problems/thick heavy mucus that clogs
lungs
 ½ of children do not survive into their 20’s
 Cause: a deletion of 3 bases in the middle
sequences of a protein (removes one a.a.)
 The cell membrane cannot pass Cl- ions because
the protein channel (CFTR) is destroyed.
Sickle Cell Disease
 Red blood cells are bent and twisted
 Get stuck in the tiny capillaries…like little damns
in the blood vessels.
 Damage to tissues, brain, heart, spleen, and tissues,
physical weakness, bruising, etc
 Cause: one nitrogen base is substituted for another
causing valine to be in place of glutamic acid
Chapter 14: The Human Genome (14-1)
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When oxygen levels are low, the blood cells
change shape and stick together
Why does this affect people with African descent?
Malaria, a parasitic disease infects red blood cells.
HAHA (normal)
HAHS (carrier)
HSHS (sickle cell sufferer)
Can die of Malaria
Not affect by SCD nor
Malaria
Severely affected by the
disease