Chapter 14- The Human Genome

• The children in this family have some traits that are similar to their mother’s and some that are similar to their father’s.

14-1 Human Heredity

• Can you predict chin shape? • Procedure

– Two parents with cleft chins, both heterozygous for cleft chin (Cc), have three children with cleft chins. The parents are sure that their fourth child will not have a cleft chin. Draw a Punnett square to see if this is possible.

• Determine the probability that the fourth child will have a cleft chin. _________

Human Heredity

• Human Chromosomes– Make us who we are.– This is the genetic information (DNA)

which is inside the human cell.

• To look at these chromosomes, biologists, photograph cells in mitosis.– Mitosis is when the cell nucleus divides

and the chromosomes are easier to see.– Biologists then take these photographs

and group them together in pairs.– This picture of chromosomes arranged in

this way is called a karyotype

Karyotype

• The human body contains 46 chromosomes– 23 (sperm)– 23 (egg)

• Together this forms a diploid zygote– 46 total chromosomes

Sex Chromosomes and Autosomes

• Sex chromosomes– Only 2 of the 46 – Determine if someone is male or female– Female: XX– Male: XY

• Autosomes– Remaining 44 chromosomes

Human Traits

• Human traits are inherited – Gregor Mendel

• Pedigree chart– A pedigree shows a relationship within a

family – A pedigree chart follows one specific trait

in a family

Cleopatra’s Pedigree Chart

Russian Royal Family Pedigree Chart

Polygenic

• Some traits are actually polygenic– Controlled by two or more genes

• Shape of your eyes• Shape of your ears• Eye color

Other Trait Influences

• Environment• Nutrition• Exercise

• Your parents might both be 6 feet tall, but if they don’t feed you, you are unlikely to grow to be 6 feet tall.

Human Genes

• Our complete set of genetic information is our genome– 30,000 genes

• Blood Group Genes:– Knowing a person’s blood group is critical

because using a wrong blood type could be life threatening

– Rh– ABO

• Are two genes that are part of your blood type

Rh

• Rhesus Monkey”

• 2 alleles that determine blood type– Rh+ is dominant & Rh- is recessive

• A person with 2 positive alleles is Rh+• A person with a positive and a negative

allele is RH+• A person with 2 negative alleles is Rh-

ABO

• There are 3 alleles that determine blood type– IA, IB and i

• Two of these alleles are codominant and one is recessive.

• Blood type is dependant upon what the antigens are on the surface of the red blood cells

• Type A blood: lAlA, or IAi• Type B blood: IBIB or IBi• Type AB blood: IAIB

• Type O blood: ii

• Based on what you know of blood types; which one of Mr. & Mrs. Lopez’s four kids must have been adopted? _____________

Recessive Alleles

• Studying genetic disorders have helped us understand how human genes work

• Many of these disorders are caused by recessive alleles

Phenylketonuria (PKU)

• People with this disorder lack the enzyme needed to break down Phenylalanine

• Causes: – A build-up of phenylalanine in tissues– Mental retardation– Can be controlled by a special diet– All babies in US are tested for this at birth

Tay-Sachs Disease

• Nervous system breakdown• Infant death

Albinism

• Lack of pigment in skin, hair, and eyes

Cystic Fibrosis Galactosemia

• Excess mucus in lungs, digestive tract, and liver

• Susceptibility to infections

• Death in early adulthood if not treated

• Inability to digest the sugar galactose.

• Causes mental retardation, eye and liver damage

Cystic Fibrosis

Dominant Alleles

• Not all genetic disorders are caused by recessive alleles

• If you have a dominant allele for a genetic disorder, it will be expressed even if you also have a normal recessive allele– Achondroplasia – Huntington’s disease – Hypercholesterolemia

Achondroplasia

• Dwarfism

Huntington’s Disease

• Mental deterioration and uncontrollable movements

• Excess cholesterol in blood• Heart disease

Hypercholesterolemia

Gene Expression

• In certain diseases, a small change in the DNA of a single gene affects the structure of a protein, causing a serious genetic disorder – Cystic fibrosis– Sickle cell anemia

Sickle Cell Anemia

• Abnormal hemoglobin produced because of a single amino acid change in the hemoglobin protein

• Causes the RBC’s to deform which causes clogging in the capillaries

Sickle Cell Anemia

Sex-Linked Genes

• Because the X and Y chromosomes determine sex, genes located here are said to be sex-linked genes

• More than 100 sex-linked genetic disorders have been mapped to the X chromosome

• Males have just one X chromosome. Thus, all X-linked alleles are expressed in males, even if they are recessive

14-2 Human Chromosomes

• Genes that are found on the X or Y chromosome.

• More genes are found on the X chromosome than the Y

Sex-Linked Genes

Colorblindness

• Three genes associated with color vision are found on the X chromosome

• Males are more often colorblind because they only have one X chromosome

Colorblindness Test

• All X-linked alleles are expressed in males even if they are recessive

Colorblindness

Examples of X-linked Recessive Disorders

• Hemophilia: blood-clotting disorder

• Duchenne Muscular Dystrophy

• Ichtyosis: scaly skin

• Norrie Disease: abnormal growth of retina

• Rett Syndrome: mental retardation

Hemophilia

Duchenne Muscular Dystrophy

X-Chromosome Inactivation

• Females have 2 X chromosomes and males only one. What to do?

• In all female cells, one X chromosome is randomly shut off.

• This causes some interesting problems if one X chromosome has a mutated gene

Chromosomal Disorders

• Get too many or too few copies of a chromosome

• Caused by non-disjunction during meiosis

• Exs. Down’s Syndrome: Trisomy 21 Turner’s Syndrome: X_ Klinefelter’s Syndrome : XXY

Down’s Syndrome

Turner Syndrome

Kleinfelter Syndrome

14-3 Human Molecular Genetics

Human DNA Analysis

• Genetic tests are now available for hundreds of disorders.

• This can allow prospective parents to determine if they are carrying recessive alleles for a disorder.

DNA Fingerprinting

• DNA is analyzed of by separating it into fragments

• This reveals a series of DNA bands of various sizes

• A pattern of bands is produced that can be distinguished from any other individual in the world (except for an identical twin).

• DNA samples can be obtained from blood, sperm, and hair strands that have tissue at their base.

DNA Fingerprinting

The Human Genome Project

• The Human Genome Project was an attempt to sequence all human DNA

• In June 2000, scientists announced that the Human Genome was complete.

• There is open availability of nearly all its data.

• You can use the Internet to read the latest genome data.

Gene Therapy

• Gene Therapy is the process of changing the gene that causes a genetic disorder

• In gene therapy, an absent or faulty gene is replaced by a normal, working gene

• This way, the body can make the correct protein or enzyme it needs, which eliminates the cause of the disorder

Gene Therapy

Ethical Issues

• What will happen to the human species of we could design our bodies? What would be the consequences?

• Society will have to develop a thoughtful and ethical consensus of what should and should not be done with the Human Genome.