Ch. 14 The Human Genome

Ch. 14 Outline 14-1: Human Heredity Human Chromosomes Human Traits Human Genes From Gene to Molecule

Ch. 14 Outline 14-2: Human Chromosomes 14-3: Human Molecular Genetics Human Genes and Chromosomes Sex-linked Genes X-Chromosome Inactivation Chromosomal Disorders 14-3: Human Molecular Genetics Human DNA Analysis The Human Genome Project Gene Therapy Ethical Issues in Human Genetics

Human Chromosomes Karyotypes: A Picture of chromosomes arranged in rows is a karyotype

Human Chromosomes Humans have 23 pairs (46 total) chromosomes. Two of the 46 chromosomes are called sex chromosome because they determine an individual’s sex. In Human’s: Female – two copies of large X chromosome Male – one X and one small Y chromosome

Karyotype

Human Chromsomes Autosomes: the remaining 44 chromosomes. They do not determine the sex of the organism. All Human egg cells carry a single X chromosome. Half of all sperm cells carry an X chromosome and half carry the Y. This ensures that about half of the zygotes will be female XX and half will be male XY.

Human Traits Biologists must identify an inherited trait controlled by a single gene Must establish that the trait is actually inherited and not the result of environmental influences

They study how the trait is passed from one generation to the next Human Traits They study how the trait is passed from one generation to the next Scientists use a pedigree chart to help study how a trait is passed from one generation to the next. Pedigree: a chart that shows the relationships within a family.

How to read a pedigree A square represents a male. A circle represents a female. A vertical line and a bracket connect the parents to their children. A horizontal line connecting a male and female represents a marriage. A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait. A half-shaded circle or square indicates that a person is a carrier of the trait. A completely shaded circle or square indicates that a person expresses the trait.

Pedigrees These Charts are used to infer the genotypes of family members. They can reveal if traits are sex-linked, dominant or recessive.

Using a Pedigree A human geneticist determined the pedigree shown in the diagram with filled symbols showing the affected individuals. How is this pattern of inheritance described?

Using a Pedigree Below is a pedigree for an inherited lung disease.  Provide the genotypes of each of the individuals marked with lower case letters.

Using a Pedigree Below is a pedigree for an inherited brain disease.  Provide the genotypes of each of the individuals marked with lower case letters. Brain Disease

Human Genes Biologists were able to identify genes that directly control a single human trait. Some of the very first genes to be identified were those that controlled blood type. Blood Group Genes Knowing a person’s blood group is important during transfusions. Two blood groups: Rh groups ABO groups

The Rh Blood Group The Rh blood group is determined by a single gene with two alleles: Positive and negative Rh+ is dominant to Rh- The Rh factor is named after the Rhesus Monkey where the factor was first isolated Very important for females to know during pregnancies.

ABO Blood Groups There are three alleles for the ABO Blood Group: IA, IB, I “i” is the recessive allele. ii  type O blood IAIB are codominant  type AB blood IAIA or IAi  type A Blood IBIB or IBi  type B Blood

ABO Blood Groups Safe Transfusions Phenotype (Blood Type Genotype Antigen on Red Blood Cell To From

Antigens and Blood

Disorders in Humans Genetic Disorders may be caused by: Recessive Alleles Ex. CF, PKU, Tay-Sachs Dominant Alleles Huntington’s Disease Codominant Alleles Sickle Cell Anemia

Concept Map Autosomol Disorders caused by Recessive alleles Dominant alleles Codominant alleles include include include Albinism Galactosemia Tay-Sachs disease Huntington’s disease Sickle cell disease Cystic fibrosis Phenylketonuria Achondroplasia Hypercholes- terolemia

Sex-Linked Genes Sex-linked genes: Genes Located on the sex chromosomes Many genes are located on the X chromosome Males have just one X chromosome. Thus, all X linked alleles are expressed in males, even if they are recessive. Sex-linked disorders are caused by genes on the X or Y chromosome Colorblindness, Hemophilia

Sex-Linked Genes : Pedigree for Color Blindness

X-Chromosome Inactivation Females have two X chromosomes but males only have one. How do females cells “adjust” to having an extra X if males can survive with just one? One of the X chromosomes in female cells are randomly switched off. Those are called Barr bodies.

Chromosomal Disorders Nondisjunction: failure of chromosomes to separate correctly in meiosis This leads to an abnormal number of chromosomes in gametes Ex: Down Syndrome (3 copies of chromosome 21  “trisomy”)

Homologous chromosomes fail to separate Nondisjunction Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II

Nondisjunction can occur with autosomes or sex Chromosomes during meiosis

Chromosomal Nondisjunction Disorders

Down Syndrome Trisomy 21 Down Syndrome 1 in 31,000 births 46 chromosomes XY=97% XX=3% 1 in 1,250 births 47 chromosomes XY or XX #21 Trisomy Nondisjunction

Down Syndrome Short, broad hands Stubby fingers Rough skin Impotency in males Mentally impaired Small round face Protruding tongue Short lifespan

Patau’s Trisomy Syndrome 1 in 14,000 births 47 chromosomes XY or XX #13 Trisomy Nondisjunction

Patau’s Trisomy Syndrome Small head Small or missing eyes Heart defects Extra fingers Abnormal genitalia Mentally impaired Cleft palate Most die a few weeks after birth

Edward’s Trisomy Syndrome 1 in 4,400 births 47 chromosomes XX =80% XY=20% #18 Trisomy Nondisjunction

Edward’s Trisomy Syndrome Small head Mentally impaired Internal organ abnormalities 90% die before 5 months of age

Turners Syndrome 1 in 5,000 births 45 chromosomes X only #23 Monosomy Nondisjunction

Turners Syndrome 96-98% do not survive to birth No menstruation No breast development No hips (curve) Broad shoulders and neck

Jacob’s Syndrome 1 in 1,800 births 47 chromosomes XYY only #23 Trisomy Nondisjunction

Jacob’s Syndrome Normal physically Normal mentally ? Normal physically Normal mentally Increase in testosterone More aggressive Normal lifespan

Kleinfelter Syndrome 1 in 1,100 births 47 chromosomes XXY only #23 Trisomy Nondisjunction

Kleinfelter Syndrome Scarce beard Longer fingers and arms Sterile Delicate skin Low mental ability Normal lifespan

Triple X Syndrome 1 in 2,500 births 47 chromosomes XXX only #23 Trisomy Nondisjunction

Triple X Syndrome Normally physically Normal mentally Tall Fertile Short lifespan

The Human Genome Project A research project to sequence (identify in order) all the bases in Human DNA ~3.2 BILLION pairs! Some discoveries: A large amount of DNA does not code for proteins Humans only have 30,000-40,000 genes (scientists expected 100,000)

The Human Genome Project Website http://www.genome.gov/ Really interesting Information about the Human Genome Project. It might help you understand stuff better. EDUCATE YOURSELF!

Gene Therapy Information about the human genome might be used to cure genetic disorders though the use of gene therapy. Gene therapy: the process of changing a gene that causes a genetic disorder It replaces the faulty gene with a normal, working gene

Ethical Issues If Human cells can be manipulated to cure disease, should biologists try to engineer people with specific traits? What will happen to the human species if we design our own bodies? Should we clone humans?