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 by homologous pairs Humans have 23 pairs (46 total) chromosomes. Two of the 46 chromosomes are called sex chromosome because they determine and individual’s sex. In Human’s: Female – Male –

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 is why the ratio of males to females is 50/50.

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

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

Human Genes 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 Antigen on (Blood Type Red Blood Cell Genotype 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 Sex-linked disorders are caused by genes on the X or Y chromosome Colorblindness, Hemophilia

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

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?