The Human Genome Chapter 14 Donna Howell Biology I Blacksburg High School

Chromosomes All human beings have 46 chromosomes: 23 from the egg, and 23 from the sperm. Two of those chromosomes are called sex chromosomes: the X and the Y. The other 44 are called autosomes. Females’ chromosomes are XX, and males’ chromosomes are XY.

Karyotype Scientists can take pictures of a cell’s chromosomes, and cut them out. When they sort them out by chromosome number, they have created a karyotype. Human female karyotype

Pedigree A pedigree is a chart that shows the relationships within a family, and allows us to infer genotypes we may not know.

Genes and the Environment Some traits are not totally controlled by our genes; the environment contributes to some, such as height. Mostly due to genes, but also dependent on nutrition.

Blood Group Genes Some of the first genes to be discovered were the human blood type genes. There are 4 types of blood: A, B, AB and O.

Recessive Alleles Some genetic disorders are caused by recessive alleles. Examples: albinism, cystic fibrosis, Tay- Sachs disease.

Dominant Alleles Some genetic disorders are caused by dominant alleles. Examples: Huntington disease, Dwarfism

Co-Dominant Alleles Some genetic disorders are caused by co- dominant alleles – both alleles contribute to the disease. Examples: sickle cell disease

From Gene to Molecule Sometimes, deletions in DNA can cause diseases. One example is cystic fibrosis. Three bases are deleted in the DNA, causing an amino acid to not be produced.

From Gene to Molecule Another example is sickle cell disease. One base in DNA is changed, causing valine to be produced instead of glutamic acid.

Sex-linked Genes Because X and Y chromosomes are different, some genes reside on one and not the other. These are called sex-linked genes.

Sex-linked Genes One example is colorblindness. This gene is located on the X chromosome. Because males only have one X, all colorblindness shows up in males, even if it is recessive.

Chromosomal Disorders Sometimes the cell makes errors when undergoing meiosis. One common error is nondisjunction. Causes abnormal number of chromosomes in gametes.

Nondisjunction One example is Down syndrome. When a chromosome fails to separate during meiosis, cells may have an extra chromosome. Called trisomy.

Sex Chromosome Disorders Disorders can also happen in the X and Y chromosomes. In females, nondisjunction causes Turner’s Syndrome; in males, it causes Klinefelter’s syndrome.

Turner’s Syndrome Woman only inherits one X chromosome. Unable to reproduce – are sterile. Sex organs do not develop at puberty.

Klinefelter’s Syndrome Man has two X chromosomes and a Y chromosome. Unable to reproduce – sterile.

DNA Testing Human DNA can be tested to find out a person’s genotype. This can be used for family planning purposes.

DNA Fingerprinting A process where DNA from two or more sources can be matched. Remember the Gene Machine? That was DNA fingerprinting! Used for crimes, paternity, etc.

Human Genome Project In 1990, the Human Genome Project began. This was an attempt to analyze the complete human DNA sequence. Completed in 2000.

Gene Therapy Information about our genes can be used to replace an absent or faulty gene with a normal, working gene.

The End