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