Interest Grabber Section 14-1 A Family Tree
Section 14-1A Family Tree
The other 44 chromosomes that do not determine sex are called the autosomes.
A circle represents a female.
A square represents a male.
A vertical line and a bracket connect the parents to their children.
A horizontal line connecting a male and female represents a marriage.
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.
2. Most traits you see expressed are polygenic. They have more than one gene regulating them.
3. This can also work the other way. Genes we have that might be bad for us cannot be expressed unless we put ourselves in the condition for them to work.
C. Human Genes – there are certain genes scientist have been able to track down due to their expression is visible or easy to find.
Red Blood Cell
2. Recessive Alleles – One of the first genetic disorders to be understood with genetics was PKU (phenylketonuria). People with PKU lack the enzyme needed to break down phenylalanine. If this is not broken down in newborns it will build up in tissues and cause severe mental retardation. Figure 14-6 shows other autosomal diseases that we know of.
Sickle cell disease
Dominant Alleles – Examples of dominant genetic diseases are dwarfism and Huntington’s disease.
Codominant Alleles – Sickle cell anemia is an example of a codominant disease. A codominant disease is where both traits are dominant and both will be expressed.
D. From Gene to Molecule – In both cystic fibrosis and sickle cell disease, a small change in the DNA of a single gene affects the structure of a protein, causing a serious disorder.
1. Cystic Fibrosis – This disease is more common in people whose descendants are from Northern Europe. It is caused by a recessive allele on chromosome 7. Children who have this disease have serious digestive disorders and produce a thick mucus in their lungs. Figure 14-8 page 347.
Chromosome # 7
The most common allele that causes cystic fibrosis is missing 3 DNA bases. As a result, the amino acid phenylalanine is missing from the CFTR protein.
Normal CFTR is a chloride ion channel in cell membranes. Abnormal CFTR cannot be transported to the cell membrane.
The cells in the person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus.
2. Sickle Cell Disease- Sickle cell disease is a common genetic disorder found in African Americans. Just one amino acid is changed in the protein. Valine is replaced by glutamic acid. Malaria helped this disorder spread throughout Africa because people who have Sickle Cell are resistant to malaria.
3. Dominant or Recessive? Things change as we learn more. At first Sickle Cell was thought to be recessive. Now we find that it is a codominant gene. Both normal and sickle cell shaped blood can be present in an individual.
14–2 Human Chromosomes – A human diploid cell contains more than 6 billion base pairs of DNA. The average human gene consists of about 3000 base pairs while the largest gene has more than 2 million base pairs.
Human Genes and Chromosomes – Chromosomes 21 and 22 are the smallest human autosomes. Chromosome 21 has 225 genes and 32 million base pairs in it alone.
Sex-Linked Genes – Because the X and Y chromosome determine sex the other genes on them are said to be sex-linked genes.
Colorblindness – is a recessive trait on the X chromosome. In males, a defective version of this produces colorblindness. For females it takes two copies of it to express.
2. Hemophilia – is a recessive disorder on the X chromosome. The difference here is that there are two genes that control it and a recessive expression in either will produce a form of hemophilia.
3. Duchenne Muscular Dystrophy – This is a sex-linked disorder that results in the progressive weakening and loss of skeletal muscle.
C. X-Chromosome Inactivation – In females one of the two X chromosomes is randomly switched off. British geneticist Mary Lyon discovered this.
D. Chromosomal Disorders – for most genetic diseases the cause is nondisjunction. This occurs during meiosis and is when homologous chromosomes fail to separate. This affects the number of chromosomes a cell will have. Figure 14-15 page 352.
1. Down Syndrome – this is also called trisomy 21, because it results from having three copies of the 21 chromosomes. Down syndrome produces mild to severe mental retardation and an increased susceptibility to many diseases and birth defects.
Sex Chromosome Disorders – When there are multiple copies of sex chromosomes it causes these disorders.
b. Klinefelter’s syndrome 47, XXY here a male receives and extra X chromosome. This causes both male and female sex organs to sometimes form. Hermaphroditic.
A. Human DNA Analysis
1. Testing for Alleles
2. DNA Fingerprinting
B. The Human Genome Project
1. Rapid Sequencing
2. Searching for Genes
3. A Breakthrough for Everyone
C. Gene Therapy
D. Ethical Issues in Human Genetics
Chromosomes contain large amounts of DNA called repeats that do not code for proteins. This DNA varies from person to person. Here, one sample has 12 repeats between genes A and B, while the second sample has 9 repeats.
Restriction enzymes are used to cut the DNA into fragments containing genes and repeats. Note that the repeat fragments from these two samples are of different lengths.
The DNA fragments are separated according to size using gel electrophoresis. The fragments containing repeats are then labeled using radioactive probes. This produces a series of bands—the DNA fingerprint.
Bone marrow cell
Normal hemoglobin gene
Genetically engineered virus