Ch. 4: Modern Genetics

Sect. 1: Human Inheritance

Sect. 2: Human Genetic Disorders

Sect. 3: Advances in Genetics

Sect. 1: Human Inheritance

Traits are inherited through 3 inheritance patterns.

1. Single gene with 2 alleles

2. Single gene with multiple alleles

3. Multiple genes working together

1. Single genes with 2 alleles.– Dominant vs. Recessive.

Examples: Widow’s Peak, Sickle Cell Anemia, Huntington’s Disease.

2. Single genes with multiple alleles.– Multiple alleles are 3 or more forms of a genes

that code for a specific trait.

Example: Blood types: A, B, & O

A & B are codominant, O is recessive.

Blood type gene found on Chromosome 93. Multiple genes that work together to produce a

trait also known as polygenic genes.– Skin color

Controlled by 6 genes; 3 received from each parent.

– HeightTotal number that control height unknown Current thinking is that there is at least 8; 4 from each parent.

– Body Build

Sex chromosomes– Chromosomes that carry genes that determine the

sex of a newborn as well as other genes.– The 23rd pair of chromosomes.– Female sex chromosomes (XX):

X-received from mom, X-received from dad.Egg cell contains only X chromosomes.

– Male sex chromosomes (XY): X-received from mom, Y-received from dad.X chromosome substantially bigger than Y chromosome.Gene located on Y, called the SRY gene initiates the release of testosterone during embryonic development to turn embryo into a male.Sperm cell contains either an X or a Y chromosome.

Sex-linked genes– Genes carried on the X or Y chromosomes.– Unlike the other 22 pairs of chromosomes, X

& Y chromosomes do not have all the same genes.

– Sex-linked traitsTraits that are controlled by genes found on either the X or the Y chromosome.

– Example: Colorblindness: inability to distinguish between certain colors.

Red-Green colorblindness

Blue-Yellow colorblindness

Achromatopsia (Total colorblindness): inability to see any colors.

– Example: Facial Hair Gene for facial hair is found on the X chromosome & is recessive.

– Example: Hemophilia Video- A day in the life ofGenetic disorder in which the blood clots slowly or does not clot properly resulting in excessive bleeding when injured.Gene for hemophilia is found on the X chromosome & is recessive.

– Example: Male-patterned baldnessGene for hair loss is found on the X chromosome & is dominant.

– Example: Retinitis pigmentosaGenetic disorder in which a person gradually loses their eyesight eventually becoming blind.Gene found on the X chromosome & is a dominant gene.

– Example: Muscular DystrophyGenetic disorder in which a person gradually lose muscle control throughout the body.

– Because females have 2 X chromosomes typically they are only carriers for sex-linked genetic disorders.

Carrier: A person who has both a dominant & recessive allele for a trait & does not express the trait.

– Because males only have 1 X chromosome if the trait is located on their 1 X, they have the trait. If it is not located on their 1 X, they don’t have the trait.

Example: – H: non-hemophilia, h: hemophilia– XHXh (female with hemophilia but a carrier)– XhY (male with hemophilia)

Environmental factors can also influence the expression of traits.– Lack of exercise.– Proper diet.

Intake of proper amounts of proteins.

Intake of proper amounts of minerals.

Intake of proper amounts of vitamins.

Sect. 2: Human Genetic Disorders

Genetic Disorders– A genetic disorder is an abnormal condition

that a person inherits through genes & chromosomes.

– Causes of genetic disorders1. Mutations in the DNA of genes

– Substitution, deletion, or addition of nitrogen base pairs in the genetic code.

2. Changes in the overall structure or number of chromosomes.– Caused by the failure of chromosomes to separate

properly during meiosis.

Examples of Genetic Disorders

1. Cystic Fibrosis is a genetic disorder in which thick mucus is produced within the lungs & intestines.

Caused by the deletion of 3 nitrogen base pairs from the DNA molecule. Day in the life of...

2.Sickle-Cell Anemia is a genetic disorder in which the red blood cells form a sickle cell shape instead of the usual round shape.

Caused by the substitution of 1 nitrogen base pair in the DNA molecule that cause the hemoglobin protein

to form incorrectly.

Hemophilia: disorder in which a person’s body does not clot properly due to the lack of the production of a specific protein.

Caused because of a recessive gene found on the X chromosome.

Hemophilia is more common in males than females.

There are 2 primary types….Hemophilia A occurs in about 1 in 5,000 – 10,000 male births.

Hemophilia B occurs in about 1 in 20,000 – 34,000 male births.

3. Down Syndrome is a genetic disorder in which a person has 3 copies of chromosome 21.

Caused by the failure of chromosome 21 to separate during Meiosis.

Typically the mother’s chromosome-21.

Also called Trisomy-21

4. Albinism is a genetic disorder in which a person does not produce substantial amounts of pigment within their skin, eyes, or hair.

Albinism results from inheritance of a recessive gene and is known to affect all organisms including humans.

Genetic counselors– Professionals that work with prospective

parents to determine the likelihood of producing offspring with particular traits.

– Tools used by genetic counselorsPunnett Squares

Karyotype: a picture of all 46 chromosomes arranged in matching pairs.

Pedigree– Chart or “family tree” that tracks which members have a

particular trait.– Circles represent female members of the family.– Fully shaded means a person has the trait.– Half shaded means a person is a carrier for the trait.– Unshaded means a person does not have the trait.

Sect. 3: Advance in GeneticsSelective breeding.– Selective breeding is the process of selecting a few organisms

with desired traits to serve as parents of the next generation. – Types selective breeding techniques.

1. Inbreeding is a technique in which 2 individuals with similar sets of alleles & traits breed in hopes of maintaining those traits/alleles in the next generation.

– Examples:

Domestic turkeys,

Purebred dogs,

Championship race horses.

2. Hybridization is a technique in which 2 breeders with different sets of alleles & traits breed in hopes of getting the best traits/alleles from both species in the next generation.

Disadvantage of hybrids most hybrid species cannot reproduce.– Mule: cross between Horse & Donkey– Liger: cross between Lion & Tiger– Golden Labrador

CloningMini A clone is an organism that has the exact same genes as the organism from which it was produced. Identical twins are natural occurring clones.

Genetic engineering– Genetic engineering is the transfer of a gene from the

DNA of one organism into another organism in order to produce an organism with desired traits.

– Bacterial engineering (For diabetes) 1. Scientists remove plasmids, small rings of DNA, from

bacterial cells.2. An enzyme cuts open the plasmid DNA. The same

enzyme removes the human insulin gene from its chromosome.

3. The human insulin gene attaches to the open ends of the plasmid to form a closed ring.

4. Some bacterial cells take up the plasmids that have the insulin gene.

5. When the cell reproduce, the new cell will contain copies of the “engineered” plasmid. The foreign gene directs the cell to produce human insulin.

Genetic engineering (GMO) has been used to incorporate genes into plants to make them

– resistant to frost, – produce more offspring, – change color, texture & taste.

Genetic engineering (GMO) has been used to incorporate genes into animals to make them

– Bigger, faster, & stronger.– Cows: produce more milk, produce more muscle tissue

Gene therapy– Process in which scientist attempt to remove or fix a faulty gene

or chromosome by replacing it with a correctly functioning gene.

Concerns about genetic engineering– Long term safety effects to humans of genetically engineered

food & animals.– Concern that people will be able to “engineer” offspring.– Concern that “engineering” specific traits could eventually leave

organisms ill prepared to handle any future changes.

Human Genome Project– The Human Genome Project was a multinational scientific endeavor to

study the human genome.

Genome is the term that refers to all the DNA contained in 1 cell of an organism.

– Sponsored by various world governments & companies to determine…

1. The number of genes in the human genetic code.

2. The function of the genes in the human genetic code.

3. The location of the genes in the human genetic code.– Goal is to use this information to better understand, diagnose, treat, and

possibly prevent genetic disorders and their effects.– It began in 1990 and was completed in 2003.– Total US investment over the 13 years is approximately 3 billion dollars.