DO NOWThe allele B carries the trait for blue body color. The allele b carries the trait for pink body color.

Cross Bb and BB

Heredity

• The passing of traits from parents to offspring– Genes on chromosomes control the traits that

show up in organisms

Gregor Mendel

• The father of genetics• First to use

mathematics of probability to explain heredity and to trace one trait for several generations

Alleles

• Different forms of a trait that a gene may have are alleles.

• During meiosis, a pair of chromosomes separates and the alleles move into separate sex cells.

• Each sex cell now contains ONE allele for each trait.

• The study of how traits are inherited is genetics.

Alleles• Dominant allele- covers up or dominates

other allele• Recessive allele- the trait seems to disappear

unless the organism has TWO copies

Hybrids

• Hybrids receive DIFFERENT genetic information for a trait from each parent

Punnett Square

• Upper case letters- dominant alleles• Lowercase letters- recessive alleles

Genotype and Phenotype

• Genotype- the genetic makeup of an organism– Homozygous- an organism

with two alleles for one trait that are the SAME

– Heterozygous- an organism with two alleles for one trait that are the DIFFERENT

• Phenotype- the way an organism looks and behaves as a result of its genotype

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Incomplete dominance

• When the offspring of two homozygous parents show an intermediate phenotype– Such as flower color in some plants, coat of some

horse breeds

Chesnut horse Cremello horse Palomino horse

Multiple Alleles

• Many traits are controlled by more than one allele

• Traits controlled by multiple alleles produce more than 3 phenotypes of that trait– Ex: blood type in

humans

Blood Type• Alleles are A, B, and O• O is recessive to both A and B• If a person inherits both A and B, both are expressed, creating

genotype/phenotype AB• Genotypes AA and AO are phenotype A• Genotypes BB and BO are phenotype B• Genotype OO are phenotype O

Polygenic Inheritance

• Occurs when a group of gene pairs act together to produce a trait

• The effects of many alleles produce a wide variety of phenotypes– Ex: height, eye and skin color

Environmental Impact

• Environment plays a role in how genes are expressed– Ex: some people have genes that make them at

risk for developing skin cancer, but if they limit their exposure to the sun, they may never get cancer

Mutations

• Genes that are altered or copied incorrectly– Can be harmful, beneficial, or have no effect– Can be caused by x-rays or radioactive substances

Bruce Banner was exposed to Gamma Radiation, turning him into the Hulk.

Chromosome Disorders

• Mistakes in meiosis can result in new organism with more or fewer chromosomes than normal– Usually fatal to unborn fetus, but not always– Ex: Down Syndrome

Recessive Genetic Disorders

• Some recessive genes are result of a mutation• These disorders occur when both parents have

a recessive allele responsible– Because parents heterozygous, they don’t show

symptoms• Ex: cystic fibrosis

Cystic Fibrosis

• Most common genetic disorder leading to death among Caucasian Americans

• People with disease produce thick mucous instead of thin fluid which normally lines lungs

• The mucus builds up, making it hard to breathe, and results in bacterial infections and prevents flow of substances necessary for digesting food

Sex Determination

• Chromosomes that determine the sex of an organism are XX in females and XY in males

• Females produce eggs with X chromosome only and males produce sperm with X or Y.

Sex Linked Disorders

• Sex-linked gene- an allele inherited on a sex chromosome– Ex: color blindness trait

for color blindness recessive on X chromosome. Because men only have one X chromosome, a male with this allele is color blind.

Pedigree

• A visual tool for following a trait through generations of a family

Genetic Engineering

• When scientists experiment with biological and chemical methods to change the arrangement of DNA that makes up a gene– Can be done to find new ways to improve crop

production and quality, including the development of plants that are resistant to disease

Methods of Genetic Engineering

• Recombinant DNA- made by inserting a useful segment of DNA from one organism into a bacterium– ex: large quantities of human insulin are made by

genetically engineered organisms• Gene therapy- a normal allele is placed in a virus. The

virus then delivers the normal allele when it infects target, and the normal allele replaces defective one.– Used to test ways of controlling cystic fibrosis and cancer

Genetically Engineered Plants

• In the past, improvements to plants were result of selecting plants with most desirable traits and breeding them, or selective breeding.

• NOW, we can find the genes that produce desirable trait in one plant and then insert those genes into another plant

Genetically Engineering Plants

Genetically Modified Organism (GMO)

Benefits• More nutritious food• Tastier food• Disease- and drought-resistant plants

that require fewer environmental resources (water, fertilizer, etc.)

• Decreased use of pesticides• Increased supply of food with

reduced cost and longer shelf life• Faster growing plants and animals• Food with more desirable traits, such

as potatoes that absorb less fat when fried

• Medicinal foods that could be used as vaccines or other medications

Risks• Modified plants or animals may

have genetic changes that are unexpected and harmful.

• Modified organisms may interbreed with natural organisms and out-compete them, leading to extinction of the original organism or to other unpredictable environmental effects.

• Plants may be less resistant to some pests and more susceptible to others.