GENETICSBy Aimee Chavez

HEREDITY The passing of traits from parents to

offspring. Gregor Mendel known as the father of

genetics. His work formed the foundation of genetics :

the scientific study of heredity.

MENDEL’S PEAS Mendel studies pea plants in the monastery

garden. They were easy to study because they have traits that exist in only two forms. For example : tall and short, seed shape, seed color, pod shape, and pod color.

They also produce a large number of offspring in one generation

MENDEL’S EXPERIMENTS Mendel decided to cross plants with opposite

forms of a trait (tall x short pea plants). He started with purebred : a plant that always produces offspring with the same form of a trait as the parent.

In his first experiment he cross bred purebred tall plants with purebred short plants. He called this the p generation (parental generation). The offspring were called the F1 generation (filial : son)

MENDEL’S EXPERIMENTS All the offspring in the F1 generation = TALL

The shortness trait had disappeared. He allowed the offspring to self pollinate and the

results in the (Tt X Tt) both these are hybrids

F2 generation = 3 TALL and 1 Short 75% Tall and 25% Short ¾ Tall and ¼ Short 3:4 Tall and 1:4 Short The shortness trait has reappeared.

DOMINANT AND RECESSIVE ALLELES Factors that control traits are called genes. The

different forms are alleles. Individual alleles control the inheritance of traits.

Traits: All of the features that an organism inherits (eye color). Result from the coded information in DNA.

Dominant: one whose trait always shows up in the organism when the allele is present.

Recessive: is masked or covered up whenever the dominant allele is present. It will only show up if there is not a dominant present.

The alleles are abbreviated with the letter of the dominant trait. TT = tall Tt = tall tt = short

ENVIRONMENTAL EFFECTS ON TRAITS:

(growth, appearance, gender) nutrition, weather, temperature, rain, pollution, fire, mountains, volcanoes, flooding, amount of light, space, soil, minerals

As we walk higher up the mountain at different elevations the temperature decreases and wind increases which affects the type of plants and animals living in area.

Predators can cause groups to adapt and become stronger for survival.

Arctic foxes: in the winter their coats are white and in other months it is brown

Siamese cats: are born white, the gene for colored fur is less active in heat and color markings develop more in cooler areas.

Some fish can switch from male to female for mating.

PROBABILITY AND GENETICS Probability: is the likelihood that a

particular event will occur. When Mendel crossed two plants that were

hybrid the results were always ¾ phenotype like the dominant trait and ¼ phenotype like the recessive.

MENDEL’S STUDIES

PUNNETT SQUARE Can be used to calculate the probability

that offspring will have a certain combination of alleles. The allele that each parent will pass on is based on chance. There are four possible combinations of alleles.

PUNNETT SQUARE

PHENOTYPES AND GENOTYPES Phenotype: an organism’s physical

appearance. Example: Tall or short Genotype: is the genetic makeup. Example: TT, Tt, tt Genotypes can be described as

homozygous: two identical alleles or heterozygous: two different alleles.

MULTIPLE ALLELES Some human traits are controlled by a single

genes that has more than two alleles. Three or more forms of a gene that code for a single trait.

One human trait is blood type. There are four main blood types, A, B,AB,O. Three alleles control the inheritance of blood types. The allele for A and B are codominant and O is recessive.

MULTIPLE ALLELES

EYE COLOR

CODOMINANCE

The alleles are neither dominant or recessive. Both alleles are expressed in the offspring.

SKIN COLOR

INCOMPLETE DOMINANCE The phenotype of the offspring is an

intermediate phase of the parents. There is no dominant or recessive. In four o’clock flowers the alleles for red and white produce pink offspring.

PEDIGREES A tool that geneticists use to trace the

inheritance of traits in humans. A circle represents the female and square the male, if either is colored in completely then the trait is present, whereas if either is colored half way then they are a carrier.

PEDIGREE OF HYPERCHOLESTEROLEMIA

SEX LINKED TRAITS: DOMINANT OR RECESSIVE?

INHERITANCE OF CYSTIC FIBROSIS