Fundamentals of Genetics Biology Chapter 10

INHERITANCE or HEREDITY- The genetic transmission characteristics from parent to offspring, such as hair, eye, and skin color.

Study of Genetics Gregor Mendel, an Austrian monk, first documented and experimented with genetics using a particulate model. He observed and used statistics to analyze: Studied pea traits of seed texture, coat color, appearance, flower arrangement and stem length of pea plants Inheritance: passing of traits by heredity Heredity: transmission of traits from parents to offspring

Mendel’s Experiments Mendel studied each characteristic and it’s two contrasting traits individually. Grew plants that were pure for a single trait of a characteristic. (pure: consistently exhibited the trait or passed it on to offspring) Mendel used plants that were pure for a specific trait in a series of experiments to determine inheritance patterns. Mendel developed three principles of inheritance (dominance, segregation, independent assortment).

Principle of Dominance and Recessiveness Mendel suggested that each trait was controlled by a “factor.” (genetic unit that controls a trait) He reasoned that how a pair of factors interacted resulted in how a trait appeared. Mendel arrived at the “principle of dominance and recessiveness.” He stated the dominant factor is the one of a pair that masks the other factor.” The factor that was masked was called recessive.

Principle of Segregation Mendel reasoned that if each parent had two factors, each offspring must have two factors. Each parent could not pass down two factors or the offspring would have four copies. Mendel concluded that each reproductive cell received only on factor for each characteristic. The principle of segregation states, “the two factors that code for characteristic separate during formation of egg and sperm.

Principle of Independent Assortment Data from complex crosses showed that traits produced by dominant factors did not always appear together. (or independently) Mendel concluded that the factors for different characteristics were not connected. In the principle of independent assortment, he stated, “factors for different characteristics are distributed to reproductive cells independently.”

Chromosomes and Genes A gene is a segment of DNA on a chromosome that controls a particular hereditary trait. Genes occur in pairs, one from each chromosome. Alleles are alternative forms of a gene or factors according to Mendel. Dominant alleles are represented with a capital letter and recessive alleles are represented with a small letter.

Alleles Alleles are the different forms of a gene for a specific trait. Mendel only studied traits with two alleles. Some traits have multiple alleles or three or more forms of a gene for the trait. Ex. Human Blood Types; height

Genotypes vs. Phenotypes A genotype is the genetic makeup of an organism. A phenotype is the physical appearance of an organism. Ex. Genotype = TT, Phenotype = Tall

Genotypes There are two types of genotypes: Homozygous: an organism has two copies of the same allele for a trait. Homozygous organisms are either 100% recessive or dominant. Ex. TT is homozygous dominant Ex. tt is homozygous recessive Heterozygous: an organism has two different alleles of a trait Ex. Tt or tT

Probability Probability is the likelihood of an event occurring. Probability is expressed as a decimal, percentage or fraction. Probability = number of one kind of event/ number of all events In genetics, expected ratios of probability occur only when many trials are performed.

What are Dominant Genes? Dominant Genes = one gene overshadows the other Angus Cattle: black is dominant, red is not Dominant: BB or Bb Recessive: bb ONLY

What are Dominant Genes? Hereford: white face is dominant Dominant: WW or Ww Recessive: ww ONLY

What are Recessive Genes? The gene that is overshadowed by a dominant gene Recessive genes can only express themselves if BOTH genes are recessive

What are Dominant Genes? Hampshire Hog: white belt is dominant Dominant: WW or Ww Recessive: ww ONLY

What are Recessive Genes? Black wool is recessive to white wool. Dominant: WW or Ww Recessive: ww ONLY

(P) Chromosome from MOM: P Chromosome from DAD: p (p)

Review of vocabulary AUTOSOME- A chromosome that is not a sex chromosome. (22 pairs). Sex chromosome: Determines the gender (1 pair). Genotype- genes present (usually abbreviated as 2 letters) TT = homozygous = purebred Tt = heterozygous = hybrid tt = homozygous = purebred When 1 allele masks/hides the effect of another, that allele is called DOMINANT and the hidden allele is called RECESSIVE.