Fundamentals of Genetics Biology Chapter 10
INHERITANCE or HEREDITY- The genetic transmissioncharacteristics fromparent 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.