Genetics Unit 9 - Lesson 1 Notes

Heredity Heredity – the passing of traits from parent to offspring. Genes on chromosomes control the traits that show up in an organism. The different forms of a trait that a gene may have are alleles. Allele Steve Steve’s chromosomes, or genes

Heredity During meiosis a pair of chromosomes separates and the alleles move into separate cells. Each chromosome now contains one gene for each trait. Steve’s chromosomes, one from mom, one from dad SPERM

sperm from mom from dad from mom from dad from mom from dad from mom from dad from mom from dad

Heredity The study of how traits are inherited is genetics.

Gregor Mendel Gregor Mendel – the Father of Genetics. Mendel was the first to use mathematics of probability to explain heredity and to trace one trait for several generations.

Gregor Mendel Purebred – receives the same genetic information for a trait from each parent. Hybrid – receives different genetic information for a trait from each parent. = + Lab (Purebred)Poodle (Purebred) Labradoodle (hybrid)

Gregor Mendel Dominant allele – covers up or dominates the other trait. Recessive allele – the trait seems to disappear. Yellow Color is dominant Curly hair is dominant

Gregor Mendel Dominant The gene that is expressed IF PRESENT When we are determining someone’s genetic makeup, we use a capitol letter to illustrate the dominant gene. Ex. B = brown eyes Recessive The gene that is not expressed in the presence of a dominant trait When we are determining someone’s genetic makeup, we use a lowercase letter to illustrate the recessive gene. Ex. b = blue eyes

Punnett Squares Probability helps you predict the chance that something will happen. A Punnett Square can help you predict what an offspring will look like. Uppercase letters stand for dominant alleles. Lowercase letters stand for recessive alleles. A Punnett Square looks something like this….

Bbbb B = Brown b = Blue Bb b b B B b b b bb b

BBbb B = Brown b = Blue BB b b B B B B b bb b

BBBb B = Brown b = Blue BB b B B B B B B bb B

bbbb B = Brown b = Blue bb b b b b b b b bb b

Bb Bb B = Brown b = Blue Bb b B B B b b B bb B

Genotype Remember, an allele is expressed by one letter…. Genotype – the genetic makeup of an organism. Homozygous – an organism with two alleles for one trait that are the same (written BB or bb - PUREBRED). Heterozygous – an organism with two alleles for one trait that are different (written Bb or Tt…HYBRID).

Dominant/Recessive Homozygous/Heterozygous QQ Pp Tt TT bb BB kk

Punnett Square Use a Punnett Square to determine the probability of each of the offspring’s genotype and phenotype when two heterozygous, tall- dominant traits (Tt) are crossed with eachother. Tt T t T TtTt TtTt tt Genotype: 25% Homozygous Tall (TT) 50% Heterozygous Tall (Tt) 25% Homozygous Short (tt) Phenotype: 75% Tall (TT) and (Tt) 25% Short (tt) T = tallt = short

Phenotype Phenotype – the way an organism looks and behaves as a result of its genotype.

Genotype/Phenotype Genotype Phenotype

Principles of Heredity 1. Traits are controlled by alleles on chromosomes. Allele Steve Steve’s chromosomes, or genes

Principles of Heredity 2. An allele’s effect is dominant or recessive. RrRRrr Roll No Roll

Principles of Heredity 3. When a pair of chromosomes separates during meiosis, the different alleles for a trait move into separate sex cells.