Genetics A study of inheritance

Gregor Mendel Father of modern genetics Conducted research with pea plants Developed ideas of dominance and trait segregation

Mendelian Genetics Mendel studied a number of characteristics in pea plants including: Height - short or TALL Seed color - green or YELLOW Seed shape - wrinkled or ROUND Seed coat color - white or GRAY Pod shape - constricted or SMOOTH Pod color - yellow or GREEN Flower position - terminal or AXIAL

Seed Shape Flower Position Seed Coat Color Seed Color Pod Color Plant Height Pod Shape Round Wrinkled Round Yellow Green Gray White Smooth Constricted Green Yellow Axial Terminal Tall Short YellowGraySmoothGreenAxialTall

Some vocabulary: 1. Generations: P or P 1 = Parent generation (1 st in a cross) F 1 = First filial (offspring of P 1 ) F 2 = Second filial (offspring of F 1 ) 2.Phenotype = description of physical appearance of an organism (which trait is expressed) 3.Genotype = Actual genetic makeup of an organism (expressed in letters,ex. “B”= Brown, “b” = blue”). BB, Bb, or bb are possible genotypes. 4.Gene = segment of DNA on a particular chromosome that controls a trait

More vocabulary: 5. Gametes = sex cells (egg or sperm) 6.Allele = form of a gene (B or b) 7.Homozygous = two of the same alleles for a trait (BB or bb) 8.Heterozygous = two different alleles for a trait (Bb) 9.Locus = the location of a gene on a chromosome

Phenotype –Physical characteristics

Phenotype –Facial structure –Eyes –Smile –Ears –Nose –Neck Notice the similarities:

Predicting Inheritance To determine the chances of inheriting a given trait, scientists use _________ squares and symbols to represent the alleles given to children by their parents. UPPERCASE letters are used to represent __________ alleles. lowercase letters are used to represent ___________ alleles. Punnett DOMINANT recessive

Predicting Inheritance For example: T = represents the allele for TALL in pea plants t = represents the allele for short in pea plants So: TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive. tt will result in a short plant. Remember there are two alleles for every trait! TWO

Mendel’s Principle of Dominance TT & Tt both result in a TALL plant, because T is dominant over t. t is recessive. tt will result in a short plant. Remember there are two alleles for every trait! Some ____________ are dominant and others are recessive. The phenotype (_____) of a dominant allele will be seen when it is paired with a recessive allele. alleles traits

Predicting Inheritance Let’s cross a totally dominant tall plant (TT) with a short plant (tt). Each plant will give only one of its’ two alleles to the offspring or F 1 generation. This is referred to as Mendel’s Law of Segregation. TT x tt TTtt

Punnett Squares The alleles from one parent go here. The alleles from the other parent go here.

Punnett Squares T T t t t t t t T T T T TT x tt

Punnett Squares TT tTt t F 1 generation

Interpreting the Results The genotype for all the offspring is ____. The genotype ratio is: The phenotype for all the offspring is Tall. The phenotype ratio is: Tt 4 Tt or All Tt All Tall or 4 Tall

Punnett Squares Tt T?? t Your Turn!!

Punnett Squares Tt TTTTt t tt F1 generation

Punnett Squares Tt TTTTt t tt This is a monohybrid cross. We worked with only one trait. The height of the plant.

Punnett Squares Tt TTTTt t tt This is a monohybrid cross. We worked with only one trait. The height of the plant. Later we will work with a dihybrid cross, using the height of the plant and either seed color or seed shape. two

3) Principle of Independent Assortment: “Factors” aka: genes for different traits are distributed to reproductive cells (gametes) independently of each other (for example, plant height is not dependent on seed color) Mendel proved this by crossing pea plants with different characteristics to see if one trait controlled another trait. They didn’t (but it turned out that all of “his” traits were found on different chromosomes).