The study of how genes are passed from Generation to Generation! Standard 3 Unit 7 Genetics (Heredity) Chapters pages:

Unit 7 Genetics Probability Chapter 6.3 Pg. 177

Heredity Patterns can be calculated using the rules of probability. If 2 plants have certain characteristics and they are bred together, you can calculate the probability of the offspring having certain characteristics. There are 2 rules to help calculate these probabilities.

Probability The likelihood that an event will occur Probability = # of one kind of possible outcome total # of all possible outcomes ADDITION RULE! When the word or is used you add the odds. So, 1/6 + 1/6 = 2/6 MULTIPLICATION RULE! When the word and appears you multiply the odds. So, 1/6 x 1/6 = 1/36

Probability What is the probability of rolling a 6 on a die? – 1/6 What is the probability of rolling a 6 or a 5 on a dice cube? – 1/6 + 1/6= 2/6 What is the probability of rolling a 6 and a 5 – 1/6 x 1/6= 1/36 – Please do the practice problems on the worksheet HW#1

End Show 11-2 Probability and Punnett Squares Slide 6 of 21 Copyright Pearson Prentice Hall Probabilities Predict Averages Probabilities predict the average outcome of a large number of events. Probability cannot predict the precise outcome of an individual event. In genetics, the larger the number of offspring, the closer the resulting numbers will get to expected values.

Traits, Genes and Alleles chap 6.4 pgs A trait is a specific characteristic that varies from one individual to another Genes: the factors that determine traits Alleles: alternate forms of a gene Homozygous: Two of the SAME alleles (AA) Heterozygous: Two different alleles (Aa) Genome: all of an organism’s genetic material Genotype: genetic makeup of a specific set of genes Phenotype: The physical characteristics or traits

Dominant allele: Gene that is expressed AA BB Recessive allele: Gene that is not expressed aa bb

Mendelian Genetics Gregor Mendel ( ) Father of Genetics Austrian Monk, spent his life working with traits of Pea Plants Traits passed in “factors” GENES! from Generation to Generation Working during the same time period as Darwin He didn’t know what a GENE was !!

Genes and Dominance Mendel studied seven pea plant traits, each with two contrasting characters. Each original pair of plants is the P (parental) generation.

The offspring are called the F 1, or “first filial,” generation. The offspring of crosses between parents with different traits are called hybrids

How do we look at gene combinations? We use : Punnett Squares The gene combinations that might result from a genetic cross can be determined by drawing a diagram known as a Punnett square. Punnett squares can be used to predict and compare the genetic variations that will result from a cross.

6 steps to solving a problem Genetics problems require the same 6 steps! 1.Identify Dominant and Recessive Phenotypes T=Tall t=Short 2.Parent phenotype x parent phenotype tall x tall 3.Parent genotype x parent genotype Tt x Tt 4.Punnett Square 5.Phenotypic ratio 3 tall: 1 short 6.Genotypic ratio 1:2:1 TT:Tt:tt

Copyright Pearson Prentice Hall Lets try this Mono- (1) hybrid(mixture) cross A capital letter represents the dominant allele for tall. A lowercase letter represents the recessive allele for short. In this example, T = tall t = short Punnett Squares

Are the parent plants heterozygous or homozygous? Homozygous organisms are TRUE-BREEDING Heterozygous organisms are HYBRID Are the parents True-breeding or Hybrids?

Copyright Pearson Prentice Hall Punnett Squares All of the tall plants have the same phenotype, or physical characteristics. BUT..All of the tall plants do not have the same genotype, or genetic makeup. One third of the tall plants are TT, while 2/3 of the tall plants are Tt. The offspring are the F1 generation

Copyright Pearson Prentice Hall Punnett Squares These F1 plants have different genotypes (TT and Tt), but they have the same phenotype (tall). Lets find out what kind of plants we will get by crossing these! TT Homozygous Tt Heterozygous

Look back at the F1 plant that have the TALL Phenotype TT, Tt How can you determine the genotype of these plants ? How can you tell the Homozygous dominant TT from the Heterozygous Tt

What do you do if you don’t know the genotype of the dominant parent?

TEST CROSS  A test cross is used to determine the genotype of a dominant trait.  (A dominant trait can be either homozygous dominant or heterozygous.)  The unknown trait is crossed with the recessive trait.  If any offspring show the recessive trait, the dominant parent had to be heterozygous.

Dihybrid Crosses…they are twice as chap 6.5 pg 186 much fun!!! Two Traits example: seed color and shape! Created by Mendel to test Laws of Independent Assortment and Segregation

Cross 2 plants that are heterozygous for the 2 traits (seed shape & pod color) Sample #1: Pea Plants R = round seedsr = wrinkled seeds Y= yellow podsy = green pods 1)Identity Dominant and Recessive 2)Parent phenotypes 3)Parent genotypes 4)1,3 1,4 2,3 2,4 5) Punnet square 6)Possible Phenotypes 7) Phenotypic ratio

If you are looking at two genes at the same time, how do you figure out the possible combinations? Look at the positions to determine combos R r Y y if this is one parent what alleles can he contribute? 1&3 1&4 2&3 2&4 RG Rg rG rg

Try this! You have a round (R) and yellow (Y) pea plant and cross it with a wrinkled (r) and green (y) plant. Both are homozygous, one dominant and the other recessive Please label and do this cross on your notes What are the phenotypes for the offspring? What are the genotypes for the offspring?

Copyright Pearson Prentice Hall Independent Assortment The alleles for round (R) and yellow (Y) are dominant over the alleles for wrinkled (r) and green (y).

Now lets take two of these offspring and cross them. Parent phenotype(F1 generation) Parent genotype(F1 generation) RrYy Determine the alleles that each parent can give: 1&3 1&4 2&3 2&4 Please do the cross and generate the F2 generation

Copyright Pearson Prentice Hall Independent Assortment The Two-Factor Cross: F 2 Mendel crossed the heterozygous F 1 plants (RrYy) with each other to determine if the alleles would segregate from each other in the F 2 generation. RrYy × RrYy

Copyright Pearson Prentice Hall Independent Assortment Represents: Independent Assortment The Punnett square predicts a 9 : 3 : 3 :1 ratio in the F 2 generation.

Copyright Pearson Prentice Hall The alleles for seed shape segregated independently of those for seed color. This principle is known as independent assortment. Genes that segregate independently do not influence each other's inheritance. Independent Assortment

Copyright Pearson Prentice Hall The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes. Independent assortment helps account for the many genetic variations observed in plants, animals, and other organisms. Independent Assortment

Mendel’s Data revealed 3 patterns, LAWS 1. Law of Dominance: traits can have 2 alleles (one dominant “A” & one recessive “a”) Dominant allele:- - overpowers or covers up the recessive - Fully expresses the protein - Represented by Capital letter A, B EX: Brown eyes Recessive allele: - is masked by the other allele - little or no protein is expressed - is represented by lower case letter a,b EX: Blue eyes

Mendell’s Laws 2. Law of segregation : 1.Organisms inherit 2 copies of each gene, one from each parent. 2.Organisms donate only one copy of each gene, thus the 2 copies of each gene segregate or separate during meiosis

Mendel’s Laws 3. Law of Independent Assortment The presence of one trait does not affect the presence of another, genes for different traits segregate independently of each other during gamete formation. (this is seen in a two factor cross, dihybrid cross) This helps account for many genetic variations observed in plants, animals and other organisms.

Genetic linkage Chapter 6.6 page Independent assortment creates a lot of variation. Crossing over in Meiosis also creates variation Genes located close together on the same chromosome tend to be inherited together. This is termed linkage