Presentation on theme: "Biology Regents Periods 2, 4 and 7"— Presentation transcript:
1 Biology Regents Periods 2, 4 and 7 Punnett Square NotesBiology RegentsPeriods 2, 4 and 7
2 What is Genetics?Genetics is the scientific study of heredity
3 What is a Trait?A trait is a specific characteristic that varies from one individual to another.Examples: Brown hair, blue eyes, tall, curly
4 What is an Allele?Alleles are the different possibilities for a given trait.Every trait has at least two alleles (one from the mother and one from the father)Example: Eye color – Brown, blue, green, hazelExamples of Alleles:A = Brown Eyesa = Blue EyesB = Green Eyesb = Hazel Eyes
5 What are Genes?Genes are the sequence of DNA that codes for a protein and thus determines a trait.
6 Gregor Mendel Father of Genetics 1st important studies of heredity Identified specific traits in the garden pea and studied them from one generation to another
7 Mendel’s ConclusionsLaw of Segregation – Two alleles for each trait separate when gametes form; Parents pass only one allele for each trait to each offspringLaw of Independent Assortment – Genes for different traits are inherited independently of each other
8 R r Dominant vs. Recessive Dominant - Masks the other trait; the trait that shows if presentRepresented by a capital letterRecessive – An organism with a recessive allele for a particular trait will only exhibit that trait when the dominant allele is not present; Will only show if both alleles are presentRepresented by a lower case letterRr
9 Dominant & Recessive Practice TT - Represent offspring with straight hairTt - Represent offspring with straight hairtt - Represents offspring with curly hairT – straight hairt - curly hair
10 Genotype vs. PhenotypeGenotype – The genetic makeup of an organism; The gene (or allele) combination an organism has.Example: Tt, ss, GG, WwPhenotype – The physical characteristics of an organism; The way an organism looksExample: Curly hair, straight hair, blue eyes, tall, green
11 Homozygous vs. Heterozygous Homozygous – Term used to refer to an organism that has two identical alleles for a particular trait (TT or tt)Heterozygous - Term used to refer to an organism that has two different alleles for the same trait (Tt)RRrrRr
12 Punnett SquaresPunnett Square – Diagram showing the gene combinations that might result from a genetic crossUsed to calculate the probability of inheriting a particular traitProbability – The chance that a given event will occur
15 Y-Yellowy-whiteGenotype:1:2:1(YY:Yy:yy)Phenotype:3 Yellow1 White
16 You Try It Now!Give the genotype and phenotype for the following cross: TT x tt (T = Tall and t = Short)
17 TT x ttStep One: Set Up Punnett Square (put one parent on the top and the other along the side)T Tt
18 TT x ttStep Two: Complete the Punnett SquareT TtTt
19 TT x tt Tt t Genotype: 4 - Tt Phenotype: 100% Tall Step Three: Write the genotype and phenotypeT TtGenotype:4 - TtPhenotype:100% TallTtRemember: Each box is 25%
20 You Try It Now!Give the genotype and phenotype for the following cross: Tt x tt
21 Tt x ttStep One: Set Up Punnett Square (put one parent on the top and the other along the side)T tt
22 Tt x ttStep Two: Complete the Punnett SquareT ttTttt
23 Tt x tt Tt tt t Genotype: Tt - 2 (50%) tt - 2 (50%) Phenotype: Step Two: Complete the Punnett SquareT ttGenotype:Tt - 2 (50%)tt - 2 (50%)Phenotype:50% Tall50% ShortTtttRemember: Each box is 25%
24 Some Terminology P1 – Original parents F1 – First generation F2 – Second generationP1 X P1 = F1F1 X F1 = F2
25 Incomplete DominanceIncomplete Dominance - Situation in which one allele is not completely dominant over another.Example – Red and white flowers are crossed and pink flowers are produced.
26 CodominanceCodominance - Situation in which both alleles of a gene contribute to the phenotype of the organism.Example – A solid white cow is crossed with a solid brown cow and the resulting offspring are spotted brown and white (called roan).+
27 Multiple AllelesMultiple Alleles- Three or more alleles of the same gene.Even though three or more alleles exist for a particular trait, an individual can only have two alleles - one from the mother and one from the father.
28 Examples of Multiple Alleles Coat color in rabbits is determined by a single gene that has at least four different alleles. Different combinations of alleles result in the four colors you see here.
29 Examples of Multiple Alleles Blood Type – 3 alleles exist (IA, IB, and i), which results in four different possible blood typesHair Color – Too many alleles exist to countThere are over 20 different shades of hair color.
30 Multiple Alleles There Are Always Multiple Alleles! Genetic inheritance is often presented with straightforward examples involving only two alleles with clear-cut dominance. This makes inheritance patterns easy to see.But very few traits actually only have two alleles with clear-cut dominance. As we learn more about genetics, we have found that there are often hundreds of alleles for any particular gene.We probably know this already - as we look around at other people, we see infinite variation.
31 Polygenic TraitPolygenic Trait - Trait controlled by two or more genes.Polygenic traits often show a wide range of phenotypes.Example: The wide range of skin color in humans comes about partly because more than four different genes probably control this trait.