Punnett Square Notes What is Genetics Genetics is
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Punnett Square Notes
What is Genetics? Genetics is the scientific study of heredity
What is a Trait? A trait is a specific characteristic that varies from one individual to another. Examples: Brown hair, blue eyes, tall, curly
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, hazel Examples of Alleles: A = Brown Eyes a = Blue Eyes B = Green Eyes b = Hazel Eyes
What are Genes? Genes are the sequence of DNA that codes for a protein and thus determines a trait.
Gregor Mendel Father of Genetics 1 st important studies of heredity Identified specific traits in the garden pea and studied them from one generation to another
Mendel’s Conclusions 1. Law of Segregation – Two alleles for each trait separate when gametes form; Parents pass only one allele for each trait to each offspring 2. Law of Independent Assortment – Genes for different traits are inherited independently of each other
Dominant vs. Recessive Dominant - Masks the other trait; the trait that shows if present Represented by a capital letter R Recessive – 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 present Represented by a lower case letter r
Dominant & Recessive Practice T – straight hair t - curly hair TT - Represent offspring with straight hair Tt - Represent offspring with straight hair tt - Represents offspring with curly hair
Genotype vs. Phenotype Genotype – The genetic makeup of an organism; The gene (or allele) combination an organism has. Example: Tt, ss, GG, Ww Phenotype – The physical characteristics of an organism; The way an organism looks Example: Curly hair, straight hair, blue eyes, tall, green
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) RR rr Rr
Punnett Squares Punnett Square – Diagram showing the gene combinations that might result from a genetic cross Used to calculate the probability of inheriting a particular trait Probability – The chance that a given event will occur
Punnett Square Parent Offspring
How to Complete a Punnett Square
Y-Yellow y-white Genotype: 1: 2: 1 (YY: Yy: yy) Phenotype: 3 Yellow 1 White
You Try It Now! Give the genotype and phenotype for the following cross: TT x tt (T = Tall and t = Short)
TT x tt Step One: Set Up Punnett Square (put one parent on the top and the other along the side) t t T T
TT x tt Step Two: Complete the Punnett Square t T T Tt Tt Tt
TT x tt Step Three: Write the genotype and phenotype t T T Tt Tt Tt Genotype: 4 – Tt 0 -TT 0 -tt Phenotype: Remember: Each box is 25% 100% Tall
You Try It Now! Give the genotype and phenotype for the following cross: Tt x tt
Tt x tt Step One: Set Up Punnett Square (put one parent on the top and the other along the side) t t T t
Tt x tt Step Two: Complete the Punnett Square t Tt tt
Tt x tt Step Two: Complete the Punnett Square t Tt tt Genotype: Tt - 2 (50%) tt - 2 (50%) TT-0 Phenotype: 50% Tall Remember: Each box is 25% 50% Short
Red hair (R) is dominant over blond hair (r). Make a cross between a heterozygous red head and a blond. R r r r Rr rr What percentage of the offspring will have red hair? 50%
Let’s try some more… In pea plants, tall pea plants (T) are dominant over short pea plants (t). Construct a Punnett Square for a heterozygous tall pea plant and a short pea plant. t t Tt tt What are the percentage of phenotypes? 50% tall 50% short
Black eyes (R) is dominant over red eyes (r) in rats. Make a cross between a homozygous rat with black eyes and a rat with red eyes. r r R Rr Rr What is the possibility of a red eye off springs? 0%
Some Terminology P 1 – Original parents F 1 – First generation F 2 – Second generation P 1 X P 1 = F 1 X F 1 = F 2
- Mendel was a
- Punnett sqyare
- What is the genotype ration between the cross yyrr x yyrr?
- The punnett square in figure 11-2
- Punnett square limitations
- Eye color punnett square
- Punnett square for curly hair
- Mendel's law punnett square
- Extension of mendelian genetics
- Punnett square jeopardy
- Punnett square steps
- Freckles punnett square
- Hemophilia punnet square
- X-linked recessive punnett square
- Asdf autism
- Dd x dd punnett square
- Punnett square tt x tt
- Genotype example
- Mendel dihybrid cross genotypic ratio
- In the punnett square shown in figure 11-1
- Blood type punnit square
- Punnett square for earlobes
- Punnett squares
- Pkd punnett square
- Punnett square ttxtt
- Punnett square jeopardy
- Bb x bb genotype
- Punnett square