Punnett Squares How can I predict the appearance of offspring based on the traits of the parents?

Two kinds of inheritance: Mendelian inheritance includes any trait which has only a pair of contrasting alleles and one of the alleles is dominant to the other allele. These traits will follow Mendel’s principles of heredity.

Two kinds of inheritance: Non-Mendelian inheritance includes traits which may share dominance, be linked with a second trait (such as sex), rely on multiple genes within the chromosomes, or have multiple forms (alleles) which may be inherited. These traits do not follow all of Mendel’s principles of inheritance.

Probability & inheritance Punnett developed a graphical method to predict the results of a cross between two parent organisms. These are called Punnett squares.

Probability & inheritance A Punnett Square shows all of the possible outcomes each time gametes from the two parents combine.

Steps to solving a Punnett square: Problem: tongue rolling is dominant to non- rolling Tongue rolling = R Non-rolling = r Assign each allele (form of the trait) a letter

Steps to solving a Punnett square: Problem: cross two heterozygous individuals Parent 1 = Rr Parent 2 = Rr Determine the genotype of each parent based on the information in the problem.

Steps to solving a Punnett square: Set up the Punnett square by putting one parent’s genotype across the top and the other down the side of the square. These represent possible gametes. Rr R r

Steps to solving a Punnett square: Complete the Punnett square by recording the letter on top of the column and on the side of the row. Always put the capital letter first. Rr R r RRRr rr

Steps to solving a Punnett square: Use the laws of probability and the Punnett square to answer any questions posed in the problem. Problem 1: what is the genotype ratio? Answer: 1RR : 2Rr : 1rr 1 : 2 : 1 Rr R r R Rr rr

Steps to solving a Punnett square: Problem 2: what is the phenotype ratio? Answer: 3 Tongue rolling : 1 Non-rolling 3 : 1 Rr R r R Rr rr

Steps to solving a Punnett square: Problem 3: what is the chance the couple will have a non-rolling child? Answer: 1/4 or 25% Rr R r R Rr rr

Fill It In … Genotype Ratio follows the format: ______ : ______ : ______ Phenotype Ratio follows the format: ______ : ______

Hybrid crosses: Punnett squares can be used to solve crosses involving only one trait (called a monohybrid cross) or crosses involving two traits (called a dihybrid cross).

Monohybrid cross The monohybrid cross requires four squares to represent all possible gamete combinations.

Dihybrid cross The dihybrid cross requires sixteen squares to represent all possible gamete combinations.

What are the different patterns of inheritance? Mendelian/simple dominance Dominant masks ressessive alleles Monohybrid Problem: tall pea plant height is dominant dominant to short pea plant height. Cross a pure breeding tall pea plant with a pure breeding short pea plant. Give the genotypic and phenotypic ratio. Solution: tall = H short = h P1 = HH P2 = hh G: 0 : 4 : 0 (HH : Hh : hh) P: 4 : 0 (tall : short) H H h h Hh

Non-Mendelian - 5 possible paths of inheritance Codominance Both alleles are equally dominant and so both are equally expressed. To represent the equal dominance each allele is assigned a different capital letter. **use as superscripts!!!

Fill It In … WORD HELP! Co = ______________

Non-Mendelian - 5 possible paths of inheritance Codominance Problem: Black feathers and white feathers are codominant in chickens. Cross a chicken with black and white feathers and a chicken with only black feathers. What is the chance they will have a chick with only white feathers? black feathers = B white feathers = W P1 = BW P2 = BB 0% chance of chick with white feathers B B B W BB BW

Non-Mendelian - 5 possible paths of inheritance Incomplete dominance Neither allele is sufficiently dominant to mask the other allele. When both alleles are present in an individual’s genotype (heterozygous) an entirely different, blended phenotype appears.

Non-Mendelian - 5 possible paths of inheritance Incomplete dominance To represent the incomplete dominance both share the same capital letter, but one is assigned a “prime” symbol. RR RR’ R’R’

Non-Mendelian - 5 possible paths of inheritance Incomplete dominance Problem: In four o’clock flowers red petals and white petals are incompletely dominant. Cross a red flower and a white flower. What is the resulting phenotype of all offspring? red = R white = R’ P1 (red) = RR P2 (white) = R’R’ All offspring are pink. RR R’ RR’

Non-Mendelian - 5 possible paths of inheritance Multiple alleles More than two alleles exist within the population for the given trait. However, each individual may only inherit two of the possible alleles To represent the multiple alleles, a base letter is used for each allele and the allele is represented by a unique superscript letter. Problem: blood type in humans is determined by multiple alleles: I A, I B, i In addition, I A and I B are codominant, while i is recessive to both. Below is a chart representing all the possible genotypes and resulting phenotypes ….

Non-Mendelian - 5 possible paths of inheritance Blood Type (phenotype) Possible Genotypes Type A I A I A or I A i Type B I B I B or I B i Type AB IAIBIAIBIAIBIAIB Type O ii

Fill It In … Draw a blood cell for each type: A - B - O - **Add AB -

Fill It In … Alleles for Blood Type: Allele for A = Allele for B = Allele for O =

Non-Mendelian - 5 possible paths of inheritance Multiple alleles Problem: Cross a heterozygous Type A female with a Type O male. What are all the possible blood types of the offspring? P1 = I A i P2 = ii Type A and Type O are the possible blood types. i i i IAIA IAiIAi IAiIAi ii

Non-Mendelian - 5 possible paths of inheritance Sex-linkage One of the pairs of chromosomes in an organism determines the sex. This pair is called the sex chromosomes.

Non-Mendelian - 5 possible paths of inheritance Sex-linkage In humans, the two types of sex chromosomes are represented by an X and a Y Inheriting two X chromosomes makes a female; inheriting an X and a Y chromosomes makes a male.

Non-Mendelian - 5 possible paths of inheritance Sex-linkage The genes located on a sex chromosome (almost always the X chromosome) are called sex-linked genes. Thus, females inherit two alleles for the trait, while males only inherit one allele for the trait.

Fill It In … What makes sex-linked genes DIFFERENT from other genes?

Non-Mendelian - 5 possible paths of inheritance Sex-linkage Problem: Colorblindness is a recessive sex-linked trait. A colorblind man has a child with a woman who is a carrier (heterozygous) for colorblindness. What is the chance they will have a colorblind son? “normal” vision = X B colorblind = X b P1 = X b Y P2 = X B X b There is a 25% chance they will have a colorblind son XbXb XbXb XBXB Y XBXbXBXb XbXbXbXb XbYXbY XBYXBY

Non-Mendelian - 5 possible paths of inheritance Sex-linkage

Non-Mendelian - 5 possible paths of inheritance Polygenic inheritance Many traits actually depend on several genes. The interaction of the many genes within one individual creates a range of phenotypes

Non-Mendelian - 5 possible paths of inheritance Polygenic inheritance For example, height, skin color and the size of your foot depend on the total number of dominant alleles inherited for these traits. This means someone with four dominant alleles will have a slightly bigger foot than someone with three dominant alleles.

Non-Mendelian - 5 possible paths of inheritance Polygenic inheritance This results in a characteristic graphical pattern seen below:

Fill It In … The SIX paths of inheritance: 1. M_______________ (A, a) 2. C_______________ (A, B) 3. I________________ D_______________ (A, A’) 4. M_______________ A_______________ (I A, I B, i) 5. S____ - l_________ (X A, X a ) 6. P_______________ (AaBbCc)

Paths of Inheritance Path Type Characteristics Mendelian 1 allele is dominant and 1 allele is recessive Codominant 2 alleles – both are equally expressed Incomplete dominance 2 alleles – if heterozygous, alleles blend together Multiple alleles More than 2 alleles possible for a trait (but each person gets 2) Polygenic A traits is controlled by more than one gene in a person

Check Yourself! 1. Name the five paths of non-Mendelian inheritance. 2. Which pattern of inheritance results in a third, blended phenotype of individuals? 3. What two patterns of inheritance does blood type follow? 4. Where are the sex-linked traits located? 5. Name three traits that follow polygenic inheritance?

Check Yourself! 1. Name the five paths of non-Mendelian inheritance. CODOMINANCE, INCOMPLETE DOMINANCE, MULTIPLE ALLELES, SEX-LINKED, & POLYGENIC 2. Which pattern of inheritance results in a third, blended phenotype of individuals? 3. What two patterns of inheritance does blood type follow? 4. Where are the sex-linked traits located? 5. Name three traits that follow polygenic inheritance?

Check Yourself! 1. Name the five paths of non-Mendelian inheritance. CODOMINANCE, INCOMPLETE DOMINANCE, MULTIPLE ALLELES, SEX-LINKED, & POLYGENIC 2. Which pattern of inheritance results in a third, blended phenotype of individuals? INCOMPLETE DOMINANCE 3. What two patterns of inheritance does blood type follow? 4. Where are the sex-linked traits located? 5. Name three traits that follow polygenic inheritance?

Check Yourself! 1. Name the five paths of non-Mendelian inheritance. CODOMINANCE, INCOMPLETE DOMINANCE, MULTIPLE ALLELES, SEX-LINKED, & POLYGENIC 2. Which pattern of inheritance results in a third, blended phenotype of individuals? INCOMPLETE DOMINANCE 3. What two patterns of inheritance does blood type follow? MULTIPLE ALLELES & CODOMINANCE 4. Where are the sex-linked traits located? 5. Name three traits that follow polygenic inheritance?

Check Yourself! 1. Name the five paths of non-Mendelian inheritance. CODOMINANCE, INCOMPLETE DOMINANCE, MULTIPLE ALLELES, SEX-LINKED, & POLYGENIC 2. Which pattern of inheritance results in a third, blended phenotype of individuals? INCOMPLETE DOMINANCE 3. What two patterns of inheritance does blood type follow? MULTIPLE ALLELES & CODOMINANCE 4. Where are the sex-linked traits located? ON THE SEX CHROMOSOMES (ESP THE X) 5. Name three traits that follow polygenic inheritance?

Check Yourself! 1. Name the five paths of non-Mendelian inheritance. CODOMINANCE, INCOMPLETE DOMINANCE, MULTIPLE ALLELES, SEX-LINKED, & POLYGENIC 2. Which pattern of inheritance results in a third, blended phenotype of individuals? INCOMPLETE DOMINANCE 3. What two patterns of inheritance does blood type follow? MULTIPLE ALLELES & CODOMINANCE 4. Where are the sex-linked traits located? ON THE SEX CHROMOSOMES (ESP THE X) 5. Name three traits that follow polygenic inheritance? (ANSWERS WILL VARY)