PUNNETT SQUARES PUNNETT SQUARES AND PEDIGREES Punnett Square

PUNNETT SQUARES

PUNNETT SQUARES AND PEDIGREES Punnett Square: a graphic used to predict genotypes and phenotypes of offspring in a given cross.

HOW TO SET UP A PUNNETT SQUARE: 1. Draw 2. a 4 square grid Put the genotype of one parent across the top and the other along the left side. 3. Fill in the boxes by copying the column down and row across into the empty spaces. B B b Bb Bb

HOW TO READ A PUNNETT SQUARE Probability: What is the chance of a specific outcome (percentage) Ratio: expression that compares two quantities (1: 4 is “one in four”) Probability: 25% of the squares are red Ratio: 1 of 4 squares are red.

For this example lets consider a genotype of brown hair (BB) for the Dad, and a genotype of blonde hair (bb) for the Mom. What are the outcomes of your cross? B B b Bb Bb Genotypes: Phenotypes: What percentage of the offspring will be brown hair? What ratio of the offspring will be Brown Hair? What percentage of the offspring will be blonde? What ratio of the offspring will be blonde?

Two heterozygous red flowers (white flowers are recessive) are crossed. Use letters R and r. What are the outcomes of your cross? Genotypes: Phenotypes: What percentage of the offspring will be red? _____ What ratio of the offspring will be red? _______ What percentage of the offspring will be white? _____ What ratio of the offspring will be white? ________

4. A homozygous dominant brown mouse is crossed with a heterozygous brown mouse (tan is the recessive color). Genotypes: Phenotypes: What is the percentage and ratio of the offspring will be brown? What is the percentage and ratio of the offspring will be tan?

5. A homozygous dominant tall plant is crossed with a homozygous recessive short plant (short is the recessive size). Genotypes: Phenotypes: What is the percentage and ratio of the offspring will be brown? What is the percentage and ratio of the offspring will be tan?

6. Tall is dominant (T) Short is recessive (t) What is the genotype of the missing parent? ______ What are the phenotypes of the parents? _______________ What are the phenotypes of the children? _______________

SEX LINKED PUNNETT SQUARES

Sex Linked Crosses Male Chromosome: XY Female Chromosome: XX Sex Linked Trait: a trait that is coded for by a recessive allele on a sex chromosome. · X chromosome is larger, so there are more X linked traits than Y linked traits. · Males only have 1 X chromosome, so if they have the recessive allele on their X, they automatically have the trait. · EXAMPLE: Colorblindness

Sex Linked Crosses

1. In fruit flies, eye color is a sex linked trait Red (R) is dominant to white (r). What are the sexes and eye colors of flies with the following genotypes: • • • X R X r _______ X R Y ________ X r _______ X R _______ X r Y ________

2. What are the genotypes of these flies: A. White eyed, male: _______ B. red eyed female (heterozygous): _______ C. White eyed, female: _______ D. red eyed, male: _______

3. Show the cross of a white eyed female Xr. Xr with a red eyed male XRY. What are the genotypes of the parents? ______ x ______ White eyed and male: ____% Red eyed and male: ____% White eyed and female: ____% Red eyed and female: ____%

4. Show the cross of a heterozygous red eyed female and a red eyed male. What are the genotypes of the parents? ______ x ______ White eyed and male: ____% Red eyed and male: ____% White eyed and female: ____% Red eyed and female: ____%

5. In humans, hemophilia is a sex-linked trait. Females can be normal, have the disease, or be carriers for the trait. Males will either have the disease or not, but they X Y: normal male X X : female who is a carrier won’t ever be carriers. X X : normal female H H H Xh. Y: male with hemophilia A. Show the cross of a man who has hemophilia with a woman who is a carrier. H h Xh. Xh: female with hemophilia B. A woman who is a carrier marries a normal man. Show the cross.

5. In humans, hemophilia is a sex-linked trait. Females can be normal, have the disease, or be carriers for the trait. Males will either have the disease or not, but they X Y: normal male X X : female who is a carrier won’t ever be carriers. X X : normal female H H Xh. Y: male with hemophilia H H h Xh. Xh: female with hemophilia C. A woman who has hemophilia marries a normal man. Draw a punnett square to answer. How many of their children will have hemophilia, and what is their sex? ____________

Dihybrid Crosses: a cross in which 2 characteristics are tracked

Two Trait Genotype Practice For a rodent, black fur (B) is dominant over brown fur (b), and a long tail (L) is dominant over a short tail (l). 1. What are the phenotypes of rabbits that have the following genotypes: BBll ___________________ bb. LL __________________ Bb. Ll__________________ ___

Two Trait Phenotype Practice For a rodent, black fur (B) is dominant over brown fur (b), and a long tail (L) is dominant over a short tail (l). Heterozygous for fur color and tail length _________________ Homozygous Dominant for fur color , homozygous recessive for tail length ____________________ Homozygous recessive for fur color, homozygous dominant for tail length _____________________

Finding Parent Allele Combinations: Outside Punnett Square F: First O: Outside I: Inside L: Last Parent Allele Combinations:

EXAMPLE: Aa. Bb x AABb (A - long hair, a– short hair, B– brown color, b – blonde color) Parent 1 Aa. Bb Possible Combinations: Parent 2 AABb Possible Combinations:

1: Put parent alleles on outside 2: Fill in Square 3: Give each possible phenotype a symbol 4: look for each phenotype Long Brown Percentage and Ratio: AB Ab a. B ab AB AABB AABb A a. B B A a. B b Ab AABb A A bb A a. B b A abb Short Brown Percentage and Ratio: Long Blonde Percentage and Ratio: Short Blonde Percentage and Ratio:

2. A male rabbit with the genotype GGbb is crossed with a female rabbit with the genotype gg. Bb the square is set up below. Fill it out and determine the phenotypes and proportions in the offspring.

• Show the cross between a gg. Bb and a GGBb. You'll have to set this one up yourself: Possible Combinations for gg. Bb: Possible Combinations for GGBb:

PEDIGREE S

X What does pedigree mean? Pedigree: a diagram that traces one trait through several generations of a family

= female = male

A horizontal line connecting two shapes represents a cross/marriage. mom dad

A vertical line extending down from a marriage/cross represents that the couple has children. mom dad

Example #1 How many girls? ___ 3 2 How many boys? ___ How many crosses/marriages? ___ 1 3 How many children do the couple have? _____ I. mom dad II. daughter #1 daughter #2 son

mom dad oldest daughter #1 youngest daughter #2 son

How many crosses/marriages? Example #2 I. II. III. 2 A C B D E F G

A C How many males? 3 _____ How many females? ______ 4 B D questions… E F G How many children do couple A and B have? ______ 3 How many children do couple E and F have? _______ 1

A C B D G E F M P H H J N How many Generations are shown in the Pedigree? K L O Q R S T

Example #3 A C How many couples have children? B D H H G E F M J L O N P K Q ? R S T 4

How do you show twins? A C B D E F

Showing Dominant or Recessive How do you show traits? Shading Homozygous Dominant (RR) ( shaded = recessive ) Heterozygous (Rr) **Some pedigrees won’t shade the heterozygous for you, you would just have to figure it out!** Homozygous Recessive (rr) Mutation

I ____ _ Rr mom RR dad R = tongue roller r = non-roller Rr son II ____ _ Rr daughter RR daughter Rr Rr Daughter 1 Genotype: _______ Rr Son’s Genotype: ______ RR Mom’s genotype: ____ Dad’s Genotype: ____ RR Daughter 2 Genotype: _______ Quick Pedigree Summary Video

Pedigree Challenge 1. Two normally-pigmented parents have 3 children. The first child (a girl) and their second child (a boy) have normal pigmentation. Their third child (a girl) has albinism. That girl marries a normally pigmented male and they have four children. The first three (two girls and a boy) have normal pigmentation. Their fourth child (a girl) has albinism like her mother. 2. Brown eyes are a dominant eye color and blue eyes are recessive. A brown eyed woman whose father had blue eyes and whose mother had brown eyes marries a brown eyed man whose parents are also brown eyed. They have a son who is blue eyes.