Complex Punnett Squares

RR

In co-dominance… What happens when two alleles are both dominant? They are called co-dominant traits. There are some very important differences between complete and co-dominance. A capital letter represents one of the co-dominant alleles. A different capital letter represents the other co-dominant allele so that the two do not get mixed up. If an organism is co-dominant for a trait, the homozygous is written with 2 capital letters. For example, RR for red or WW for white in snapdragons. The heterozygous individual shows both alleles expressed equally. If a snapdragon plant shows red and white co- dominance, it will show a flower with both red and white. The genotype is denoted as RW.

Co-Dominance Practice 1. In cattle, red and white are co- dominant. Roan occurs when both red and white are present. Show what would happen if a roan bull was crossed with a white cow. What is the probability of the roan offspring? 2. In snapdragons, flower color is controlled by co-dominance. The two alleles are red (R) and white (W). The heterozygous genotype is expressed as red with white spots. A red and white- flowered plant is crossed with a white- flowered plant. What is the probability of producing a red and white-flowered plant?

Co-Dominance Practice 3. In horses, brown (B) and white (W) are co-dominant. A white horse and a brown and white spotted horse were crossed. What is the probability of producing a white horse? 4. Jim has a brown horse and a brown and white spotted horse. His daughter, Lilly, really wants a white horse. Can Jim breed the two horses he has to produce a white horse for Lilly?

In blood types… In humans, there are four blood types (phenotypes): A, B, AB, and O Blood type is controlled by three alleles. A ( ), B ( ), and O ( i ) O is recessive; two O alleles must be present for the person to have type O blood. This is denoted by ii. A and B are co-dominant. If a person receives an A allele and a B allele, their blood type is type AB. And, of course, = type A and = type B

In blood types… Blood TypeGenotype Can Receive Blood From Can Give Blood To A or A or OA or AB B or B or OB or AB AB AB, A, B, or O (universal acceptor) AB OiiO O, A, B, or AB (universal donor)

In blood types… The blood type determines what antibodies are located within the blood. Type A blood has type B antibodies (proteins that identify and neutralize foreign objects). If type B blood is put into their bodies, their immune system reacts as if it were a foreign invader, which can cause death. Type AB blood has no antibodies, any blood can be donated to them – they are called the "universal acceptors". Type O blood has no surface markers on it, so antibodies in the blood do not react to type O blood. They are called the "universal donors" since they can give their blood to any other blood type. When doing blood type crosses, you will need to know whether the type A or B person is heterozygous or homozygous. Type O's are automatically homozygous (ii) and type AB is automatically heterozygous ( ). Crosses are performed the same as any other.

Blood Types Practice 5. Write the genotype for each person based on the description: a. Homozygous for type B b. Heterozygous for the A allele c. Type O d. Type A and had a Type O parent e. Type AB f. Blood can be donated to anybody g. Can only get blood from a Type O donor 6. Determine the possible genotypic and phenotypic ratios of the children born to a heterozygous mother with Type A blood and a heterozygous father with Type B blood. What percentage of the offspring will be able to donate blood to their mother?

RR

In incomplete dominance… What happens when two alleles share dominance? They are called incomplete dominant traits. There are some very important differences between complete and incomplete dominance. A capital letter represents one of the incompletely dominant alleles. The same capital letter and a prime (‘) symbol represents the other incompletely dominant allele so that the two do not get mixed up. If an organism is incompletely dominant for a trait, the homozygous is written with 2 capital letters. For example, RR for red or R’R’ for white in carnations. The heterozygous individual shows both alleles expressed equally. If a carnation flower shows red and white incomplete dominance, it will show a flower that is pink (a blending of red and white). The genotype is denoted as RR’.

Incomplete Dominance Practice 7. In horses, the golden palomino color is a result of incomplete dominance. A horse can inherit the palomino color when they inherit both a brown (B) and a white (B’) allele. Show what would happen if a brown horse was crossed with a palomino horse.

Incomplete Dominance Practice 8. In parakeets, feather color is an incompletely dominant trait. You go to the pet store and find a clutch (group of baby birds) that is the following phenotypic ratios: 25% blue feathers, 50% green feathers, and 25% yellow feathers. What are the genotypes of the parent parakeets? Use a Punnett square to support your findings. 9. What would be the genotypic and phenotypic ratios if a blue parakeet was crossed with a green parakeet? 10. If a bird breeder wanted to have all green parakeets, what would be the best birds to breed? Use a Punnett square to support your answer.

In X-linked traits… What happens when the traits for an organism are controlled by the genes located on the X chromosome? They are called X-linked traits. The chromosomes are named for the letters they resemble. A female carries 2 "X" chromosomes (XX). A male carries one "X" and one "Y" (XY).

In X-linked traits… When a trait is X-linked it is ALWAYS connected to the X chromosome. NOTHING is written on the Y chromosome. If it is indicated as an X-linked trait, you must write the X chromosome and the dominant and recessive gene as a superscript. Note the male chromosome does not carry an allele for the X-linked characteristic, so no superscript is used. For Example:

X-linked Practice 11. Jenny and Steve are proud parents of a baby boy. They are wondering if their baby could be colorblind, a recessive, X-linked trait. Jenny is homozygous for normal vision and Steve is a colorblind male. Complete a Punnett Square to show the possibilities of their children. 12. Red eyes are dominant over white eyes in fruit flies. However, it was discovered that the appearance of white eyes is an X-linked recessive trait carried by the female. What are the possible offspring of a carrier female and a red-eyed male?

Pedigrees A pedigree is a chart or “family tree” that tracks the members of a family that have a certain trait. Geneticists use pedigrees to follow a human trait to learn how the trait was inherited. Female = Male = Affected = Unaffected = Carrier (if known) = Mating pair = line connecting Offspring are connected to their parents and go in birth order from left to right

Pedigrees Practice How to solve: On the pedigree, mark each person’s genotype. If a dominant individual’s genotype is unknown, write A-. You can figure out if they are heterozygous by looking at their offspring. Albinism is a recessive disorder affecting humans. If someone has this disorder, they cannot produce skin pigment, and have the genotype aa. The pedigree below shows people with albinism.

Pedigrees Practice a. How many people have the disorder? b. The original parents must have what genotypes? How did you figure this out? c. If the starred male has a baby with an affected female for albinism, what is the probability that the child will have the disorder? Use a Punnett square to justify your answer.