Opening Activity: Latin Root Word: Review of Old Information:

Transcription

1 Section: 3.4 Opening Activity: Latin Root Word: Review of Old Information: Name: 1. In seals, the allele for long whiskers (L) is dominant and the allele for short whiskers (l) is recessive. What are the genotypic and phenotypic ratios from a cross of a homozygous dominant and heterozygous seal for the above trait? SHOW ALL WORK!!! Genotypic Ratio: Phenotypic Ratio: 2. In the land of Oompah, red hair (H R H R ) is dominant to blue hair (H B H B ), and the heterozygous condition (H R H B ) produces purple hair. Blue hair is highly valued, in fact, blue haired Oompahs even get special benefits. Oscar Oompah has purple hair but he wants to find a wife that will give him blue haired children. What genotype for hair color should his wife have? What would be his second choice? Use punnet squares to prove your point!!! First Choice: Second Choice: 3. The color green is dominant to the color yellow. If a homozygous green pea plant is crossed with a homozygous yellow pea plant then what would be the genotypic and phenotypic ratios of the offspring? Genotypic ratio Phenotypic ratio 4. Two heterozygous white (brown fur is recessive) rabbits are crossed. What are the genotypic and phenotypic ratios of the offspring? Genotypic ratio Phenotyipc ratio 5. A breeder performs a testcross to determine whether an Alaskan malamute is homozygous dominant (DD) or heterozygous (Dd) for a recessive dward allele. Half the offspring appear dwarf. What is the genotype of the dog? Circle one: DD or Dd

2 New Information: Incomplete Dominance In some cases, an intermediate phenotype is shown Neither allele is dominant In snapdragons, flower color can be red, pink, or white. The heterozygous condition results in pink flowers (or an intermediate trait) A white snapdragon crossed with a red snapdragon produces all pink offspring Two pinks crossed together produce 1/4 white, 2/4 pink, and 1/4 red When dealing with incomplete dominance and codominance it does not matter what letter you use, as long as the heterozygous condition always denotes the intermediate trait. is a situation in which both alleles are equally strong and both alleles are visible in the hybrid genotype. When an phenotype occurs and no allele dominates, incomplete dominance results Complete the Punnet square for a cross between a homozygous red flowered snapdragon (RR) and a homozygous white-flowered snapdragon (rr). Give the ratio for the phenotype and the genotype? C R C R -red C r C r -white C R C r -pink Genotypic ratio Phenotypic ratio Codominance Both alleles can be expressed For example, red cows crossed with white will generate roan cows. Roan refers to cows that have red coats with white blotches. This phenotype might seem to support the blending theory. (The blending theory predicts pink F1 progeny.)

3 The F2 progeny, however, demonstrate Mendelian genetics. When the F1 roan individuals mate, the F2 progeny have a phenotypic ratio of 1 red:2 roan:1 white. This mode of inheritance is called incomplete dominance. The phenotypic outcomes for cow color and incomplete dominance in general can be explained biochemically. One allele of the gene codes for an enzyme that functions in the production of the red color. The other allele codes for the gene to make white color. If both alleles are present, both are expressed, resulting in a cow that has some red and some white. Mendel's laws are not compromised here, he just happened to find in peas examples of complete dominance only. Not all alleles are dominant and recessive. Some alleles are equally strong and are by the other. Alleles which are equally strong are said to be " ". Codominance When alleles are present, they are expressed in the phenotype. The hybrid is a of both alleles. When expressing codominant alleles, both alleles are represented by different letters. Complete the Punnet square for a cross between a black chicken (BB) and a white chicken (ww). Give the phenotype of the offspring? C B C B -Black C W C W -white C B C W -checkered What is the phenotype if the offspring? What is the name of the inheritance pattern in which both alleles are expressed equally? Blood Types and Codominance In humans, there are four blood types (phenotypes): A, B, AB, and O Blood type is controlled by three alleles. A, B, O O is recessive, two O alleles must be present for the person to have type O blood A and B are codominant. If a person receives an A allele and a B allele, their blood type is type AB Crosses involving blood type often use an I to denote the alleles - see chart.

4 When doing blood type crosses, you will need to know whether at type A or B person is heterozygous or homozygous. Type O's are automatically OO and type AB is automatically AB. Crosses are performed the same as any other. The blood type determines what antibodies are located within the blood. Type A blood has type B antibodies. If type B blood is put into their bodies, their immune system reacts as if it were a foreign invader, the antibodies clump the blood - 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, antibodies in the blood do not react to type O blood, they are called the "universal donors" Activity: Human blood types are determined by genes that follow the CODOMINANCE pattern of inheritance. There are two dominant alleles (I A and I B ) and one recessive allele (i). 1. Write the genotype for each person based on the description: a. Homozygous for the B allele 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 2. Pretend that Joe is homozygous for the type B allele, and Amy is type O. What are all the possible blood types of their baby?

5 3. Draw a Punnett square showing all the possible blood types for the offspring produced by a type O mother and an a Type AB father 4. Mrs. Clink is type A and Mr. Clink is type O. They have three children named Matthew, Mark, and Luke. Mark is type O, Matthew is type A, and Luke is type AB. Based on this information: a. Mr. Clink must have the genotype b. Mrs. Clink must have the genotype because has blood type c. Luke cannot be the child of these parents because neither parent has the allele. 5. Two parents think their baby was switched at the hospital. Its 1968, so DNA fingerprinting technology does not exist yet. The mother has blood type O, the father has blood type AB, and the baby has blood type B. a. Mother s genotype: b. Father s genotype: c. Baby s genotype: or d. Punnett square showing all possible genotypes for children produced by this couple e. Was the baby switched? 6. Two other parents think their baby was switched at the hospital. The mother has blood type A, the father has blood type B, and the baby has blood type AB. a. Mother s genotype: or b. Father s genotype: or c. Baby s genotype: d. Punnett square that shows the baby s genotype as a possibility: e. Was the baby switched? 7. Based on the information in this table, which man could not be the father of the baby? Justify your answer with a Punnett square. Name Mother Baby George John Dan Jack Blood Type Type A Type B Type O Type AB Type A Type B

6 8. Based on the information in this table, which man could not be the father of the baby? Justify your answer with a Punnett square. Name Mother Baby George John Dan Jack Blood Type Type O Type AB Type O Type AB Type A Type B 9. Explain why blood type data cannot prove who the father of a baby is, and can only prove who the father is not.