Download Forms of Dominance

Heading Forms of Dominance Genes can follow 3 different rules of dominance. For each rule, read the example and then try to use it on the problems that follow.
RULE #1: Complete Dominance If a gene uses the Complete Dominance rule (also called simple dominance), then the dominant allele completely masks (covers up) the recessive allele. EXAMPLE: If R= red flowers and r= white flowers, Then Rr = red flowers • The R completely hides the r. 1. The gene for tongue rolling shows complete dominance. Rolling your tongue is completely dominant over non-­‐rolling. Fill in the phenotypes to match each genotype. RR = _______________________________ Rr = ____________________________ rr = _______________________________ 2. Fruit flies can have white eyes (dominant) or red eyes (recessive). What color eyes will the following flies have? WW = _____________________________ Ww = ____________________________ ww = ______________________________ 3. One type of dwarfism is caused by a dominant gene (D), while the recessive gene (d) causes normal height. Which genotypes would be dwarfs and which would would be normal height? DD = _______________________________ Dd = _____________________________ dd= ________________________________ 4. A disease called sickle-­‐cell anemia is carried on a recessive allele. The dominant allele makes healthy red blood cells. Fill in the possible genotypes for each phenotype. Healthy red blood cells = _______ or ________ Sickle cell anemia = _________ RULE #2: Incomplete Dominance If a gene uses the Incomplete Dominance rule, then the dominant allele mixes with the recessive allele to make an in-­‐between version of the trait. EXAMPLE: If R= red flowers and r= white flowers, Then Rr = pink flowers • The flowers are a mixture of red and white 5. Straight hair (H) is incompletely dominant over curly hair (h). What kind of hair will each genotype have? HH = _______________________________ Hh = _____________________________ hh = _______________________________ 6. A lizard can have a long tongue (dominant) or a short tongue (recessive). If this trait uses incomplete dominance, which trait will each genotype have? TT = _______________________________ Tt = _____________________________ tt = _______________________________ 7. Insects can have curly antenna (dominant) or straight antenna (recessive). With incomplete dominance, what kinds of antenna will the following genotypes have? AA = _______________________________ Aa = _____________________________ aa = _______________________________ 8. A flower can show incomplete dominance for flower color. The dominant allele is for blue flowers. The recessive allele is for red flowers. What are the genotypes for each color of flower? Red: ______ Purple ______ Blue ______ RULE #3: Co-­‐dominance In co-­‐dominance, you have two dominant traits that are completely expressed at the same time. EXAMPLE: If R=red flowers and W=white flowers Then RW = both red and white flowers • The plant has both red and white flowers at the same time, because both traits get completely shown. • There is NO MIXING • Notice that each allele gets its own capital letter, since both are dominant. 9. One type of lizard shows co-­‐dominance for stripes. They can have red stripes (R) or blue stripes (B). Write the phenotype for each combination of alleles. RR = _______________________________ RB = _____________________________ BB = _______________________________ 10. Ducks can have long feathers (L) or yellow feathers (Y). If this is a co-­‐dominance trait, write the phenotype for each pair of alleles. YY = _______________________________ LL = _____________________________ LY= _______________________________ 11. Imagine a type of dog that has a co-­‐dominant gene. They might get an allele for mouse-­‐
chasing (M) or they might get an allele for cat-­‐chasing (C), or they might get both. Write the phenotype for each possible dog. MM = ______________________________ CC = _____________________________ MC = ______________________________ 12. Butterfly wings can be yellow(Y), red(R), or both yellow and red. Write the genotype for each color. Red Wings: ______ Yellow Wings: _____ Yellow AND Red Wings: ______ Try This! Make up your own problems. Write one problem that follows each rule. You can even make up silly or funny traits. J Make sure to answer each question to show what you know!