Genetics Practice Problems II - Simple Worksheet 1. For each genotype below, indicate whether it is heterozygous (He) or homozygous (HO) Aa_He Ee _He_ II ___HO mm __HO Cc _He__ Gg _Ho_ KK __HO oo ___HO Dd _He__ Hh _He LL ___HO VV ____HO 2. For each of the genotypes below determine what phenotypes would be possible. Yellow haired martians are dominant Long wood noses are dominant to to blue haired. short wood noses YY _____yellow Yy_____yellow________ yy________blue________ NN __________yellow Nn_________yellow__ nn ___________blue Smart students are dominant to dumb students. Or the otherway? Long whiskers in cats are recessive. SS __smart CC_____smart_ Ss __smart Cc_____smart_______ ss __dumb cc______dumb 3. For each phenotype below, list the genotypes (remember to use the letter of the dominant trait) Cleft chin is dominant to no cleft. Dimples are dominant to no dimples Cc_ cleft Cc__ Dimples Cc__ cleft Cc___ Dimples cc__ no cleft cc___ No dimples 4. Set up the Punnett squares for each of the crosses listed below. Round heads are dominant to square heads. RR Rr RR rr RR x Rr Rr Rr rr rr rr x Rr What percentage of the offspring will be round? 75% What percentage of the offspring will be round? 50% 5. In pea plants purple flowers are dominant to yellow flowers. If two purple flowered plants are crossed, what percentage of their offspring will be yellow flowered? 25% 6. A yellow flowered plant is crossed with a plant that is heterozygous for the trait. What percentage of the offspring will have purple flowers? 50% 7. Two plants, both heterozygous for the gene that controls flower color are crossed. What percentage of their offspring will have yellow flowers? 50% What percentage will have purple flowers? 50% 8. In rams, the allele for long horns is dominant. What genotype would a heterozygous short horned ram have? 75% What genotype would a pure breed short horned ram have? 25% What genotype would a long horned ram have? 50% SHOW ALWORK! 9. Dihybrid Cross. In a monohybrid cross, only one trait is examined. For example will a plant be tall or short. In a dihybrid cross, two traits are examined such as tall and yellow. We have two mice that are very fast and full of Action AA, Aa. (aa would be slow) They are also Brown BB, Bb (bb would be white) In a dihybrid cross, AaBb x AaBb, what fraction of the offspring will be homozygous for both recessive traits- meaning slow and white? This is where a punnett square helps Predicting the genotype of offspring : the gametes There are four possible combinations of gametes for the AaBb parent. Half of the gametes get a dominant A and a dominant B allele; the other half of the gametes get a recessive a and a recessive b allele. Both parents produce 25% each of AB, Ab, aB, and ab. Possible gametes for each AaBb parent : Do A’s first: AB, and Ab, then a’s aB, ab Since each parent has four different combinations of alleles in the gametes, there are sixteen possible combinations for this cross. Therefore we use a 4 square by 4 square Punnett Square. 10) A Horticulturalist (plant grower for your purposes) has two characters that she wants to consider when crossing two plants. She has two heterozygous plants for two traits. The two traits relate to shape and color. The plants are RrYy. Round Yellow. To solve this problem you need to know the gamets are RY (x) Ry (x) rY ( x ) ry. RR= round, rr=wrinkled YY=yellow, yy= green 11) List the number of purebred (RRYY)100% plants from this combination. 12) List the number of heterozygous combinations and what types of plants they produce. 13) List the number of rryy (wrinkled green) 14) A Martian has homozygous dominant green skin and heterozygous long arms. He mates with a Martian that has heterozygous green skin and homozygous long arms. What will their offspring look like? Use a Punnett square to figure this out. 15)Also, draw or describe the most common looking baby they will produce.
