University:
High School
Course:
High School Genetics
Academic year:

2020
Views:

442

Pages:

6
Author:

H Call

Homework #2 Genetics practice problems: Name: Key ****Remember to ALWAYS: 1. list alleles and traits for each problem ex: B-Black b=brown 2. list parental genotype 3. list possible gametes Part 1: Monohybrid crosses homozygous 1. In humans, free earlobes (F) is dominant over attached earlobes (f). If one parent is dominant for free earlobes, while the other has attached earlobes can they produce any children with attached earlobes? Parent phenotype Free-FF allached F F Parent genotypes Gametes Punnett f Answer? NO- All offspring are heterozygous. FF and phenotype is dominant Free earldoes 2. In humans widow's peak (W) is dominant over straight hairline (w). A heterozygous man for this trait marries a woman who is also heterozygous. parent genotype Ww f Ww W Www Ww gametes Ww List possible genotypes of their offspring. Ww- widows peak Ww widows peak Straight hair line List the phenotypie ratio for their children. W W ww widow's peak: strought 3:1 3. In guinea pigs, the allele for short hair is dominant. What genotype would a heterozygous short haired guinea pig have? What genotype would a purebreeding short haired guinea pig have? What genotype would a tong haired guinea pig have? Ss S S=shat S= long S 4. Show the cross for a pure breeding short haired guinea pig and a long haired guinea pig. Parent genotype Gametes SS SSX ss All heterozygous Dominant Shothain 5 What percentage of the offspring will have short hair? 100% 5. Show the cross for two heterozygous guinea pigs. Parent genotype: OS X S5 Gametess 3/4 = Short Yu-long What percentage of the offspring will have short hair? 75% What percentage of the offspring will have long hair? 250% S S Ss SS Part 2: Working Backwards to determine Parental Genotypes: Some times we only know about the offspring and we want to learn about the parents. If you have been paying attention, you should have started to notice a pattern. For example, when both parents are heterozygous the phenotypic ratio always comes out 3 to 1. If one parent is homozygous recessive and the other is heterozygous, the phenotypic ratio always comes out 1 tol. Keeping this in mind see if you can solve the next two problems. 6. A male tail pea plant is crossed with a female short pea plant. The resulting phenotype ratio is 1 tall: 1 short. Tall (T) is dominant. What are the genotypes of the P1 generation? must be heterozygous get short offspring Tall pea plant's genotype (male): X Short pea plant's genotype (female): t Possible gametes: Possible gametes: ++ Show your Punnett square to prove your answer. T-tall t-shart t Genotype ratio: tt 1:1 2:2 reduces to t t At Phenotype ratio: Shot: tall 1:1 t 7. A male tall pea plant is crossed with a female short pea plant. The resulting phenotype ratio is 100% tall. What are the genotypes of the P1 generation? if NO shout the dominant must be Homozygous. Tall pea plant's genotype (male): X Short pea plant's genotype (female): Possible gametes: Possible gametes: ++ Show your Punnett square to prove your answer. Genotype ratio: Te +=100% Phenotype ratio: Tall - 100% t t t t