SOLUTIONS: STUDY QUESTIONS 1

1) List and describe three differences between mitosis and meiosis.

See handout or Fig. 13.7 of your text.

2) What are Mendel’s 1st and 2nd Laws, and what is the difference between them?

Mendel’s “1st” Law is the Law of Segregation. It states that alternate alleles at a locus account for phenotypic variation in inherited characters. The 2 alleles for each character segregate, during meiosis, ultimately ending up in separate gametes.

Mendel’s “2nd” Law is the Law of Independent Assortment. It states that 2 pairs of alleles will segregate independently of each other during meiosis, assuming that they are on separate chromosomes.

Application of both of Mendel’s Laws involves basic rules of probability. The Law of Segregation focuses on a single gene; the Law of Independent Assortment concerns patterns of segregation at 2 or more loci, and is predicated on the Law of Segregation.


3) If you cross individuals with these genotypes:

AA Bb Cc DD x Aa bb Cc Dd (assume no linkage of the 4 genes),

What is the probability of an offspring being Aa bb cc Dd?

(1 x _) x (1/2 x 1) x (1/2 x _) x (1 x _) = _ x _ x _ x _ = 1/32

What is the probability of an offspring being AA Bb CC DD?

_ x _ x _ x _ = 1/32

4) Tall bean plants (T) are dominant over short bean plants (t). Follow the cross from pure breeding parents through the heterozygotes and to the F2 generation.

P T T x t t

F1 T t x T t

F2 T T T t t t Genotype ratio 1 : 2 : 1
Phenotype ratio 3 : 1

If T is partially (incompletely) dominant, both the genotype and phenotype ratios in the F2 will be 1 : 2 : 1 (phenotypes will be
1 tall plant : 2 intermediate height plants : 1 short plant)