Introduction to Cell Biology and Genetics: Exercises and Solutions
EXERCISES: Biological Variability and Characters
Exercise 1
What is cytokinesis?
Solution
The distribution of cytoplasm between two daughter cells and separation of two cells.
Exercise 2
Enter the name order of the four phases of mitosis.
Solution
Four phases: prophase, metaphase, anaphase, and telophase.
Exercise 3
Identify the stage that each of the following descriptions refers to:
- Disappearance of chromosomes and chromatin appearance.
- Duplication of genetic material.
- Union of chromosomes to mitotic spindle.
- Distribution of cytoplasm between the two cells.
- Chromatin condensation into chromosomes.
Solution
- Prophase: Disappearance of chromosomes and chromatin appearance.
- Interphase: Duplication of genetic material.
- Metaphase: Union of chromosomes to the mitotic spindle.
- Cytokinesis: Distribution of cytoplasm between the two cells.
- Prophase: Condensation of chromatin into chromosomes.
Exercise 4
Identify the type of chromosomes based on the following descriptions:
Chromosome A, Chromosome B, Chromosome C
Solution
- A: Metacentric
- B: Acrocentric
- C: Telocentric
Exercise 5
What is the karyotype?
Solution
It is the chromosome set in somatic cells (non-sex cells) of a species that displays the characteristics of each chromosome pair.
Exercise 6
The following drawings represent the chromosomes of somatic cells and gametes of a particular plant.
Cell A, Cell B, Cell C, Cell D
a. Indicate which of these drawings represent somatic cells and which represent gametes.
b. Indicate whether they represent haploid or diploid cells.
c. What is the characteristic number of chromosomes for this species?
Solution
a & b:
- Cell A: Gamete, Haploid
- Cell B: Somatic cell, Diploid
- Cell C: Gamete, Haploid
- Cell D: Somatic cell, Diploid
c. Six chromosomes (2n = 6).
Exercise 7
What are the characteristics of the nuclear material of gametes?
Solution
The nucleus of a gamete contains half the number of chromosomes characteristic of the species (one chromosome from each homologous pair).
Exercise 8
At what stage are homologous chromosomes located in the center of the cell during meiosis?
Solution
Metaphase I
Exercise 9
Which of the following statements are correct?
a) Sex cells have 2n chromosomes.
b) Somatic cells are diploid and have 2n chromosomes.
c) Half of a child’s chromosomes come from the father and the other half come from the mother.
d) In meiosis I, homologous chromosomes are separated.
e) In meiosis I, the two chromatids of a chromosome are separated.
f) In meiosis II, homologous chromosomes are separated.
g) In meiosis II, the two chromatids of a chromosome are separated.
Solution
b, c, d, and g are correct.
Exercise 10
What is the function of cell division by mitosis?
Solution
To produce daughter cells with the same genetic information as the mother cell. This allows for the adjustment of cell numbers to the needs of the organism.
Exercise 11
How are the arms of a submetacentric chromosome characterized?
Solution
The arms are unequal in length, but not excessively so.
Exercise 12
Explain the meaning of the term “haploid cell”.
Solution
This term refers to cells that have half the number of chromosomes characteristic of the species, i.e., the haploid number (n). Gametes are haploid cells.
Exercise 13
What are the results of cell division by meiosis in an organism?
Solution
Meiosis allows for:
- Maintaining the number of chromosomes across generations.
- Generating genetic variability in offspring.
- Regular sexual reproduction in sexually reproducing organisms.
Exercise 14
We are studying the plumage of a tropical bird. There are two alleles for this trait: the F allele, which determines dark green plumage, and the f allele, which determines light green plumage. In the population, there are only dark green and light green birds. Heterozygous individuals for this trait have dark green plumage. Answer the following questions:
a. What is the character we are studying?
b. Which alleles control this character?
c. What is the genotype and phenotype of heterozygous individuals?
d. What kind of inheritance pattern is this?
e. What genotype do individuals with light green plumage have?
Solution
a. We are studying the character of plumage color in a tropical bird species.
b. There are two alleles: F, which determines dark green color, and f, which determines light green color.
c. Heterozygous individuals have the genotype Ff and the phenotype (observable trait) of dark green plumage.
d. This is a case of dominant/recessive inheritance, as in heterozygous individuals, one of the two alleles (f) remains hidden in the phenotype.
e. The light green plumage is determined by the recessive allele (f), which is only expressed in the homozygous state (ff). Therefore, the genotype of individuals with light green plumage is ff.
Exercise 15
In mice, the gene that determines tail length is controlled by two alleles. The L allele, which determines a short tail, is dominant over the l allele, which determines a long tail.
a. What character are we studying?
b. State the two possible genotypes that mice with a short tail may have.
c. What will be the phenotype corresponding to the ll genotype?
Solution
a. We are studying the character: tail length in mice.
b. There are two possible genotypes that result in mice with short tails because the L allele (short tail) is dominant over the l allele (long tail): LL (homozygous dominant) and Ll (heterozygous).
c. Mice with the ll genotype will have long tails.