Which statement cannot be inferred from the karyotype shown?

1. The cell contains DNA.
2. The cell contains 46 chromosomes.
3. The cell is diploid.
4. The cell is prokaryotic.

1. The DNA is found wrapped around histones to form nucleosomes, which further compact and ultimately form linear chromosomes. The prokaryotic genome is found as a loop and in eukaryotes as a double-stranded linear structure.
2. The DNA is wrapped around the nucleosomes to show a compact structure. The eukaryotes show a loop structure and prokaryotes show a double-stranded linear genome.
3. The genetic material shows ringed heterochromatin structure. The prokaryotes show multiple loops, and eukaryotes show a condensed chromatin.
4. The genetic material is wrapped around histones. The prokaryotes have a condensed structure in nucleoids, but eukaryotes have double-stranded linear structure.

Which statement about structure 1 on the karyotype is NOT true?

1. Structure 1 consists of homologous chromosomes.
2. The two parts of structure 1 will have genes in different loci.
3. The two parts of structure 1 originate from different parents.
4. The two parts of structure 1 will have slightly different sequences of nucleotides.

Based on the karyotype provided, the nondisjunction of which chromosome causes Down syndrome?

1. chromosome 21
2. chromosome 22
3. X chromosome
4. Y chromosome

1. anaphase - metaphase - prophase - cytokinesis
2. anaphase - prophase - metaphase - cytokinesis
3. prophase - anaphase - metaphase - cytokinesis
4. prophase - metaphase - anaphase - cytokinesis

In a study on cell division, researchers culture synchronously dividing human cells with thymidine, which causes the cells to arrest at the G₁ boundary. The cells are then placed in medium lacking thymidine, which releases the block, and the cells begin to divide again. Starting with Sample A and ending with Sample D, the DNA content of the cells is measured at different times after thymidine is removed. Results for four samples (A–D) are shown in the graph.

Figure 10.18

Which sample presents the expected results for cells in S phase?

1. sample A
2. sample B
3. sample C
4. sample D

1. 1. cell cycle progression
   2. p53
   3. p21
   4. CHK2
2. 1. p53
   2. p21
   3. CHK2
   4. cell cycle progression
3. 1. p21
   2. p53
   3. CHK2
   4. cell cycle progression
4. 1. CHK2
   2. p53
   3. p21
   4. cell cycle progression

Figure 10.20

The insulin growth factor (IGF-1) promotes cell proliferation as shown in the diagram. The expression of which protein in the diagram is controlled through negative feedback?

1. active Cdk4
2. cyclin D1
3. cyclin D1/Cdk4 complex
4. IGF-1

Explain why p53, p21, and CHK2 are considered tumor suppressor genes, not proto-oncogenes. Give an example of a proto-oncogene.

1. p53, p21, and CHK2 suppress the proteins that regulate the cell cycle, whereas proto-oncogenes, like phosphorylated Rb, help in cell cycle progression.
2. p53, p21, and CHK2 are negative cell cycle regulators, whereas Cdks are proto-oncogenes, which could cause cancer when mutated.
3. p53, p21, and CHK2 suppress the proteins that regulate the cell cycle, whereas Rb is considered a protooncogene, as it is the most primitive.
4. The three proteins help stop the formation of tumors, whereas Cdk’s are called proto-oncogenes because they are the most primitive of all.