Biology I Honors Semester II Exam Review – Step-by-Step Study Guidance

Q53. What is the following illustration, and why is it an important tool? Is this a normal set of human chromosomes? Why or why not? Is this a male or female? Can you identify a genetic disorder?

Background

Topic: Human Karyotypes and Chromosomal Analysis

This question is testing your understanding of karyotypes, how they are used to diagnose chromosomal abnormalities, and how to interpret the number and types of chromosomes present in a human cell. It also asks you to distinguish between male and female karyotypes and to identify possible genetic disorders.

Key Terms and Concepts:

• Karyotype: An organized profile of a person's chromosomes, arranged and numbered by size from largest to smallest.

• Autosomes: Chromosomes 1–22, which are the same in both males and females.

• Sex Chromosomes: The X and Y chromosomes that determine biological sex (XX = female, XY = male).

• Chromosomal Disorder: A condition caused by an abnormal number or structure of chromosomes (e.g., Down syndrome, Turner syndrome).

Step-by-Step Guidance

1. Examine the image and identify how many total chromosomes are present. Remember, a typical human karyotype has 46 chromosomes (23 pairs).

2. Check the arrangement of chromosomes: pairs 1–22 are autosomes, and the last pair is the sex chromosomes. Look for any missing or extra chromosomes in any pair.

3. Determine the sex of the individual by looking at the sex chromosomes: XX indicates female, XY indicates male.

4. Look for any abnormalities, such as an extra chromosome in any pair (e.g., three chromosomes at pair 21 indicates Down syndrome), or a missing sex chromosome (e.g., a single X indicates Turner syndrome).

Try solving on your own before revealing the answer!

Final Answer:

This is a human karyotype, which is used to analyze chromosome number and structure. In this karyotype, there are 45 chromosomes, with only one X chromosome and no Y chromosome, indicating Turner syndrome (a genetic disorder where a female is missing one X chromosome). This is not a normal set of human chromosomes, and the individual is female due to the presence of only an X chromosome.

Q72. By analyzing the cladogram above, which organism do all of the others share as a common ancestor? Did lungs evolve before or after feathers? Which organism evolved most recently?

Background

Topic: Evolutionary Relationships and Cladograms

This question is testing your ability to interpret a cladogram, which is a diagram that shows evolutionary relationships among different species based on shared characteristics and ancestry.

Key Terms and Concepts:

• Cladogram: A branching diagram showing the evolutionary relationships among species.

• Common Ancestor: The most recent ancestral species from which all organisms in the cladogram are descended.

• Derived Characteristic: A trait that evolved in the lineage leading up to a clade and that sets members of that clade apart from other individuals.

Step-by-Step Guidance

1. Start at the base (leftmost side) of the cladogram to identify the earliest ancestor shared by all organisms in the diagram.

2. Follow the branches and note where each derived characteristic (e.g., jaws, lungs, claws, feathers, fur) appears. This will help you determine the order in which traits evolved.

3. Locate the point where "lungs" and "feathers" appear on the diagram. Compare their positions to determine which evolved first.

4. Identify the organism at the tip of the most recent branch (furthest right) to determine which evolved most recently according to the cladogram.

Try solving on your own before revealing the answer!

Final Answer:

All the organisms share the hagfish as a common ancestor. Lungs evolved before feathers, as indicated by their positions on the cladogram. The chimp is the most recently evolved organism shown in this diagram.