Activity 6: Chromosomes
INTRODUCTION
What can you tell by looking at a karyotype? In this assignment, you’ll use your powers of observation to put to work what you’ve learned about genetics.

INSTRUCTIONS
1. Review the information on chromosomes from the lectures and the textbook.

2. Complete the exercises below.

QUESTIONS

Question 1 (20 points)
Chromosomes form matching pairs, known as homologous pairs. You can see which chromosomes form a pair by examining their size, the pattern of bands and where the centromere is located. (The centromere appears as the skinny “waist” on the chromosome, where the pair attach is held together in an X shape during cell division.)

Look at the image below of homologous pairs of chromosomes.

5 sets of chromosomes that are homologous pairs

Now look at the image below. Examine the size and the banding patterns. Two of the pairs are homologous.

4 pairs of chromosomes. Pair 1 are the same size and band pattern. Pair 2 are the same size and different band pattern. Pair 3 are different sizes and band patterns. Pair 4 are the same size and band pattern.

Which pairs are homologous?

Type your answer here.

Question 2 (10 points)
Humans normally have 23 pairs of chromosomes. 22 of these are called autosomes and 1 pair is called the sex chromosomes. There are two sex chromosomes, which are known as X and Y. Genetic maleness is determined by the presence of a Y chromosome. If a Y chromosome is present, the individual is genetically male. If there is no Y chromosome, the individual is genetically female.

Look at the image below of the karyotype. Is it male or female?

A karyotype with one X and one Y chromosome

Type your answer here.

Question 3 (10 points)
Is the karyotype below male or female?

A karyotype with two X chromosomes and 3 copies of chromosome 21.

Type your answer here.

Question 4 (20 points – 10 points per question)
Look at the karyotype in Question 3 again.

· What is unusual about Chromosome 21?

· What is this genetic disorder known as? (Review ‘Chromosomal Disorders’ in your textbook.)

Type your answers here.

Question 5 (10 points)
Is the karyotype below male or female?

A karyotype with one X chromosome and zero Y chromosomes.

Type your answer here.

Question 6 (10 points)

Look at the karyotype in Question 5 again, especially the sex chromosomes.

Does this karyotype depict an individual with a normal karyotype? An individual with XYY syndrome? An individual with Turner syndrome? (Review the Lecture 7 article.)

Type your answers here.

Question 7 (20 points)
How can you immediately tell that the karyotype below is not from a human?

A karyotype with 23 autosomes, making 24 total pairs of chromosomes.

Type your answer here.