11.3 Assessment Answers

What is a karyotype? Images of chromosomes stained during metaphase 2. How many pairs of autosomes do humans have? 22 How many pairs of sex chromosomes? 1

3. How are chromosomes arranged in a karyotype 3. How are chromosomes arranged in a karyotype? They are arranged in decreasing size. They are matched up using banding patterns and centromere position.

4. Where are telomeres located and what do they do 4. Where are telomeres located and what do they do? Protective caps on the ends of each chromosome. They function to protect the genetic material located near end of chromosome.

5. What is nondisjunction 5. What is nondisjunction? The improper separation of sister chromatids during meiosis. When it occurs, what happens to the chromosome number? The wrong number of chromosomes result. Instead of two, there may be one or three

6. What is trisomy? A cell with three copies of a chromosome instead of two 7. What is monosomy? A cell with one copy of a chromosome instead of two

8. Describe the gametes that result after nondisjunction in meiosis I. Four gametes, all abnormal( 2 trisomy, 2 monosomy) Describe the gametes that result after nondisjunction in meiosis II. Two gametes normal , 1 gamete monosomy, 1 gamete trisomy

10. A person with Down syndrome has a problem with which chromosome 10. A person with Down syndrome has a problem with which chromosome? 21 What is the problem? 3 copies of chromosome 21 11. What are some characteristics that occur in people with Down syndrome? Distinctive facial features, short stature, heart defects, and mental disability.

What is the name of the disorder that has XO in the sex chromosomes? Turner’s syndrome 13. What do the chromosomes look like for Kleinfelter’s syndrome? They have xxy for the 23rd pair of chromosomes

14. Why do couples decide to have fetal tests performed 14. Why do couples decide to have fetal tests performed? To see if they’re child might have a genetic disorder or chromosomal abnormality 15. Why are fetal tests only performed when they are absolutely necessary? They could cause harm to mother or fetus

What does a geneticist want to discover when looking at a karyotype? He/she will look to make sure the fetus has 2 copies of each chromosome on every chromosome. If the child does not, there will be a genetic problem.

Why is a missing section of the X or Y chromosome a bigger problem in males than missing sections would be in one of the x chromosomes in females? Since males only receive one X chromosome, missing a section that contains vital information could be deadly. With females who have two X’s, deletion in one x could be made up by the other x chromosome

Create a karyotype of a female organism in which 2n=8 showing trisomy of chromosome 3. For humans 2n=46. In this case we will have 4 pairs of chromosomes showing 3 chromosomes on chromosome 3

19. Hypothesize why chromosomes need telomeres 19. Hypothesize why chromosomes need telomeres. To protect the chromosome during cell division from losing genetic information at the end of the chromosome

Explain why a girl with Turner’s syndrome has red green color blindness even though both of her parents have normal vision. Females normally inactivate an X chromosome, so a girl with Turner’s only has one X chromosome, which has the allele for colorblindness. Her mom was normal but carried the gene.