AP Biology questions on Chromosomal Inheritance

🧬 Quick Study Guide

• 🔬 Chromosomal Theory of Inheritance: Genes have specific positions (loci) on chromosomes, and it is the chromosomes that undergo segregation and independent assortment.
• 👨‍⚕️ Thomas Hunt Morgan's Experiments: Used fruit flies (Drosophila) to show genes are located on chromosomes; specifically, linked genes are on the same chromosome.
• 🔗 Linked Genes: Genes located close together on the same chromosome tend to be inherited together.
• 🔄 Recombination Frequency: The percentage of recombinant offspring; used to estimate the relative distance between linked genes. Formula: $\frac{\text{Number of recombinants}}{\text{Total number of offspring}} \times 100$
• 🗺️ Genetic Maps: Use recombination frequencies to create a linkage map, which shows the order of genes on a chromosome. Map units (centimorgans) represent 1% recombination frequency.
• ❌ Sex-Linked Genes: Genes located on sex chromosomes (X or Y). X-linked recessive disorders are more common in males.
• 👯 Nondisjunction: Failure of chromosomes to separate properly during meiosis, resulting in aneuploidy (abnormal chromosome number).
• 📊 Aneuploidy: Conditions like Trisomy 21 (Down Syndrome), Monosomy X (Turner Syndrome), and XXY (Klinefelter Syndrome) result from aneuploidy.

🧪 Practice Quiz

1. Which of the following statements best describes the chromosomal theory of inheritance?
   1. A) Genes are located on proteins.
   2. B) Genes are located on chromosomes.
   3. C) Genes are located in the cytoplasm.
   4. D) Genes are located in the mitochondria.
2. What is the primary reason that linked genes are inherited together?
   1. A) They are located on different chromosomes.
   2. B) The distance between them is very large.
   3. C) They are located close together on the same chromosome.
   4. D) They are always dominant.
3. If two genes are located on the same chromosome and have a recombination frequency of 20%, what does this indicate?
   1. A) The genes are unlinked.
   2. B) The genes are very close to each other.
   3. C) 20% of the offspring will show recombinant phenotypes.
   4. D) 80% of the offspring will show recombinant phenotypes.
4. A human female has one X chromosome (XO). What condition does she have?
   1. A) Klinefelter syndrome
   2. B) Down syndrome
   3. C) Turner syndrome
   4. D) Hemophilia
5. What process results in aneuploidy?
   1. A) Independent assortment
   2. B) Crossing over
   3. C) Nondisjunction
   4. D) DNA replication
6. In fruit flies, gray body (G) is dominant to black body (g), and long wings (L) are dominant to short wings (l). In a testcross of a fly heterozygous for both genes, the offspring were: gray-long 40%, gray-short 10%, black-long 10%, black-short 40%. What is the recombination frequency between these genes?
   1. A) 10%
   2. B) 20%
   3. C) 40%
   4. D) 80%
7. A man with hemophilia (a recessive, sex-linked condition) has a daughter who is phenotypically normal. However, she has a son with hemophilia. What are the genotypes of the man, his daughter, and her son?
   1. A) Man: XHY; Daughter: XHXH; Son: XHY
   2. B) Man: XhY; Daughter: XHXh; Son: XhY
   3. C) Man: XHY; Daughter: XHXh; Son: XhY
   4. D) Man: XhY; Daughter: XHXH; Son: XHY