Prelim+1+F23+KEY

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Apr 3, 2024

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BioMG2800 © Department of Molecular Biology and Genetics Cornell University 1 BIOMG 2800 Lectures in Genetics and Genomics First Preliminary Exam September 12, 2023 There are 11 pages to this exam, including this page. Be sure you have a complete set before you begin. Pages 10 and 11 are blank pages at the end. You may remove these and use them for scratch paper (you do not need to turn them in). Put all answers in the boxes or on the lines provided. Only answers in the boxes or lines will be graded. Please turn off all cell phones and other electronic devices. You may use a non-internet capable calculator. ___Answer Key_______ _______________ Name: LAST, FIRST Net ID 1. ________/10 2. ________/12 3. ________/20 4. ________/20 5. ________/20 6. ________/18 Total ________/100

BioMG2800 © Department of Molecular Biology and Genetics Cornell University 2 1. (10 Points) For the following statements, indicate whether they are true or false. XY chromosomes are not homologous to each other, but they can still pair during meiosis I, and undergo cross-overs (via the PAR regions). T For any given gene, the only case when parents (maternal and paternal) do not contribute equally to their offspring is when that gene is linked to another gene on the same chromosome. F When a single nondisjunction event occurs in meiosis, all 4 resulting gametes will always have an abnormal number of chromosomes F In humans, X-chromosome inactivation induces dosage compensation by randomly inactivating one of the X chromosomes in females. T Genes B and R are 20 map units apart. In an individual with genotype B r / b R , a gamete with genotype B R will be produced 10% of the time T

BioMG2800 © Department of Molecular Biology and Genetics Cornell University 3 2. (12 points) A farmer conducted several rounds of breeding to expand their Highland cow stocks. The cows had various hair lengths: long, medium, short, or curly. Each breeding scheme started with several pairs of true-breeding Highland cows of the hair types indicated in the table below. Each set of pairings yielded identical F1s of a single hair type (not recorded). The F1s from each breeding pair were then intercrossed (F1 X F1) to produce the F2 offspring with the hair types indicated in the table below. Original breeding pairs F2 Offspring (number) Long x Medium Long (15), Medium (42) Medium x Short Medium (33), Short (12) Medium x Curly Curly (15), Medium (45) Long x Short Long (27), Short (9) Short x Curly Curly (12), Short (39) Long x Curly Long (45), Curly (12) Using the data above provide a genetic explanation for how hair type is determined. For your answer, indicate (i) how many gene(s), (ii) how many alleles for each gene, and (iii) the dominant/recessive relationship(s) between all allele(s) for each gene involved. Use notation like A 1 > A 2 or A > a to indicate which allele is dominant. If two alleles are co/incompletely dominant to each other, use notation like A 1 = A 2 , etc. 1 gene (A) + 1 pt with 4 alleles (A l , A m , A s , A c ) + 2 pts A L = long, A M = medium, A S = short, A C = curly A M > A L > A S > A C +9 pts for the allelic relationships:

BioMG2800 © Department of Molecular Biology and Genetics Cornell University 4 3. (20 points) You have identified a new species of mongoose and determined that they are a diploid organism. You also determine this species uses the same mechanism of sex determination as humans (where females are homogametic and males are heterogametic). The five cells shown below (A-E) represent different cell types from the same animal. Assume, for this question, that nondisjunction (NDJ) only occurs during meiosis and that only a single NDJ event would occur. i. (3 pts) What is N for this organism? ____ 3 _____ ii. (2 pts) Is this animal a male, a female, or cannot determine? ___ female _____ iii. (15 pts) Match the single best description to each of the cells. 1. A cell in G1 2. A cell after DNA replication (before meiosis or mitosis) 3. A cell in metaphase of mitosis 4. A cell in metaphase of Meiosis I 5. A cell in metaphase of Meiosis II 6. A normal gamete 7. A gamete resulting from a single non-disjunction in meiosis I 8. A gamete resulting from a single non-disjunction in meiosis II. 9. A gamete resulting from a single non-disjunction in meiosis I or II (can’t tell). Cell A 2 Cell B 6 Cell C 9 Cell D 9 Cell E 1

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