Q: Which formula is used to calculate recombination frequency, and what does $$1\ centimorgan\ (cM)$$ represent?

$$\text{Recombination frequency} = \frac{\text{Number of recombinant offspring}}{\text{Total number of offspring}} \times 100$$; $$1\ cM$$ represents a 1% recombination frequency.

Question 1

Which of the following best explains why sexual reproduction provides a selective advantage to populations living in changing or unpredictable environments?

Accepted Answer

It increases genetic diversity, allowing populations to adapt more readily to environmental changes.

Question 2

In human cells, which of the following correctly describes the difference between diploid ($$2n) $$and haploid ($$n) $$cells?

Accepted Answer

Diploid cells contain two sets of homologous chromosomes, while haploid cells contain one set.

Question 3

During meiosis, how many times does DNA replicate, and how many daughter cells are produced at the end of Meiosis II?

Accepted Answer

DNA replicates once during S phase, and four daughter cells are produced.

Question 4

Which of the following correctly lists the five substages of Prophase I in order and matches each with its major event?

Accepted Answer

Leptotene (chromosome condensation), Zygotene (synapsis begins), Pachytene (crossing over), Diplotene (chiasmata visible), Diakinesis (terminalization of chiasmata)

Question 5

What is the primary structural function of the synaptonemal complex during meiosis?

Accepted Answer

It holds homologous chromosomes together during synapsis, facilitating crossing over.

Question 6

During Anaphase I of meiosis, why do sister chromatids remain attached while homologous chromosomes separate?

Accepted Answer

A protective protein called shugoshin prevents centromeric cohesin from being cleaved.

Question 7

Given a human cell ($$2n = 46$$), what are the chromosome number ($$n) $$and DNA content ($$C) at $$the end of Telophase II of meiosis?

Accepted Answer

$$n = 23$$, $$C = 1C$$

Question 8

If nondisjunction occurs during Meiosis I in human oogenesis, what percentage of resulting gametes will have an abnormal chromosome number?

Accepted Answer

100%

Question 9

Why does oogenesis in humans produce polar bodies instead of four equal functional gametes, as seen in spermatogenesis?

Accepted Answer

To concentrate cytoplasmic resources into a single oocyte, maximizing its developmental potential.

Question 10

At which two points do human oocytes arrest during development, and what molecular factors enforce Metaphase II arrest until fertilization?

Accepted Answer

Prophase I and Metaphase II; Cytostatic Factor (CSF) and Emi2 maintain Metaphase II arrest.

Question 11

How do the physical movements of chromosomes during Meiosis I explain Mendel’s Law of Segregation?

Accepted Answer

Homologous chromosomes separate into different gametes, ensuring each gamete receives only one allele of each gene.

Question 12

Which formula is used to calculate recombination frequency, and what does $$1\ centimorgan\ (cM)$$ represent?

Accepted Answer

$$	ext{Recombination frequency} = \frac{	ext{Number of recombinant offspring}}{	ext{Total number of offspring}} 	imes 100$$; $$1\ cM$$ represents a 1% recombination frequency.

Question 13

During the Double-Strand Break Repair (DSBR) model in meiosis, which endonuclease creates deliberate double-strand breaks in DNA during Prophase I?

Accepted Answer

SPO11

Question 14

What is the role of recombinase proteins RAD51 and DMC1 during strand invasion in meiotic recombination?

Accepted Answer

They facilitate the invasion of single-stranded DNA ends into homologous duplex DNA to initiate homologous recombination.

Question 15

Which double-stranded DNA crossover structure forms prior to resolution during the DSBR model of meiotic recombination?

Accepted Answer

Holliday junction

Question 16

A geneticist observes that two genes are inherited together more often than not. Which of the following best explains this observation?

Accepted Answer

The genes are linked and located close together on the same chromosome.

Question 17

A patient is diagnosed with Down syndrome due to trisomy 21. Which meiotic error most likely caused this condition, and during which stage?

Accepted Answer

Nondisjunction during Meiosis I, resulting in gametes with an extra chromosome 21.

Question 18

Which of the following best describes the Law of Independent Assortment as explained by chromosome behavior during meiosis?

Accepted Answer

Different pairs of homologous chromosomes align and separate independently during Metaphase I.

Cell Biology Study Guide: Meiosis, Chromosomes, and Genetic Recombination

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