MCAT Biology : Recombination and Meiosis

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #1 : Recombination And Meiosis

How does meiosis incorporate genetic variation into the creation of haploid cells? 

Possible Answers:

The deletion and addition of certain DNA sequences in telophase I

The exchange of DNA sequences during prophase I

Crossing over in somatic cells

The random separation of entire tetrads during anaphase I

Correct answer:

The exchange of DNA sequences during prophase I

Explanation:

Meiosis only takes place in germ cells and is used to make haploid cells. In order to be genetically unique, chromosomes will exchange DNA sequences in a process called crossing over. This process of exchanging genetic material takes place during prophase I. Somatic cells are never involved in meiosis or crossing over, and DNA will never be deleted or added from the genome. Though separation of tetrads occurs during anaphase I and follows the law of independent assortment, the entire tetrad does not remain joined. This would result in nondisjunction.

Example Question #2 : Recombination And Meiosis

Which of the following statements are true about the significance of meiosis?

I. Enhances genetic variation

II. Maintains ploidy in sexually reproducing organisms

III. Allows for the potential repair of damaged DNA

Possible Answers:

II and III

I, II, and III

I only

I and II

Correct answer:

I, II, and III

Explanation:

All of the answers describe the diverse purposes of meiosis. Genetic variation is enhanced through the process of recombination and the separation of homologous chromosomes. Maintenance of ploidy in sexually reproducing organisms is achieved because gametes contain exactly half the number of chromosomes present in the mature organism. During fertilization, a gamete from a male and a gamete from a female combine and the result is a cell of normal ploidy. Meiosis also allows the cell an opportunity to repair damaged DNA via recombination between homologous chromosomes.

Example Question #2 : Recombination And Meiosis

Cellular division is an essential part of the cell cycle. When a cell divides it passes genetic information to daughter cells. The amount of genetic information passed on to daughter cells depends on whether the cell undergoes mitosis or meiosis. Mitosis is the most common form of cell division. All somatic cells undergo mitosis, whereas only germ cells undergo meiosis. Meiosis is very important because it produces gametes (sperm and eggs) that are required for sexual reproduction. Human germ cells have 46 chromosomes (2n = 46) and undergo meiosis to produce four haploid daughter cells (gametes).

A couple has ten children that look very different from one another. This phenomenon can be attributed to which of the following?

Possible Answers:

Cell differentiation

Ploidy of the gametes

Independent assortment

Crossing over

Correct answer:

Crossing over

Explanation:

One of the key characteristics of sexual reproduction is that it involves recombination. Recombination is the process by which genetic material is exchanged between chromosomes to create new alleles. This leads to innumerable possibilities for an offspring and is the reason why a couple can have ten unique children.

Recombination in meiosis occurs during prophase I. In prophase I genetic material between homologous chromosomes is exchanged in a process called crossing over. This exchange between genetic material leads to the ten children with different appearances.

Independent assortment helps explain why the offspring may not resemble the parent, but does less to explain why they do not resemble each other. During independent assortment, the homologous pairs are separated randomly such that a unique combination of maternal and paternal alleles are present in each cell after meiosis I. This can result in the expression of recessive alleles in the offspring that were not expressed in either parent.

Example Question #61 : Cell Biology, Molecular Biology, And Genetics

Which of the following is inherited via an autosomal recessive allele?

Possible Answers:

Huntington's disease

Cystic fibrosis

Hemophilia

Color-blindness

Correct answer:

Cystic fibrosis

Explanation:

Of the given answer options, only cystic fibrosis is inherited via an autosomal recessive inheritance pattern. Color-blindness and hemophilia are both X-linked recessive disorders. Huntington's disease is an autosomal dominant disorder.

Example Question #62 : Cell Biology, Molecular Biology, And Genetics

45 map units equals approximately what percent chance of recombination?

Possible Answers:

0%

90%

Not enough information is given.

45%

55%

Correct answer:

45%

Explanation:

1 map unit equals 1% chance of recombination; therefore, 45% is the best answer.

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