BIOL 189: Chapter 9 - Sexual Reproduction and Meiosis

What is a gene?

A segment of DNA that contains genetic information.

What are chromosomes?

Distinct structures that package DNA.

How many chromosomes do humans normally have?

46 chromosomes arranged in 23 pairs.

What are homologous chromosomes?

Pairs containing the same genes, one maternal and one paternal.

What are autosomes?

Chromosome pairs 1-22.

What are sex chromosomes?

The 23rd chromosome pair.

What is the difference between haploid and diploid?

Haploid (N) has one chromosome set; diploid (2N) has two.

What are the chromosome numbers in human sperm and egg cells?

23 chromosomes each; both are haploid (N).

What are somatic cells?

Body cells that are diploid and produced through mitosis.

What are gametes?

Reproductive cells (sperm and eggs) produced through meiosis.

What is the difference between sexual and asexual reproduction?

Sexual reproduction uses two parents and creates genetic diversity. Asexual reproduction uses one parent and produces clones.

What happens during mitotic cell division?

DNA duplicates once, followed by one division, producing two genetically identical cells.

How many cell divisions occur during meiosis?

Two divisions: meiosis I and meiosis II.

What separates during meiosis I?

Homologous chromosome pairs separate.

What separates during meiosis II?

Sister chromatids separate and become daughter chromosomes.

What is the final result of meiosis?

Four haploid cells, each with one chromosome set.

What is crossing over (recombination)?

Exchange of DNA between homologous chromosomes during prophase I; it increases genetic diversity.

What is independent assortment?

Random alignment of homologous chromosome pairs during metaphase I.

How does random fertilization increase genetic diversity?

Any sperm can fuse with any egg, creating unique chromosome combinations.

What is nondisjunction?

An error in meiosis where chromosomes fail to separate properly, causing abnormal chromosome numbers.

What is the difference between trisomy and monosomy?

Trisomy (n+1) means an extra chromosome; monosomy (n−1) means one is missing.

What is aneuploidy?

Having an extra or missing individual chromosome.

What is polyploidy?

Having extra complete sets of chromosomes.

Which two disorders are examples of autosomal trisomy?

Trisomy 21 (Down syndrome) and trisomy 18 (Edwards syndrome).

What causes Turner syndrome?

Having only one X chromosome.

What causes Klinefelter syndrome?

Having XXY sex chromosomes.

How does maternal age affect aneuploidy risk?

The risk of aneuploidy increases with the mother's age.

When does DNA duplication occur before meiosis?

During the S phase of interphase.

What happens during metaphase in mitosis compared with meiosis I?

Mitosis: individual chromosomes line up single-file. Meiosis I: homologous pairs line up together.

What is a zygote?

A diploid cell formed when a sperm fertilizes an egg.

What happens when a parent cell reproduces?

It splits into two identical daughter cells.

What must happen to DNA before cell division?

The parent cell's DNA must be duplicated.

What do daughter cells receive after mitotic division?

A full copy of the parent cell's DNA.

Why is mitotic cell division called mitosis?

It involves separation of the two copies of DNA.

What are cells produced through mitotic cell division called?

Somatic cells.

What does it mean when daughter cells are clones?

They are genetically identical to their parent cell.

Does every species have the same chromosome number?

No. Chromosome numbers vary between species.

Where do the two chromosomes in a human homologous pair come from?

One comes from the mother and one from the father.

What do homologous chromosome pairs have in common?

They contain the same genes but may have different alleles.

What are alleles?

Different versions of the same gene.

What does N represent in chromosome notation?

One set of chromosomes (haploid).

What does 2N represent in chromosome notation?

Two sets of chromosomes (diploid).

How many chromosome sets do asexually reproducing organisms have, according to the lecture?

One set; they are haploid.

How many chromosome sets do sexually reproducing organisms have?

Two sets; they are diploid.

Which cells are produced by mitosis?

Somatic cells.

Which cells are produced by meiosis?

Gametes (sperm and egg cells).

Which cells undergo mitosis?

Somatic cells.

Which cells undergo meiosis?

Germ-line cells.

How many chromosomes do human sperm and eggs have instead of homologous pairs?

23 individual chromosomes instead of 23 pairs.

Are human sperm and egg cells diploid or haploid?

Haploid (N).

Are human somatic cells diploid or haploid?

Diploid (2N).

Are bacteria haploid or diploid, according to the lecture?

Haploid.

What happens when a sperm fuses with an egg?

A zygote is formed.

What happens to chromosome number during meiosis?

It is reduced by half.

What process allows a zygote to grow and develop?

Mitosis produces additional cells.

How many times does DNA duplicate before mitosis or meiosis?

Once, during interphase.

How many cell divisions occur in mitosis?

One cell division.

How many cell divisions occur in meiosis?

Two cell divisions.

What happens to chromosomes during interphase?

DNA duplicates during S phase; DNA is normally loose chromatin.

What happens during prophase of mitosis?

Chromosomes condense, centrosomes move to opposite poles, and the nuclear envelope breaks down.

What additional event happens during prophase I of meiosis?

Recombination (crossing over) between homologous chromosomes.

What happens during metaphase of mitosis?

Individual chromosomes line up single-file along the metaphase plate.

What happens during metaphase I of meiosis?

Homologous chromosome pairs line up along the metaphase plate.

What happens during anaphase of mitosis?

Sister chromatids separate and become daughter chromosomes.

What happens during anaphase I of meiosis?

Homologous chromosome pairs are pulled apart.

What happens during telophase of mitosis?

Daughter chromosomes enter two nuclei and chromosomes decondense.

What happens during telophase I of meiosis?

Chromosomes enter two nuclei and decondense.

What is cytokinesis?

The division of the cell's cytoplasm.

What happens during prophase II of meiosis?

Chromosomes condense, centrosomes move to opposite poles, and the nuclear envelope breaks down.

How many chromosomes and chromatids are in a human cell during prophase II?

23 chromosomes containing 46 sister chromatids.

How do chromosomes line up during metaphase II?

Individual chromosomes line up single-file along the metaphase plate.

How many chromosomes and chromatids are present during human metaphase II?

23 chromosomes containing 46 sister chromatids.

What happens during anaphase II?

Sister chromatids separate and move to opposite poles as daughter chromosomes.

How many daughter chromosomes are present during human anaphase II?

46 total; 23 move toward each pole.

What happens during telophase II?

Daughter chromosomes enter nuclei and decondense.

How many daughter chromosomes are in each human nucleus during telophase II?

23 daughter chromosomes.

How many haploid cells result after meiosis is complete?

Four haploid cells.

How many copies of each chromosome do mitosis-produced cells contain?

Two copies of each chromosome in humans.

How many copies of each chromosome do meiosis-produced cells contain?

One copy of each chromosome.

When does chromosome duplication occur in cells preparing for meiosis?

During the S phase of interphase.

What is another name for chromosomal crossover?

Recombination.

During which stage of meiosis does chromosomal crossover occur?

Prophase I.

Why does crossing over increase genetic diversity?

It exchanges DNA between homologous chromosomes, creating new combinations.

What determines how homologous pairs line up during metaphase I?

Random alignment, known as independent assortment.

Does the alignment of one homologous pair affect another pair?

No. Each pair positions itself independently.

Can a gamete receive all maternal or all paternal chromosomes?

Yes, but most gametes contain a random mixture.

What is the approximate number of chromosome arrangements possible in one human gamete?

2^23, or approximately 8 million.

How many chromosome combinations can result from random fertilization?

Approximately 70 trillion possible combinations.

What does random fertilization mean?

Any sperm can fuse with any egg.

Are the X and Y chromosomes homologous?

No, they are not homologous.

What is the difference between genetic diversity and cloning?

Sexual reproduction creates genetic diversity; asexual reproduction produces genetically identical clones.

What happens during nondisjunction in meiosis I?

Homologous chromosomes fail to separate; all resulting gametes are abnormal.

What happens during nondisjunction in meiosis II?

Sister chromatids fail to separate; half the resulting gametes are abnormal.

What does n+1 represent?

Trisomy: a cell has one extra chromosome.

What does n−1 represent?

Monosomy: a cell is missing one chromosome.

What is Trisomy 21?

Down syndrome.

What is Trisomy 18?

Edwards syndrome.

What chromosome combination causes Turner syndrome?

A single X chromosome.

What chromosome combination causes Klinefelter syndrome?

XXY.

What is the difference between aneuploidy and polyploidy?

Aneuploidy involves extra or missing individual chromosomes; polyploidy involves extra complete chromosome sets.