Chapter 13: Meiosis and Sexual Life Cycles

Asexual Reproduction

When a single individual is the only parent and passes copies of all of its genes to its offspring without gamete fusion

Sexual Reproduction

When two parents give rise to offspring that have unique combinations of genes from the two parents because of gamete fusion

Gametes

Vehicles that transmit genes from one generation to the next

Homologous Chromosomes

Two chromosomes composing a pair that have the same length, centromere position, and staining pattern

What determines whether you are genetically male or female?

Sex chromosomes, also known as the X and Y chromosomes determine whether you are genetically male or female.

Autosomes

The other 22 chromosomes that aren’t sex chromosomes.

Diploid Cell

A cell that has 2 sets of chromosomes

Haploid Cell

A cell that has 1 set of chromosomes

Zygote

A diploid cell produced by the union of haploid gametes during fertilization; fertilized eggs

Where do most of the differences between Meiosis and Mitosis?

Majority of the differences occur during Meiosis I

Synapsis

Homologous chromosomes loosely pair up; aligned gene by gene

Tetrads

A group of 4 chromosomes

Crossing Over

Non-sister chromatids that exchange DNA segments

Chiasmata

X shaped regions where crossing over occured

Why is crossing over of benefit to the organism’s species?

Crossing over is beneficial because it produces recombinant chromosomes which combine DNA from each parent. (Helps genetic variation by combining DNA from 2 parents into 1 chromosome)

Prophase I

Chromosomes condense, homologous pairs find each other (synapsis) to form tetrads, and they exchange genetic material through crossing over, creating genetic variation; the nuclear envelope breaks down, and spindle fibers form, setting the stage for chromosome separation in later stages.

Metaphase I

Tetrads line up at the metaphase plate, with one chromosome facing each pole. Microtubules from one pole are attached to the kinetochore o of one chromosome of each tetrad. Microtubules are attached to the kinetochore of other chromosomes.

Anaphase I

Pairs of homologous chromosomes separate, 1 chromosome moves toward each pole guided by spindle apparatus, sister chromatids remain attached at the centromere and move together toward the pole.

Telophase I

Each half of the cell has a haploid set of chromosomes, each chromosome has 2 sister chromatids, cytokinesis occurs at the same time forming 2 daughter cells.

What is created at the end of Meiosis I?

2 haploid daughter cells are created.

What is created at the end of Meiotic Division?

There are 4 daughter cells, each with haploid set of unreplicated chromosomes. Each daughter cell is genetically different from the other daughter cells and parent cell.

Does every zygote have a unique identity?

Yes, every zygote have a unique identit.

What are changes in an organism’s DNA and also the original source of genetic diversity?

Mutations are changes in an organism’s DNA and also the original source of genetic diversity.

What are alleles?

Alleles are different versions of genes

What is independent assortment?

Independent assortment is the random alignment of separation of homologous chromosome pairs during Metaphase I.

What is random fertilization?

Random fertilization is a process that adds to genetic variation because any sperm can fuse with any ovum.

Does crossing over increase genetic variation?

Crossing over increases genetic variation.