chapter 13

Flashcards about Meiosis

What is Meiosis?

A nuclear division that leads to halving of chromosome number.

In many animals, what chromosomes do females have?

They have two X chromosomes.

In many animals, what chromosomes do males have?

They have an X and a Y chromosome.

What are autosomes?

Non-sex chromosomes.

What are homologous chromosomes or homologs?

Chromosomes of the same type.

What is a gene?

Section of DNA that influences a trait.

What are alleles?

Different versions of a specific gene.

What is Karyotype?

Identifies the number and types of chromosomes present in a species.

What is diploid?

Two homologs of each chromosome and two alleles of each gene.

What is haploid?

Only one of each type of chromosome and just one allele of each gene.

What is haploid number (n)?

Indicates the number of distinct types of chromosomes present.

What is a cell’s ploidy?

Indicates the number of complete chromosome sets it contains.

What does it mean to be Haploid?

Having one of each type of chromosome (n).

What does it mean to be Diploid?

Having two of each type of chromosome (2n).

What does it mean to be Polyploid?

Having more than two of each type of chromosome.

What is a Sex chromosome?

Chromosome associated with an individual’s sex.

What is an Autosome?

Any chromosome other than a sex chromosome.

What is an Unreplicated chromosome?

A chromosome that consists of one double-helical molecule of DNA packaged with proteins.

What is a Replicated chromosome?

A chromosome after DNA replication, consists of two identical chromatids, each containing one double-helical DNA molecule packaged with proteins.

What are Sister chromatids?

The two identical chromatids in a replicated chromosome.

What are Homologous chromosomes (homologs)?

Chromosomes that have the same genes in the same position and are the same size and shape.

What are Non-sister chromatids?

Chromatids on different members of a homologous chromosome pair.

What is a Bivalent?

Paired, replicated homologous chromosomes that exist during prophase one and metaphase one of meiosis.

What is the Haploid number?

The number of different types of chromosomes in a cell; symbolized n.

What is the Diploid number?

The number of chromosomes present in a diploid cell; symbolized 2n.

What is Ploidy?

The number of each type of chromosome or the number of haploid chromosome sets present; shown by the number in front of n (for example, 2n).

What happens during Meiosis I?

Each daughter cell has one set of chromosomes; a diploid parent produces two haploid daughter cells.

What happens during Meiosis II?

Each of the two daughter cells from meiosis I divides; the result is four haploid cells.

What happens during Early Prophase I?

Nuclear envelope begins to break down, chromosomes condense, spindle apparatus begins to form, and homolog pairs come together in a pairing process called synapsis.

What is a bivalent?

The structure that results from synapsis, consisting of two homologs.

What are non-sister chromatids?

The chromatids of the homologs.

What happens during Late Prophase I?

The two homologs become attached to microtubules from opposite poles of the spindle apparatus and the homologs begin to separate.

What are chiasmata?

Where exchange (crossing over) occurs between homologous non-sister chromatids.

What happens during Metaphase I?

Paired homologs line up at the metaphase plate; alignment of the homologs is random.

What happens during Telophase I?

The homologs finish migrating to the poles of the cell.

What is the key difference between mitosis and meiosis?

Homologs pair in meiosis but not in mitosis and the pairs separate during anaphase I resulting in a reduction division.

What is the result of meiosis?

Produces four haploid daughter cells that are genetically distinct from each other and from the parent cell.

What causes Meiosis to result in gametes with a chromosome composition different from each other and from the parent cells?

Independent shuffling of maternal and paternal chromosomes and crossing over during meiosis I.

What are the differences between asexual and sexual reproduction?

Asexual reproduction produces clones that are genetically identical to one another and to the parent, while sexual reproduction produces offspring with unique chromosome complements.

How does fertilization affect genetic variation?

Each gamete is genetically unique, a given sperm and egg come together at random, and random joining of gametes increases genetic variation in offspring.

What causes Down syndrome?

Caused by an extra copy of chromosome 21, also known as trisomy 21.

What leads to Gametes with Abnormal Chromosome Numbers?

If both homologs or both sister chromatids move to the same daughter cell.