Bio: Meiosis

If nondisjunction happens in anaphase II

1 daughter cell will have 2 copies, 1 will have no copies, and 2 will have 1 copy as normal

What 3 mechanisms contribute to variation in meiosis

1. Independent assortment of chromosomes 2. Crossing over 3. Random fertilization

What are the 4 key differences between mitosis and meiosis

1. Recombination in prophase I in meiosis 2. Homologous pairs allign on the metaphase plate in metaphase I of meiosis, chromosomes allign on the metaphase plate in mitosis 3. Separation of homologos at anaphase I in meiosis sister chromatids remains attached, splits in mitosis 4.Two rounds of cell division in meiosis, one in mitosis

If nondisjunction happens at anaphase I

2 of the daughter nuclei will have both members of that homologous pair, the other 2 will have none

aneuploidy

A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number.

Homologous pairs separate and move to opposite poles during

Anaphase I

Chromatids separate and chromosomes move to opposite poles during which stage of meiosis

Anaphase II

Trisomy and monosomy are examples of

Aneuploidy

Translocation

Change to a chromosome in which a fragment of one chromosome attaches to a nonhomologous chromosome

Polyploidy

Condition in which an organism has extra sets of chromosomes

The most common aneuploidy that allows survival is

Down syndrome (trisomy 21)

A triploid nucleus can undergo meiosis

False, it does not have an even number of chromosomes

Each somatic cell has 46 pairs of chromosomes

False, it has 23 pairs

Attachment points during crossing over is called centromere

False, it's the chiasmata

Haplontic organisms spend most of their time in the diploid stage

False, most time in the haploid stage

A tetrad is visible in prophase I and II

False, only in prophase I

During anaphase I of meiosis sister chromatids are separated

False, sister chromatids remain attached

During meiosis II we still see crossing over, and DNA duplication

False, there is no crossing over and no DNA duplication

Gametes are diploid

False, they are haploid

In metaphase I of meiosis individual chromosomes are positioned in the middle of the cell

False, this happens in mitosis

Matching pairs of chromosomes are called

Homologous chromosomes

Monozygotic is another name for

Identical twins

Contrast prophase I from prophase in mitosis

In prophase I homologous chromosomes stick together in pairs and crossing over occurs and the microtubules attach to the homologous chromosomes not the sister chromatids

The condition of missing a chromosome

Monosomy

How do we get identical twins

One egg is fertilized and early in the cell division the cell will divide in two producing two ppl

During meiosis, segments of nonsister chromatids can trade places. This recombination of maternal and paternal genetic material is a key feature of meiosis. During what phase of meiosis does recombination occur?

Prophase 1

Crossing over produces

Recombinant chromosomes

Diplontic organisms

Spend most of their time in the diploid stage. (ex. humans)

Synpasis

The lining up of homologous pairs of chromosomes so they can cross over

Synapsis

The pairing of replicated homologous chromosomes during prophase I of meiosis.

Most plants and some fungi display alternation of generations which means

They spend an equal amount of time in the haploid and diploid stage

In mitosis during anaphase what would happen to the chromatids

They would separate

What are the goals of meiosis

To reduce the number of chromosomes to haploid To ensure a full complement of chromosomes To generate genetic diversity

What is the condition of having an extra chromosome

Trisomy

Most common form of aneuploidy is

Trisomy 16

A tetraploid nucleus has an even number of chromosomes

True

During early prophase I homologous pairs align and undergo crossing over (recombination)

True

During prophase II the chromosomes condense and attach to the spindle microtubules

True

Each chromosome has one paternal and one maternal copy

True

In both mitosis and meiosis the chromosomes are duplicated during interphase

True

Single celled Eukaryotas and some multicellular organisms can reproduce asexual

True

The 4 chromatids of each pair of chromosomes form a tetrad or bivalent

True

The centromere is also where the spindle microtubules attach during both meiosis and mitosis

True

When starting from a diploid cell meiosis produces two haploid cells by the end of telophase 1

True

When starting from a diploid cell mitosis produces two diploid cells

True

How do we get fraternal (dizygotic) twins

Two eggs are fertilized

Recombination results in

Two recombinant chromosomes and two non recombinant chromosomes

Nondisjunction

When a homologous chromosome pair fails to separate at anaphase I or a pair of chromatids fails to separate at anaphase II

Meiosis starts with a single diploid cell and produces

four haploid cells

What is another name for dizygotic

fraternal twins

During prophase 1 of meiosis

homologous chromosomes stick together in pairs

A cell preparing to undergo meiosis duplicates its chromosomes during

interphase

Gametes-- eggs and sperm-- are made by a special sort of cell division called

meiosis

Each pair of chromosomes lines up independently of the other pairs in which phase of meiosis

metaphase I of meiosis

The correct order of events during meiosis is

prophase I, metaphase I, anaphase I, telophase I, cytokinesis, meiosis II

Meiosis occurs only in

reproductive organs

The part of the chromosome where two sister chromatids are joined

the centromere

Sexual reproduction

two parents give rise to offspring that have unique combinations of genes