Cell Division in Biology

To reproduce their own kind

Daughter cells are genetically identical to each other and the parent cell

Asexual reproduction produces offspring with identical genes, while sexual reproduction produces offspring with unique genes

Single circular DNA molecule

Binary fission

To grow and develop from a fertilized egg

Beginning at a single origin of replication

Somatic cells have a different number of chromosomes than gametes

To maintain chromosome structure and control gene activity

It becomes highly compact and visible with a microscope

Two identical daughter cells with the same number of chromosomes

An ordered sequence of events that extends from the time a cell is first formed from a dividing parent cell until its own division

Division of the nucleus

Anaphase II

Locus

Four haploid gametes

To increase genetic variation

Mitosis

Interphase

A diploid zygote

Both mitosis and meiosis

Cytokinesis

A zygote with 70 trillion diploid combinations

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gametes with an altered number of chromosomes

All of the above

Trisomy 21

The Y chromosome is smaller than the X chromosome

Attachment of a segment to a nonhomologous chromosome

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It increases genetic variation

2^n possible combinations of chromosomes

Cell division is essential for reproduction, growth, and cell renewal and repair in living organisms.

Cell division ensures genetic identity by duplicating the chromosomes and sorting the new sets of chromosomes into the resulting pair of daughter cells.

Asexual reproduction produces offspring with no genetic variation, while sexual reproduction produces offspring with unique combinations of genes from two parents.

The chromosome of a prokaryote is typically a single circular DNA molecule.

Cell division is necessary for growth, cell renewal and repair, and production of gametes (sperm and egg cells) in multicellular organisms.

Cell division enables organisms to reproduce their own kind by producing genetically identical daughter cells that can grow and develop into new individuals.

Bacterial chromosomes replicate by beginning at the origin of replication, and the cell elongates while the chromosome is replicating. The outcome is two daughter chromosomes that actively move apart, and the plasma membrane pinches inward, dividing the cell into two.

Somatic cells are diploid (2n) and have two sets of chromosomes, whereas gametes are haploid (n) and have half as many chromosomes as somatic cells. Somatic cells divide by mitosis, and gametes divide by meiosis.

Eukaryotic chromosomes are composed of chromatin, consisting of one long DNA molecule and proteins that help maintain the chromosome structure and control gene activity. To prepare for division, chromatin becomes highly compact and visible with a microscope.

Chromosome duplication in eukaryotic cells results in sister chromatids, which are joined together along their lengths by cohesins and are cinched especially tightly at the centromere. During cell division, the sister chromatids separate from each other and sort into separate daughter cells.

The cell cycle is an ordered sequence of events that extends from the time a cell is first formed from a dividing parent cell until its own division. The two stages are the growing phase and the division phase.

Prokaryotic cells have a single, circular chromosome, whereas eukaryotic cells have multiple, linear chromosomes with more complex structures. Prokaryotic cells replicate their chromosomes in a simpler process compared to eukaryotic cells.

In prophase, chromatin condenses into chromosomes, and the nuclear envelope breaks down. This stage prepares the cell for chromosome separation in both mitosis and meiosis.

Homologous chromosomes contribute to genetic variation through crossing over, which increases genetic diversity by creating new combinations of alleles.

In mitosis, chromosomes line up at the metaphase plate as identical sister chromatids. In meiosis I, pairs of homologous chromosomes line up at the metaphase plate.

The two consecutive cell divisions in meiosis (meiosis I and meiosis II) increase genetic variation by allowing for independent assortment and crossing over, resulting in unique haploid gametes.

The centromere is the specialized region on a chromosome that attaches to microtubules, allowing for proper chromosome separation during mitosis and meiosis.

Diploid organisms have a life cycle that begins with a diploid zygote, followed by mitosis and growth, whereas haploid organisms have a life cycle that begins with a haploid gamete and involves meiosis to produce haploid offspring.

In anaphase, sister chromatids or homologous chromosomes separate, leading to the distribution of genetic material to daughter cells in mitosis and meiosis.

Mitosis produces genetically identical diploid cells, whereas meiosis produces genetically unique haploid gametes, resulting in genetic variation in offspring.

Cytokinesis is the division of the cytoplasm, which completes the cell division process in both mitosis and meiosis.

These mechanisms contribute to genetic diversity by increasing the number of possible genetic combinations in offspring, resulting in genetic variation and diversity.

Independent assortment of chromosomes contributes to genetic variation by allowing each pair of chromosomes to align independently at the metaphase plate, resulting in 2^n possible combinations of chromosomes. This, combined with crossing over, produces approximately 70 trillion possible diploid combinations.

Crossing over, or genetic recombination, increases genetic variation by exchanging corresponding segments between nonsister chromatids of homologous chromosomes. In humans, an average of 1-3 crossover events occur per chromosome pair, further increasing genetic variability.

Nondisjunction during meiosis results in the failure of chromosomes or chromatids to separate normally, producing abnormal gametes with altered chromosome numbers. This can lead to zygotes with abnormal chromosome numbers, resulting in genetic disorders or abnormalities.

Trisomy 21, also known as Down syndrome, is a genetic disorder characterized by the inheritance of three copies of chromosome 21. Symptoms include characteristic facial features, short stature, heart defects, susceptibility to respiratory infections, and varying degrees of developmental disabilities. The incidence of trisomy 21 increases with the age of the mother.

Sex chromosome abnormalities seem to have a lower impact on survival due to the small size of the Y chromosome and X chromosome inactivation. The most common human sex chromosome abnormalities include a single Y chromosome producing 'maleness' and the absence of a Y chromosome yielding 'femaleness'.

Alterations in chromosome structure that can cause birth defects and cancer include inversions, deletions, duplications, and reciprocal translocations. For example, an inversion can cause a reversal of a chromosome segment, while a deletion can result in the loss of a chromosome segment.

The number of crossover events increases genetic variation by allowing for more possible combinations of genes. This, combined with independent assortment, results in a unique genetic identity for each individual.

Independent assortment contributes to genetic variation by allowing each pair of chromosomes to align independently, while crossing over increases genetic variation by exchanging corresponding segments between nonsister chromatids. These processes interact to produce genetic diversity by allowing for a vast number of possible combinations of chromosomes and genes.

Meiosis contributes to genetic variation through the processes of independent assortment and crossing over, resulting in a unique genetic identity for each individual. This genetic variation is essential for the survival and adaptation of a species, and is the raw material for natural selection to act upon.

Genetic variation is essential for human health, as it allows for adaptation to changing environments and provides a buffer against genetic disorders. Mechanisms such as independent assortment and crossing over increase genetic variation, which can reduce the risk of genetic disorders by providing a diverse range of genetic combinations.