chromosomes.html: 13_04DuplicatedChromosome_L.jpg
A chromosome consists of 2 sister chromatids joined at the centromere. Each homologous pair is composed of one chromosome from the maternal set and one from the paternal set.

crossing_over.html: 13_11CrossingOver_L.jpg
In crossing over, nonsister chromatids of homologous chromosomes exchange portions. The recombinant chromosomes carry genes derived from different parents. gender.html: ../ch15/15_06aSexDetermination-L.jpg
Human somatic cells have 22 pairs of homologous autosomes plus one pair of sex chromosomes. XX individuals are female, while XY are male.

hydra_budding.html: 13_02HydraBudding_LP.jpg
The asexual reproduction of a hydra. The bud, a localized mass of mitotically dividing cells, develops into a small hydra, which detaches from the parent. (hint)

independent_assortment.html: 13_10IndependentAssort_L.jpg
In independent assortment, each pair of chromosomes sorts its maternal and paternal homologues into daughter cells independently of the other pairs in metaphase I, giving 2²³, or about 8 million, combinations in humans.

karyotype-lymphocytes.html: 13_karyotype-lymphocytes.jpg

karyotype.html: 13_03KaryotypePrep.jpg
A karyotype is a display of condensed chromosomes arranged in pairs. A digital photograph of chromosomes of a cell in mitosis is electronically arranged into pairs according to size and shape. This karyotype shows the chromosomes from a human male. Each chromosome consists of 2 sister chromatids. (hint)

life_cycle.html: 13_05HumanLifeCycle.jpg
The human life cycle. Ovaries produce the female gamete ovum, and testes produce the male gamete sperm. The gametes are haploid, consisting of one set (n = 23 in humans) of chromosomes. The number of chromosomes in the diploid zygote and all somatic cells arising from it is 46, consisting of two sets (2 n = 46).

meiosis.html: 13_07MeiosisOverview.jpg
Overview of meiosis. After chromosomes replicate in interphase, the diploid cell divides twice, yielding four haploid daughter cells. One chromosome was inherited from the female parent, the other from the male parent.

meiosis_2.html: 13_08bAnimalMeiosisTwo.jpg
Meiosis II separates sister chromatids, producing 4 haploid cells.

meiosis_I-anaphase.html: 13_08meiosis_I-anaphase.jpg
In anaphase I, the homologous pairs move toward opposite poles of the cell. Notice sister chromatids remain attached, and some of the chromatids have exchanged genetic material.

meiosis_I-metaphase.html: 13_08meiosis_I-metaphase.jpg
In metaphase I, the paired tetrads, formed by synapsis during prophase I, line up on the metaphase plate. Note the alignment of maternal and paternal homologues along the metaphase plate is random.

meiosis_I-prophase.html: 13_08meiosis_I-prophase.jpg
In prophase I, homologous chromosomes pair up into tetrads in a process called synapsis. Crossing over of DNA segments occurs at chiasmata, and genetic information is exchanged between the homologues.

meiosis_I-telephase.html: 13_08meiosis_I-telephase.jpg
At the end of telephase I and cytokinesis I, two haploid cells are produced with two chromatids still attached to each chromosome.

meiosis_I.html: 13_08aAnimalMeiosisOne.jpg
Meiosis I separates homologous chromosomes and results in reduction from diploid to haploid cells.
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meiosis_II.html: 13_08bAnimalMeiosisTwo.jpg
Meiosis II is similar to mitosis, except the cell undergoing division is haploid rather than diploid, and sister chromatids separate in anaphase II. Meiosis now has produced 4 haploid cells.

mitosis-meiosis.html: 13_09MitosisVMeiosis.jpg
Mitosis

• One cell division produces two diploid, genetically identical daughter cells.
• Functions in growth and repair of somatic cells.

• Two cell divisions produce four haploid, genetically different daughter cells.
• Synapsis of homologous chromosomes, forming tetrads and resulting in crossing over between sister chromatids.
• Produces gametes for sexual reproduction and genetic variation of offspring.

random_fertilization.html: 13_x1SpermAndEgg_UP.jpg
The random fusion of gametes during fertilization produces a zygote with 2²³ x 2²³, or over 70 trillion, combinations of chromosomes.

sexual_life_cycles.html: 13_06SexualLifeCyclesA.jpg
An idealized life cycle of animals. Haploid gametes fuse by fertilization to form a diploid zygote. The zygote undergoes many rounds of mitosis to produce the diploid multicellular organism. Diploid germ cells undergo meiosis ro produce haploid gametes.

variation.html: 13_01SissySpacek_JackFisk.jpg
Heritable variation. The family of Sissy Spacek and Jack Fisk exhibits genetic variation. Sexual reproduction produces variation in the gametes and unique combinations of genes in the offspring, even though the offspring inherit traits from both parents.