As - Cell Division - Ocr

Front 1

alleles

Back 1

different versions of the same gene.

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anaphase

Back 2

third stage of mitosis when chromatids are separated to opposite poles of the cell.

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asexual reproduction

Back 3

the production of genetically identical offspring from a single parent.

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cell cycle

Back 4

the highly ordered sequence of events that takes place in a cell, resulting in division of the nucleus and the formation of two genetically identical daughter cells.

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centromere

Back 5

region at which two chromatids are held together.

Front 6

checkpoints

Back 6

control mechanisms of the cell cycle.

Front 7

chiasmata

Back 7

sections of DNA, which became entangled during crossing over, break and rejoin during anaphase 1 of meiosis sometimes resulting in an exchange of DNA between bivalent chromosomes, forming recombinant chromatids and providing genetic variation.

Front 8

chromatids

Back 8

two identical copies of DNA (a chromosome) held together at a centromere.

Front 9

chromatin

Back 9

uncondensed DNA in a complex with histones.

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continuous variation

Back 10

a characteristic that can take any value within a range, e.g. height.

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diploid

Back 11

normal chromosome number; two chromosomes of each type − one inherited from each parent.

Front 12

discontinuous variation

Back 12

a characteristic that can only result in certain discrete values, for example, blood type.

Front 13

gametes

Back 13

haploid sex cells produced by meiosis in organisms that reproduce sexually.

Front 14

genetic variation

Back 14

a variety of different combinations of alleles in a population.

Front 15

meiosis

Back 15

form of cell division where the nucleus divides twice (meiosis I and meiosis II) resulting in a halving of the chromosome number and producing four haploid cells from one diploid cell.

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metaphase

Back 16

second stage of mitosis when chromosomes line up at the metaphase plate.

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mitosis

Back 17

nuclear division stage in the mitotic phase of the cell cycle.

Front 18

mitotic phase

Back 18

period of cell division of the cell cycle. Consists of the stages mitosis and cytokinesis.

Front 19

prophase

Back 19

first stage of mitosis when chromatin condenses to form visible chromosomes and the nuclear envelope breaks down.

Front 20

recombinant chromatids

Back 20

chromatids with a combination of DNA from both homologous chromosomes, formed by crossing over and chiasmata in meiosis.

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reduction division

Back 21

cell division resulting in the production of haploid cells from a diploid cell; meiosis.

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telophase

Back 22

fourth stage of mitosis when chromosomes assemble at the poles and the nuclear envelope reforms.

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zygote

Back 23

the initial diploid cell formed when two gametes are joined by means of sexual reproduction. Earliest stage of embryonic development.

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cytokinesis

Back 24

cell division stage in the mitotic phase of the cell cycle that results in the production of two identical daughter cells.

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haploid

Back 25

half the normal chromosome number; one chromosome of each type.

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interphase

Back 26

growth period of the cell cycle, between cell divisions (mitotic phase). Consists of stages G1, S and G2.

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multipotent

Back 27

a stem cell that can only differentiate into a range of cell types within a certain type of tissue.

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pluripotent

Back 28

a stem cell that can differentiate into any type of cell, but not form a whole organism.

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specialised

Back 29

having particular structure to serve a specific function.

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stem cells

Back 30

undifferentiated cells with the potential to differentiate into any of the specialised cell types of the organism.

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totipotent

Back 31

a stem cell that can differentiate into any type of cell and form a whole organism.

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undifferentiated

Back 32

an unspecialised cell originating from mitosis or meiosis.

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cartilage

Back 33

strong, flexible connective tissue found in many areas of the bodies of humans and other animals.

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differentiation

Back 34

the process of a cell becoming differentiated. Involves the selective expression of genes in a cell’s genome.

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independent assortment

Back 35

the arrangement of each homologous chromosome pair (bivalent) in metaphase 1 and metaphase 2 of meiosis is independent of each other and results in genetic variation.

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meristematic tissue (meristems)

Back 36

tissue found at regions of growth in plants. Contains stem cells.

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tissue

Back 37

a collection of differentiated cells that have a specialised function or functions in an organism.