Unit 3

Front 1

1st division of meiosis

Back 1

separates homologous pairs

Front 2

reduction division

Back 2

the usually first division of meiosis in which chromosome reduction occurs

Front 3

interphase 1

Back 3

the interval between the end of one mitotic or meiotic division and the beginning of another

Front 4

prophase

Back 4

the initial stage of mitosis and of the mitotic division of meiosis characterized by the condensation of chromosomes consisting of two chromatids, disappearance of the nucleolus and nuclear membrane, and formation of mitotic spindle

Front 5

metaphase

Back 5

the stage of mitosis and meiosis in which the chromosomes become arranged in the equatorial plane of the spindle

Front 6

anaphase

Back 6

the stage of mitosis and meiosis in which the chromosomes move toward the poles of the spindle

Front 7

telophase

Back 7

the final stage of mitosis and of the second division of meiosis in which the spindle disappears and the nuclear envelope reforms around each set of chromosomes

Front 8

tetrad

Back 8

group or arrangement of four: as a : a group of four cells produced by the successive divisions of a mother cell or tetrad of spores

Front 9

synapsis

Back 9

the association of homologous chromosomes that is characteristic of the first meiotic prophase

Front 10

independent assortment

Back 10

formation of random combinations of chromosomes in meiosis and of genes on different pairs of homologous chromosomes by the passage according to the laws of probability of one of each diploid pair of homologous chromosomes into each gamete independently of each other pair

Front 11

2nd division of meiosis

Back 11

separates sister chromatids

Front 12

telophase 2

Back 12

the final stage in the first division of meiosis that may be missing in some organisms and is characterized by the gathering at opposite poles of the cell of half the original number of chromosomes including one from each homologous pair

Front 13

Mendelian Inheritance

Back 13

inheritance of characters specifically transmitted by genes in accord with Mendel's law -- called also particulate inheritance

Front 14

metaphase 1

Back 14

In metaphase I the tetrads are again arranged across the center by the movements of the kinetochores with the two centromeres opposite each other, but this time the sister chromatids will not be pulled apart as in mitosis.

Front 15

anaphase 1

Back 15

In anaphase I the chromatids holding the chromosomes together loosen. The two homologous chromatids of each tetrad are separated into separate poles. Since the chromosomes from each parent can go into either pole this is another means to increase genetic diversity.

Front 16

telophase 1

Back 16

In this phase, like in mitosis the chromosomes are moved into opposite poles and the nuclear envelope reforms and the spindle is broken down. Remember that there are two chromosomes, not one as in mitosis.

Front 17

crossing over: tetrad

Back 17

genetic analysis of organisms whose four products of meiosis remain together in groups of four called tetrads.

Front 18

crossing over: synapsis

Back 18

The synapsis and exchange of chromosomes is such that no segments are lost or gained, and four complete chromosomes emerge in a tetrad.

Front 19

independent assortment

Back 19

allele pairs separate independently during the formation of gametes.

Front 20

haploid

Back 20

have one set of chromosomes (n=1), which is the same as a gamete (pollen or egg cell). Haploids can be distinguished from diploids (n=2) by using gene markers which are closely linked with the gene under study so they can be visually detected or by their physical characteristics.

Front 21

prophase 2

Back 21

In meiosis the cell goes directly from telophase I to prophase II without the interphase. In prophase II the nuclear envelope is again dissolved and the spindle is set up again. Prophase II is identical to prophase of mitosis except that there is half the amount of chromosomes.

Front 22

metaphase 2

Back 22

Again the chromosomes move into the center and line up. Now there are two chromosomes, instead of two tetrads, so that the chromatids will split off this time.

Front 23

anaphase 2

Back 23

The kinetochores move towards the poles, splitting up the sister chromatids

Front 24

telophase 2

Back 24

In telophase II the chromatids concentrate in the poles and the nuclear envelope is reformed and the spindle again is dissolved. The cells divide for the last time, leaving a total of four haploid cells, which have half the chromosomes of a diploid cell. Unlike the daughter cells from mitosis, the daughter cells produced here cannot immediately cycle back to interphase.

Front 25

• Law of Segregation

Back 25

Mendel's first law, stating that allele pairs separate during gamete formation and then randomly re-form as paris during the fasion of gametes at fertilization

Front 26

Law of Independent Assortment

Back 26

Mendel's second law, stating ahat each allel pairs segregates independently during gamete formation ; applies when genes for two characteristics are located on different pairs of homologous chromosomes

Front 27

incomplete dominance

Back 27

A form of intermediate inheritance in which heterozygous alleles are both expressed, resulting in a combined phenotype.

Front 28

codominance

Back 28

A condition in which both alleles of a heterozygous pair are expressed independently.
codon A sequence of three bases on messenger RNA that specifies the position of an amino acid in a protein.

Front 29

multiple alleles

Back 29

Any of a set of three or more alleles, or alternative states of a gene, only two of which can be present in a diploid organism.

Front 30

polygenic inheritance

Back 30

The phenotypic expression of a trait involving the interaction of many genes.