Chromosomes, Dna, And Meiosis

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are rod-shaped structures made of DNA and protein.

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Chromosomes

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Chromosomes consist of two identical halves. Each half is called a .

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Sister Chromatid

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Chromatids form as the DNA makes a of itself before cell

division.

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copy

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The two chromatids are attached at a point called a .

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centromere

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Each species has a characteristic of chromosomes in each cell.

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number

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Humans have total chromosomes that exist as .

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46 and 23 pairs

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Human and animal chromosomes are categorized as either

chromosomes or .

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sex, autosomes

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In humans, sex chromosomes are either X or Y. Females have chromosomes and males normally have an chromosomes and a
chromosome.

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2 x; x; y

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All of the other chromosomes in an organism are .

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autosomes

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Every cell of an organism that reproduces by sexual reproduction has copies of each autosome.

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2

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The organism receives a copy of each autosome from each (one from the egg and one from the sperm).

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parent

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The two copies of each autosome are called chromosomes, or homologs.

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homologous

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Homologous chromosomes are the same size and shape and carry genes for the same .

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traits

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Cells having two sets of chromosomes are (2n). In humans the diploid number is .

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diploid, 46

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Sperm and egg cells are cells(1n), which only contain one set of 23 chromosomes.

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haploid

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The DNA of each chromosome contains sections called that contain instructions for our traits.

(For example, there are genes for eye color, hair color, etc)

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genes

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Because we get half of our chromosomes from our mother’s egg

and half of our chromosomes from our father’s sperm, we have forms of the genes for all of our characteristics (one on each

homologous chromosome).
(For example, mom could have passed down the blonde hair color gene while dad could have passed down the brown hair color gene).

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2

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is the process of nuclear division that reduces the number of chromosomes in new cells to half the number in the

original cell.

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Meiosis

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Meiosis produces 4 ,or sex cells.

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gametes

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Human are sperm cells and egg cells.

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gametes

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Cells preparing to divide by meiosis undergo the G1, S, and G2 phases of .

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interphase

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The stages of the first cell division are called and the stages of the second cell division are called .

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Meiosis I, Meiosis II

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In Meiosis I separate. In Meiosis II, separate.

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homologous chromosomes, chromatids

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In Prophase I:

A. coils tightly into chromosomes.

B. fibers appear

C. Nucleolus and nuclear membrane .

D. Homologous chromosomes pair up, which is called a and crossing over occurs.

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Chromatin, Spindle, Disappear, tetrad

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, when portions of homologous chromosomes exchange genetic material, occurs during prophase I and results in genetic .

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Crossing-over, Variation

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In metaphase I:

a. Tetrads line up randomly along the of the dividing cell

b. Spindle fibers attach to the centromere of one chromosome

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midline, homologous

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In anaphase I: Each homologous chromosome (consisting of two chromatids) moves to the pole of the dividing cell.

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opposite

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In telophase I and cytokinesis:
a. Chromosomes reach opposite ends of the cell b. Cytoplasm division begins

c. New membranes form

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nuclear

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Meiosis II includes four phases that are just like ; sister chromatids separate.

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mitosis

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Four cells result.

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haploid

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reproduction is the formation of offspring through meiosis and the union of a sperm and an egg.

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Sexual

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Offspring produced by sexual reproduction are genetically from the parents due to the combination of inherited genes and the that occurs during meiosis.

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different, crossing-over

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occurs between gametes when 1 sperm is allowed into the egg to fertilize it.

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Fertilization

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Because gametes are (only 23 chromosomes in humans),

the end result is a cell that is (all 46 chromosomes that are found in humans).

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haploid, diploid