Meiosis

somatic cells

somatic cells

(non-sex cells) in an organism have two sets of chromosomes

diploid cells

cells with two sets of chromosomes

karyotype

an ordered display of the pairs of chromosomes from a cell

autosomes

non-sex chromosomes

homologous chromosomes

pairs of chromosomes; unlike sister chromatids, they are NOT attached and are not exact genetic copies; look alike and carry the same genes but may carry different alleles

alleles

alternative versions of the same gene (brown v blue for eye color)

gametes

sex cells; only contain a single set of chromosomes

haploid cells

cells with one set of chromosomes

zygote

when two haploid cells fuse at fertilization, the created zygote is diploid with 46 total chromosomes

meiosis

produces gametes with only one set of chromosomes (haploid); begins after interphase, which includes DNA replication

meiosis 1

the homologous chromosomes separate

meiosis 2

the sister chromatids separate in a similar manner as mitosis; in the end, 4 haploid gametes are created

meiosis 1: prophase 1

the chromosomes condense, the nuclear envelope breaks down, and the mitotic spindle forms

crossing over

homologous chromosomes pair up and exchange DNA; exchanges genetic material between paternal and maternal DNA

meiosis 1: metaphase 1

homologous chromosomes line up at the metaphase plate; maternal and paternal chromosomes orient randomly toward either pole

meiosis 1: anaphase 1

homologous chromosomes migrate toward opposite poles of the cell

independent assortment

the sorting of homologous chromosomes

meiosis 1: telophase 1 and cytokinesis

the spindle disassembles, the chromosomes begin to decondense and the nuclear envelope reforms; cytokinesis separates one cell into two

meiosis 2: prophase 2

chromosomes condense, nuclear envelope breaks down, and the mitotic spindle forms

meiosis 2: metaphase 2

chromosomes line up at the metaphase plate

meiosis 2: anaphase 2

sister chromatids split at their centromeres and migrate toward opposite poles of the cell

meiosis 2: telophase 2 and cytokinesis

the spindle disassembles, the chromosomes begin to decondense and the nuclear envelope reforms; cytokinesis divides the 2 cells into 4

nondisjunction

can occur if homologous chromosomes fail to separate during anaphase 1; can also occur if sister chromatids fail to separate during anaphase 2

aneuploid cell

gametes with extra or missing chromosomes