biology chapter five : meiosis

genetics

the scientific study of heredity and variation

heredity

transmission of traits from one generation to next

variation

differences in appearance that offspring show from parents and siblings

genes

unit of heredity that are made up of segments of DNA

locus

the specific location of a gene on a certain chromosome

gametes

reproductive cells that pass genes from one generation to the next

# of chromosomes in a gamete

23 chromosomes

____ cells in an organism have the same genome (except ______)

ALL - gametes

how cells have different function if same genome

the genes that are expressed by the cell may be controlled in different ways, and not all cells will produce the same proteins

karyotype

an ordered display of the pairs of chromosomes from a cell

chromosomes

threadlike structure of protein and DNA carrying genetic info in the form of genes

recombinant chromosomes

the chromosome that results from combining genes inherited from each parent in crossing over

chromatid

one half of a duplicated chromosomes

synapsis

the action of two homologous chromosomes forming a tetrad

tetrad

group of four chromatids

chiasmata

x shaped region where each tetrads crosses over

centromere

region of a chromosome where the two sister chromatids attach. how chromosomes are counted

homologous pair

chromosomes that are the same length and carry genes controlling the same inherited characters

sex chromosomes

X and Y

females have

a homologous pair of X chromosomes (XX)

human males have

one X and one Y chromosomes

autosomes

the 22 pairs of chromosomes that do not determine the sex

haploid (ex.)

contain a single set of chromosomes

ex : gamete cells

humans n = 23

diploid (ex.)

contains two sets of chromosomes

ex : somatic cells

humans n = 46

fertilization

union of gametes

zygote

fertilized egg containing one set of chromosomes from each parent

meiosis

reduces the number of chromosome sets from diploid to haploid in two sets of cell division, meiosis I and meiosis II

# daughter cells from meiosis

four

chromosomes and chromatids # before interphase

chromosomes : 46

chromatids : 46

interphase

where a cell spends most of its life, preforming daily functions and preparing for cell division

chromosomes and chromatids # after interphase

chromosomes : 46

chromatids : 92

prophase I

- nuclear membrane and nucleolus dissolve

- chromatin condenses to chromosomes

- centrioles start moving

- homologous chromosomes pair up and form tetrad

- crossing over occurs

metaphase I

- homologous pairs line up randomly along the equator by independent assortment

- spindles attach to kinetochore

anaphase I

- spindle fingers pull away homologous chromosome pairs

telophase I

- cleavage furrow forms

- nuclear membrane and nucleolus reform

- DNA unravels

cytokinesis I

- final splitting of the cell

- organelles divide

- two different daughter cells are formed

chromosomes and chromatids # after meiosis I

chromosomes : 23

chromatids : 46

prophase II

- nuclear membrane and nucleolus dissolve

- chromatin condenses to chromosomes

- centrioles start moving

PROMETAPHASE

- centrioles reach the poles

- spindles form

metaphase II

- spindles attach to the kinetochore

- chromosomes line at the equator (NOT in pairs)

anaphase II

- spindles pull apart sister chromatids

telophase II

- cleavage furrow forms

- nuclear membrane and nucleolus reform

- DNA unravels

cytokinesis II

- final splitting of the cell

- organelles divide

- four different daughter cells formed

chromosomes and chromatids # after meiosis II

chromosomes : 23

chromatids : 23

three mechanisms that contribute to genetic offspring

- independent assortment of chromosomes

- crossing over

- random fertilization

independent assortment of chromosomes

each pair of chromosomes sorts maternal and paternal homologous into daughter cells independently of the other pair during metaphase

crossing over

non-sister chromatids of homologous pairs exchange DNA segments combining DNA randomlyfrom the two parents into a single chromosome during prophase

random fertilization

the male and female gamete that fuse to produce offspring are selected randomly from the pool of male and female gametes