Meiosis and Chromosomes

What is meiosis

production of gametes

gametogenesis

the process in which cells undergo meiosis to form gametes.

DNA

deoxyribonucleic acid

how many haploids does one diploid produce

4

reduction division

the first cell division in meiosis, the process by which germ cells are formed.

what happens during meiosis I (PMAT 1)

homologous chromosomes separate into two haploid cells

what happens during meiosis II (PMAT 2)

chromatids of each chromosome separate forming a total of 4 haploid cells

Interphase

chromosome/DNA replicate

Prophase I

chromosomes condense;
nucleus breaks down; synapsis occurs, forming a tetrad;
crossing-over occurs

synapsis

homologous chromosomes pair up

what is crossing over

exchange of sections of chromosomes and thus the genetic info

what is chiasma

where crossing over occurs

recombinant chromatids

a combination of maternal and paternal genes that did not exist before the crossover

Metaphase I

homologous chromosomes move to the middle being pulled by spindles

Anaphase I

Homologous chromosomes separate and begin moving to opposite sides;
nondisjunction can occur

what is nondisjunction

homologous pairs do not separate

Telophase I

cytoplasm divides and nuclei form;
two new cells have 1/2 the number of chromosomes of the original cell (haploid but still duplicated)

Prophase II

chromosomes condense;
nucleus breaks down;
no replication occurs

Metaphase II

chromosomes (2 chromatids each) line up in the center

Anaphase II

singular chromosomes separate and chromosomes move to opposite poles of the cell;
nondisjunction can occur if chromatids do not separate

Telophase II

cytokinesis;
nuclei from around four haploid cells

meiosis allows for

genetic recombination because of crossing over and independent assortment

genetic recombination

source of variation among organisms because of crossing over and independent assortment

how many eggs are produced and why

only one egg is usually produced due to unequal dividing of the cytoplasm containing organelles

what are the other three cells called

polar bodies

how many sperm are produced

4 with flagellum and many mitochondria (do not confuse with meiosis!!!!!!!!!!!!!!!)

histone

protein that DNA wraps around

nucleosomes

bead-like units formed by DNA wrapped around histones, make up chromatin

super coil

chromatin coiled up even more, many super coils become a chromosome

gene

segment of DNA on a chromosme coding for the making of a polypeptide(protein)

chromatid

two identical sides
of a chromosome created in preparation for cell division

centromere

place where chromatids connect

telomeres

ends of
chromosomes
made of
repeating
nucleotides;
shorten with
cell division
and prevent
loss of
genetic
information

kinetochore

a structure on the centromere where spindle fibers attach

homologous chromosomes

Chromosomes
usually occur
in pairs (one from
mom and one from
dad) that are
similar to each other
(same structure)

how many pairs of homologous chromosomes do humans have

23 pairs

diploid (2n)

cells containing both members of a homologous pair

somatic cells

body cells, diploid

haploid (n)

cells containing one member of a homologous pair

gametes

reproductive cells - sperm and egg, which come from germ cells in testes and ovaries, haploid

fertilization

fusion of two haploid cells- one from each parent

zygote

diploid (fertilized egg), has full set of DNA to develop into new organism

karyotype

photograph of chromosomes of an individual arranged by size and shape

amniocentisis

extraction of fetal amniotic fluids to collect cells with chromosomes for karyotyping

chronic villi sampling

extraction of chorionic tissue (becomes the placenta) to collect cells with chromosomes for karyotyping

autosomes

chromosomes that are the same in male and female (chromosomes pair 1-22)

sex chromosomes

one pair that determines sex (chromosome pair 23- X is longer), XX is female, XY is male

chromosomal structure abnormalities

mutation

mutation

change in genetic material, four types:
deletion
duplication
inversion
translocation

deletion

fragment breaks off and is lost

duplication

fragment breaks off and attaches to homologous chromosome giving it two copies

inversion

fragment breaks off and reattaches backwards

translocation

fragment breaks off and joins non homologous chromosome

effect of mutations

some dont have an effect, some are harmful, some are helpful, provide genetic variety in a species

melanistic

blacker pigmentation (mutation)

two types of mutations

germ cell mutations, somatic cell mutations

germ cell mutations

occur in gametes, can be passed on to offspring

somatic cell mutations

occur in other cells, not passed on to offspring

trisomy

diploid cell with an extra chromosome

trisomy 21

down syndrome

trisomy 13

patau syndrome

trisomy 18

edward's syndrome

monosomy X

turner's syndrome- short, sterile, other possible health complications

trisomy xxy

klinefelter's syndrome

monosomy

diploid cell missing a chromosome

polyploidy

an extra entire set of chromosomes, plants with polyploidy tend to be heartier

what do chromosome number abnormalities result from

defective gametes, occur because homologous chromosomes separated incorrectly during cell division (nondisjunction)

what happens to defective gamete

becomes a part of the zygote/ new organism