meiosis Flashcards
diploid cell
cell that has two full sets of chromosomes
haploid nuclei
nuclei with one set of chromosomes within special gamete cell
zygote
when two haploid nuclei fuse together to form new diploid cell called zygote
polyploidy
having more than two sets of chromosomes per nuclei
where are gametes formed
in special sex organs
gonads
sex organs in animals
anthers
male sex organs in plants
female sex organs in plants
ovaries
where are the male gametes formed in
the pollen made in anthers
where are female gametes made in plants
ovules contained in ovaries
male sex organs in animals
testes
what gametes do testes produce
spermatozoa
female gonads
ovaries that produce female gametes ova or eggs
male gametes description
many
mini
motile
female gamete description
few
fat
fixed
what does meiosis form in male flowering cells
microspores
what does meiosis form in female flowering cells
megaspores
what does meiosis give rise to
four haploid daughter cells
homologous pairs
two chromosomes of each pair stay close together
crossing over
where chromatids break and recombine
prophase 1
each chromosomes condensed with 2 chromatids
-homologous pairs with each other
-crossing over occurs
metaphase 1
spindle forms
-pairs of chromosomes line up on metaphase plate
anaphase 1
centromeres dont divide
-one chromosome from homologous pair moves to each end of cell
-chromosomes number in each cell half
telophase 1
nuclear membrane divides
-cells begin to divide
-continues to full cytokenesis
-during this interphase no further replication of dna
prophase 2
new spindles formed
metaphase 2
chromosomes made up of pair of chromatids
-line up on metaphase plate
anaphase 2
centromeres divide
-chromatids move to opposite ends of cell
telophase 2
nuclear envelope reforms
-chromosomes return to interphase
-cytokenesis occurs
-gives four daughter cells
-each has half number of chromosomes of original diploid cell
2 ways variation occurs in meiosis
independent assortment
crossing over
whats independent assortment
chromosomes that came from organisms 2 parents distributed into gametes and into offspring at random
whats crossing over
when large multi enzyme complexes cut and join bits of maternal and paternal chromatids together
chiasmata
points where chromatids break
importance of crossing over
-added genetic variation
errors lead to mutations to have more genetic variation
chromosome mutations
parts of chromosomes break off and become reattached in wrong place
translocation
when a piece from one pair of homlogous chromosomes breaks off and reattaches to different pair of chromosomes
unbalanced translocations
when one chromosome gains an extra one and can change phenotype of organism
effect of translocation mutations
lead to core binding factor acute myeloid leukaemia
non disjunction mutations
members of one homologous chromosomes fails to seperate during anaphase 2 one of gametes had two copies of chromosome and other has none
effects of non disjunction mutations
monosomy
polysomy
monosmy
only one member of homologous pair present in normal gamete
polysomy
three or more rather than 2 of chromosome pair
aneuploidy
when cell lacks whole chromosome or has more than two chromosomes
whats down syndrome an example of
non disjunction
polysomy
babies with down syndrome have what
trisomy of chromosome 21
what happens if there is non disjunction of chromosome 21 in ovum or sperm
one of gametes will have two copies of chromosome
problems of down syndrome
heat disorders
lack of muscle tone
visual problems
mutagens
ionising radiation- increases mutation rate
-chemicals
age
ova vulnerable
whats turners syndrome an example of
non disjunction
monosomy
what happens if theres non disjunction of sperm cells
ova fertilised with no sex cells from sperm
embryo monosomy only x chromosome
genotype of egg cell with monosomy
XO that results in turners syndrome
effect female of turners syndrome
is female but doesnt go through puberty without being given extra sex hormones
kleinfelters syndrome
when male chromosome has XY and results in cell with XXY genotype
effect of kleinfelters syndrome
develop breast tissue
little facial hair
may be infertile
less muscle development
