grade 7 life science
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where do sex cells form?
the female sex cell
forms in the ovary
the male sex cell
forms in the testis
proces in which an egg cell and sperm cell join together
produces a new cell (zygote)
a type of reproduction in which the genetic materials from two different cells combine, producing an offspring.
a new cell that forms from fertilization
following feritilization, what processes does the zygote go through?
mitosis and cell division
organisms that reproduce sexually form what two kinds of cells?
body cells - similiar chromosomes, occur in pairs
cells that havepairs of chromosomes
- pairs of chromosomes that have genes for the same traits
- arranged in the same order
why aren't chromosomes identical?
because one chromosome is inherited from each parent
why is having the correct number of chromosomes important?
if a zygote has too many or too few chromosomes it will not develop properly
cells that have only one chromosome from each pair
how do diploid cells differ from haploid cells?
- in a "diploid" cell there are 2 copies of each chromosome
- in a "haploid" cell there is only 1 copy of each chromosome
Most of your body's cells are diploid. only the gametes, the sperm and the eggs, are haploid
- diploid cells reproduce by mitosis
- haploid cells reproduce by meiosis
what process do organisms use to produce sex cells?
one diploid cell divides and makes four haploid cells
meiosis only occurs during the formation of sex cells
what happens to a reproductive cell before the beginning of meiosis I?
- cell grows and duplicates chromosomes
what are the phases of meiosis I
- prophase I
- metaphase I
- anaphase I
- telophase I
duplicated chromosomes form pairs
homologous chromosomes form pairs
membrane around nucleus breaks apart
- homologous chromosome pairs line up in middle of cell
- spindle fiber attaches to each chromosome
chromosome pairs separate and are pulled toward opposite ends of cell
(sister chromatids stay together)
nuclear membrane forms around each group of duplicated chromosomes
cytoplasm divides through cytokinesis, making 2 daughter cells
sister chromatids remain together
what happens during meiosis II?
the 2 cells formed previously go through a second division of the nucleus and cytoplasm
this reduction division results in a haploid gamete or spore
phases of meiosis II
- prophase II
- metaphase II
- anaphase II
- telophase II
chromsomes not copied again before prophase II, remain as thickened sister chromatids
- nuclear membrane breaks apart
- nucleolus disappears in each cell
sister chromatids of duplicated chromosomes are pulled away move towards opposite ends of cell
pairs of sister chromatids line up along middle of cell in single file
nuclear membrane forms around each set of chromatids , which are again called chromosomes
cyoplasm divides through cytokinesis and four haploid cells form.
why is meiosis important?
it ensures that the chromosome number of a species stays the same from generation to generation and creates genetic variation
why is sexual reproduction beneficial?
offspring inherit half their dna from each parent resulting in genetic variation among offspring
the inheritance of one trait does not influence the inheritance of another trait
may be an advantage if the environment changes
advantages of sexual reproduction
disadvantages of sexual reproduction
time and energy; growth and development, finding a mate
one parent organism produces offspring without meiosis and fertilization
cell division in prokaryotes that forms two genetically identical cells
- dna molocule copied
- copy attaches to cell membrane
- cell elongates, pulling copies apart
- cell membrane pinches inward along the middle
- cell splits and forms 2 new identical offspring
types of asexual reproduction
- mitotic cell division
- animal regeneration
- vegetative reproduction
- a new organism grows by mitosis and cell division on the body of its parent.
- bud is genetically identical to its parent, when large enough it can break from the parent and live on its own
occurs when an offspring grows from a piece of its parent
form of asexual reproduction in which offspring grow from a part of a parent plant
typically involving structures such as roots, stems, and leaves
asexual reproduction performed in the laboratory that produces identical individuals from a cell or from a cluster of cells taken from a multicellular organism
advantages of asexual reproduction
enables organisms to reproduce without a mate
enables some organisms to rapidly reproduce a large number of offspring
disadvantages of asexual reproduction
results in little genetic variation
mutations will be passed to offspring, possibly affecting the offsprings ability to survive
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