35 terms

Science Chapter 7 Meiosis and Sexual Reproduction


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Sexual Reproduction -
Produces an offspring when genetic materials from two different sex cells combine.
a. egg, female sex cells
b. sperm, male sex cell
An egg cell and a sperm cell join together
The new cell that forms is called the zygote
Body cells
are diploid; they have pairs of chromosomes.
sex cells
are haploid; they have only one chromosome from each pair of chromosomes.
If a zygote has to many or to few chromosomes,
it will not develop properly.
cells that have pairs of chromosomes
Homologous chromosomes-
Pairs of chromosomes that have genes for the same traits arranged in the same order
Different organisms have different number of
The Phases of Meiosis
only occurs during the formation of sex cells
During interphase, what happens?
the reproductive cells grows and duplicate its chromosomes.
Meiosis involves two divisions of the nucleus and the cytoplasm .
These divisions, known as meiosis I and meiosis II, result in four haploid cells.
During meiosis I,
each pair of duplicated homologous chromosomes separates.
After meiosis I,
the two cells formed during this stage go through a second division of the nucleus and cytoplasm called meiosis II.
During meiosis II,
sister chromatids separate to produce four haploid cells.
Meiosis forms sex cells with the
correct haploid number of chromosomes.
Miosis occurs only during the formation of sex cells
a. egg
b. sperm
Meiosis creates genetic variation by producing
haploid cells.
Prophase I-
duplicated chromosomes condense and thicken
Metaphase I-
Homologous chromosomes pairs line up in the middle of the cell
Anaphase I-
Chromosome pairs separate and are pulled toward the opposite ends of the cell
Telophase I-
A nuclear membrane forms around each group of duplicated chromosomes
Prophase II-
Chromosomes are not copied again before prophase II
Metaphase II-
The pairs of sister chromatids in line up along the middle of the cell in single file
Anaphase II-
Sister chromatids begin to separate and are pulled to opposite ends of the cells
Telophase II-
a nuclear membrane forms around each set of chromatids
Why is meiosis important?
It forms sex cells with the correct haploid number of chromosomes,
1. helps maintain diploid cells in offspring,
2. divides during meiosis and cell division
How do mitosis and meiosis differ?
During mitosis and cell division, a body cell and its nucleus divide once and produce two identical cells, while during meiosis, a reproductive cell and its nucleus divide twice and produce four cells-two pairs of identical haploid cells
1. two pairs of identical haploid cells
2. meiosis happens in the reproductive organ
Advantages to sexual reproduction
1. the offspring has half the DNA from each parent
2. due to genetic variation, within a population have slight differences
3. selective breeding includes mustard plants to make broccoli and other things
Disadvantages to sexual reproduction
1. time and energy.
2. the organisms have to grow and develop
asexual reproduction-
one parent organism produces offspring without meiosis and fertilization
1. Inherits all DNA from parents
cell divides in prokaryotes that forms two genetically identical cells
a. begins when a prokaryotic DNA molecule is copied
b. begins to pull apart, pinching the membrane together
a new organism grows by mitosis and cell division on the body of its parent
a. identical to its parent
b. when it becomes big enough, it can break away from its parent organism
Another type of regeneration, occurs when an offspring grows from a piece of its parent
a. humans
b. sea creatures
Vegetative reproduction-
a form of asexual reproduction in which offspring grow from a part of a parent plant
a. includes roots, stems, and leaves
a type of reproduction performed in a laboratory the produces identical individuals from a cell or from a cluster of cells taken from a multicellular organisms
a. genetically identical to its twin
b. enables plant growers to reproduce plants that might have become infected with a disease