CHAPTER 10
SEXUAL REPRODUCTION AND
GENETICS
• SECTION 10.1 – MEIOSIS
• MAIN IDEA – MEIOSIS PRODUCES HAPLOID GAMETES.
• All of the differences you see in the room, different hair color, eye
color, ear shapes, is the result of 2 sex cells combining during sexual
reproduction.
• QUESTION: How are the following cell parts involved in mitosis?
• Chromosome, spindle fibers, nucleus, and nucleolus
• CHROMOSOMES AND CHROMOSOME NUMBER
• Everyone has characteristics passed on to them from their parents.
• Each characteristic is called a trait.
• Ex: hair color, height or eye color
• The instructions for each trait are located on the chromosomes, which are found
in the nucleus of cells.
• The DNA on the chromosomes is arranged in segments called genes that control
the production of proteins.
• Each chromosome has 100’s of genes.
• HOMOLOGOUS CHROMOSOMES
• Human body cells (somatic cells) have 46 chromosomes.
• Each parent gave you 23 chromosomes creating 23 PAIRS of
chromosomes or 46 chromosomes.
• The chromosomes that make up a pair (the one from mom & the one from
dad) are called homologous chromosomes
• Homologous chromosomes in body cells have the same length, same
centromere position, and carry genes that control the same inherited
traits.
• These genes each code for the same trait (ex: earlobe) but maybe not
the same type of trait (earlobe)
• HAPLOID AND DIPLOID CELLS
• Gametes are sex cells that have half the number of chromosomes.
• In humans the number of chromosomes in a gamete is 23.
• Each species has a different # of chromosomes
• The symbol n can be used to represent the number of chromosomes in a gamete.
• Cells with n number of chromosomes is called a haploid cell.
• Haploos means single.
• Fertilization is the process by which one haploid gamete (egg) combines with
another haploid gamete (sperm)
• Fertilization creates cells that are 2n (one n chromosome from mom & one n chromosome
from dad)
• 2n cells are called diploid cells
• MEIOSIS I
• Gametes are formed during a process called meiosis.
• Meiosis is a type of cell division that reduces the number of chromosomes
• Meiosis is a reduction division.
• Mitosis maintains the chromosome #, meiosis reduces the chromosome #
by half through the separation of homologous chromosomes.
• Cells begin as 2n, but create gametes with n number of chromosomes
• Meiosis occurs in the reproductive structures of organisms that reproduce sexually.
• Meiosis involves 2 consecutive cell divisions called meiosis I & meiosis II
•INTERPHASE
•Just like with mitosis, cells that undergo meiosis
also go through interphase as part of their cell
cycle.
•While in interphase cells carry out various
metabolic processes, including the replication of
DNA and the synthesis of proteins
• PROPHASE I
• Cells entering prophase I, the replicated (copied) chromosomes become visible.
• Creating sister chromatids
• Homologous chromosomes (mom’s sister chromatid + dad’s sister chromatid)
form during synapsis and are held tightly together. Can be called a tetrad.
• Crossing over occurs this time.
• Crossing over is a process when segments of chromosomes are exchanged
between a pair of homologous chromosomes.
• Prophase I continues with the centrioles moving to the cell’s opposite poles,
spindle fibers forming and binding to the sister chromatids at the centromere.
• PROPHASE I
• METAPHASE I
• 2nd phase of meiosis
• Homologous chromosomes line up at the equator of the
cell.
• Spindle fibers are attached to the centromere of each
homologous chromosome
• ANAPHASE I
• During anaphase I homologous chromosomes separate.
• Sister chromatids are pulled to opposite poles of the cell
• Chromosome number is reduced from 2n to n when the
homologous chromosomes separate.
• TELOPHASE I
• Homologous chromosomes (sister chromatids) reach the cell’s opposite poles.
• Sister chromatids are still joined at the centromere
• Sister chromatids might not be identical from when it started
because of crossing over.
• During telophase I, cytokinesis usually occurs pinching in the animal
cell or forming cell plate in plant cells.
• May or may not go into interphase. If cell goes into interphase, DNA
is NOT duplicated again.
• Telophase I
•MEIOSIS II
•Meiosis is only half done after meiosis I.
•Prophase II the sister chromatids condense and
spindle apparatus forms
•Metaphase II the sister chromatids line up at the
equator by the spindle fibers.
• MEIOSIS II
• Anaphase II the sister chromatids are pulled apart at the
centromere by the spindle fibers and the chromosomes move
toward the opposite poles of the cell.
• Telophase II the chromosomes reach the poles and the nuclear
membrane and nuclei reform.
• At the end of meiosis II, cytokinesis occurs creating 4 haploid
cells each with n number of chromosomes
• MEIOSIS II
•MEIOSIS PROVIDES VARIATION
•Genetic variation is produced during crossing
over and during fertilization when gametes
randomly combine.
•Depending on how chromosomes line up at the
equator, 4 gametes with 4 different
combinations of chromosomes can result.
• SEXUAL REPRODUCTION VS. ASEXUAL REPRODUCTION
• Asexual reproduction the organism inherits all of its
chromosomes from a single parent and are genetically
identical to the parent.
• Ex: bacteria
• Sexual reproduction allows variation and beneficial
mutations to accumulate faster in the population.