Chapter 3 Flashcards
What two types of cells do multicellular organisms have that reproduce sexually?
- Somatic cells (Body Cells) Diploid, sex cells (Games)
Haploid
What are gametes?
- Gametes = sex cells
• Half the chromosomes of parent cell and are tiny
fraction of all cells
What are the two gametes?
- Sperm and egg/ova
How many chromosones are among a species?
- Animals among a species: equal # of chromosomes
How sexually reproducing organisms maintain the same number of chromosomes?
- Meiosis
What is meiosis?
- Meiosis = Type of cell division that results in 4 daughter
cells with 1/2 chromosome # of parent cell.
• Happens only in the cells that produce gametes;
reproductive cells
• Sometimes called reduction division: It reduces
chromosome # 1/2.
• Two phases: Meiosis I + II
What happens in meiosis I?
- Contains prophase, metaphase, anaphase, telophase
• Results in 2 diploid daughter cells w. = chromosomes
as the parent cell; each has one homologous
chromosome
• Sister Chromatids stay together
• Prophase: Chromatids shorten + thicken, visible
with light microscope
• Metaphase: Homologous chromosomes line up in
middle joined with their sister chromatids
• Anaphase: Pairs of homologous chromosomes
separate and move to opposite poles along with their
sister chromatids
What happens in meiosis II?
- Contains metaphase ii, anaphase ii, telophase ii
• Metaphase II: Sister chromatids lineup at the equator.
• Anaphase II: Sister Chromatid pulled to opposite poles
+ separated.
• Telophase: Pinching and cytokinesis occurs,
nuclear membrane starts to reform
What are cells that have 1/2 chromosome #?
- Haploid cells
What are cells that have full chromosomes #?
- Diploid cells
How many chromosomes do humans have?
- 46 chrosones/23 pairs.
What happens during interphase?
- Chromosomes replicate to form sister chromatids.
What are homologous chromosomes?
- A pair of corresponding chromosomes
• The gene on one of the chromosomes in the pair
correspond to the other genes on the other
chromosomes in the pair.
• Each parent contributes one-half of chromosomes.
What is the joining or fusing of two gametes?
- Federalization
What happens in fertilization?
- The sperm would fuse into an egg to form a zygote?
What happenes to a zygote after fertilization?
- It reproduces through cell division/mitosis
• Each new cell will contain the same genome as the
zygote
What produces variation among members of the same species?
- Homologous chromosomes.
What are the different forms of the same gene called?
- Alleles
- How many alleles can be contained for the same type of gene?
- Two
- What is a dominant allele?
- An allele that will express its trait if it is present.
- What is an recessive allele?
- An allele that will only be expressed if both
chromosomes contain the recessive allele
- What if an individual has one of each allele?
- The dominant allele is expressed
- What is an incomplete dominance?
- When two different alleles produce a mixture of a trait
- What is codominance?
- When both traits are expressed in one individual.
- How many alleles are contributed to a child?
- Each parent contributes only one of its two alleles ni its
sperm cell or egg cell.
What are the advantages of sexual reproduction
- The offspring is genetically different from their parents
• This variation allows individual organisms to
adapt to changes in the environment.
• They can then reproduce and pass on the traits that
helped them survive to their offspring. - In outbreaks, some humans who are exposed to a
disease can fight it. They can reproduce and pass on
their ability to fight the disease to their children
What is a disadvantage of sexual reproduction?
- The individual needs to find a mate.
• Also tends to produce fewer offspring than asexual
reproduction and can be a lot slower.
• Most organisms that reproduce sexually have to grow
and develop before they start to produce gamest
What is an advantage of asexual reproduction?
- If a parent does well in its environment, the offspring
will also do well in the same environment because the
offspring are genetically identical to the parent. - Only one parent is necessary
- The parent does not need to find a mate
- They can reproduce very rapidly
• Bacterium living in a good environment can
reproduce every 20 minutes.
What is an disadvantage of asexual reproduction?
- Offspring cannot adapt to the environment as they are
genetically identical
• The offspring will be affected the same way as the
parent
What is conjugation?
- When two unicellular organisms transfer or exchange
some of their genetic material
• Organisms that can reproduce asexually by binary
fission can also reproduce sexually by conjugation
• Only occurs in some bacteria and certain protists,
such as paramecium
• The details of conjugation are slightly different in
different species
• Conjugation increased the diversity of individuals in
unicellular species- May be a factor that helps some bacteria to become
resistant to antibiotics
- May be a factor that helps some bacteria to become
How does E.Coli use conjugation?
- In E.coli, one cell copies an extra piece of its DNA,
called a plasmid, and donates the plasmid copy to
another cell
• Both the daughter cells then reproduce asexually
by binary fission
• The offspring they produce contain the same
amount of DNA as the parent
What are hermaphrodites?
- An organism that produces both male and female sex
cells in the same individual
• Hermaphrodite can mate with any other member of
their species to produce offspring
Why are species hermaphrodites?
- Because plants and some animals are attached to one
location throughout their life and rarely come in
contact with other members of their species. To get
around this situation, species become hermaphrodites
to allow them to reproduce with any other member of
their species.
How do earthworms reproduce?
- Two earthworms attach, exchange sperm, and then
seperate
• The sperm cells are stored in a special sac until the
eggs are ready
• Within a few days, fertilization takes place in a in a
mucus ring secreted by the clithellum, the thickened
band on a earthworm- The ring becomes a cocoon for the fertilized eggs
and slips off in the soil.
• The baby earthworms hatch about a week later
- The ring becomes a cocoon for the fertilized eggs
How do hermaphrodite organisms prevent the their sperm from fertilizing their own eggs?
- They produce sperm and eggs at different times
How do aquatic hermaphrodites such as sponges and barnacles reproduce?
- In sponges, the sperm are released into the water and
are carried by water movement to other sponges
• Fertilization occurs internally after the sperm enters
the sponge’s central cavity through tiny pores- The baby sponges called larvae are mobile and are
released into the water
• They swim to other locations, anchor themselves
to the bottom, and grow
- The baby sponges called larvae are mobile and are
- Barnacles have a penis, which extends into a
neighbouring barnacle to deposit the sperm
• The barnacle larvae are expelled into the water and
are carried by water currents to other locations
What is a flowers male reproductive system?
- The male reproductive structure is the stamen
• The stamen is made of the filament, a stalk that
supports the anther
• The anther is the top of the stamen and produces
pollen
- Pollen grains contain the male gametes (Sperm)
• There are usually several stamens on each flower
What is a flowers female reproductive system
- The female reproductive system is the pistil
• The top of the pistil is the stigma- The sticky stigma receives a pollen grain which will
travel down the style to the ovary, were the eggs are
contained
- The sticky stigma receives a pollen grain which will
Which flower structures surround the female and male structures?
- Petals and the stamen
• Petals are the coloured leaf-like structures of most
flowers- The organisms that pollinate flowers are attracted to
the coloured petals
• Sepals are tiny leaf-like structures that protect the
flower while it’s in the bud stage - Sepals are located at the base of the flower where it
joins the stem
- The organisms that pollinate flowers are attracted to
How do flowers reproduce
- Flowers reproduce by cross-pollination or by self-
pollination
What is pollination?
- The process by which pollen is moved from the male
structures to the female structures
• Pollination occurs in a variety of ways
What is self-pollination?
- Self pollination is when the pollen produced by a
flower can pollinate other flowers on the same plant