Chapter 6: “ Meiosis is the basis of sexual reproduction”
Sexual Reproduction
- requires 2 parents
- produces off spring that are genetically different from one another, the parents, and any other
member of their species
Haploid vs Diploid
Haploid= half the genetic content (n) gametes or sex cells (egg and sperm) These are the only cells in
your body that are haploid
Diploid = genetic equal to the parent. Full genetic content (2n) body cells are diploid.
Meiosis
The process that produces gametes with half the number of chromosomes (haploid) as body cells
(diploid) occurs in the sex cells.
DNA replication occurs only once in the process.
Meiosis I: the result is two daughter cells.
Meiosis II: the result is four haploid cells, each with half the number of chromosomes.
Meiosis l
Prophase I: homologous chromosomes pair up.
Metaphase I: homologous chromosomes line up in the middle of the cell.
Anaphase I: homologous chromosomes separate and are pulled to opposite sides.
Telophase I: one chromosome from each pair is at each pole of the cell.
Interkinesis: phase between cell division; cell will grow and make proteins but will not replicate DNA
Meiosis ll
Prophase II: one chromosomes of the homologous pair in each cell.
Metaphase II: the x-shaped chromosomes form a single line across the middle
Anaphase II: sister chromatids move to opposite poles of the cell.
Telophase II: a nuclear membrane forms around the chromosomes.
Cytokinesis – the two daughter cells are separated
Core Lab page 176-177
Mitosis vs Meiosis
Mitosis
Meiosis
Where it occurs
In body cells
In sex organs to produce sex cells
# of daughter cells produced
Two daughter cells
Four daughter cells
# of chromosomes
Same number as parent
cell
Half the number of one parent cell
Type of reproduction
Asexual reproduction
Sexual reproduction
Intercourse is not required for sexual reproduction to occur, only in animals that have internal
fertilization.
“mating” refers to the process by which the gametes arrive at the same place at the same time.
Sexual Reproduction
1. Mosses: (fig 6.14 page 185)
Water allows the egg and sperm cells to meet / Reproduces both sexually (specific male and female
parts) and asexually (spores)
2. Flowering plants (fig 6.20 page 188)
Pollen (male gamete) is formed in the male part of the flower and the egg in the female
The fertilized egg will become a seed
Pollination is the transfer of pollen from the male structure to the female structure of the plant.
Identify the male and female structures.
Pollen can be transported by:
Pollinators such as bees and other insects, fruit bats / Wind / Water
3. Insects…
In many insects, the male deposits a package of sperm inside the female.
Insects often change a great deal between hatching and adulthood.
This change in form is called metamorphosis. Metamorphosis can be incomplete or complete.
Incomplete metamorphosis The adult and the nymph resemble one another
Ex. Grasshopper (fig 6.25 page 192)
Complete metamorphosis The adult and the larva look completely different
EX. Butterfly (fig 6.26 page 193)
Internal Sexual Reproduction vs External Sexual Reproduction
External
Internal
Egg and sperm unite outside the parents bodies
Sperm is deposited inside the female body to meet
the egg
Large numbers of offspring produced at one time
yet only a few survive to adulthood
More off spring survive even though less are
produced
Fertilized eggs are not protected from predators or
weather
Embryo is protected from predators
Very little energy required to find a mate
More energy required to find a mate
Gametes may not connect so not every egg will be
fertilized
Gametes may not connect so not every egg will be
fertilized
Asexual Reproduction vs Sexual Reproduction
Asexual Reproduction
Sexual Reproduction
1 parent cells
Two parent cells
No gametes; cell divides
2 sex cells unite to form a zygote
Little variation in offspring
Greater variation in offspring
Little energy required
Greater energy requited
Less parental care
Greater parental care
Studying Genetic Changes
Gregor Mendel
Mid-1800s - Experimented with inherited traits in pea plants. Suggested involvement of a dominant and
recessive factor in the transmission of traits.
Francis Crick & James Watson
1953 - Described the structure of DNA and how it replicates. This paved the way for why and how
mutations occur.
Genetic Engineering
To the food we eat and health related issues.
Lead to fears inside and outside the scientific community
The Human Genome Project
1986-2003 Genome: consists of the full set of genetic material that makes up an organism.
Made a map to identify genes
This information may be used to check for particular diseases.
Ex. Allderdice syndrome where part of one chromosome is reversed. Identified in Sandy Point NL.
Diagnosing a Genetic Disorder
A special “picture” of a person showing all their chromosomes arranged in a particular order called a
karyotypes studied. Can help to determine if there is any abnormalities in the chromosomes.
Can identify syndromes such as Down’s Syndrome (extra 21st chromosome)
We have no cure for genetic conditions such as Allderdice Syndrome, Down’s Syndrome and Cystic
Fibrosis