Week 12 Flashcards
Binary fission
Asexual reproduction
Single parent cell doubles its DNA, then divides into two cells. Usually occurs in bacteria.
Asexual reproduction
Budding
miniature adult grows on surface of parent breaks off, resulting in the formation of two individuals. Occurs in yeast and some animals (like the hydra below).
Asexual reproduction
Fragmentation
Organisms break into two or more fragments that develop into a new individual. Occurs in many plants, as well as some animals (like coral, sponges, and starfish).
Asexual reproduction
Parthenogenesis
An embryo develops from an unfertilized cell. Occurs in invertebrates, as well as in some fish, amphibians, and reptiles.
Sexual reproduction
Each parent contributes a gamete - a sex cell that has half of the normal DNA of a regular body cell. In males, the gametes are sperm and in females, the gametes are eggs.
When these two gamete combine during fertilization, the result is a zygote, which then continues to develop into an embryo.
What are nematodes
LArge group of microscopic worms
Caenorhabditis elegans are commonly found as what ?
Self fertilizing hermaphrodite (both male and female)
How do c elegans reproduce
Asexually and sexually (SOMETIMES)
Because of what did sex primarily evolve ?
Because of pathogens
What are pathogens
diseases – parasitic viruses, bacteria, fungi that infect other cells or organisms to take advantage of them.
P. antipodarum Snail Reproduction
Threatened with infection by more than a dozen species of trematode worms.
Sexually reproducing snails generate the most resistant offspring.
Asexual clones may rise in frequency, but parasites quickly evolve to infect these common genotypes, reducing their frequency.
When does coevolution occur
Coevolution occurs as parasites and hosts each try to gain the upper hand in the relationship.
What is the “backbone” of DNA
The sugar phosphate
Name the pyrimidine bases
Cytosine
Thymine
Uracil
N
Name the purine bases
Guangine
Adenine
How are nitrogenous bases held together
Hydrogen bonds
The second strand in the nitrogenous bases does what
+ what is it called
IT runs the opposite direction and called antiparallel
What plays a key role in shaping the structures of molecules
Intermolecular forces
Phosphodiester bond
Strong covalent bonds in backbone
Hydrogen bonding
Between base pairs - weak positive / negative attractions
Base
Stacking attraction from hydrophobic interactions
DNA is copied to make what
New cells
DNA replications works because…..
DNA replication works because each “parent” strand serves as a template for the synthesis of new “daughter” strands, using the base-pairing rules of A with T and G with C.
What enzyme is primarly responsible for replicating DNa
DNA Polymerase
During replication, in which direction is DNA synthesized
5’ to 3 direction
Which one is the lagging and leading strand ?
Strand that opens in the 3’ to 5’ direction is the lagging strand
Strand that runs in the 5’ to 3’ direction is the leading strand
Why does DNA replication occur in the 5’ to 3’ direction
Because DNA polymerase can only add incoming nucleotides to the 3’ side of the growing strand
Incoming nucleotides are accepted if…
..they are correctly base pair with the template (complementary base pairing)
What do incoming nucleotides have to do in order to form a bond to daughter strand ?
Incoming nucleotide has to bind to free 3’ –OH group to
form bond to “daughter” strand.
Can DNA polymerase start without a free 3’ OH group
NO
What does RNA primase do
RNA primase inserts an RNA primer at the origin of replication, thus providing a free 3’OH for DNA polymerase to start building the new strand of DNA
DNa replication occurs for 2 purposes
1) Mitosis: Cell Division for Growth or Asexual Reproduction
2) Meiosis: Cell Division to Create Gametes for Sexual
Reroduction (eggs and sperm)
Evolution requires..
.. variation
Evolution Requires Variation
Variation in Traits: All organisms exhibit a range of traits (size, color, ear shape, timing of development, behavior).
Phenotype: The visible, expressed traits of an organism.
Natural Selection: Selects for the best phenotypes in a given environment, against those that do not succeed.
Need for Variation: Variation in phenotypes is essential for natural selection to cause evolutionary change over time.
Sources of Heritable Phenotypic Diversity
Genetic Diversity: Key to phenotypic variation.
Genetic Mutation: Random changes in DNA sequences.
Horizontal Gene Transfer (Prokaryotes):
Prokaryotes reproduce asexually.
Horizontal gene transfer is separate from mitosis/replication/reproduction.
Sexual Recombination of Genes (Eukaryotes): Shuffling of genes during sexual reproduction creates genetic variation.
Why Have Sex?
Outcrossing (Sexual Reproduction): Combines genes from two sources, creating genetic diversity.
Genetic Diversity: Leads to phenotypic diversity, or a range of traits.
Unpredictable World: Diversity acts as insurance, providing opportunities for some individuals to succeed under new natural selection regimes.
Natural Selection: Can reduce genetic diversity, but sexual reproduction increases it more quickly than asexual reproduction.
Asexual Reproduction
Single Parent: Only one parent is needed for reproduction.
Offspring: The offspring is a clone of the parent, having the same genetic material.
Mitosis (Eukaryotes)
Process: Cell replicates itself, resulting in two identical daughter cells.
Purposes:
Growth
Wound repair
Asexual reproduction
Somatic Cells Formation: This process forms all somatic (body) cells in multicellular organisms, excluding gametes (eggs and sperm).
Diploid vs Haploid Cells
Diploid (2N):
2 sets of chromosomes (di = 2, ploidy = number of chromosomes, or N)
Have homologous chromosomes: two copies of each chromosome, one from mom, one from dad.
Example: Humans have 22 pairs of autosomes + 1 pair of sex chromosomes, totaling 23 pairs (2N = 46).
Haploid (N):
Contains only 1 copy of each chromosome.
Example: Gametes (sperm and eggs) in humans are haploid with 23 chromosomes
Homologous chromosomes
one copy from each parent (from gametes)
Diploid Cells (2N)
Definition: Diploid cells contain two complete sets of chromosomes, one from each parent.
Chromosome Number: For humans, diploid cells have 46 chromosomes (23 pairs).
Homologous Chromosomes: Each pair consists of one chromosome from the mother and one from the father.
Purpose: These cells are involved in growth, development, and repair in multicellular organisms, forming all somatic (body) cells except gametes.
Haploid cells means no _________ chromosomes in cell
No homologous chromosomes in cell
Two fold cost of sex
problems with sexual reproduction
Asexual populations grow at double the rate of sexual populations.
The problems:
1) In a sexual population, half the individuals cannot technically
reproduce – the males!
2) All offspring inherit only 50% of each parent’s DNA.
