Biology Midterm II

Stages of the Cell Cycle

G1, S, G2, M

Interphase

Most of a cell's life. 3 phases : G1, Synthesis, G2.

G1 Phase

growth phase

G1 Checkpoint

checks for cell size, nutrients, growth factors and DNA damage; once passed, the cell is irreversibly committed to division.

G2 checkpoint.

checks if the DNA has been replicated and for DNA damage.

Synthesis

Phase in the cell cycle where the DNA replicates. After replication, each chromosome is made up of 2 identical chromatids attached by a centromere.

Spindle Checkpoint (M phase)

ensures that all of the chromosomes are attached to the spindle in preparation for anaphase

Contact Inhibition

Normal cells grow in a single layer. Once cells touch each other, cell division stops.

Mitosis

The actual process of making daughter cells with an equal # of chromosomes to the parent cell (2n). Is the division of the nucleus.

Stages of Mitosis

prophase, metaphase, anaphase, telophase

Cytokinesis

Division of the cytoplasm. Occurs during/after telophase. Cleavage furrow (animals) or cell plate (plants) starts to form until it eventually divides in two.

Spermatogenesis

Formation of sperm. Primary spermocyte, secondary spermocytes, spermatids.

primary spermatocyte (2n)

Prior to sex cell division. Diploid. End of Meiosis I

secondary spermatocytes

Beginning of Meiosis II. Diploid.

spermatids

Will mature into sperm. 4 haploid cells that are formed when the secondary spermocyte undergoes meiosis II.

primary oocyte (2n)

Product of Meiosis I that occurs during oogenesis. Begins before birth.

secondary oocyte

Beginning of Meiosis II. Diploid cell. Starts at puberty. Results in 1 ovum and 3 polar bodies.

Polar bodies

Cells produced in females that do not participate in reproduction, nourish the ovum.

Cross-section of seminiferous tubules

Lumen = center, surrounded by spermatids. Secondary spermatids surround it.

Chromosomes

Genetic information bundled into packages of DNA

Sister chromatids

Identical copies of a chromosome; full sets of these are created during the S subphase of interphase.

homologous chromosomes

2 identical chromosomes - 1 maternal + 1 paternal origin.

Karyotype

Pictorial of chromosomes from a cell.

Meiosis

Cell division that produces reproductive cells in sexually reproducing organisms

Why is chromosome reduction important?

The total chromosome \# for a species is constant. If the chromosome \# did not reduce, then the \# of chromosomes in offspring would double every time fertilization occurs.

Prophase I

The chromosomes condense, and the nuclear envelope breaks down. crossing-over occurs.

Metaphase I

Pairs of homologous chromosomes move to the equator of the cell.

Anaphase I

Homologues separate and move to the opposite poles of the cell.

Telophase I

Cytoplasm divides, 2 diploid daughter cells are formed

Crossover

a form of genetic recombination that occurs during prophase I of meiosis

Anaphase II

sister chromatids separate

Advantages of pea plants for genetic study

available in many varieties, flower color, short generation time, large number of offspring from each mating, easy to control mating.

Law of Segregation

Two alleles for a heritable character segregate during gamete formation and therefore end up in different gametes. During fertilization, each zygote receives 1 allele from the sperm and egg for a total of 2 alleles per gene.

Law of Independent Assortment

Two or more genes assort independently—that is, each pair of alleles segregates independently of any other pair of alleles—during gamete formation.

Law of Dominance

If two alleles at one locus differ, the dominant allele determines the trait expressed. Recessive traits are only expressed if two recessive alleles are inherited.

monohybrid cross ratio

3 dominant : 1 recessive.

monohybrid x recessive ratio

1 dominant : 1 recessive.

dihybrid cross ratio

9:3:3:1

dihybrid heterozygous x dihybrid recessive ratio

1 : 1 : 1 : 1

Causes of deviation from phenotypic ratios

Incomplete or codominance of alleles. Sex-linked Genes, Linkage of A and B genes (if they are located on the same chromosomes), Variations of the 9:3:3:1 ratio, Multiple genes determine a single trait (e.g multifactorial, polygenic), Pleiotropy.

Codominance

When each dominant allele is equally expressed. Applies when there are multiple dominant alleles.

Incomplete Dominance

The heterozygote displays an intermediate phenotype.

Sex-linked genes

these traits are determined by genes found on chromosome pair 23, or the sex-determining gene pair.

Examples of sex-linked genes

color blindness and hemophilia

Recessive epistasis ratio

9:3:4 ratio.

recessive epistasis

The expression of one combination of alleles (AA, Aa, aa) depends on the combination of another set of alleles (BB, Bb, bb).

Polygenic Inheritance

Occurs when a trait is controlled by several gene pairs (2+), each of which is additive. Leads to a range of graded traits.

Multifactorial Inheritance

a pattern of inheritance in which a trait is influenced by both genes and environmental factors

Pleiotropy

The ability of a single gene to have multiple effects.

Examples of Pleiotropy

sickle cell anemia, cystic fibrosis

Types of chromosomal anomalies

Structural and Numerical

Structural Anomalies

Single gene mutations, macro mutations.

Numerical Anomalies

Polyploidies and Aneuploidies.

Single Gene Mutations

Small changes in base sequences affecting a single gene. Invisible on karyotypes. Must use pedigrees (family trees) to study inheritance patterns and identify mutated genes.

Inheritance Patterns

Autosomal dominant, Autosomal Recessive, X-linked dominant, X-linked recessive, Y-linked, Mitochondrial

Macromutations

Major rearrangement of genes on a chromosome. These are structural changes observed by karyotype.

Types of Macromutations

Deletion, Inversion, Duplication, Reciprocal Translocation

Polyploidies

extra set of chromosomes. Often non-viable in animals but important for evolution in plants.

Aneuploidies

One or a few extra or missing chromosomes. Results from nondisjunction during Meiosis I or II. When these abnormal gametes fertilize normal gametes the resulting zygote is aneuploid.

Trisomy 13

Patau syndrome, 1/15,000 live births

Trisomy 18

Edward's Syndrome. 1/5000 live births.

Trisomy 21

Down syndrome. 1/700 live births.

Turner syndrome (XO)

1 missing X chromosome. Only viable monosomy in humans. Rudimentary ovaries, leading to no puberty.

Klinefelter Syndrome (XXY)

an extra X chromosome causes physical abnormalities (e.g sterility, mental disability).

Metafemale syndrome (XXX)

Leads to irregular menstruations, early menopause. Disability increases with the # of X chromosomes.

Jacobs "Supermale" Syndrome (XYY)

Tall, possible mental disability.

Sex Chromosomal Aneuploids

More frequently occur, due to inactivated X chromosomes (Barr bodies).

Barr bodies

inactivated X chromosomes found only in females

Mitochondrial

Disease inherited from mother. Can cause vision impairments and muscle weakness.

Phenylketonuria (PKU)

Sufferers lack an enzyme that converts phenylalanine to tyrosine. Phenylalanine therefore accumulates and is converted to toxic forms called phenylketones, which damage the central nervous system. Autosomal recessive condition.

Sickle Cell Anemia

Caused by a point mutation in hemoglobin. Autosomal recessive.

Red Blood Cells (RBC) which express this mutated form of hemoglobin have an abnormal "sickle-like" shape, which can clog blood vessels and result in tissue damage.

Cystic Fibrosis

Caused by a single point mutation in a gene which encodes a Cl- membrane transporter. Afflicted individuals do NOT express this transporter. Cl- is therefore NOT pumped out, leading to water flow (which normally follows the movement of chloride out of the cell) not occurring. Mucus secreted in the respiratory tract is therefore too thick and causes inflammation of the airways, leading to infections.

types of interspecific interactions

competition, predation, herbivory, symbiosis (parasitism, mutualism, and commensalism), and facilitation

Competition

the struggle between organisms to survive in a habitat with limited resources

Predation

An interaction in which one organism kills another for food.

Herbivory

interaction in which one animal (the herbivore) feeds on producers (such as plants)

Symbiosis

Individuals of two species live in close contact with each other.

Parasitism

The parasite derives its nourishment from a second organism which is harmed.

Mutualism

Both species benefit from the interaction.

Commensalism

One species benefits from the interaction, while the other is unaffected by it.

Facilitation

Species have positive effects on the survival and the reproduction of other species without the intimate contact of a symbiosis.

Useful Traits of Prokaryotes

Small size and rapid reproduction, large \# of mutations and adaptations, rapid evolution.

Chemoheterotrophs

An organism that must consume organic molecules for both energy and carbon.

Photoheterotrophs

An organism that uses light to generate ATP but that must obtain carbon in organic form.

Photoautotrophs

Organisms that use light as a source of energy to synthesize organic substances. Water splitting/non-water splitting.

Chemoautotrophs

Organisms that use hydrogen sulfide or ammonia as energy source instead of light.

Domain Bacteria

Prokaryotes with peptidoglycan in their cell wall.

Prokaryotic Cell Structure

Haploid, with a singular circular chromosome, therefore recessive mutations are readily expressed.

Shapes of Bacteria

coccus (round), bacillus (rods), spirillum (helical).

Strepto -

chains

staphylo -

grape-like clusters

Metabolism of bacteria

chemoheterotrophs or photoautotrophs

Bacterial Chemoheterotrophs

Saprobes, Parasites, Mutalistic symbionts, Organisms using nitrogen fixations

Saprobes

Decomposers which derive their nutrients from dead organic material.

Parasites

Heterotrophs which absorb their nutrients from a living host (e.g Lyme Disease caused by "spirillum" bacteria.)

Mutualistic Symbionts

(e.g E.Coli living in the digestive tract of animals and aiding in the digestion of food for the host while simultaneously receiving shelter + free food).

Organisms using Nitrogen Fixation

Conversion of atmospheric nitrogen to a form usable by other organisms (e.g Ammonia or Nitrate). Examples include Rhizobium fixing N2 in roots or legumes.

Bacterial Photoautotrophs

Bacteria that use light to make their own food; example includes cyanobacteria (filamentous).

Ecological Importance of Chemoheterotrophs

Decomposers recycle material back into the ecosystem.

Ecological Importance of Photoautotrophs

Producers providing oxygen and organic material (e.g fixed nitrogen) for other materials. Especially important in aquatic environments.