Week 2 Flashcards
What does the P value really mean?
The P value is the probability of a departure form the null expectation that is greater than or equal to what was observed
Autosomal Inheritance in Humans
Transmission of genes carried on autosomes
What is an autosome
Chromosomes found in both males and females
Pattern of inheritance for autosomal dominant traits
- Equal or similar frequency in males and females
- Each individual with the trait has at least one parent with the trait
- Either sex can transmit the trait to an offspring
- Even if both parents have the trait, they may produce offspring who do not have it
- Parents with a dominant phenotype that produce offspring with recessive phenotype must be heterozygous
Pattern of Inheritance for autosomal recessive traits
- Equal frequency in males and females
- If both parents have the trait, all offspring also will have it
- The trait is often not seen every generation but frequently seen among siblings in the same generation
- Unaffected parents of offspring with a recessive phenotype must be heterozygous
Diploid- Dominant life cycle
Majority of time spent as a diploid, Short period of time spent as haploid (gamete)
- Humans
Haploid-Dominant Life Cycle
- Spend majority of life cycle as haploid
- Most fungi and some unicellular eukaryotes
Species with blended diploid-dominant and haploid-dominant life cycles
- Some algae and all plants have multicellular diploid (sporophyte) and haploid (gametophyte) life stages
- In seeded plants, the gametophyte stage is only a few cells; the female gametophyte is contained within the flower
Cell Division
Tightly regulated process
- Too little prevents appropriate development and growth
- Too much leads to cancer, morphological anomalies and death
Mitotic Cell Cycle
- M phase: Cell division occurs
- Interphase: Longer period between cell divisions, including chromosome replication
- G0: Cell division is arrested; cell remains specialized but no longer divides and eventually dies (apoptosis)
Stages of interphase
- G1: Active gene expression and cell activity; preparation for DNA synthesis
- S Phase: DNA replication and Chromosome duplication
- G2: Preparation for cell division
Nucleolus
Where ribosome subunits are assembled
Centrosome
An organelle where spindle fibers form, that contains two microtubule structures called centrioles
Kinetochore
A disc-shaped structure where spindle fibers attach to pull sister chromatids apart
Prophase
Chromosomes condense
Prometaphase
Microtubules attach to chromosomes; nuclear membrane breaks down
Metaphase
Chromosomes align on the metaphase plate
Anaphase
Sister chromatids seperate
Telophase
New nuclear membranes form
Cytokinesis
The process by which the daughter cells separate
Purpose of cell cycle checkpoints
- Loss of cell cycle control is a major cause of cancer
- Failure of checkpoint leads to programmed cell death (apoptosis)
Cell Cycle Check points
- G1 Checkpoint: Pass if cell size is adequate, nutrient availability is sufficient, and growth factors are present
- S-Phase Checkpoint: Pass if DNA replication is complete and has been screened to remove base-pair mismatch or error
- G2 Checkpoint: Pass if cell is adequate and chromosome replication is successfully completed
- Metaphase Checkpoint: Pass if all chromosomes are attached to mitotic spindle
Meiosis
- Begins with diploid precursor cell that was generated by mitosis
- Chromatids are then duplicated, but remain connected to each other at the centromere
- The first round of cell division occurs (meiosis I), which results in each homologous chromosome becoming isolated in a different cell
- The second round of cell division occurs (Meiosis II), which results in each chromatid becoming isolated in a different cell (gametes)
What three major events occur in Meiosis I
- Homologous chromosome pair
- Crossing over (recombination) occurs
- Homologous chromosomes separate to daughter cells
Meiosis: Prophase I
Homologous chromosomes pair (synapsis) and recombine
Meiosis: Metaphase I
Pairs of homologous chromosomes align at the metaphase plate
Meiosis: Anaphase I
Chromosomes separate; sister chromatids remain attached
Meiosis: Telophase I
The nuclear membrane reforms; Cleavage furrow appear
Meiosis: Cytokinesis
The process by which cells seperate
Meiosis II
Separates sister chromatids into separate daughter cells
Recombination
- Occurs between non-sister chromatids of homologous chromosomes
- Occurs prior to homolog separation during meiosis I
The Synaptonemal Complex
A protein structure that forms between homologous chromosomes during meiosis I in eukaryotes
- Mediates recombination
How does meiosis relate to the law of segregation?
Homolog separation in meiosis II is the biological basis of segregation
How does meiosis relate to the law of independent assortment?
In meiosis one, there are alternative combination of which of the homologous chromosomes goes into each gamete
Differences in Oogenesis and Spermatogenesis
- Each miotic cell division of oogenesis results in 1 egg + 2 (or three) polar bodies (unequal cell division)
- Each cell division of spermatogenesis results in four sperm cells (equal cell division)
-Eggs are non-motile, sperm is motile - Growth phase in spermatogenesis is short (about 70 days), long in oogenesis (years)
- Millions of sperm are produced each day
- One egg is produced each mensural cycle, 1 ejaculate contains 200-300 million sperm
Oogenesis in Humans: Numbers of Oocytes throughout development
- Primary oocytes are established in female fetuses by 20 weeks after fertilization
- At this point, there are 7 million primary oocytes
- By birth, the number of primary oocytes decreases due to degeneration to 1-2 million (by puberty there are 60,000 - 80,000)
- About 500 mature oocytes are produced during a woman’s life
Oogenesis in humans: formation of an egg
IN UTERO
- Oogonium undergoes mitosis to become primary oocyte (which is stuck in prophase I)
AFTER PUBERTY
- Meiosis I occurs forming secondary oocyte and first polar body
- Secondary oocyte undergoes meiotic arrest in metaphase II and ovulation occurs
- When fertilized meiosis II is induced creating fully developed egg and secondary polar body
Types of zygosity
- Homozygous: Alleles are same
- Heterozygous: Alleles are different
- Hemizygous: Only one allele (e.g men at most x-linked genes)
What is a reciprocal cross?
- Allows one to examine the effects of sex on phenotypes
- Uses concept that males have only one X chromosome so they will express recessive phenotypes for x-linked genes even though they have only one recessive X-linked allele
- Cross of a female with recessive phenotype and male with dominant phenotype and then compare results to cross of reverse
