Biology 207 Chapter 1 & 2 & 3

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Blending Inheritance

Back 1

-discredited concept that some "essence" contained all the heritable information for an individual
-mating combines the essences from each parent
-once blended the essences could not be separated

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Mendel

Back 2

-first scientist to study heredity
-disproved blending inheritance
-proposed particulate inheritance (alleles)

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Alleles/genes

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Mendel's discrete factors of heredity (unit of inheritance)

example: gene for eye development, allele for blue eyes

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Griffith's Experiment

Back 4

Used 2 strains of s. pneumoniae:
1. smooth S-type (virulent) and rough R-type (not virulent)
2. Injected into mice (S=dead, R=live)
3. heat killed S =live (turned non-virulent)
4. heat killed S + R= dead (turned virulent)

Conclusion: some component of the S-Type stains contained genetic information that could be transferred to the R-type strains

**transformation**

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Avery, MacLeod and McCarty's experiement

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same as griffith's BUT

1. DNase to heat treated S + R= live (non virulent)
2. Protease to heat treated S + R= dead (still virulent)

Conclusion: DNA is the genetic material

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Hershey and Chase's experiement

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-Used bacteriophages grown either in the presence of radioactive sulfur or phosphorus.
-Looked to see if sulfur (protein) or phosphorus (DNA) entered the bacterium.
-After removing the phage, only observed phosphorus

Conclusion: DNA is the genetic material

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Beadle and Tatum

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-demonstrated the relationship between genes and metabolic pathways
- "One gene, one protein" rule (many exceptions, but generally true)
- grew fungus that was prototrophic for most amino acids, mutated it, and observed if it could grow on complete or minimal media and which AA could "rescue" it (metabolic pathways)

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Prototrophic

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can synthesize amino acids from minimal medium (simple sugars, a few vitamins and minerals)

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Auxotrophic

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-can not grow on minimal medium (can't synthesize AA's.
-Needs to be fed amino acids (metabolic pathways for synthesizing certain AA have been disrupted... ie, the gene that codes for a certain intermediate has been mutated)

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Chargaff's Rules

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-observations about the relative amount of each nucleotide that was present in almost any extract of DNA

- A=T and C=G

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Central Dogma

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-each gene is encoded in DNA... as needed, this genetic information is transcribed into RNA and then translated into protein

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c-value

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DNA content

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model organisms

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small c-value, diploid.

S. cerevisiae (yeast), C. elegans (round worm), d. melanogaster (fruit fly), M. musculus (mouse), D. rerio (zebrafish), A. Thaliana (plant)

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metabolic pathway

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A series of chemical reactions catalyzed by enzymes and are connected by their intermediates, i.e. the reactants of one reaction are the products of the previous one, and so on.

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Neurospora

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-fungus used by Beadle and Tatum to study metabolic pathways

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genome

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-complete set of DNA within the nucleus of an organism

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Core histones

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-proteins around which DNA is coiled (like a spool of thread)

-DNA is coiled twice around to form "nucleosome"

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nucleosome

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-DNA coiled 2x around a core histone protein. Looks like "beads on a string"

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histone H1

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-next level of organization
-helps compact the DNA strand

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30 nm fibre

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compact DNA (nucleosomes)

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scaffold proteins

Back 21

-wind the 30 nm fibre into coils (next level of organization in compacting the DNA)

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chromatin

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proteins + DNA

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Euchromatin

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-more loosely compact chromatin
-tends to contain more genes that are being transcribed

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heterochromatin

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-densely compacted DNA
-rich in short, highly repetitive sequences of DNA

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satellite DNA

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-short, highly repetitive sequences of DNA
-different buoyant density compare to main band of DNA (following centrifugation)

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centromere

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-usually heterochromatic
-each chromosome has one centromere
-centromeric proteins link the centromere to microtubules that transport chromosomes during cell division

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metacentric

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-when the centromere is located near the middle of a chromosome

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acrocentric

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-centromere is closer to one end of the chromosome

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telocentric

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c-entromere is at, or very near, the end of the chromosome

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telomere

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-repetitive sequences near the ends of linear chromosomes
-important in maintaining the length of the chromosomes during replication and protecting the ends of the chromosomes from alterations

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homologous chromosomes

Back 31

pairs of similar, but not identical, chromosomes
- one from each parent
-contain the same gene loci but not necessarily the same alleles

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non-homologous chromosomes

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-contain different gene loci
-may or may not be distinguishable based on cytological features (length, centromere position, banding patterns)

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sister chromatids

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when a chromosome undergoes replication during S-phase, itself and it's duplicate are called sister chromatids

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non-sister chromatids

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come from two separate, but homologous chromosomes (same genes, same order, not necessarily identical)

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DNA polymerase

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enzymes that do replication of DNA
- synthesize new nucleic acid strand by attaching nucleotide to the 3'OH group
- hence the 5' to 3' direction of replication (new strand is MADE 3' to 5'

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telomerase

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-RNA-directed DNA polymerases.
-posses a small piece of RNA that serves as a portable template

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mitosis

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-cell division method used by somatic cells
-end product is two Identical cells

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prophase

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-replicated chromosomes condense
-nucleus starts to break apart

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metaphase

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-chromosomes position themselves near the middle of the dividing cell
-line up along the metaphase plate (equatorial plate)

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anaphase

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-the sister chromatids from each replicated chromosome moves toward opposite poles of the dividing cell
-the chromosomes are pulled to opposite ends of the cell by microtubels

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telophase

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-the nuclear membrane starts to reform around each identical set of chromosomes at each end of the dividing cell

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cytokinesis

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division of the cytoplasm

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meiosis

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-cell division method used by germ line cells (gametocytes) to make gametes
-each gamete has half the the chromosomes
-end result is 4 non-identical cells that grow to form gametes (sperm, egg)

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meiosis

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Nuclear division in eukaryotes that reduces the chromosome number to half of the starting value and creates genetic variation among its products. Meiosis only occurs in specialize cells or at specific times in the life cycle of a eukaryotic cell.

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meiosis I

Back 45

First nuclear division of meiosis that reduces the ploidy of the primary meiocyte by half. The division consists of prophase I, metaphase I, anaphase I and telophase I.

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meiosis II

Back 46

Second nuclear division of meiosis in which each secondary meiocyte divides to form two gametes in a process similar to that of mitosis. The division consists of prophase II, metaphase II, anaphase II and telophase II.

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gamete

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Any cell whose ploidy is half of its progenitor cell and was formed through meiosis.

ie. "n"

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Synaptonemal complex

Back 48

proteins bind homologous chromosomes along their length

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bivalent

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-structure of the chromosomes in meiosis I.

XX

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crossing over

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A reciprocal exchange of genetic material that occurs within a bivalent between non-sister chromatids during prophase I of meiosis.

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reductional cell division

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number of chromosomes is decreased

example, meiosis I

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rescue

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Artificially supporting the growth of an auxotroph through the addition of a supplement or supplements, such as an intermediate or end product, to the solid or liquid media one intends to grow the organism on or in.

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equational cell divisions

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example, meiosis II and mitosis (number of chromosomes per cell is unchanged)

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G1 phase

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-Period of interphase that occurs immediately after a nuclear division and cytokinesis until the beginning of S-phase.
-cell does normal cell functions
-lag before the cell undergoes DNA synthesis

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gap2 (G2) phase

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Period of interphase that occurs immediately after S-phase until the beginning of nuclear division.

cells undergoing meiosis do not usually have a G2 phase

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M phase

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mitosis (or meiosis) and cytokinesis

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Interphase

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The longest, in terms of time, phase of the cell cycle. During this period cells grow, function as they are designed to, and prepare themselves for division. Interphase is broken down into three phases: G1, S-phase and G2

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G0 phase

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some cells never leave G1 (never divide) and enter into a permanent, non-dividing stage (Go phase)

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n-value

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number of chromosomes

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replicated chromosome

Back 60

pair of sister chromatids (still counts as 1 chromosome)

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N-value and C-value during cell cycle

Back 61

1. gametes= 1c and 1n
*fertilization*
2. zygote= 2c and 2n
*gap 1*
3. 2c and 2n (unchanged, cell is growing)
*synthesis*
4. 2n and 4c (DNA has doubled)
*gap2* or meiosis I
(2n and 4c OR 1n and 2c)
*mitosis or meiosis II*
5. 2n and 2c OR 1n and 1c

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karyogram

Back 62

A visual display of all chromosomes found in a cell. The chromosomes are usually arranged by type and size
-homologous chromosomes are grouped together

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karyotype

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written description of the chromosomes including anything out of the ordinary.

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autosome

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Any chromosome in the genome of an organism excluding the sex chromosomes.

humans have 22 autosomes

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sex chromosomes

Back 65

General term for chromosomes that directly or indirectly determining the sex of an individual.

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diploidy

Back 66

Term used to designate the basic chromosome number in somatic cells. Diploid cells are designated as 2x, they contain twice the number of chromosomes of gametes from the same spices.

example, 2x=2n=46 (n=23, x=23). This means we have 23 PAIRS (ie. 46) chromosomes in our somatic cells)

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polyploidy

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more than 2 homologous chromosomes.

Example, bread wheat has 6 homologous chromosomes

2n=6x=42 (n= 21, x=7)

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Monoploid

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bees and other hymenoptera use ploidy to determine sex.
Male = n (unfertilized egg) (haploid or monoploid)
female = 2n (fertilized egg)

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endoreduplication

Back 69

-tissue-specific genome amplification
-cell undergoes extra rounds of DNA synthesis (S-phase) without undergoing mitosis to produce an endopolyploid cell.

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aneuploidy

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addition or subtraction of one or more chromosomes from a group of homologs and is usually deleterious to the cell. (ie. trisomy 21)

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Polytene chromosomes

Back 71

over-sized chromosomes which have developed from standard chromosomes and are commonly found in the salivary glands of Drosophila melanogaster.

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allele

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One of many different forms a gene can have. Every gene has its own set of alleles with each allele having a particular phenotypic effect. Alleles of a single gene exist at that particular gene’s locus.

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mendel's first law (law of equal segregation)

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-during gamete formation, the two alleles at a gene locus segregate from each other
-each gamete has an equal probability of containing either allele.

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homozygous

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State in a diploid organism in which two identical alleles exist at a given locus.

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heterozygous

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State in a diploid organism in which two different alleles exist at a given locus

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hemizygous

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A condition in diploid organisms in which there is only one copy of a gene in the genome. This occurs most often for genes contained on the sex chromosomes in the heterogametic sex however, it can also occur because of mutation.

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wild-type

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Genotypes or phenotypes that are non-mutant and are generally the most frequent in a wild population.

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varients

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multiple "wild type" appearance

example, red hair or brown hair

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locus

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specific position along a chromosome

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genotype

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The genetic make-up of an organism. Most often described in terms of the allele(s) an individual is composed of at each loci, but can be more general or more specific.

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phenotype

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Physical, physiological or behavioural characteristics of an organism.

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dominant

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Alleles or phenotypes that, when expressed, mask the expression of other alleles or phenotypes to the extent that only the dominant phenotype is produced. See also recessive.

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recessive

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An allele or phenotype that is masked by the expression of a another allele or phenotype such that the recessive phenotype is not produced. See also dominant

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incomplete dominance/semi-dominance

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both alleles affect the trait additively.
-phenotype is an intermediate of both allels

example, purple flower allele colour (A) + white flower allele colour (a) = PINK flowers (Aa)

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Co-dominance

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heterozygote expresses the the phenotype of both alleles simultaneously

example, ABO blood type in humans

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haplosufficient

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one normal allele produces more than sufficient protein to have the same effect as the amount of protein produced by two normal alleles.

majority of wild type alleles are haplosufficient. This means that even if one allele is mutated and has a complete loss of function, the other allele will still produce enough protein to yield a normal wild type phenotype (DOMINANCE)

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haploinsufficient

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opposite of haplosufficient

ie. non-functional, mutated allele is dominant

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dosage compensation

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The male Y chromosome has a few genes on it, while the female X chromosome has many genes on it. To make up for the males only having a single X chromosome the genes on it are expressed at twice the normal rate... a process called dosage compensation

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sex-linked

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Genes on sex chromosomes are sex-linked because the are inherited together with the sex determining system

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reciprocal cross

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A controlled cross in which the phenotypes of the male and female parents are swapped from those of a previous cross.

-Whenever the reciprocal crosses give different results and whenever the male and female offsrping have different phenotypes, the usual explanation is sex-linkage

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Phenotype

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Physical, physiological or behavioural characteristics of an organism

genotype x environment = phenotype

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penetrance

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proportion of individuals (5) with a particular genotype that display a corresponding phenotype

-incomplete, or complete

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Expressivity

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describes the variability in mutant phenotypes observed in individuals with a particular phenotype.

-narrow (one or the other) or broad (range, blending)

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sampling effects

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the random selection of a non-representative subset of individuals for observation

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chi-square

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statistical procedure for determining whether deviation between observed and expected in due to sampling effects

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mutations

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Any change to a sequence of DNA from that of the standard (wild-type) sequence. The change does not necessarily results in a change in phenotype

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mutant

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mutation changes the phenotype of an individual, that ind. is a mutant