Bio-101-Chap-5-6-7

• (1) molecules of DNA from parent to offspring
• (2) the instructions on how to create a body and control its growth and development are encoded in the DNA molecule.

Francis Crick

James Watson

DNA is a macromolecule of nucleic acid. The building unit of DNA is termed a nucleotide whose three components are (1) a sugar molecule, (2) a phosphate group and (3) a nitrogen-containing molecule called a base

A double helix is like a spiral ladder with two railings, consisting of a phosphate group and a sugar, that holds it together, and steps or rungs, consisting of two base base pairs held together by hydrogen bonds.

• The four bases of DNA are adenine (A) thymine (T), guanine (G), and cytosine (C).
• A-T
• G-C

DNA is like a cookbook in that just as a cookbook contains detailed instuctions on how to make a variety of foods, and organism's DNA carries detailed instructions to build an organism and keep it running.

A genome is a full set of DNA, which are in manageable pieces called chromosomes.

A gene is a sequence of bases in a DNA molecule that carries the information necessary for producing a protein or RNA molecule.

Alleles are alternative versions of a gene that code for the same feature.

There does not seem to be any relationship between the size of an organism's genome and the organism complexity.

Only 5% of human DNA is actually genes

The function of the non-coding DNA is a big mystery. Perhaps it is a reservoir of potentially useful sequences, or it may function in regulating when genes are turned on or off.

If the genes that an organism carries for a particular trait-its genotype-are like a recipe in a cookbook, the physical manifestation of the instructions is the organism's phenotype-the cookies or macroni and cheese.

The two main steps in going from a gene to the production of a proteins are (1) transcription, and (2) translation

In transcription, one specific gene is copied and made into a specific RNA. This occurs in the nucleus where the DNA is located.

In step 1 of transcription, the enzyme RNA polymerase is responsible for copying a gene and making the specific RNA molecule. To do this it must recognize and bind with a promoter site, a part of the DNA molecule that indicates the start of a gene.

In transcription, RNA polymerase builds a messenger RNA (mRNA) using the gene as a template. The complementary bases are the same as DNA, except where the DNA has an adenine, the RNA is made with a complementary base of uracil.

The RNA that has been transcribed from a gene is always mRNA.

A termination sequence is always at the end of a gene, the RNA polymerase stops transcribing.

The mRNA is capped and tailed to protect it from damage, and help the protein-making machinery recognize it's a mRNA.

Translation occurs in the cytoplasm at the ribosomes.

The ingredients required for translation are (1) free amino acids, (2) ribosomes (3) transferRNA (tRNA) molecules that carry the building blocks (amino acids) of proteins.

Each three-base sequence in the mRNA is a codon, which always matches with tRNA that carries the amino acids.

mRNA always carries the same three-base sequence (AUG) to start translation.

mRNA has a specific three-base sequence that terminates translation.

A cell measures how old it is with an end section of each DNA called a telomere. Each time a cell divides the telomere gets a bit shorter, until it starts losing essential DNA, which then causes almost certain death for the cell.

Individuals with Hutchinson-Gilford progeria syndrome are born with shorter than normal telomeres, which causes them to age rapidly.

When cells rebuild their telomeres after each cell division, the cell then doesn't know when to stop dividing, a condition called cancer.

The prokaryotes have a single circular piece of DNA that is attached to one side of the cell membrane, while eukaryotes have multiple free floating linear strands of DNA contained in the nucleus.

The method of cell division in prokaryotes is called binary fission, and the replicated DNA and subsequent cell are genetically identical, and is therefore called asexual reproduction, since the division of the cell is also the reproduction of the individual.

Cells that don't divide once an organism matures, like muscle and neuron cells are in the Gap 1 (G1) stage of interphase.

If a cell is going to divide, it must prepare for this by replicating its DNA or chromosomes.

The division of the nuclear contents is called mitosis, while the division of the rest of the cells contents is called cytokinesis.

When DNA replicates itself the two DNA double helices are identical because of complementary base pairings.

The one purpose of mitosis is to enable existing cells to generate new, genetically identical cells.

The purposeful dying of a cell is called apoptosis, and is necessary for those cells which can accumulate significant genetic damage over time, which include cells lining the digestive tract and liver.

Sister chromatids are identical

Sister chromatids of a chromosome are pulled apart during anaphase of mitosis.

Malignant tumors are very harmful because they metastasize and spread throughout the body.

The chromosomes must be reduced in half in the gametes in anticipation of combining one individual's genome with another's during fertilization.

In all, the two important outcomes of meiosis are (1) reduce the amount of genetic material in gametes and (2) produce gametes that differ from one another with respect to the combinations of alleles they carry.

Homologous chromosomes separate during the second division of meiosis, while sister chromatids separate during the second division of meiosis.

In prophase 1 of meiosis, after the homologous chromosomes pair up, crossing-over occurs, and makes very sperm and egg genetically unique.

In Anaphase 1 random assortment occurs between the homologous pairs, which also makes sperm and egg unique.

Sexual reproduction leads to offspring that are all genetically unique, which allows the population of organism to cope better with changes in their environment. The sources of genetic variation are crossing over and the reassortment of homologs during meiosis, and the combining of alleles from two parents during fertilization. The disadvantage is an inefficient transfer of genetic information, which might lead to many offspring not surviving.

The advantage of asexual reproduction is an efficient transfer of genetic information, which will lead to many offspring surviving. The disadvantage is the environment changes the less suited they will be as a population.

The male determines the sex/gender of the child because half his sperm contain the Y-chromosome and half the X-chromosome, while the female eggs contain X-chromosomes. If the Y-chromosome sperm fertilizes the egg the baby becomes a female, and if the X-chromosome sperm fertilizes the baby becomes a male.

If the Y-chromosome is present the gonads become testes and, if not they become ovaries.

Amniocentesis is the procedure for removing cells from the amniotic fluid, and used to check for chromosomal abnormalties in the fetus.

Down syndrome people have an extra copy of chromosome #21,and is called a Trisomy 21.

Down Syndrome and other disorders caused by missing a chromosome, or having an extra copy of a chromosome, are the consequence of nondisjunctions, or the unequal distribution of chromosomes during meiosis.

When people get an extra chromosome and survive, it is likely that that extra chromosome is a short one, because long ones carry more genes, which enables more things to go wrong.

• Turner's syndrome=XO (deficient one X-chromosme=45 chromosomes
• Klinefelter's syndrome=XXY (one too many X-chromosomes=47 chromosmes
• Super males=XYY (one toomany Y-chromosomes)
• Metafemales=XXX, or XXXX, etc

By using the differences in weight, and fluorescent dyes, initial result suggest a 70-90% success rate in selecting the sex of our offspring.

Allele

Single-gene traits

Mendel described true-breeders as plants that produced offspring with the same variant of the trait as the parents.

To figure out which trait is dominant and recessive, Mendel cross a pure-breeding Purple flowered pea plants with pure-breeding white flowered pea plants. Because all the offspring had purple flowers, purple flowers is a dominant trait.

Because 1/4 of the offspring had white flowers, he found that these purple flowered pea plants were not pure-breeders.

Mendel's three (3) hypothesis were (1) Each parent put only one copy of gene into a sperm or egg, (2) the offspring receive two copies of gene, one from each parent, and (3) the trait observed in an individual depends on the two copies of the gene.

homozygous

heterozygous

Segregation

The outward appearance is called the phenotype, while the organisms genetic composition is called the genotype.

A test cross, using a know genotype, the recessive trait that is always due to homozygosity, is used to determine the genotype of an organism that has the dominant trait, whose genotype is either homozygous dominant, or herterozygous. If any of the offspring exhibit the recessive trait then the genotype of the dominant trait was heterozygous.

Incomplete dominance is exhibited when the heterozygote appears to be intermediate between the two homozygotes. When you cross a true-breeding red flowered snapdragon with a true-breeding white flowered snapdragon all the heterzygote are pink flowered.

Codominance occurs when the heterozygote displays characteristics of both homozygotes. In sickle cell anemia the individual blood has both normal red blood cells, and sickle celled red blood cells.

Multiple allelism is where a trait is due to three or more alleles, but the individual can only posses two at a time. In the ABO blood types, there is the A-allele, the B-allele, and the O-allele. Individuals are either AA, AO, BB, BO, AB or OO.

Polygenetic inheritance is due to two or more pairs of alleles which usually have an additive effect. Eye and skin color, and height are good examples.

Pleiotropy is where one gene can influence multiple unrelated traits such as the gene that produces male. Maleness is solely due to one gene on the Y-chromosome called the sex-determining region of the Y-chromosome (SRY), and causes all male characteristics.

When a trait is sex-linked and is due to a recessive gene, males have the trait more frequently. When a trait is sex-linked and is due to dominant gene, females get itmore frequently.

Because they are the same chromosome and closely linked to one another, making it virtually impossible for crossing-over to occur between them.