Chapter 3: Genetics: Reproducing Life and Producing Variation

Somatic Cells

Diploid cells that form the organs, tissues, and other parts of an organism's body.

Gametes

Sexual reproductive cells, ova and sperm, that have a haploid number of chromosomes and that can unite with a gamete of the opposite sex to form a new organism.

Genome

The complete set of chromosomes for an organism or species that represents all the inheritable traits.

Homoplasmic

Refers to nuclear DNA, which is identical in the nucleus of each cell type (except red blood cells).

Mitochondria

Energy-producing (ATP) organelles in eukaryotic cells; they possess their own independent DNA (mtDNA)

Adenosine Triphosphate (ATP)

An important cellular molecule, created by the mitochondria and carrying the energy necessary for cellular functions.

Matriline

DNA, such as mitochondrial DNA, whose inheritance can be traced from mother to daughter or to son.

Heteroplasmic

Refers to a mixture of more than one type of organellar DNA, such as mitochondrial DNA, within a cell or a single organisms' body, usually due to the mutation of the DNA in some organelles but not in others.

Nuclear DNA vs Mitochondrial DNA (mtDNA)

mtDNA comes only from mother (ovum, 37 gene)

mDNA: homoplasmic

mtDNA: heteroplasmic

The Structure of DNA

The compact chromosomal packaging of DNA enables hundreds of genes to be housed inside a cell's nucleus. The unwinding of this packaging reveal the genetic material.

DNA includes only one type of sugar (deoxyribose, the first part of the chemical name of DNA) and one type of phosphate group.

DNA includes four different types of nitrogen bases. A gene is a specific and unique sequence of these bases.

Nucleotide

The building blocks of DNA, made up of a phosphate group, a sugar, and a single nitrogen base.

Complementary Bases

Adenine - Thymine

Guanine - Cytocine

Zygote

The fertilized egg.

Karyotype

The picture of the chromosomes for an individual organism or a species, such as number, size, and type.

Sex Chromosomes

The pair of chromosomes that determine an organism's biological sex.

Patriline

DNA whose inheritance can be traced from father to daughter or son, such as the Y Chromosome, which passes from father to son.

Steps of DNA Replication

1. The two strands of DNA become the parent template strands for replication. Each strand will replicate, using its nitrogen bases to synthesize a complementary strand.

2. Replication begins with the separation of the two strands of DNA. Enzymes break the relatively weak hydrogen bonds that hold together the paired nitrogen bases. In effect, the DNA is "unzipped," creating the two parent template strands.

3. Each parent strand serves as a template for the creation of a new complementary DNA strand. The exposed, unpaired nitrogen bases on the parent strands attract complementary free-floating nucleotides. The nitrogen bases- for example, a free-floating nucleotide with a cytocine base will attach itself to a guanine base.

Mitosis vs Meiosis

Mitosis : Production of Identical Somatic Cells

Meiosis: Production of Gametes (Sex Cells)

Diploid

A cell that has a full complement of paired chromosomes.

Haploid

A cell that has a single set of unpaired chromosomes, half of the genetic material.

Cross-over

The process by which homologous chromosomes partially wrap around each other and exchange genetic information during meiosis.

Recombination

The exchange of genetic material between homologous chromosomes, resulting from a cross-over event.

Haplotypes

A group of alleles that tend to be inherited as a unit due to their closely spaced loci on a single chromosome.

Haplogroup

A large set of haplotypes, such as the Y-chromosome or mitochondrial DNA, that may be used to define a population.

Translocations

Rearrangements of chromosomes due to the insertion of genetic material from one chromosome to another.

Nondisjunctions

Refers to the failure of the chromosomes to properly segregate during meiosis, creating some gametes with abnormal numbers of chromosomes.

Monosomy

Refers to the condition in which only one of a specific pair of chromosomes is present in a cell's nucleus.

Trisomy

Refers to the condition in which an additional chromosome exists with the homologous pair.

Law of Independent Assortment

The traits liked to different chromosomes are inherited independently from one another. (ex. hair color is inhered independently from eye color)

Linkage

The inheritance of a package of genes (such as haplotypes) from the same chromosome. (an exception to Mendel's Law of Independent Assortment)

Amino Acides

Organic molecules combined in a specific sequence by the ribosomes to form a protein.

Essential Amino Acids

Those amino acids that cannot be synthesized in the body; they must be supplied by the diet.

Structural Proteins

Proteins that form an organism's physical attributes

Regulatory Proteins

Proteins involved in the expression of control genes.

Protein Synthesis

1. Transcription, which occurs in the nucleus, involves the creation of mRNA from one strand of DNA.

2. After the mRNA strand is completed, it leaves the nucleus and goes to the ribosomes, in the cytoplasm.

3. Translation takes place at the ribosomes. A protein is formed as the mRNA is "read" and the appropriate amino acids are linked together.

Transcription (in nucleus)

1. As in DNA replication, transcription begins with enzymes "unzipping" the DNA. Unlike replication, however, transcription uses only one strand of DNA.

2. Once the DNA strands have opened, messenger RNA (mRNA) attaches free-floating RNA nitrogen bases to the exposed, unpaired DNA nitrogen bases.

3. Once completed, the DNA closes back up, and the mRNA strand leaves the nucleus and goes to one of the ribosomes on the endoplasmic reticulum.

Translation (at ribosome)

1. Translation begins as the mRNA binds to a ribosome. In effect, the "message" carried by the mRNA is "translated" by a ribosome.

2. The ribosome "reads" the mRNA three nitrogen bases at a time. When a codon matches the transfer RNA (tRNA) molecule's anticodon, the tRNA's amino acid is added to the protein chain. For example, if the codon has the bases AUG, then the tRNA with the anticodon of UAC will attach the amino acid methionine to the chain.

3. As the ribosome moves the mRNA one codon at a time, tRNA continues to attach the appropriate amino acid to the protein chain. The amino acids are attached by a peptide bond, creating a polypeptide chain, which when completed is the protein. As each amino acid is added, the tRNA is released.

4. Eventually, a "stop" codon is reached, which indicates that the protein is completed. The mRNA leaves the ribosomes, and the protein is released.

At a ribosome, a molecule of tRNA brings the anticodon for each codon on the mRNA. The tRNA carries its anticodon on one end and the associated amino acid on the other.

Transcription

The first step of pretein synthesis, involving the creation of mRNA based on the DNA template.

Translation

The second step of protein synthesis, involving the transfer of amino acids by tRNA to the ribosomes, which are the added to the protein chain.

Ribonucleic Acid (RNA)

A single-stranded molecule involved in protein synthesis, consisting of a phosphate, ribose sugar, and one of four nitrogen bases.

Uracil

One of four nitrogen bases that make up RNA; It pairs with adenine.

Messenger RNA (mRNA)

The molecules that are responsible for making a chemical copy of a gene needed for a specific protein, that is, for the transcription phase of protein synthesis.

Ribosomal RNA (rRNA)

A fundamental structural component of a ribosome.

Transfer RNA (tRNA)

The molecules that are responsible for transporting amino acids to the ribosomes during protein synthesis.

Anticodons

Sequences of three nitrogen bases carried by tRNA, they match up with the complementary mRNA codons and each designate a specific amino acid during protein synthesis.

Triplets

Sequences of three nitrogen bases each in DNA, known as codons in mRNA.

Codons

The sequences of three nitrogen bases carried by mRNA that are coded to produce specific amino acids in protein synthesis.

Peptide bond

Chemical bond that joins amino acids into a protein chain.

Polypeptide

Also known as a protein, a chain of amino acids held together by multiple peptide bonds.

Coding DNA

Sequences of a gene's DNA (also known as exons) that are coded to produce a specific protein and are transcribed and translated during protein synthesis.

Noncoding DNA

Sequences of a gene's DNA (also known as introns) that are not coded to produce specific proteins and are excised before protein synthesis.

Structural Genes

Genes that are responsible for body structures, such as hair, blood, and other tissues.

Regulatory Genes

Genes that turn other genes on and off, and essential activity in growth and development.

GenesHomeotic (Hox) genes

Discovered in 1983 by Swiss and American researchers, these regulatory genes are coded to produce proteins that turn on many other genes, in particular those that determine the regions of the body during embryological development may be altered. For example, a mutation in the Hox genes of a fruit fly can cause a leg instead of an antenna to grow from the head.

Locus

The location of an allele, or gene. on a chromosome.

Polymorphism

Refers to the presence of two or more separate phenotypes for a certain gene in the population.

Antigens

Substances, such as bacteria, foreign blood cells, and enzymes, that stimulate the immune system's antibody production.

Antibodies

Molecules that form as part of the primary immune response to the presence of foreign substances; they attach to the foreign antigens.

Law of Segregation

Mendel's First Law, which asserts that the two alleles for any given gene (or trait) are inherited, one from each parent; during gamete production, only one of the two alleles will be resent in each ovum or sperm.

Homozygous

Refers to the condition in which a pair of alleles at a single locus on homologous chromosomes are the same.

Heterozygous

Refers to the condition in which a pair of alleles at a single locus on homologous chromosomes are different.

Codominance

Refers to two different alleles that are equally dominant; both are fully expressed in a heterozygote's phenotype.

Polygenic

Refers to one phenotypic trait that is affected by two or more genes.

Heritability

The proportion of phenotypic variation that is due to inheritance rather than to environmental influence.

Pleiotropy

Refers to one gene that affects more than one phenotypic trait.