Genetics: Chromosomal Basis of Inheritance

• Genetics: A Review of Chapter 5

Chromosomal Basis of Inheritance

• Gametes are sex cells, such as eggs and sperm.
• Gametes are haploid, with half the number of chromosomes present in somatic (body) cells.
• Fertilization reestablishes the diploid chromosome number.
• Fertilization involves the union of egg and sperm, which produces a zygote.
• Genotype refers to what is encoded by the genome.
• Phenotype refers to the traits seen in the animal as a result of the genome and the impact of the environment.

Central Dogma of Biology

• DNA undergoes replication and transcription to produce RNA, which then undergoes translation to produce Protein.
• The central dogma of biology is how all cells function.

Gene

• A gene is a series of nucleotides (called a sequence) that encodes a functional protein(s).

Artificial Cloning

• Artificial cloning demonstrates the DNA in somatic cells

Regulation of Gene Expression

• Every somatic cell (body cell) has all the DNA needed for all that organism's functions.
• Every cell has essentially the same DNA.
• Tissues differentiate because they use only some of the genes present in every cell
• In a particular cell or tissue, most genes are inactive at any given moment
• Regulation of Gene Expression controls which genes are turned on in which cells at what times (gene regulation).
• Gene regulation is important because all cells contain the the same DNA, and allows for specialized cells

Variability

• Variability allows animals to adapt to changing environments.
• Some organisms are better able to survive than others.
• Natural selection is the creative force of evolution, acting on biological variation.
• Without variation: No continued adaptation, no evolution and extinction.

Phenotypic Variation

• Phenotype is affected by genes and the epigenetics (the environment around the organism).
• Genetic material gets reshuffled and amplified via independent assortment of chromosomes, from crossing over events, from the random fusion of gametes, and from gene mutations.

Gene Mutations

• Gene Mutations are due to a change in the sequence of bases in DNA
• Mutations are random.
• Mutations can be beneficial, neutral, or harmful for the organism.
• Mutations do not "try" to supply what the organism "needs."
• Synonymous (silent) mutations result in the same protein, with no effect on function.
• Non-synonymous mutations result in a changed protein.
• Mutations that occur in non-reproductive cells won't be passed onto offspring.
• Assumed error rate of to 1×10-8 per base pair.
• Proofreading mechanisms fix about 99% of those errors, bringing error rate to about 1×10-10 per bp
• The human genome is about 3.2 × 10º base pairs, meaning that with every cell division, about 0.32 mutations are introduced.
• Assumed that it takes about 30 cell divisions to make an egg cell and about 400 cell divisions to make mature sperm
• Sperm cells have about 128 new mutations and mature egg genome has about 10 new mutations, for a total of 138 new mutations in every new zygote

Adaptation

• In humans, untreated HIV virus infection (AIDS) is nearly 100% fatal without treatment
• Some species are able to adapt to the HIV virus

Mutations at the molecular level

• HIV virus sticks to Helper T cells in order to be taken into the cell.
• Sticking is performed via a receptor protein, CCR5, that binds to GP 120 of the HIV
• Some people have a mutation that deletes the last 32 AA of CCR5
• Individuals missing the receptor, CCR5, cannot get HIV

How gene duplication contributes to evolution

• Gene duplications arise from unequal crossing-over, during meiosis between misaligned homologous chromosomes.
• Duplicated genes aren't necessary for survival.
• if mutations happen in the copied gene, the animal might still be ok.
• Mutations can accumulate over generations until the gene acquires a new function (neofunctionalization)
• New functions mean new structures and functions = evolution.