Genetics: DNA structure

• Genetics is related to many areas such as:
• Transgenic organisms
• Designer babies
• End of life
• Healing disease
• Biodiversity
• Superbugs and antibiotics
• Cloning humans/animals
• Jurassic Park
• Origins of Life
• Cyber-organisms
• PETA animals as bio-factories
• Economic circumstances
• Genetics will cover:
• DNA structure
• Protein synthesis
• Cell division, and
• Inheritance.

DNA

• DNA is short for deoxyribonucleic acid.
• DNA is a set of coded instructions which produce physical characteristics.
• The double-helix structure was first described by James Watson and Francis Crick in 1953.
• Watson-Crick model describes DNA, the same structure for all organisms.
• DNA is made of smaller molecules called nucleotides.
• Each nucleotide consists of:
• A group of phosphates
• A deoxyribose
• One of four nitrogenous bases:
• Adenine (A)
• Thymine (T)
• Guanine (G)
• Cytosine (C)
• A nucleotide is connected to other nucleotides to form a strand.
• The phosphate and sugar groups always alternate.
• DNA is composed of strands of two nucleotides linked together in a ladder.
• The backbone is made of alternating deoxyribose sugar and phosphate groups.
• The steps are the nitrogenous bases.
• The bases are joined using hydrogen bonds.
• "A" of one strand compliments and pairs with "T" on the other.
• There are 2 hydrogen bonds between A and T.
• "C" of one strand compliments and pairs with "G" on the other.
• There are 3 hydrogen bonds between C and G.
• DNA sequence example: A, T, T, C, A, G, G, T, C, C, A, C
• Sequence for complementary strand: T A A G T C C A G G T G

Code of Life

• DNA contains the instructions for life.
• Just like Morse Code, it is the unique sequence and the number of bases which contain the complex and detailed life instructions.
• Genes are DNA segments which code for a particular protein responsible for a particular physical trait.
• The genes are unique using two methods.
• The code of the bases (the unique sequence)
• The length of the bases.
• Genes that code for Eye color could be A T G G C G T A A.
• Genes that code for hair color may be G G C C T A A A G C T A A T C G A T C G.
• A cell’s DNA stretched out would be 2m long.

Chromosomes

• Packages of DNA are Chromosomes.
• Chromosomes have very large section of DNA wrapped around proteins called histones.
• Being tightly wrapped around histones allows a large molecule to fit inside a cell.
• All DNA is inside the cell's nucleus.
• Karyotyping sorts unarranged chromosomes inside a cell into matching pairs used to study chromosomes of an individual.
• Chromosomes are matched based on their size and banding pattern.
• Human chromosomes have 23 pairs.
• Pairs ranging from 1-22 are called autosomes.
• Pair number 23 are called sex chromosomes.

Homologous Chromosomes

• Homologous chromosomes are sorted in matched pairs based on size and pattern.
• Each 'band' represents a locus.
• A single chromosome can have thousands of genes.
• Chromosomes with matching banding patterns are called homologous chromosomes and have the same gene in the same location.
• In homologous chromosomes inherited from either male or female parent.
• Genetic locus is location on a chromosome of a particular gene.

Sex Chromosomes

• Females are X X chromosome.
• Males are X Y chromosome.
• Y Chromosomes are shorter than X chromosomes.
• The sex chromosomes have the genes which produce the sexual characteristics.
• A body cell has 46 chromosomes, or 23 pairs, known as diploid in number.
• Egg and sperm cells only have 23 chromosomes, known as haploid in number.

Genes Part 2

• Genes are sections of DNA which code for a particular protein.
• Genes have a different sequence and a different amount of bases.
• DNA is condensed into chromosomes which fit inside the nucleus of a cell.

Protein Synthesis

Proteins and their building blocks

• Proteins are molecules composed of amino acids.
• There are 20 different kinds of amino acids.
• Genes are sections of DNA that contain the order and number of amino acids creating a functioning protein.
• DNA is inside the nucleus, but amino acids are found in the cytoplasm

Two stage synthesis

• Protein synthesis takes place in two stages.
• Transcription occurs in the nucleus.
• DNA is translated to a single-stranded molecule to travel out of the nucleus into the cytoplasm.
• Translation occurs in protein-making ribosomes, which are factories found in the cytoplasm.
• mRNA is translated in a protein chain at the ribosome.

Transcription

• In DNA, the four bases and Adenine, Thymine, Guanine and Cytosine.
• In RNA, the four bases and Adenine, Uracil, Guanine and Cytosine.
• The sequence of bases on DNA is transcribed onto mRNA using complementary base pairing:
• A pairs with U.
• G pairs with C.

mRNA Translation

• The bases on mRNA have three groups.
• Each triplet codes for an amino acid.
• Molecules called tRNA carry amino acids.
• mRNA and tRNA meet in the ribosome.
• mRNA consists of the instructions and message for the protein.
• Amino acids are the buildings blocks for protein.
• tRNA delivers guys to bring amino acids to the factory.
• Ribosomes are protein making factories.
• tRNA have anticodons which compliment mRNA codons.
• tRNA "clicks" onto the mRNA codon and deposits the amino acids in the correct order.

Mitosis & Meiosis

Mitosis

• Mitosis is a type of cell division which occurs only in somatic cells.
• During the process, a cell duplicates and forms two "daughter" cells.
• Body cells have 46 chromosomes (23 pairs) and are diploid in numbers.
• Mitosis is responsible for overall growth and repair of cells.
• With mitosis a cell duplicates itself, resulting in 2 identical daughter cells.

Mitosis: prepare to divide!

• Interphase must replicate its DNA to prepare for cell division.
• Each of the of the 46 chromosomes is replicated.

Phases of Mitosis (PMAT)

• Prophase:
• Chromosomes condense.
• Nuclear membrane disappears.
• Metaphase:
• The 46 chromosomes line up in single file.
• Spindle fibers connect to centromeres.
• Anaphase:
• The sister chromosomes separate.
• Telophase:
• Nuclear membrane reforms.
• Each new cell has its components.
• Cytoplasm divides, cell membranes form, chromosomes decondense to messy noodles.
• The end result of mitosis is two identical, diploid (46) cells.

Meiosis Cell Production

• Egg and sperm carry 23 chromosomes in humans.

• Meiosis only occurs in the sex cells to produce either (egg or sperm) cells.

• Meiosis produces four daughter cells with different chromosomes with haploid number of 23.

• A parent cell undergoing PMAT twice becomes meiosis 1 and meiosis 2.

• Because the chromosomes decrease division occurs, starting from 46 to 23.

• In Metaphase 1 chromosomes line up in their homologous pairs,

• Chromosomes line up in homologous pairs with banding pattern

• In metaphase 1 the chromosomes form homologous pairs when replicated.

• One replicated chromosome travels to each pole during anaphase 1.

• Telophase 1 is divided with two cells and one replicated chromosome in each pole.

Phases of Meiosis II

• Metaphase 2: consists of chromosomes lined in one single file.

• Anaphase 2: Sister chromatids separate.

• Telophase II consists of four haploid daughter cells.

• Homologous chromosomes line up in pairs during Meiosis I.

• Two cells with 23 chromosomes result at the end of Meiosis.

• In Meiosis 2, 2 haploid double-stranded cells produce 4 haploid single-stranded cells.

• Meiosis produces four genetically different cells.

• This is due to two processes:

• Crossing Over.

• Independent Assortment.

Crossing Over

• Crossing over happens in Prophase 1.
• Homologous chromosomes sections are swapped with each other.
• Recombinant chromosomes are used during crossing over.
• Genetic variation occurs due to genetic differences in population.
• You have traits from your parent’s DNA.

Independent Assortment

• In Metaphase 1, is when homologous pairs line up randomly.
• Daughter cells can end up with an uneven percentage of maternal vs paternal chromosomes.

##Inheritance

Inherited Traits defined

• Our physical traits are dependent on our genes such as:
• A Widow's peak or lack thereof.
• Hitchhiker's thumb or normal thumb.
• Segments of DNA that are coded produce a particular trait, such as hair color.
• Homologous chromosomes are copies of each gene.
• Different versions of a gene is called an allele.
• Examples blue eyed versus brown eyed alleles.
• Between alleles the same gene is stronger.

Dominant vs Recessive

• A dominant allele is expressed no matter what.
• You need one dominant allele for the trait to show.
• A recessive allele will only be expressed if chromosomes carry the allele.
• Two recessive traits are needed to be expressed.
• Phenotype: is physical trait expressed
• For example- ear lobes either: -- Attached represented by small e: a recessive trait -- Free is represented by capital E: a dominant trait

Genotype vs Phenotype

• Genotypes = what allele you have:
• Dominant = EE: A zygous, which is a free allele.
• Ee: A zygous, and a free allele.
• Recessive = ee: A zygous, and an attached allele.

Predicting the Traits: Punnett Squares

• Punnett squares predict all the possible genotypes of the offspring.
• To use a punnett square:
• Draw a 3x3 box.
• Indicate the female traits .
• Write the male traits.
• The alleles of the cross are the potential offspring.

Autosomal Dominant/Recessive

• The trait can be autosomal dominant or recessive when finding the gene on one of the first 22 traits.
• A small x indicated either x-linked dominance or repressiveness.