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• Science 9 covers "DNA and Genetics"

Genetics Overview

• Certain traits or characteristics are inherited or heritable from parents.
• Due to sexual reproduction, variation occurs in how genes are expressed.

DNA Basics

• DNA, as inherited material, causes variation in the double-helix configuration.
• Arrangement of DNA is located inside the nucleus of all the cells.
• The DNA is the transmitter of the genetic code.
• Offspring resemble parents because characteristics pass from generation to generation.
• Breeding programs use genetic information to produce plants and animals with specific characteristics.

Watson, Crick, and Franklin

• James Watson and Francis Crick explained in 1953 that DNA has chemical building blocks.
• These blocks carry instructions causing diversity.
• The work was accomplished based on X-ray photos by Rosalind Franklin.

DNA Molecule Construction

• DNA molecule construction is in the form of a twisted ladder.
• The sides of the ladder are identical.
• Its steps are components with four chemicals that are different: Guanine, Cytosine, Adenine, and Thymine.
• Composition and arrangement of these chemicals code what cells can read.
• Arrangement into instructions is the "genetic code", that makes a particular organism look the way it does and acts as a blueprint.

DNA Location & Structure

• DNA is in the nucleus of animal and plant cells.
• DNA fits into the nucleus because it is exquisitely thin.
• 20 billion strands the width of a human hair.
• DNA divides into segments: chromosomes and shorter units called genes.
• All genes add up to become the genome.
• Chromosomes are large DNA pieces containing many genes.
• Base pair refers to the terms nucleotide, with slightly different meanings.
• A nucleotide is the structure of Cytosine, Adenine, Guanine, or Thymine, attached with deoxyribose sugar attached to phosphate.
• A base is Cytosine, Adenine, Guanine, or Thymine.
• A always pairs to T, and G always pairs to C, as base pairs.
• DNA is the large molecule in cells' nuclei that stores/passes on offspring information.
• The name is deoxyribonucleic acid.
• Humans have 46 chromosomes and 25,000 genes in their genome.
• The human genome has over 3 billion base pairs.
• There is 1 meter of DNA packed into every cell.
• If formed into a single strand, total DNA would stretch 10 billions miles.

Chromosomes & Sex

• Because DNA is responsible for a cell's physical and chemical characteristics, lots of DNA is inside the cell.
• DNA is approximately 2 meters in length.
• Total length is 1,000,000 bigger than what cell fits into, therefore DNA arranges itself into packages, or chromosomes.
• Each cell nucleus has 46 chromosomes arranged in 23 pairs.
• X chromosomes: Present in both males and females, contains genes needed for body and vision functions.
• Y chromosomes: Only in males and contains gene development.
• Mothers always provide an X chromosome and fathers provide either Y or an X.

Genes & Alleles

• Genes are DNA segments contributing to phenotype or exterior look/function.
• Genes occupy a fixed position or a locus on a chromosome.
• Offspring inherit genes from both parents.
• Genes in color are represented with two possibilities.
• Possible forms are known as alleles.
• Alleles are different versions of same gene.
• Genotype has a genetic code that informs cells for a particular trait.
• Phenotype is a visible expressed trait.

Cell Division - Mitosis

• Mitosis produces two new cells with same the number of chromosomes.
• Mitosis are used for growth and repair, replacing dead cells.
• 50-70 billion cells die in one's body every day.
• Mitosis essentially produces more of the same cells.

Cell Division - Meiosis

• 2nd type of cell division.
• Meiosis produces 1/2 the DNA of a normal cell or gamete.
• The cell division is used for sexual reproduction.
• Produces cells with 1/2 the DNA that is 1/2 the chromosomes of a cell.
• Gametes are male and female.
• Mules are from horses and donkeys.
• Mules get mules 63 chromosomes.
• Mules are very sterile.

Traits, Purebreds and Hybrids

• Traits are genetically determined characteristics.
• A purebred is an organism with identical alleles/genes.
• A hybrid: organism produces offspring that are genetically dissimilar from parents.
• Dominant traits express preferentially over another.
• Alleles are what causes a kitten to have black coat.
• Recessive traits are preferentially masked but not expressed or visible.
• A zygote is a cell that results from the fusing of male and female gametes, has a set of chromosomes.
• Homozygous refers to having two of the same alleles, with the same version.
• Heterozygous refers to having two different alleles.
• An upper case letter is used for the dominant trait and a lower case letter is used for a recessive trait.
• Incomplete dominance: intermediate inheritance or combined phenotype.