Molecular Biology Concepts

• Chromosomes consist of DNA, which contains genetic information in the form of gens.
• A gene is a segment of DNA that codes for a protein.
• An allele is an alternative form of a gene.
• Sex inheritance in humans is determined by X and Y chromosomes.
• Inheritance is the transmission of genetic information from generation to generation.
• Genotype refers to the genetic makeup of an organism, described by the alleles present.
• Phenotype refers to the observable features of an organism.

Homozygous vs Heterozygous

• Homozygous means having two identical alleles of a particular gene.
• Two identical homozygous individuals breeding together will be pure-breeding.
• Heterozygous means having two different alleles of a particular gene.
• A heterozygous individual will not be pure-breeding.

Dominant vs Recessive Alleles

• A dominant allele is expressed if it is present in the genotype.
• A recessive allele is only expressed when there is no dominant allele of the gene present.

Genetic Diagrams

• Pedigree diagrams are used to track the inheritance of characteristics.
• Genetic diagrams can be used to predict the results of genetic crosses.

Protein Creation

• The sequence of bases in a gene determines the sequence of amino acids used to make a specific protein.
• Different sequences of amino acids result in different protein shapes.
• DNA controls cell function by controlling the production of proteins, including enzymes, membrane carriers, and receptors for neurotransmitters.

Protein Synthesis Steps

• The gene coding for the protein remains in the nucleus.
• Messenger RNA (mRNA) is a copy of a gene.
• mRNA molecules are made in the nucleus and move to the cytoplasm.
• The mRNA passes through ribosomes.
• The ribosome assembles amino acids into protein molecules
• The specific sequence of amino acids is determined by the sequence of bases in the mRNA.
• Most body cells in an organism

DNA Structure

• DNA is formed of two strands that twist together forming a spiral known as a double helix.
• Each strand is formed of a sequence of bases.
• Bases of one strand form hydrogen bonds with bases of the other strand.
• There are four types of bases represented by A, T, C, and G
• A and T are joined together by two hydrogen bonds
• C and G are joined together by three hydrogen bonds.
• The sequence of bases provides codes for the types of proteins that have to be made in the cells.

Importance of Proteins

• Different types of proteins lead to development of characteristics, for example black hair is a protein while yellow hair is a different protein.
• Different types of proteins may be enzymes or hormones that affect the activity of the body or maybe antibodies for immunity.

Protein Synthesis

• The gene coding for the protein remains in the nucleus
• mRNA molecules carry a copy of the gene to the cytoplasm.
• the mRNA passes through ribosomes.
• the ribosome assembles amino acids into protein molecules.
• the specific order of amino acids is determined by the sequence of bases in the mRNA.
• Genetic information is transmitted from generation to generation.
• A chromosome is a coiled thread of DNA and protein found in the nucleus of cells, it is made up of a string of genes.
• Every species is characterized by having a certain number of chromosomes.
• Humans have 46 chromosomes in every cell of the body except for gametes, which have only 23 chromosomes.
• Chromosomes can be seen clearly in the cell by a light microscope only when the cell is dividing because they become shorter and fatter.
• Chromosomes carry genes.

Genetic Code

• The sequence of bases in a gene is the genetic code for putting together amino acids in the correct order to make a specific protein.
• DNA has only four bases, but proteins have 20 different amino acids, meaning that the four DNA 'letters' have to be combined to make different 'words', each one signifying a particular amino acid.

DNA and Cell Function

• DNA controls cell function by controlling the production of proteins (some of which are enzymes), antibodies, and receptors for neurotransmitters.
• DNA carries a code that instructs the cell about which kinds of proteins it should make.
• Each chromosome carries instructions for making many different proteins; a part of the DNA molecule coding for one protein is called a gene.
• Proteins are made up of long chains of amino acids, there are 20 different amino acids.
• The sequence of amino acids in a protein molecule determines the final shape of the molecule, and this shape affects how the protein works.
• DNA contains a code that determines exactly the sequence of amino acids a cell should string together when making a particular protein.
• A gene determines what protein will be made, and proteins affect an organism's features.
• Many proteins act as enzymes; other proteins have different functions, such as antibodies and receptors for neurotransmitters.

Types of Nuclei

• Haploid: A nucleus with one set of unpaired chromosomes, exemplified in gametes.
• Diploid: A nucleus with two sets of chromosomes, found in all body cells except gametes.
• Autosomes: Chromosomes responsible for different characteristics except sex.
• Sex Chromosomes: Chromosomes responsible for sex determination, represented by X and Y.
  • Y is shorter than X
  • Males have X and Y chromosome
  • Females have two X chromosomes

Homlogous chromosomes

• Homologous Chromosomes: Chromosomes that carry genes for the same characteristics in the same position.
  • Have the same position of centromere.
  • One comes from the father (paternal), while the other comes from the mother (maternal).

Definitions

• Genes: A specific length of DNA occupying a position called a locus on a chromosome, codes for making a particular protein.
• Alleles: One of two or more different forms of a gene.
• Inheritance: The transmission of genetic information from generation to generation.
• Chromosome: A thread-like structure of DNA, carries genetic information in the form of genes.
• Haploid Nuclei: A nucleus containing a single set of unpaired chromosomes, e.g., in gametes.
• Diploid Nuclei: A nucleus containing two sets of chromosomes, e.g., in body cells.
• Genotype: Genetic makeup of an organism in terms of alleles present (e.g., Tt or GG).
• Phenotype: Observable features of an organism.
• Homozygous: Having two identical alleles of a particular gene.
• Heterozygous: Having two different alleles of a particular gene.
• Dominant Allele: An allele that is expressed if it is present.
• Recessive Allele: Is only expressed when there is no dominant allele of the gene present.
• Types of Inheritance: Monohybrid and Dihybrid.
• Monohybrid: A cross between organisms showing contrasting variations for only one characteristic.
• Dihybrid: A cross between organisms showing contrasting variations for two characteristics.
  • Example: If black is dominant, black offspring from a black and white animal suggest black is dominant (A), while the allele for white is recessive (a)

Monohybrid Crosses

• Dominant: Allele which is expressed always, can be classified into: Homozygous or Hetrozygous.
• Recessive: The allele which is expressed in the absence of the dominant one.
• Each individual receives two alleles for each characteristic, one from each parent.

Allele types

• If the two alleles are identical the individual exhibits homozygous traits.
• If the two alleles are different, the individual exhibits heterozygous traits.
• In crosses between two homozygous individuals with different phenotypes, the result is 100% heterozygous dominant (e.g., GG x gg = Gg).
• Homozygous Cross Result Phenotype ratio:100%

Solving Genetic problems

• If two heterozygous individuals with the same phenotype are bred, the phenotype ratio is 3:1 (e.g., Rr x Rr = 3 red: 1 white)
• In a cross between a heterozygous dominant and a homozygous recessive, phenotype ratio is 1:1.

Test Cross

• Test Cross: Involves breeding a dominant phenotype with a recessive phenotype to ascertain if the dominant is heterozygous or homozygous

Sex Inheritance

• Humans body cells have 46 chromosomes or 23 pairs.
• 22 of these pairs are matching chromosomes, the 23rd pair, are the sex chromosomes.
• Female cells have two matching chromosomes and are XX
• While male pairs are non matching being XY

Sex Linked Traits

• Some characteristic traits are determined by the gene being linked to a sex chromosome, more common in one sex than the other.
  • Color blindness and haemophilia are often cited examples.
• Colour blindness is caused by an recessive allele and means individuals cat distinguish red, orange, yellow and green colours.
• It is determined by the use of cards that test the detection of sensitive cones

Co-Dominance Inheritance

• A situation in which both alleles in heterozygous organisms contribute to the phenotype
• Two alleles are expressed, where neither is dominant over the other, even when found at heterozygous pairs

Types of Blood

• ex. Blood Group: Three alleles IA, IB,O
  • Type A; which can have gentotype of IA IO or IA IA
  • Type B; which can have gentotype of IB IO or IB IB
  • Type AB; which can have gentotype of IA IB
  • Type O; which can have gentotype of IO IO

Test cross analysis

• Offspring shows no parental trait
• Means parents are heterozygous

Types of Nuclear Division

• Mitosis: Nuclear division giving rise to genetically identical cells, taking place in all reproductive organs.
  • Gives 2 identical cells
• Meisosis: Is reduction division, where chromosome are halved and result cells are genetically different
  • Gives 4 non identical daughter cells

Mitosis vs Meisosis

• Each nucleus involved in Mitosis, has the diploid number of chromosomes vs Meisosis which has the haploid.
• First is important for Growth, asexual reporduciton, where the second causes gene variation and sexual reproduction

Genetic Variation

• Meiosis produces genetic variation by forming new combinations of alleles from the maternal and paternal chromosomes.
• Stem cells are unspecialised cells that divide to create more versions that become specialised for functional organs.