Mitosis and Meiosis

Term 1 Summary

• Every cell contains a nucleus.
• Every nucleus contains chromosomes.
• An adult has a full set of chromosomes.
• Sex cells contain half the chromosomes.
• Sex cells are also called gametes.
• A zygote forms when gametes fuse.

Mitosis

• Mitosis is a form of cell division for growth and repair.
• Chromosomes duplicate before mitosis.
• Mitosis produces two identical daughter cells.
• The new cells are diploid, having the full number of chromosomes in the nucleus.
• Cytokinesis is the final step where the cell divides in two.
• Cancer cell mitosis is uncontrolled and rapid.

Mitosis and Meiosis Similarities

• Both processes start from a single cell.
• Both involve cell division.
• DNA must replicate before each process.

Key features of Mitosis

• Facilitates growth and repair.
• Daughter cells have a full set of chromosomes.
• Produces two daughter cells.
• Results in identical daughter cells.

Key features of Meiosis

• Involved in reproduction.
• Separates chromosomes in half.
• Produces four daughter cells.
• Results in non-identical daughter cells.

Mendel’s Ideas

• Traits are single heritable units, not a blend between generations.
• Gamete formation knowledge predicts simple trait inheritance.
• Each parent contributes one chromosome pair to their gametes during meiosis.
• Offspring proportions can be predicted using a Punnett square, as it is a random event.

Homozygous

• Cells contain identical genes for a characteristic and are pure breeding.

Heterozygous

• Cells contain different genes for a characteristic and are hybrid.

Genetics

• It is the study of genes and heredity.

Hereditary

• Is the transfer of characteristics from one generation to the next.

Gene

• It is considered, the basic unit of heredity passed from parent to child.

Allele

• Is the alternate form of a gene.

Genotype

• Is the genetic makeup of an organism.

Phenotype

• Is the physical expression of a gene.

Karyotype

• Is how genetics identify, organize, and study human chromosomes.

Chromosomes

• Humans have 46 chromosomes (23 pairs) in every somatic cell.
• The first 22 pairs are autosomes and the 23rd pair are sex chromosomes.
• Females have XX sex chromosomes, while males have XY.

Pedigree

• Is a graphical representation of inheritance patterns of a trait over generations.

Recessive Autosomal Characteristics

• Appear in offspring of unaffected parents.
• Cannot occur if both parents are affected but their offspring are unaffected.
• Affects both sexes equally.
• May skip generations but reappear later.

Dominant Autosomal Characteristics

• Typically appear in every generation.
• Unaffected parents do not transmit the condition to offspring.
• Affects both sexes equally.
• Disappears and does not reappear in later generations

Complimentary Roots

• Are formed by the pairing of specific bases.

Gene Mutation

• Is a permanent alteration in the DNA sequence of a gene.

Hereditary Mutations

• Are inherited from a parent and present throughout life in every cell.

Acquired (or Somatic) Mutations

• Occur sometime during a person's life, present only in certain cells.

Mutation Types

• Include substitution, deletion, and insertion

Base Substitution

• It occurs when a normal base is substituted for a different base
• Outcomes could be silent, nonsense, or missense

Silent Mutation

• The base does not affect the amino acid, and there is no observable change to the sequence.

Nonsense Mutation

• The base affects the amino acid and the sequence no longer makes sense.

Missense Mutation

• The base alteration affects the amino acid, rendering the sequence to make sense in an alternate way.

Deletion

• One or more base pairs are lost from the DNA resulting in a frameshift.
• Deletion of one or two bases alters the translational frame, resulting in a non-functional product

Insertion

• The insertion of additional base pairs causes frameshifts, based on multiples of three being inserted.

Errors in DNA Replication

• DNA polymerase may rarely incorporate a noncomplementary base into the daughter strand.
• During the next round of replication, the missincorporated bases mutations may occur
• Exonuclease functions as a proofreading mechanism recognizing mismatched base pairs and excising them.

Errors in DNA Recombination

• DNA often rearranges by recombination, occasionally leading to DNA loss and mutation.

Nucleotides

• Are the basic building blocks of nucleic acids (RNA and DNA).

Codons

• Cells decode mRNAs by reading nucleotides in groups of three.

Features of Codons

• Most codons specify an amino acid.
• Three "stop" codons mark the end of a protein.
• One "start" codon, AUG, marks the beginning of a protein and encodes methionine.

Gene Cloning

• Is a molecular biology technique that makes many identical copies of a piece of DNA, like a gene.

Gene Cloning Method

• Cut out the gene of interest.
• Paste it into a bacterial plasmid.
• Grow billions of bacteria.

Gene Cloning Usage

• Creation of GMOs (genetically modified organisms).
• Manufacturing pharmaceuticals and vaccines.
• Genetic research in university labs.

Whole Organism Cloning

• Reproductive cloning is the process by which a whole organism is cloned.
• Plants are uncontroversial to clone while animals are slightly controversial to clone.
• An organism's phenotype is the result of genes and environmental influences.

Steps for Whole-Animal Cloning

• Somatic (body) cell collection by scientists
• Obtaining an egg cell and remove its nucleus carefully
• Insert the nucleus from the somatic cell (containing the animal's DNA to be cloned) into the enucleated egg cell
• Stimulate the egg cell with the donor nucleus to begin dividing and turning into an early-stage embryo
• Culture resulting embryo in a laboratory to develop into a blastocyst
• Transfer the blastocyst to the uterus of a surrogate mother to develop and grow into a clone of the original animal.

Gene Cloning in Human Medicine

• Cut open the plasmid and "paste" in the gene using restriction enzymes (cut DNA) and DNA ligase (joins DNA).
• Insert the plasmid into bacteria and use antibiotic selection to identify the bacteria that took it up.
• Grow lots of plasmid-carrying bacteria and use them as "factories" to make the protein; harvest and purify it.