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Genetics - Coggle Diagram
Genetics
Patterns of heredity and examples
Dominant-Recessive
Dominant allele masks the effect of recessive
Incomplete Dominance
Neither allele is completely dominant and therefore the offspring shows a blend
Codominance
Both alleles are expressed equally
Sex-Linked
Traits controlled by genes on sex chromosomes
Polygenic
Traits controlled by many genes showing a range of variation
Probability of genetic disorders based on pedigree chart
Decide likely inheritance mode (autosomal dominant, autosomal recessive, X-linked, mitochondrial, polygenic). Use who’s affected (every generation? only males? mother→all children?)
Assign genotypes (use capitals for wildtype, lowercase for mutant: A = normal, a = mutant). Mark known genotypes; unknowns remain as probabilities.
Use Mendelian ratios for crosses (Aa × Aa, Aa × aa, etc.) to get child probabilities.
Use conditional probability (Bayes) when you have information (e.g., an unaffected child reduces carrier chance).
Report risk as a probability and state assumptions
Mechanism of inheritance of traits from parents to offspring
Gene & Chromosomes
There are 23 pairs of chromosomes in humans. The mother provides one pair, while the father provides the other half. The genes are located in each of those chromosomes
Gamete Formation
Body cells produce haploid gametes (eggs or sperm) with just 23 chromosomes during meiosis.
Fertilization
The zygote regains its diploid number (46 chromosomes) after the combination of sperm and egg
Expression of Traits
Same alleles: homozygous (AA or aa).
Difference alleles: heterozygous (Aa). Dominant alleles mask recessive ones
Sex Inheritage
Sex chromosomes determine sex: XX denotes female, XY denotes male. It's also usually determined by the father's sperm
Structure and location of genetic material in the form of chromatin, chromosomes, genes, and DNA
Chromatin
Structure: DNA wraped around histone protein and forming nucleosomes
Located inside the cell nucleus; can be euchromatin (loosely packed, active) or heterochromatin (tightly packed, inactive)
Chromosomes
Structure: Highly condensed chromatin forming thread-like structures, each containing a single long DNA molecule with many genes
Located in the cell nucleus; become visible under a microscope during cell division
Genes
Structure: A gene is a segment of DNA located at a specific locus on a chromosome.
Located along the DNA strand within chromatin in the nucleus.
DNA
Structure: DNA (deoxyribonucleic acid) is a double helix made of nucleotides (A, T, C, G).
Located in the cell nucleus, but also in mitochondria as mitochondrial DNA.
Mechanism of DNA Replication
Initiation
It starts at specific points where the helicase will unzip DNA double helix by breaking the hydrogen bonds. This process will create a replication fork
Elongation
There'll be leading strand (synthesized continuously toward the replication fork) and lagging strand (synthesized discontinuously away from the fork, forming short fragments)
Termination
Replication continues until the entire DNA molecule has been copied
Mechanism of DNA Transcription
Initiation
RNA polymerase binds to the promoter region of the DNA, once bound, the DNA strands unwind, and RNA polymerase begins synthesizing RNA using the template strand of DNA
Elongation
RNA polymerase moves along the DNA template strand, it adds ribonucleotides that are complementary to the DNA bases, elongating the RNA molecule in the 5' to 3' direction. The DNA re-forms its double helix after the polymerase passes, leaving the growing RNA transcript trailing behind
Termination
RNA polymerase reaches a terminator sequence on the DNA, The RNA transcript is released, and the RNA polymerase detaches from the DNA. In eukaryotic cells, the RNA transcript often undergoes further processing, such as the addition of a 5’ cap, a poly-A tail, and splicing to remove introns before becoming mature mRNA.
Genotype vs Phenotype
Genotype
The complete genetic makeup of an organism.
It represents the alleles inherited from both parents (e.g., AA, Aa, or aa).
It can't be directly observed but determines how traits may be expressed.
Phenotype
The observable characteristics of an organism. Explains why individuals with the same genotype may still look or behave differently.
Includes physical appearance (eye color, height), biochemical features, and behaviors.
Determined by the interaction between genotype and environment.
Chromosomal eximination
A test that evaluates the number and structure of human chromosomes. It can detect abnormalities such as an extra or missing chromosome, or structural changes like deletions, duplications, translocations, and inversions. The outcome of this test is a karyotype image
Indication
Prenatal Indications:
Women over 35 years old are at higher risk of chromosomal aneuploidies, abnormal results from ultrasound findings, having a history of chromosomal abnormalities in previous pregnancies or family members.
Postnatal Indications:
Children with intellectual disability, autism, or other developmental delays or features that may show chromosomal abnormalities, couples experiencing recurrent miscarriages may undergo chromosomal analysis to identify potential chromosomal issues in their parent, infertile couples may undergo chromosomal testing to identify any genetic or chromosomal abnormalities.
Adult Indications:
Used to diagnose and classify leukemias, lymphomas, myelomas, and other cancers by identifying acquired chromosomal abnormalities, adults experiencing infertility may undergo chromosomal testing to identify any genetic or chromosomal abnormalities
Mendelian vs Non-Mendelian
Mendelian
Traits controlled by a single gene with two alleles where one is completely dominant to the other,
Non-Mendelian
It doesn’t follow dominant-recessive pattern
ex: incomplete dominance, codominance, gene linkage
Mechanism of Translation and Meaning of Genetic Code
DNA Translation
Initiation
The small ribosomal subunit binds to the mRNA near the start codon (AUG). Then, tRNA carrying the amino acid methionine (initiator tRNA) pairs with AUG using its anticodon (UAC). The large ribosomal subunit joins, forming a complete ribosome with three binding sites (A site, P site, E site)
Elongation
A new tRNA with an anticodon complementary to the next codon on the mRNA enters the A site, a peptide bond forms between the amino acid in the P site and the one in the A site, ribosome shifts (translocates) down the mRNA, the cycle then repeats elongating the peptide chain
Termination
The ribosome reaches a stop codon (UAA, UAG, or UGA), no tRNA matches, but there's a release factor that binds to the ribosome, causing the polypeptide chain to be released, and ribosome disassembles, freeing the completed protein
Genetic Code
Link the base triplet sequence of DNA to the matching codons of RNA and the amino acids they set are known as the genetic code (a group of 3 nucleotides. They're used to store genetic information
Gene Mutation and Types
A change in a sequence of your DNA that alters the information to form and function.
Types
Point Mutations (Base Substitutions)
Insertions
Deletions
Frameshift Mutations
Duplication
Inversion
Translocation
Repeat Expansion / Microsatellite Instability
Regulatory Mutations
Splice Site Mutations
Medinna Rasha - 2506557816