Chromosomal Mutations

Menstrual Cycle

• A periodic cycle of changes occurs in the ovaries (ovarian cycle) and the endometrium/uterine lining (uterine cycle).
• These changes are crucial for human development.
• Four key hormones drive the menstrual cycle: FSH, LH, estrogen, and progesterone.
• Estrogen and progesterone are always present together.

Phases of Menstrual Cycle

Follicular Phase

• FSH stimulates follicle formation in the ovaries.
• Follicles are fluid-filled sacs containing developing eggs.
• Estrogen and progesterone, triggered by follicles, thicken the uterine wall for blastocyst implantation.
• A blastocyst is a fertilized egg.
• The blastocyst's outer layer becomes the placenta if pregnancy occurs, delivering nutrients and removing waste.
• Key events comprise follicle development, uterine wall thickening, and LH production.

Ovulation Phase

• LH triggers the release of the egg cell.
• The egg awaits fertilization in the ampulla of the fallopian tube.
• The primary event is the release of the egg cell from the ovary.

Luteal Phase

• Empty follicles transform into the corpus luteum.
• The corpus luteum maintains elevated estrogen and progesterone levels to sustain the thick uterine lining.
• The main event is the transformation of the empty follicle.
• Sustained estrogen and progesterone maintains thickening of the uterine wall.
• If fertilization occurs, hCG is produced, maintaining the corpus luteum and uterine lining.
• Pregnancy kits detect hCG.
• If no fertilization occurs, the corpus luteum decays, hormone levels drop, and the uterine lining sheds, initiating the menstrual phase.

Menstrual Phase

• The uterine lining sheds and is expelled as menstrual flow.

Central Dogma of Molecular Biology

• States DNA (Replication) --(transcription)--> RNA --(translation)--> PROTEIN.
• Coded genetic information in DNA is transcribed into mRNA cassettes.
• Each mRNA cassette programs the synthesis of a specific protein.
• Proposed by Francis Crick in 1958.

DNA

• Deoxyribonucleic Acid.
• Deoxyribo- indicates the sugar, while -nucleic Acid refers to the phosphate and base.
• DNA is a double helix of two nucleotide strands.
• Nucleotides are DNA's building blocks; their binding makes DNA a polymer.
• A polymer contains repeating monomer units.
• DNA is found in the nucleus of all cells except blood cells.
• DNA is organized into chromosomes, which carry genetic information.
• Genes are smaller, specific segments of DNA.
• In 1953, Francis Crick and James Watson discovered DNA's double helix structure with paired nitrogen bases.

RNA

• Ribonucleic Acid.
• Ribo- indicates the ribose sugar content, not deoxyribose.
• RNA is single-stranded.
• RNA contains Uracil (U) instead of Thymine (T).

DNA Replication

• The process where DNA duplicates itself during cell division.
• It ensures identical genetic information is passed to new cells.
• A nucleotide monomer consists of phosphate, pentose deoxyribose sugar, and a nitrogenous base.

Complementary Base Pairing

• It ensures replicated DNA matches the source DNA.
• Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C).

DNA Replication Phases and Enzymes

• Topoisomerase uncoils the DNA.
• Helicase separates the DNA strands.
• DNA primase identifies the starting point.
• DNA polymerase replicates new DNA based on the template strand.
• The double helix is uncoiled, and strands are separated.
• DNA primase is synthesized, marking the start.
• DNA polymerase replicates a new strand by matching bases to the template.

Transcription

• Transcription of DNA to mRNA falls under gene expression.
• Gene expression is the process of genetic information directing the assembly of a protein.
• RNA Polymerase transcribes DNA into RNA.

Transcription Phases

• RNA polymerase binds to the promoter region, initiating DNA unwinding and mRNA synthesis.
• RNA polymerase reads the strand and creates a complementary mRNA strand.
• Upon reaching a termination signal, transcription stops, and the mRNA detaches.

Translation

• After transcription, mRNA moves to the cytoplasm and then the ribosome for protein synthesis.
• The ribosome uses tRNA to translate the mRNA sequence into amino acids.
• Amino acids combine to form proteins.
• Amino acids are monomers that form polymers called proteins.
• There are 22 known amino acids, 20 are directly coded during translation.

Protein Synthesis

• During translation, mRNA sequences (codons) are read in triplets and translated into specific amino acids.
• Methionine (Met), encoded by [AUG], marks the start of protein synthesis.
• [UAA], [UAG], [UGA] are STOP codons.

Chromosomal Mutation

• Mutation of chromosomal segments involving changes in number or structure.
• Humans typically have 23 pairs of chromosomes, totaling 46.
• Mutations arise from issues during cell division or mutagens.

Statistics

• 3-5% of people are affected by birth defects/genetic conditions.
• A 20-year-old has less than a 1/1000 chance of having a baby with Down syndrome.
• A 35-year-old has a 1/350 chance.
• A 40-year-old has about a 1/100 chance.

Types of Mutation

Numerical Mutation

• Changes in chromosome number.

Trisomy

• An extra chromosome, for example, Down syndrome (Trisomy 21) or Edward syndrome (Trisomy 18).

Monosomy

• Lack of a chromosome, for example, Turner syndrome (Monosomy X).

Structural Mutation

• Changes in chromosome structure

Deletion

• Loss of a chromosome segment, for example, Cri-du-chat syndrome.

Duplication

• Extra copies of gene segments, for example, Pallister-Killian Syndrome.

Inversion

• Chromosome segment reversal, for example, Hemophilia A.

Translocation

• Transfer of a chromosome segment to another, for example, Acute myeloid leukemia (AML).

Test your knowledge of chromosomal mutations. This quiz covers types such as inversions, translocations, and conditions resulting from missing chromosomes. Match mutations to the correct descriptions.