Advanced Genetics & Reproduction: Structured Study Notes

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CHAPTER 8: Chromosomes & Human Genetics

Karyotyping vs. Pedigree Analysis

Karyotyping and pedigree analysis are essential tools in human genetics for identifying chromosomal abnormalities and tracking inheritance patterns.

Karyotyping: Laboratory process where chromosomes are stained, arranged, and photographed to identify chromosomal abnormalities (e.g., extra or missing chromosomes).
- Detects: Down syndrome, Turner syndrome, etc.
- Usually uses cells arrested in metaphase.
Pedigree Analysis: Diagram of a family's genetic relationships and phenotypes used to track inheritance patterns of traits (dominant, recessive, sex-linked).

Syndromes

Certain syndromes are caused by chromosomal abnormalities. The table below summarizes key examples:

Syndrome	Chromosomal Basis	Key Features
Down (Trisomy 21)	Extra chromosome 21	Intellectual disability, short stature, heart defects, distinct facial features
Turner (XO)	Missing an X (monosomy X)	Female only, short stature, webbed neck, no secondary sex traits
Klinefelter (XXY)	Extra X in males	Sterile, tall, small testes, some female traits (breast tissue)

Chromosomal Mutations

Chromosomal mutations alter the structure or number of chromosomes, leading to genetic disorders.

Type	Definition	Example
Deletion	Loss of chromosome segment	Cri-du-chat syndrome
Duplication	Extra copy of a segment	Huntington's may involve repeats
Inversion	Reversal of a segment	Usually no phenotype unless crossing-over disrupted
Translocation	Segment moves to another non-homologous chromosome	Chronic myeloid leukemia (CML)

Genetic Disorders

Genetic disorders can be inherited in different ways and have distinct molecular causes.

Disorder	Inheritance	Description
Cystic Fibrosis	Autosomal recessive	Defective chloride channel → mucus buildup
Achondroplasia	Autosomal dominant	Dwarfism; abnormal cartilage formation
Huntington's	Autosomal dominant	Late-onset neurodegeneration
Alzheimer's	Multifactorial	Protein plaques and tangles in brain cells

Prenatal Testing

Prenatal tests help detect chromosomal or genetic disorders before birth.

Test	Sample	Timing	Notes
Amniocentesis	Amniotic fluid	14–16 weeks	Detects chromosomal or genetic disorders
Chorionic Villus Sampling (CVS)	Placental tissue	8–10 weeks	Earlier results but higher risk
Ultrasound	Sound imaging	Anytime	Detects structure, growth, and development

CHAPTER 9: Mendelian Genetics

Blending vs. Particulate Theory

Early genetic theories attempted to explain inheritance patterns.

Blending: Traits mix evenly (now discredited).
Particulate Theory (Mendel): Traits are inherited as discrete "particles" (genes).

Fertilization Types

Self-Fertilization: Same individual provides sperm & egg (common in plants).
Cross-Fertilization: Two different parents contribute gametes → genetic variation.

Pure-Breeding vs. Hybrid

Pure-Breeding Strain: Homozygous for a trait (AA or aa).
Hybrid: Heterozygous (Aa).

Generations

P (Parental): Original cross.
F1: First filial (offspring of P).
F2: Offspring of F1 × F1.

Genes, Alleles, Loci

Allele: Variant form of a gene.
Locus: Gene's position on a chromosome.

Dominant vs. Recessive

Dominant: Expressed even if one allele present.
Recessive: Only expressed when both alleles recessive.

Zygosity

Term	Definition
Homozygote	Two identical alleles (AA or aa)
Heterozygote	Two different alleles (Aa)
Carrier	Heterozygote carrying a recessive allele

Punnett Square

Tool to predict genetic crosses using probabilities.

Genotype vs. Phenotype

Genotype: Genetic makeup (e.g., Aa).
Phenotype: Observable trait (e.g., tall).

Segregation & Independent Assortment

Segregation: Alleles separate during gamete formation.
Independent Assortment: Genes for different traits assort independently.

Cross Types

Cross	Traits	Example	Ratio
Monohybrid	1 trait	Aa × Aa	3:1
Dihybrid	2 traits	AaBb × AaBb	9:3:3:1
Testcross	Unknown × homozygous recessive	Reveals genotype	-

Dominance Variations

Type	Description	Example
Incomplete Dominance	Blended phenotype	Pink snapdragons
Codominance	Both alleles expressed	AB blood type

Complex Inheritance

Pleiotropy: One gene affects multiple traits (e.g., sickle-cell).
Polygenic: Multiple genes affect one trait (height, skin color).
Epistasis: One gene suppresses another's expression.

Sex Chromosome Effects

Dosage Compensation: Equalizes X-linked gene expression in XX vs. XY.

Crossing Over

Exchange of DNA between homologous chromosomes leads to genetic recombination.

Parental Phenotypes: Same as parents.
Recombinant Phenotypes: New allele combos due to crossing over.

Linkage & Maps

Linked Genes: Located close together → inherited together.
Chromosome Map: Shows gene order based on recombination frequencies.

Sex Chromosomes vs. Autosomes

Sex Chromosomes: X and Y; determine sex.
Autosomes: All other chromosomes.

Criss-Cross Inheritance

X-linked traits pass from mother → son and father → daughter.

Mutant vs. Wild-Type Alleles

Mutant: Altered form — may cause disease or variation.

CHAPTER 10: Molecular Genetics

Bases

Type	Bases	Structure
Pyrimidines	C, T (DNA); C, U (RNA)	Single ring
Purines	A, G	Double ring

DNA vs. RNA

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Bases	A, T, G, C	A, U, G, C
Strands	Double	Single
Function	Stores info	Transmits/builds proteins

Central Dogma

The central dogma describes the flow of genetic information:

Replication: DNA → DNA
Transcription: DNA → RNA
Translation: RNA → Protein

DNA Processes

Step	Function
Unwinding	Helicase separates strands
Pairing	Complementary bases align
Joining	Ligase seals fragments

Key Enzymes

Enzyme	Function
DNA Polymerase	Synthesizes DNA
RNA Polymerase	Transcribes RNA
Ribosome	Assembles proteins

Gene Regions

Region	Function
Promoter	Start site for transcription
Terminator	Stop signal

Codes

Term	Definition
Triplet Code	DNA base triplet (→ codon)
Codon	mRNA base triplet

Translation Steps

Initiation: Ribosome assembles at start codon (AUG).
Elongation: tRNAs add amino acids.
Termination: Stop codon halts synthesis.

Genetic Code

Universal, redundant (multiple codons = same amino acid).

RNA Types

RNA	Function
mRNA	Carries code from DNA
tRNA	Transfers amino acids
rRNA	Builds ribosome structure

Mutations

Type	Effect
Missense	Amino acid change
Nonsense	Stop codon created
Frameshift	Insertion/deletion shifts reading frame
Mutagen	Environmental cause (radiation, chemicals)

CHAPTER 11: Gene Regulation & Cancer

Gene Expression vs. Cellular Differentiation

Expression: Turning genes on/off.
Differentiation: Cells specialize despite identical DNA.

Operon System

Part	Function
Operon	Group of genes regulated together
Operator	On/off switch
Promoter	RNA polymerase binding site
Repressor	Protein that blocks transcription
Inducer	Molecule (like lactose) that inactivates a repressor → genes expressed

Histone & Nucleosome

DNA wraps around histone proteins forming nucleosomes — controls access for transcription.

Exons vs. Introns

Exons: Coding regions.
Introns: Noncoding regions removed during splicing.

Cancer Basics

Term	Meaning
Benign Tumor	Non-invasive
Malignant Tumor	Invades tissues
Metastasis	Spread to new sites
Oncogene	Mutated proto-oncogene → cancer
Carcinogen	Cancer-causing agent

CHAPTER 12: Biotechnology

Biotechnology Techniques

Technique	Function
RFLP (Restriction Fragment Length Polymorphism)	DNA cut pattern analysis
PCR (Polymerase Chain Reaction)	Amplifies DNA
Gel Electrophoresis	Separates DNA fragments by size
DNA Fingerprinting / Forensics	Identify individuals based on DNA band patterns

CHAPTER 27: Reproduction & Development

Female Reproductive Anatomy

Structure	Function
Ovary	Produces eggs & hormones
Oviduct (Fallopian Tube)	Transports egg; site of fertilization
Uterus	Houses embryo/fetus
Cervix	Neck of uterus
Vagina	Birth canal
Clitoris	Erectile tissue
Bartholin's Glands	Lubrication

Male Reproductive Anatomy

Structure	Function
Epididymis	Sperm storage/maturation
Vas Deferens	Transports sperm
Urethra	Sperm + urine exit
Seminal Vesicle	Adds fructose-rich fluid
Prostate	Secretes alkaline fluid
Bulbourethral Gland	Lubrication
Seminiferous Tubules	Site of spermatogenesis
Interstitial Cells	Make testosterone

Reproductive Hormones

Hormone	Role
Testosterone	Male traits
FSH	Stimulates gamete production
LH	Triggers ovulation/testosterone
Estrogen	Develops female traits
Progesterone	Maintains uterine lining
Releasing Hormone (GnRH)	From hypothalamus; starts FSH/LH release

Menstrual Cycle: Monthly shedding of endometrium if no fertilization occurs.

Developmental Stages

Stage	Description
Fertilization → Zygote → Morula → Blastula → Gastrula → Neurula	Sequential stages of embryonic development
Cleavage	Rapid cell division
Gastrulation	Germ layers form
Neurulation	Nervous system forms

Germ Layers

Layer	Forms
Ectoderm	Skin, brain
Mesoderm	Muscles, bones, blood
Endoderm	Gut, lungs

Extraembryonic Structures

Structure	Function
Inner Cell Mass	Embryo source
Trophoblast	Forms chorion
Chorion	Outer membrane → placenta
Endometrium	Uterine lining
Placenta	Nutrient/gas exchange

Hormones in Pregnancy

Hormone	Function
Chorionic Gonadotropin (hCG)	Maintains corpus luteum; pregnancy test hormone
Oxytocin	Triggers labor contractions & milk ejection