Human Heredity (ATC)

Genetic changes can cause disease.

• Disorders may be single-gene (cystic fibrosis, sickle cell) or chromosomal (Down syndrome).
• Some are dominant, recessive, or sex-linked.
• Cancer results from mutations that cause uncontrolled cell growth.
• Genetic counseling assesses inherited risk.

Chromosomes carry the genes passed to offspring.

• Humans have 46 chromosomes (23 pairs).
• Traits follow Mendelian inheritance patterns.
• Alleles may be dominant or recessive.
• Sex chromosomes (XX/XY) determine sex and sex-linked traits.

Several tools predict and track inheritance.

• Punnett squares predict offspring genotype ratios.
• Pedigrees trace traits through family trees.
• Karyotypes display chromosomes to detect abnormalities.
• These tools reveal inheritance patterns.

Viruses and immunity interact with our genes.

• Some viruses insert genetic material into host DNA.
• Retroviruses (e.g., HIV) reverse-transcribe RNA into DNA.
• The immune system recognizes and responds to genetic/foreign markers.
• Viral infection can alter gene expression.

Genes are expressed and regulated to produce traits.

• Genotype is the genetic code; phenotype is the visible trait.
• Gene expression turns genes into proteins.
• Regulation controls which genes are active and when.
• Environment can influence expression.

Changes to DNA and its regulation affect traits.

• Mutations alter DNA sequence and may be harmful, neutral, or beneficial.
• Types include point, insertion, and deletion mutations.
• Epigenetics changes gene activity without changing the sequence.
• Both can be inherited and influence disease.

Technology lets us read and edit genes.

• Genome sequencing maps all of an organism's DNA.
• Genetic testing screens for disease risk.
• Gene therapy and tools like CRISPR can correct defects.
• Reproductive technologies raise ethical questions.

Genes direct the making of proteins.

• DNA stores the code; RNA carries it.
• Transcription copies DNA into mRNA.
• Translation builds proteins from mRNA at ribosomes.
• This central dogma (DNA → RNA → protein) drives cell function.

Cell division passes genetic material to new cells.

• Mitosis makes identical body cells; meiosis makes gametes with half the chromosomes.
• Meiosis creates variation through crossing over and independent assortment.
• Nondisjunction causes chromosome number errors.
• Mutations during division can be inherited.