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Chapter 14 and 15 - Coggle Diagram
Chapter 14 and 15
Chapter 14- Mendel and the Gene Idea
Mendel and the foundation of genetics
Traits are inherited as discrete units (genes). EX:Mendel’s pea plants – flower color (purple vs. white)
Mendel’s Key Concepts (Monohybrid Crosses)
Alleles: Different forms of a gene.
Dominant vs. Recessive: Dominant masks recessive in heterozygotes.
heterozygous-Hybrid breeding
homozygous dominate- true breeding
homozygous recessive- 2 identical copies of recessive alleles
Genotype( genetic makeup) vs. Phenotype(observational traits)
Probability & Mendelian Inheritance
Punnett squares predict offspring genotypes; independent events multiply probabilities.
Dihybrid & Multicharacter Crosses
Two traits can be inherited independently if genes are on different chromosomes (Mendel’s Law of Independent Assortment).
Extending Mendelian Genetics
Degrees of Dominance: Complete, incomplete, codominance.
ABO blood groups (IA, IB, i).
Multiple Alleles: More than two alleles exist in population.
Cystic fibrosis – affects lungs, pancreas, mucus thickness.
Pleiotropy: One gene affects multiple traits.
ex-Sickle-cell disease – heterozygotes (AS) show incomplete dominance; both normal and sickle hemoglobin made (codominance).
Gene Interactions
Epistasis: One gene masks expression of another.
ex-Skin color – controlled by many genes
Polygenic Inheritance: Multiple genes affect a trait.
Nature vs. Nurture / Environmental Effects
Phenotype = Genotype + Environment.
ex-Heart disease risk – genetic predisposition + diet, exercise, smoking.
Human Genetics
Pedigrees: Analyze inheritance of traits in families.
ex-Widow’s peak, PTC tasting.
Recessive Disorders: Only homozygous recessive affected; heterozygotes are carriers.
ex-Cystic fibrosis, albinism, Tay-Sachs.
Dominant Disorders: Heterozygotes affected; homozygous dominant may be rare or lethal.
ex- Achondroplasia, Huntington’s disease.
Carrier Probability: Two carrier parents → 1/4 chance child is affected; if one parent is a carrier, adjust probability.
Genetic Testing & Counseling
Carrier Testing: Detect heterozygous carriers of recessive disorders.
ex-ay-Sachs, cystic fibrosis, sickle-cell.
Fetal Testing: Early detection of genetic disorders.
Screening: Ultrasound, blood tests.
Diagnostic: Amniocentesis, chorionic villus sampling (CVS).
Newborn Screening: Detect disorders at birth for early treatment.
ex-PKU – treated with special diet.
Chapter 15-The Chromosomal Basis of Inheritance
Chromosome Theory of Inheritance (15.1)
Genes occupy specific loci on chromosomes; chromosome behavior explains inheritance patterns.
Chromosomes segregate and assort independently → explains Mendel’s laws.
Meiosis I = separation of homologous chromosomes
Meiosis II = separation of sister chromatids
Sex-Linked Inheritance (15.2)
Sex is genetically determined; sex chromosomes carry unique inheritance patterns.
Human Sex Determination
XX = female
XY = male
SRY gene on Y → triggers testes development
X-Linked Genes
Fathers pass X → daughters only
Mothers pass X → both sons and daughters
Male Rule
Males express all X-linked alleles (no second X to mask)
X-Inactivation
One X in females condenses into Barr body
Mosaic expression (different cells express different alleles)
Linked Genes & Recombination (15.3)
Genes on the same chromosome do not assort independently unless far apart.
Linked Genes
Located on the same chromosome
Tend to be inherited together
Do not produce a 1:1:1:1 ratio
Recombinant Offspring
Caused by crossing over during Prophase I
requency reflects distance between genes
Map Units
1 map unit (cM) = 1% recombination
Used to build genetic linkage maps
Alterations in Chromosome Number (15.4)
Nondisjunction → abnormal chromosome number → disorders.
Nondisjunction
Homologous chromosomes (Meiosis I) OR sister chromatids (Meiosis II) fail to separate
Produces aneuploid gametes
Aneuploidy Types
Trisomy (2n + 1) — extra chromosome
Monosomy (2n – 1) — missing chromosome
Polyploidy
Extra full sets of chromosomes
More common in plants
Alterations in Chromosome Structure (15.5)
Chromosomes can break and rejoin incorrectly.
Structural Changes
Deletion: removes a segment
Duplication: segment repeated
Inversion: segment reversed
Translocation: segment moves to nonhomologous chromosome
Effects
Can disrupt genes
Can alter gene dosage
Can lead to cancer or severe disorders