Biology
Genetics
Principles of Inheritance
Part 1: Outline
 An introduction to Heredity
o Offspring acquire genes from parents by inheriting chromosomes.
o Like begets like, more or less: a comparison of sexual and asexual
reproduction.
 The Role of Meiosis in Sexual Life Cycles
o Fertilization and meiosis alternate in sexual life cycles.
o Meiosis reduces chromosome number from diploid to haploid.
 Origins of Genetic Variation
o Sexual life cycles produce genetic variation among offspring.
Objectives
1. Explain why organisms reproduce only their own kind and why offspring
more closely resemble their parents than unrelated individuals of the same
species.
2. Explain what makes heredity possible.
3. Diagram the human life cycle and indicate where in the human body that
mitosis and meiosis occur; which cells are the result of meiosis and
mitosis; and which cells are haploid.
4. List the phases of meiosis I and Meiosis II and describe the events
characteristic of each phase. Recognize the phases of meiosis from
diagrams or micrographs.
5. Describe the process of synapsis during prophase I and explain how
genetic recombination occurs.
6. Describe the key differences between mitosis and meiosis. Explain how
the end result of meiosis differs from that of mitosis.
7. Explain how independent assortment, crossing over, and random
fertilization contribute to genetic variation in sexually reproducing
organisms.
Key Terms
Heredity
Variation
Karyotype
Gene
Asexual reproduction
Locus
Clone
Sexual reproduction
Life cycle
Sex chromosomes
Autosome
Gamete
Haploid cell
Fertilization
Syngamy
Zygote
Diploid cell
Homologous chromosome
1
Gametophyte
Meiosis I
Meiosis II
Synapsis
Tetrad
Chiasmata
Crossing over
Recombinant chromosome
Somatic cell
Biology
Genetics
Part 2: Outline
 Gregor Mendel’s Discoveries
o Mendel brought an experimental and quantitative approach to
genetics.
o By the law of segregation, the two alleles for a character are
packaged into separate gametes.
o By the law of independent assortment, each pair of alleles
segregates into gametes independently.
o Mendelian inheritance reflects rules of probability.
o Mendel discovered the particulate behavior of genes.
 Extending Mendelian Genetics
o The relationship between genotype and phenotype is rarely simple.
 Mendelian Inheritance in Humans
o Pedigree analysis reveals Mendelian patterns of inheritance.
o Many human disorders follow Mendelian patterns of inheritance.
o Technology is providing new tools for genetic testing and
counseling.
Objectives
1. Describe the favored model of heredity in the 19th century prior to Mendel.
2. Explain how observations by Mendel and others and Mendel’s hypothesis
of inheritance differed from the blending theory of inheritance.
3. Define true breeding, hybridization, monohybrid cross, P generation, F 1
generation, and F2 generation.
4. Use a Punnett square to predict the results of a monohybrid cross and
state the phenotypic and genotypic ratios of F1 and F2 generations.
5. Distinguish between the following pairs of terms: dominant and recessive;
heterozygous and homozygous; genotype and phenotype.
6. Explain how a testcross can be used to determine if a dominant
phenotype is homozygous or heterozygous.
7. Use a Punnett square to predict the results of a dihybrid cross and state
the phenotypic and genotypic ratios of the F1 and F2 generations.
8. Define Mendel’s law of independent assortment.
9. Given an example of incomplete dominance and explain why it is not
evidence for the blending theory of inheritance.
10. Explain how the phenotypic expression of the heterozygote is affected by
complete dominance, incomplete dominance, and co-dominance.
11. Describe the inheritance of the ABO blood system and explain why the I A
and IB alleles are said to be co-dominant.
12. Define and give examples of pleiotropy and epistasis.
13. Describe a simple model for polygenic inheritance and explain why most
polygenic characters are described in quantitative terms.
14. Given a simple family pedigree, deduce the genotypes for some of the
family members.
15. Explain how a lethal recessive gene can be maintained in a population.
2
Biology
Genetics
16. Describe the inheritance and expression of cystic fibrosis, Tay-Sachs
disease, and sickle-cell anemia.
17. Explain why consanguinity increases the probability of homozygosity in
offspring.
18. Explain why lethal dominant genes are much rarer than lethal recessive
genes.
19. Explain how carrier recognition, fetal testing, and newborn screening can
be used in genetic screening and counseling.
Key Terms
Character
Trait
True-breeding
Hybridization
P generation
F1 generation
F2 generation
Alleles
Dominance
Recessive
Law of segretation
Homozygous
Heterozygous
Phenotype
Genotype
Testcross
Monohybrid
Dihybrid
Law of independent
assortment
Incomplete dominance
Complete dominance
Punnett Square
Epistasis
3
Quantitative characters
Polygenic inheritance
Norm of reaction
Multifactorial
Pedigree
Carrier
Amniocentesis
Chorionic villus sampling
(CVS)
Codominance
Pleiotropy
Biology
Genetics
Part 3: Outline
 Relating Mendelism to Chromosomes
o Mendelian inheritance has its physical basis in the behavior of
chromosomes during sexual life cycles.
o Morgan traced a gene to a specific chromosome.
o Linked genes tend to be inherited together because they are
located on the same chromosome.
o Independent assortment of chromosomes and crossing over
produce genetic recombinants.
o Geneticists can use recombination data to map a chromosome’s
genetic loci.
 Sex Chromosomes
o The chromosomal basis of sex varies with the organism.
o Sex-linked genes have unique patterns of inheritance.
Objectives
1. Describe the contribution of Thomas Hunt Morgan to current
understanding of chromosomal inheritance.
2. Define and compare linked genes and sex-linked genes. Explain why the
inheritance of linked genes is different from independent assortment.
3. Explain how Sturtevant created linkage maps.
4. Explain how genetic maps are constructed for genes located far apart on a
chromosome.
5. Explain how sex is genetically determined in humans.
6. Explain why sex-linked genes are more common in human males.
7. Describe the inheritance patterns and symptoms of color blindness,
Duchenne muscular dystrophy, and hemophilia.
8. Distinguish among nondisjunction, aneuploidy, trisomy, triploidy, and
polyploidy.
9. Distinguish among deletions, duplications, inversions, and translocations.
Key Terms
Wild type
Sex-linked gene
Inversion
Nondisjunction
Trisomic
Polyploidy
Duplication
Genetic recombination
Aneuploidy
Monosomic
4
Deletion
Linked gene
Translocation
Genetic map
Linkage map