Biology 30 Unit II: GENES AND HEREDITY
INTRODUCTION
Genetics is the study of patterns of inheritance as traits are passed from parents to offspring. It has been
long understood that plants and animals inherit characteristics from their parents. Prehistoric people
recognized a child's resemblance to its parents, bred calves from cows that gave the most milk, and saved
the most productive grain for seed. However, the breeding of plants and animals was not put on a
scientific basis until the twentieth century.
Modern genetics began in a abbey garden when a monk named Gregor Mendel studied the mechanisms of
inheritance in garden peas. He published his completely new and thoroughly documented model of
inheritance in 1866. However, scientists who read Mendel's paper dismissed his model as trivial because
it was so simple. It was rediscovered in 1900 after his death, and today Mendel is considered to be the
"Father of Genetics".
Lesson 1 Mendelian Genetics
Objectives:
1. Define the following terms:
a) genetics
b) heredity
c) hereditary traits
d) acquired traits
e) chromosomes
f) genes
2.
Define and compare the following terms:
a) phenotype and genotype
b) dominant and recessive
c) homozygous and heterozygous
d) alleles and genes
e) purebred and hybrid
3.
Define and use these terms:
a) parental generation (P1)
b) first filial generation (F1)
c) second filial generation (F2)
4.
Use a Punnett square to illustrate a monohybrid cross, and work out the genotypic and phenotypic
ratios expected from such a cross. Express probabilities as fractions and as percentages.
5.
Explain Mendel's first three laws of heredity:
a. Law of segregation (First Law)
b. Law of independent assortment (Second Law)
c. Dominance
d. Unit characters (genes)
6.
Explain what is meant by the term "test cross". Design a test cross to determine the genotype of an
organism having a dominant phenotype.
7.
Explain Mendel's law of independent assortment.
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8.
Use a Punnett square to illustrate a dihybrid cross, and work out the genotypic and phenotypic ratios
expected from such a cross. Express probabilities as fractions and as percentages.
9.
Perform an experiment to investigate the relationship between chance and genetic inheritance.
10. Perform an investigation to demonstrate the inheritance pattern of a trait controlled by a single pair of
genes or by two pairs of genes.
11. Explain inheritance by incomplete dominance, codominance, and multiple alleles by using a Punnett
square to illustrate the crosses and work out the genotypic and phenotypic ratios expected from such
crosses. Express probabilities as fractions and as percentages.
12. Determine the following relationships between alleles by observing phenotype and genotype ratios:
a) dominant-recessive
b) co-dominant or incompletely dominant
c) multiples alleles
d) lethal alleles
13. Describe the genetic basis for procedures such as selective breeding, embryo transplants, and genetic
screening.
Reference: Biology by Nelson, pp. 468 - 481
Lesson 2 Chromosomal Basis of Heredity
Objectives:
1. Explain the chromosome theory.
2.
Describe the pattern of sex determination and distinguish between autosomes and sex chromosomes.
3.
Explain the inheritance of sex-linked traits.
4.
Use a Punnett square to illustrate a cross involving a sex-linked trait, and work out the genotypic and
phenotypic ratios expected from such a cross. Express probabilities as fractions and as percentages.
5.
Determine relationship between alleles controlling sex-linked traits by observing phenotype and
genotype ratios.
6.
Interpret and illustrate genetic data using pedigree charts.
7.
Describe linked genes and explain the significance of crossing-over on genetic recombination.
8.
Interpret recombination frequencies and construct simple gene maps.
9.
Explain the effect of crossing over on phenotype ratios in a population.
Reference: Biology by Nelson, pp. 494 - 512
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Unit II STS Connections
Students should be able to demonstrate the interrelationships among science technology and society
through one of the following:




Evaluating, from a variety of perspectives, the needs and interests of society and the role of genetic
counseling in the identification and treatment of potentially disabling genetic disorders. (e.g. PKU,
Tay Sachs)
Discussing the role of gene banks used to preserve endangered species and genotypes, particularly of
plants and animals used in agriculture; and the responsibility of society to protect the environment for
future generations.
Discussing biotechnology And gene replacement therapy in the treatment of human genetic disorders.
Discussing the Human Genome Project in terms of the needs, interests and financial support of
society.
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