Biology Unit 4 –Meiosis & Mendelian Genetics
Topics
 Chromosomes
 Meiosis & Gametogenesis
 Genetic Variation
 Inheritance patterns
 Sex-linked Inheritance
 Linked Genes
 Mutations
Key Terms
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Chromosome
Chromatid
Sex chromosomes
Autosomes
Binary fission
Mitosis
Interphase
Centromere
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Diploid cell
Haploid cell
Homologous chromosomes
Gametes
Meiosis
Germ line
Crossing over
Sister chromatids
Alleles
Gametogenesis
Nondisjunction
Deletion
Inversion
Textbook Correlation
Concepts 10-2
Concepts 10-3
Concepts 10-4
Concepts 11.1-11.4
Concept 12.2
Concept 12.3
Concepts 12.4
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Duplication
Translocation
Locus
Allele
Dominant
Recessive
Homozygous
Heterozygous
Phenotype
Genotype
Law of dominance
Law of segregation
Law of independent assortment
Incomplete dominance
Codominance
Epistasis
Pleiotrophy
Autosomes
Hemophilia
Color blindness
Sex-linked traits
Carrier
Suggested work:
 Concept Checks
 Test Your Understanding
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Biology Unit 4 –Meiosis & Mendelian Genetics
Offspring acquire genes from parents by inheriting chromosomes.
Define genes:____________________________________________________________
In animals and plants, reproductive cells that transmit genes from one generation to the
next are called _________________________.
There are two types of reproduction, asexual and sexual. Describe each one.
 Asexual reproduction

Sexual reproduction
Human chromosomes come in pairs called homologues. So while there are 46 of them
altogether, there are actually only 23 distinct chromosomes. The homologous
chromosomes which make up each pair are similar in size and shape and express similar
traits. This is the case in all sexually reproducing organisms. In fact, this is the essence
of sexual reproduction: Each parent donates half its chromosomes to its offspring.
Gamates
What are gametes and where do they come from?
Are gametes haploid or diploid? (Circle one)
Meiosis
Meiosis is very similar to mitosis. The major distinction is that meiosis consists of two
groups of divisions, meiosis I and meiosis II.
Summarize the phases of meiosis I:
1. Prophase I, include synapsis, tetrad, chiasmata, and crossing over.
**Understanding prophase I is critical to understanding meiosis. Study the unique events of
prophase I carefully**
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Biology Unit 4 –Meiosis & Mendelian Genetics
2. Metaphase I
3. Anaphase I
4. Telophase I
Summarize meiosis II:
1. Prophase II:
2. Metaphase II:
3. Anaphase II:
4. Telophase II:
Meiosis and fertilization are the key events in sexually reproducing life cycles. The
human life cycle in figure 10.5 is typical of a sexually reproducing animal.
Reproduce figure 10.5.
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Biology Unit 4 –Meiosis & Mendelian Genetics
Organize Your Thoughts
 In Prophase I:
1. Synapsis occurs, forming___________________.
2. ______________ __________ occurs between ________________
________________ in the tetrads.
3. Crossing over increases __________________ _________________.
4. Areas of crossing over form __________________________.
Genetic Variation
In mitosis, every daughter cell is exactly like the parent cell. Meiosis and sexual
reproduction, however, result in a reassortment of the genetic material. This
reassortment, called genetic recombination, originates from three events during the
reproductive cycle:
Describe the following three sources of variation.
1. Crossing over:
2. Independent assortment of homologues:
3. Random joining of gametes:
Classical Genetics (Mendelian Genetics)
Gregor Mendel: The Father of Genetics
What is genetics? In its simplest form, genetics is the study of heredity. It explains how certain
characteristics are passed on from parents to children. Much of what we know about genetics was
discovered by the monk Gregor Mendel in the 19th century. Since then, the field of genetics has
vastly expanded. As scientists study the mechanisms of genetics, they’ve developed new ways of
manipulating genes. For example, scientists have isolated the gene that makes insulin, a human
hormone, and now use bacteria to make large quantities of it. But before we get ahead of ourselves,
let’s study the basic rules of genetics.
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Biology Unit 4 –Meiosis & Mendelian Genetics
Explain the chromosomal theory of inheritance.
Differentiate between genes, alleles, genotype, and phenotype.
Explain the difference between dominant and recessive inheritance.
Explain Mendel’s Law of Segregation.
Explain Mendel’s Law of Independent Assortment.
Explain and give examples of the following genotypes: homozygous dominant;
heterozygous; homozygous recessive.
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Biology Unit 4 –Meiosis & Mendelian Genetics
Demonstrate two generations of a monohybrid cross using a Punnett square. Identify the
P1 generation, F1 generation, and F2 generation.
Demonstrate a dihybrid cross using a Punnett Square.
What is the significance of the famous phenotypic ratio of 9:3:3:1? Explain what each
number represents.
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Biology Unit 4 –Meiosis & Mendelian Genetics
Explain a test cross and how it is used.
Beyond Mendelian Genetics
These are the basics of inheritance. However, genes do not operate in isolation from one
another; this makes genetics more complex than Mendel’s experiments and the Punnett
square might suggest. Many different factors can affect phenotype and genotype in
offspring. Explain and give examples of the following topics:
1. Incomplete dominance
2. Codominance
3. Epistasis
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Biology Unit 4 –Meiosis & Mendelian Genetics
4. Polygenic inheritance
5. Multiple alleles
6. Linked genes
7. Pleiotrophy
8. Genetic recombination
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Biology Unit 4 –Meiosis & Mendelian Genetics
Human Genetic Disorders
Explain a single-gene defect.
Describe the following single-gene defects.
 Autosomal recessive disorders
(a) Sickle-cell anemia
(b) Phenylketonuria (PKU)
(c) Cystic fibrosis
(d) Tay-Sachs disease
 Autosomal dominant disorders
(a) Achondroplastic dwarfism
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Biology Unit 4 –Meiosis & Mendelian Genetics
(b) Huntington’s disease
(c) Osteogenesis imperfecta
Explain sex-linked disorders (inheritance). What is the role of the mother and of the
father in sex-linked inheritance?
Describe the following sex-linked disorders:
(a) Hemophilia
(b) Red-green color blindness
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Biology Unit 4 –Meiosis & Mendelian Genetics
(c) Duchenne’s muscular dystrophy
Explain what Barr bodies are and how they are formed.
What is a pedigree?
Draw out a pedigree to show the inheritance pattern of a sex-linked recessive disorder.
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Biology Unit 4 –Meiosis & Mendelian Genetics
Draw out a pedigree to show the inheritance pattern of an autosomal dominant disorder.
Disorders Involving Whole Chromosomes
Explain nondisjunction.
Describe the following nondisjunction disorders:
(a) Trisomy-21 (Down Syndrome)
(b) Turner’s syndrome
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Biology Unit 4 –Meiosis & Mendelian Genetics
(c) Klinefelter’s syndrome
Detection of Abnormal Chromosomes By Amniocentesis and
Karyotyping
Describe the process of amniocentesis.
What is a karyotype and how is it used?
Some Inheritance Patterns are Exceptions to Standard Mendelian Inheritance
In mammals, geneticists have identified traits that differ, depending on which parent passed along the allele
for those traits. This phenomenon is called genomic imprinting.
Explain genomic imprinting.
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Biology Unit 4 –Meiosis & Mendelian Genetics
Grid-In Questions (numerical responses)
1. A yeast cell in the early portion of interphase of meiotic cell division has 24 fg of
DNA (fg = 1 x 10-15 grams). If the yeast cell completes meiotic division to form
four haploid cells, how many fg of DNA would be expected in each haploid cell?
Answer:___________
2. In pea plants T = Tall, t = dwarf, R = Round seeds, and r = wrinkled seeds. If a
TtRr plant is crossed with a Ttrr plant, what fraction of the offspring will be tall
and wrinkled?
Answer:___________
3.
In fruit flies gray body is dominant to black body and normal wings are dominant to vestigial
wings. Flies heterozygous for both gray bodies and normal wings were crossed with flies that had
black bodies and vestigial wings. The following results were obtained:
Phenotype
Gray body/normal wings
Gray body/vestigial wings
Black body/vestigial wings
Black body/normal wings
Number of flies
482
472
103
92
The results indicate that the genes for wings and body color are on the same chromosome. The
recombinant offspring are a result of crossing over. How many map units (expressed as a percent) apart are
the two genes? The formula for calculating recombination frequency is:
Recombination Frequency = number of recombinants / total number of offspring x 100
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Biology Unit 4 –Meiosis & Mendelian Genetics
Essay #1
Geneticists can determine which genes will be expressed in offspring by tracking inheritance patterns and
using Punnett squares.
(a) Explain the role of alleles in determining the genotype and phenotype of offspring.
(b) Discuss the purpose of a “test cross.” Create a sample Punnett square for the test cross of the
alleles Aa and AA, where A is the dominant allele. Explain the outcome of the cross.
(c) Suppose the dominant allele H codes for Huntington’s disease. If one parent has the alleles HH
and the other parent has the alleles Hh, will any of their children have Huntington’s disease?
Explain why and how you came to your conclusion.
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Biology Unit 4 –Meiosis & Mendelian Genetics
Essay #2
Discuss Mendel’s laws of segregation and independent assortment with respect to
(a) genes that are not linked
(b) genes that are linked
(c) crossing over
(d) sex-linkage
(e) Down syndrome
(f) Turner syndrome
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Biology Unit 5 --Cell Reproduction--Mitosis & Meiosis
Essay #3
Describe the process of cell division in plants and animals giving specific attention to the
following:
a. The stages of mitosis, cytokinesis, and other phases of the cell cycle.
Biology Unit 5 --Cell Reproduction--Mitosis & Meiosis
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Essay #2
Describe meiosis in animal cells giving special attention to the following:
a. The stages of meiosis.
b. The function of meiotic daughter cells and the organs where meiosis takes place.
c. Contribution to genetic variation.
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