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CHAPTER 13
MEIOSIS AND SEXUAL LIFE CYCLES
OUTLINE
I. An Introduction to Heredity
A. Offspring acquire genes from parents by inheriting chromosomes
B. Like begets like, more or less: a comparison of asexual versus sexual
reproduction
II. The Role of Meiosis in Sexual Life Cycles
A. Fertilization and meiosis alternate in sexual life cycles
B. Meiosis reduces chromosome number from diploid to haploid: a closer look
III. Origins of Genetic Variation
A. Sexual life cycles produce genetic variation among offspring
B. Evolutionary adaptation depends on a population’s genetic variation
OBJECTIVES
After reading this chapter and attending lecture, the student should be able to:
1. Explain why organisms only reproduce their own kind, and why offspring more closely
resemble their parents than unrelated individuals of the same species.
-Organisms can only produce their own kind because like produces like, you cannot
have the creation of one species from another. Offspring resemble their parents
because of the genetic information they inherited from their parents.
2. Explain what makes heredity possible.
-Heredity is made possible by sexual reproduction.
3. Distinguish between asexual and sexual reproduction.
-Asexual reproduction is when an organism basically clones itself, its offspring is an
exact genetic copy of itself. Sexual reproduction is when two organisms reproduce and
their offspring is a genetic combination of both its parents.
4. 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.
5. Distinguish among the life cycle patterns of animals, fungi, and plants.
-Animals are born, nurtured by their parents, reproduce, nurture their young and die.
Fungi and plants reproduce asexually, grow, and die.
6. List the phases of meiosis I and meiosis II and describe the events characteristic of
each phase.
- Prophase 1: the nucleolus disappears, chromatin condenses into chromosomes, the
nuclear envelope breaks down, and the spindle apparatus forms. Unlike mitosis, once
the chromosomes are condensed, homologous chromosomes pair (called synapsis).
Metaphase 1: homologous pairs of chromosomes (tetrads) are spread across the
metaphase plate. Anaphase 1: begins when homologues within tetrads uncouple as
they are pulled to opposite poles. Telophase 1: nuclear membrane develops around the
chromosomes (each pole will form a new nucleus that will have half the number of
chromosomes, but each chromosome will contain two chromatids.
Prophase 2: the nuclear envelope disappears and the spindle apparatus develops (no
chiasmata and no crossing over). Metaphase 2: chromosomes align singly on the
metaphase plate (not in tetrads as before). Anaphase 2: begins as each chromosome is
pulled apart into two chromatids by the microtubules of the spindle apparatus.
Chromatids migrate to respective poles. Telophase 2: nuclear envelope appears at
each pole and cytokinesis occurs, the result is four haploid cells.
7. Recognize the phases of meiosis from diagrams or micrographs.
9. Describe the process of synapsis during prophase I, and explain how genetic
recombination occurs.
-Synapsis is when homologous chromosomes pair after being condensed. Genetic
recombination is the reassortment of genetic material and occurs during sexual
reproduction.
10. Describe key differences between mitosis and meiosis; explain how the end result of
meiosis differs from that of mitosis.
-Mitosis merely duplicates cells, the two daughter cells are clones the original cell, it
occurs during growth and development of multicellular organisms and during repair of
existing cells. It ends with two diploid daughter cells. Meiosis, however, produces
gametes for sexual reproduction, fertilization gives rise to a diploid cell (zygote). It ends
with four haploid daughter cells.
11. Explain how independent assortment, crossing over, and random fertilization
contribute to genetic variation in sexually
reproducing organisms.
-Independent assortment, crossing over and random fertilization basically mix genetic
information in such a way so as not to produce identical cells. It contributes to genetic
variation by making each “mix” completely different from the next.
12. Explain why inheritable variation was crucial to Darwin's theory of evolution.
-Each progeny inherits different adaptations from its parents in order to evolve and better
adapt to its environment. If inheritable variation was not possible, then evolution would
not occur.
13. List the sources of genetic variation.
-Crossing over, independent assortment of homologues, and random joining of gametes.
CHAPTER 14
MENDEL AND THE GENE IDEA
OUTLINE
I. Gregor Mendel’s Discoveries
A. Mendel brought an experimental and quantitative approach to genetics:
science as a process
B. By the law of segregation, the two alleles for a character are packaged into
separate gametes
C. By the law of independent assortment, each pair of alleles segregates into
gametes independently
D. Mendelian inheritance reflects rules of probability
E. Mendel discovered the particulate behavior of genes: a review
II. Extending Mendelian Genetics
A. The relationship between genotype and phenotype is rarely simple
III. Mendelian Inheritance in Humans
A. Pedigree analysis reveals Mendelian patterns in human inheritance
B. Many human disorders follow Mendelian patterns of inheritance
C. Technology is providing new tools for genetic testing and counseling
OBJECTIVES
After reading this chapter and attending lecture, the student should be able to:
5. State, in your own words, Mendel's law of segregation.
- the random separation of alleles to separate gametes.
6. Use a Punnett square to predict the results of a monohybrid cross and state the
phenotypic and genotypic ratios of the F2
generation.
- I know this
7. Distinguish between genotype and phenotype; heterozygous and homozygous;
dominant and recessive.
- genotype is your gene type, what kind of alleles you have, phenotype is what traits
show outwardly. Heterozygous is two different alleles, homozygous is two of the same.
Dominant traits are the ones that show and cover recessive traits which are less
common.
8. Explain how a testcross can be used to determine if a dominant phenotype is
homozygous or heterozygous.
- a test cross allows one to see the genotype of a characteristic (big B’s will determine
homo or hetero)
9. Define random event, and explain why it is significant that allele segregation during
meiosis and fusion of gametes at fertilization
are random events.
- I know this
13. State, in your own words, Mendel's law of independent assortment.
- homologous chromosomes segregate independently of the segregation of other
chromosome pairs.
14. Use a Punnett square to predict the results of a dihybrid cross and state the
phenotypic and genotypic ratios of the F2
generation.
- I know this
16. Give an example of incomplete dominance and explain why it is not evidence for the
blending theory of inheritance.
- an example of incomplete dominance would be the crossing of a red and white flower
and the emergence of its pink progeny (not one or the other, but both).
17. Explain how the phenotypic expression of the heterozygote is affected by complete
dominance, incomplete dominance and codominance.
- phenotypes depend on dominant or recessive traits, whatever is expressed depends
on the dominance.
18. Describe the inheritance of the ABO blood system and explain why the IA and IB
alleles are said to be codominant.
- I know this
19. Define and give examples of pleiotropy.
- pleiotropy is when a single gene has more than one phenotypic expression. Ex: the
gene in pea plants that expresses the round or wrinkled texture of seeds also influences
the phenotypic expressions of starch metabolism and water absorption.
20. Explain, in their own words, what is meant by "one gene is epistatic to another."
- one gene is affected by another
23. Describe how environmental conditions can influence the phenotypic expression of a
character.
- it can cause mutation which masks the true expression or can change something in the
genotype.
24. Given a simple family pedigree, deduce the genotypes for some of the family
members.
- I know this
CHAPTER 15
THE CHROMOSOMAL
BASIS OF INHERITANCE
OUTLINE
I. Relating Mendelism to Chromosomes
A. Mendelian inheritance has its physical basis in the behavior of chromosomes
during sexual life cycles
B. Morgan traced a gene to a specific chromosome: science as a process
C. Linked genes tend to be inherited together because they are located on the same
chromosome
D. Independent assortment of chromosomes and crossing over produce genetic
recombinants
E. Geneticists can use recombination data to map a chromosome’s genetic loci
II. Sex Chromosomes
A. The chromosomal basis of sex varies with the organism
B. Sex-linked genes have unique patterns of inheritance
III. Errors and Exceptions to Chromosomal Inheritance
A. Alterations of chromosome number or structure cause some genetic disorders
B. The phenotypic effects of some genes depend on whether they were inherited
from the mother or father
C. Extranuclear genes exhibit a non-Mendelian pattern of inheritance
OBJECTIVES
After reading this chapter and attending lecture, the student should be able to:
4. Define linkage and explain why linkage interferes with independent assortment.
- linkage is when two or more genes reside on the same chromosome, these genes do not
assort with others, they stay together.
6. Explain how crossing over can unlink genes.
- different parts of different genes cross over therefore unlinking genes, they separate.
10. Describe sex determination in humans.
- sex is determined by the male in humans, they are the ones who can give an X or a Y to the
progeny.
11. Describe the inheritance of a sex-linked gene such as color-blindness.
- sex linked genes are usually inherited from the mother who can carry such a defect without
being affected.
12. Explain why a recessive sex-linked gene is always expressed in human males.
- males carry a Y which carries neither a recessive nor a dominant gene, so if they inherit a
recessive X gene from their mother they have nothing to mask it.
14. Distinguish among nondisjunction, aneuploidy, and polyploidy; explain how these major
chromosomal changes occur
and describe the consequences.
-nondisjunction is when the chromosomes don’t properly separate, aneuploidy is when the
condition of a cell or of an organism has additions or deletions of a small number of
whole chromosomes from the expected balanced diploid number of chromosomes,
polyploidy is when a cell or an organism has three or more chromosome sets.
16. Distinguish among deletions, duplications, translocations, and inversions.
- I know this.