Chapter 7
Meiosis and Sexual Reproduction
Section 1: Meiosis
Section 2: Sexual Reproduction
Section 1
Meiosis
Objectives:
•Summarize the events that occur during meiosis.
•Relate crossing-over, independent assortment, and
random fertilization to genetic variation.
•Compare spermatogenesis and oogenesis.
Section 1
Meiosis
Formation of Haploid Cells
•Meiosis and Chromosome Number Meiosis reduces
the number of chromosomes by half to form
reproductive cells. When the reproductive cells unite in
fertilization, the normal diploid number is restored.
•Meiosis I During Meiosis I, homologous
chromosomes separate. Crossing-over during prophase
I results in the exchange of genetic material between
homologous chromosomes.
•Meiosis II During Meiosis II, the two chromatids of
each chromosome separate. As a result of meiosis, four
haploid cells are produced from one diploid cell.
Section 1
Meiosis
Meiosis and Genetic Variation
•Independent Assortment Independent assortment,
the random distribution of homologous chromosomes
during meiosis, contributes to genetic variation in
sexually reproducing organisms.
•Crossing Over and Random Fertilization Both
crossing-over and the random fertilization of gametes
contribute to genetic variation in sexually reproducing
organisms.
•Importance of Genetic Variation Genetic variation
is essential for evolution to occur.
Section 1
Meiosis
Meiosis and Gamete Formation
•Meiosis in Males In sexually reproducing eukaryotic
organisms, gametes form through the process of
spermatogenesis in males.
•Meiosis in Females In sexually reproducing
eukaryotic organisms, gametes form through the
process of oogenesis in females.
Section 2
Sexual Reproduction
Objectives:
•Differentiate between asexual and sexual
reproduction.
•Identify three types of asexual reproduction.
•Evaluate the relative genetic and evolutionary
advantages and disadvantages of asexual and sexual
reproduction.
•Differentiate between the three major sexual life
cycles found in eukaryotes.
Section 2
Sexual Reproduction
Meiosis and Gamete Formation
•Meiosis in Males In sexually reproducing eukaryotic
organisms, gametes form through the process of
spermatogenesis in males.
•Meiosis in Females In sexually reproducing
eukaryotic organisms, gametes form through the
process of oogenesis in females.
Section 2
Sexual Reproduction
Sexual and Asexual Reproduction
•Asexual Reproduction Asexual reproduction is the
formation of offspring from one parent. The offspring
are genetically identical to the parent.
•Sexual Reproduction Sexual reproduction is the
formation of offspring through the union of gametes
from two parents. The offspring are genetically
different from their parents.
•Types of Asexual Reproduction There are many
types of asexual reproduction such as fission,
fragmentation, and budding. All types lead to clones of
the parent.
Section 2
Sexual Reproduction
Sexual and Asexual Reproduction continued
•Genetic Diversity Whereas sexual reproduction
increases variation in the population by making
possible genetic recombination, asexual
reproduction leads to a lack of genetic diversity
among offspring. This lack of diversity is a
disadvantage in a changing environment.
•Evolution of Sexual Reproduction
Sexual reproduction may have begun as a
mechanism to repair damaged DNA.
Section 2
Sexual Reproduction
Sexual Life Cycles in Eukaryotes
•Haploid Life Cycle In the haploid life cycle, the
simplest of all life cycles, the haploid cell occupies
the major portion of the life cycle.
•Diploid Life Cycle In the diploid life cycle, the
adults are diploid and the diploid individual
occupies the major portion of the life cycle.
•Alternation of Generations Some organisms
have a life cycle that alternates between diploid
and haploid phases.