Background
 The passage of genetic information is critical to the
reproduction of cells
 Genes are segments of DNA representing units of
hereditary information
 The physical location of a gene on the
chromosome is called its locus
Types of Reproduction
 Asexual reproduction
 Single parent cell/organism produces an identical
offspring
 Except for mutations, the offspring of asexual
reproduction are clones of their parents
 Sexual reproduction
 Results in greater variation in genetic material
Two types of cells in humans
 Gametes-haploid cells (n), carry one set of
chromosomes
ex. In humans, an egg (1N) and sperm (1N) are
reproductive cells that fuse together creating a diploid
zygote
 Somatic cells (Diploid cells) carry two sets of
chromosomes (2n)
 In diploid cells, you can pair
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chromosomes in relation to its
size, shape, and banding
positions
Karyotyping-arranging
chromosomes in relation to
number, size, type.
The chromosomes of a pair are
called homologous
chromosomes
One homologous pair decides
your gender
The remaining 22 pairs of
chromosomes are called
autosomes
Significance of homologous pairs?
 Their origin!
 One member of each homologous pair comes from each
parent
Ex. Human gametes  haploid cells- single set of chrom (23)
- Each parent contributes one set of chromosomes and is a
member of each homologous pair.
- Fertilization
- Egg+ Sperm  Zygote
n
n
2n
How are Gametes Formed?
 Meiosis:
 Chromosome number is halved by dividing
chromosome members of each homologous pair into
different gametes
 Goes through two rounds of cell division, produces 4
daughter cells w/ half the chromosome number
Tetrad-four sister chromatids that pair up
Chiasmata-crossing over occurs bwtn nonsister chromatids
Mechanisms of genetic variation
 Independent assortment
 Arrangement of homologous pairs at the metaphase plate in
Metaphase I is completely random
 Crossing Over
 Produces recombinant chromosomes which combine genes
inherited from parents
 Random Fertilization
 Random nature of fertilization that adds to genetic variation
Life Cycles
 Life cycle- sequence of stages in the reproductive
history of an organism
 Asexual Life Cycles  bacterium by binary fission
Sexual Life Cycles
ANIMALS (HUMANS)
 Haploid sperm fuses w/
haploid egg  diploid
zygote
 Zygote grows by mitosis
to produce a multicelluar
organism
Fungi
 Plants (some algae)
 undergo "alternation of generations" where they exist as
haploid organisms (gametophytes) and diploid
organisms (sporophytes).
Meiosis/mitosis Compared
Property
Mitosis
Meiosis
DNA replication
Occurs during interphase before
mitosis
Occurs during interphase before
mitosis I begins
Number of divisions
One, including prophase,
metaphase, anaphase, and
telophase
Two,
Each including PMAT
Synapsis of homo. chromosomes
Does not occur
Occurs during prophase I along
w/crossing over btwn nonsister
chromatids
Number of daughter cells and
genetic composition
Two, each diploid (2n) and
genetically identical to parent
Four, each haploid (n) containing
half as many chromosomes as
parent; genetically different from
parent and from each other
Role in animal body
Enables multicellular adult to
arise from zygote; produces cells
for growth, repair, and asexual
reproduction
produces gametes; reduces
number of chromosomes by half
and introduces genetic variability
among gametes
Mechanisms of genetic variation
diagram
Independent Assortment
Crossing Over
Vocabulary
heredity - the transmission of traits from one generation to the next.
variation - offsprings differ somewhat in appearance from parents and siblings.
genetics - the scientific study of heredity and hereditary variation.
gene pool - the total aggregate of genes in a population at any one time.
asexual reproduction - a type of reproduction involving only one parent that produces
genetically identical offspring by budding or by the division of a single cell or the entire
organism into two or more parts.
clone - a lineage of genetically identical individuals.
sexual reproduction - a type of reproduction in which two parents give rise to offspring
that have unique combinations of genes inherited from the gametes of the two parents.
life cycle - the entire sequence of stages in the life of an organisms, from the adults of one
generation to the adults of the next.
Somatic cell - any cell in a multicellular organism except a sperm or egg cell.
karyotype - a method of organizing the chromosomes of a cell in relation to number, size,
and type.
homologous chromosomes - chromosome pairs of the same length, centromere position,
and staining pattern that possess genes for the same traits at corresponding loci. One
homologous chromosome is inherited from the organism's father, the other from the
mother.
sex chromosomes - the pair of chromosomes responsible for determining the sex of an
individual.
autosome - a chromosome that is not directly involved in determining sex, as opposed to
the sex chromosomes.
gamete - a haploid egg or sperm cell; gametes unite during sexual reproduction to produce
a diploid zygote.
haploid cell -a cell containing only one set of chromosomes (n).
More Vocabulary
haploid cell -a cell containing only one set of chromosomes (n).
fertilization - the union of haploid gametes to produce a diploid zygote.
zygote - the diploid product of the union of haploid gametes in conception; a fertilized egg.
diploid cell - a cell containing two sets of chromosomes (2n), one set inherited from each
parent.
meiosis - a two-stage type of cell division in sexually reproducing organisms that results in
gametes with half the chromosome number of the original cell.
alternation of generations - a life cycle in which there is both a multicellular diploid form, the
sporophyte, and a multicellular haploid form, the gametophyte; characteristic of plants.
sporophyte - the multicellular diploid form in organisms undergoing alternation of generations
that results from a union of gametes and that meiotically produces haploid spores that grow into
the gametophyte generation.
gametophyte- the multicellular haploid form in organisms undergoing alternation of
generations, which mitotically produces haploid gametes that unite and grow into the
sporophyte generation.
meiosis I - first division of cells
meiosis II - second meiotic division that separates sister chromatids and is virtually identical in
mechanism to mitosis.
synapsis - the pairing of replicated homologous chromosomes during prophase I of meiosis.
tetrad chiasma - the X-shaped, microscopically visible region representing homologous chromatids
that have exchanged genetic material through crossing over during meiosis.
crossing over - the reciprocal exchange of genetic material between nonsister chromatids
during synapsis of meiosis I.