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SEXUAL
REPRODUCTION
Chapter 10
LET’S REVIEW!
• The cell cycle is when a cell
makes a copy of itself for:
• Growth, Repair, Replacement
• BODY (autosomal/somatic)
cells reproduce by mitosis
• some organisms do also, but
we will talk about that later!
CHROMOSOMES
• Homologous Chromosomes:
chromosomes that make a
pair
• They have the same length,
same centromere position,
and control the same
inherited trait
GAMETES
• Gamete: Sex cell (sperm and egg)
• Have half the # of chromosomes as compared to
autosomal cells
• Ensures that an organism has the same number of
chromosomes from generation to generation
• In humans, each gamete has 23 chromosomes
• n = number of chromosomes in a gamete
GAMETES
• Haploid: n
• Diploid: 2n (female n + male n)
• When 2 human gametes combine through
fertilization, 23 homologous chromosomes
are formed
• Meaning - Mom has 23 chromosomes,
Dad has 23 chromosomes  You have
46 chromosomes
MEIOSIS
• Process that creates gametes, occurs in
reproductive structures
• Cell reproduction that reduces the # of
chromosomes
• Mitosis MAINTAINS the number of chromosomes
in the cell
• Meiosis REDUCES it by half by splitting
homologous chromosomes
• 2n  n
INTERPHASE
• Replication of DNA
• Protein synthesis
MEIOSIS I
• Prophase I: Centrioles move to opposite
poles, spindle fibers form and bind to sister
chromatids at the centromere
• Crossing Over (synapse): chromosome
segments are exchanged between
homologous chromosomes
MEIOSIS I
• Metaphase I: Homologous
chromosomes line up at
center of cell
• Anaphase I: Homologous
chromosomes separate
and pulled to opposite
ends of cell, chromosome
# is reduced from 2n to n
MEIOSIS I
• Telophase I: Chromosomes
reach poles
• Each pole contains only
one chromosome of the
original homologous
chromosomes
MEIOSIS II
• Prophase II:
chromosomes condense
• Metaphase II: HAPLOID
(n) number of
chromosomes line up at
the equator
MEIOSIS II
• Anaphase II: sister
chromatids are pulled
apart
• Telophase II:
chromosomes reach
poles and nuclear
membranes and nuclei
form
MEIOSIS II
Chromosomes
DO NOT
replicate
between I and II
 end result is 4
haploid cells,
each with n
number of
chromosomes
MEIOSIS V MITOSIS
SEXUAL VS. ASEXUAL
REPRODUCTION*
• Asexual
• The organism inherits all of its chromosomes
from one parent
• Individual is genetically identical to its
parent
MEIOSIS IN MALES VS FEMALES
• In females it is called
oogenesis
• Begins while in utero during
the third trimester and stops
until puberty.
• Results in 1 healthy egg
(ovium) and 3 polar bodies
(cells with a nucleus and no
cytoplasm) when completed
• It is only complete after
fertilization has occurred.
MEIOSIS IN MALES VS FEMALES
• In males it is called
spermatogenesis
• Doesn’t occur until puberty
• Results in 4 haploid sperm
cells.
• Completed every ~74 days.
MEIOSIS IN MALES VS FEMALES
Completed Monthly
GREGOR MENDEL
• Genetics: the study of heredity
• Heredity: the passing of traits from
parent to offspring (INHERITANCE)
• Gregor Mendel: Father of Genetics
• Austrian Monk who experimented with
garden peas in 1866, he noticed certain
traits seemed to be passed from one
generation to another
GREGOR MENDEL
• Mendel worked with peas, which self-fertilize
• Some varieties always made green seeds, some
always made yellow seeds, so he cross-pollinated the
peas by hand
• Parent Generation (P): 1st line of crosses
• First Generation(F1): offspring of the parent generation
• F2 Generation: second cross, using the F1 offspring
ALLELES
• He determined there must be
TWO forms of a gene controlled
by different factors
• Alleles: alternative form of single
gene
• For example: height
• Tall or short
• Alleles are NOT genes, they are
two different versions of one
gene!
ALLELES
• Alleles are either dominant or recessive
• Dominant: represented by a capital letter (T = tall)
• This is the trait that is seen
• Recessive: represented by a lowercase letter (t =
short)
• This trait is not seen, it is masked by the
dominant allele ~ it’s there, just hidden!
ALLELES
• If the dominant allele is present, it will show up
– DOMINANCE
• There must be 2 recessive alleles in order to
show up
• We inherit an allele for a specific gene from
each parent
ALLELES
• Homozygous: individual inherits 2 of the same allele
• TT – homozygous dominant OR tt – homozygous
recessive
• Heterozygous: individual inherits 2 different alleles,
one dominant and one recessive
• Tt
• Since the dominant allele is present, it will show
GENOTYPE & PHENOTYPE
• Genotype: organism’s allele
pairs
• Heterozygous, homozygous
dominant, or homozygous
recessive
• Phenotype: observable
appearance of genes
PUTTING IT ALL TOGETHER…
GENOTYPE (HETEROZYGOUS)
=
ALLELE
ALLELE
PHENOTYPE
LAW OF SEGREGATION
• Two alleles for a trait separate during meiosis
• Each gamete will have a different allele
• They will be reunited during fertilization
LAW OF INDEPENDENT
ASSORTMENT
• When gametes are made during meiosis each only gets
one copy of a gene
• This is random; the inheritance of one gene does not
influence the inheritance of another gene; they are
independent
• Every person with brown hair doesn’t have brown eyes
• Some genes are inherited together (LINKED) because the
genes are very close to each other on the chromosome.
• people with red hair are also fair-skinned.
PUNNETT SQUARE
• Used to predict the possible offspring between
two known genotypes
• Monohybrid: crossing one trait at a time
• Dihybrid: crossing two traits
PUNNETT SQUARE
Parent 1- Pure
Short
Parent 2 – Pure Tall
F1 Generation
TONGUE ROLLING
• Dominant Trait ~ T
• 2 parents are heterozygous (Tt) for the trait
• What possible phenotypes will their children have?
T t
T TT Tt
t Tt tt
Tongue
roller
Tongue
roller
Tongue
roller
Non-tongue
roller
PUNNETT SQUARES
• Determining ratios
Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Punnett Square—
Dihybrid Cross
 Four types of alleles
from the male gametes
and four types of alleles
from the female
gametes can be
produced.
 The resulting phenotypic
ratio is 9:3:3:1.
PUNNETT SQUARE
Chapter
10
Sexual Reproduction and Genetics
10.3 Gene Linkage and Polyploidy
Genetic Recombination
 The new combination of genes produced by crossing over and
independent assortment
 Combinations of genes due to independent assortment can be
calculated using the formula 2n, where n is the number of chromosome
pairs.
Chapter
10
Sexual Reproduction and Genetics
10.3 Gene Linkage and Polyploidy
Gene Linkage
 The linkage of genes on a chromosome results
in an exception to Mendel’s law of independent
assortment because linked genes usually do
not segregate independently.
Chapter
10
Sexual Reproduction and Genetics
10.3 Gene Linkage and Polyploidy
Polyploidy
 Polyploidy is the occurrence of one or more
extraof all
sets
chromosomes
in an organism.
 A triploid
organism, for
instance, would
be designated 3n,
which means that
it has three complete sets of chromosomes.