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Sexual Reproduction and
Genetics
Chapter 10

The instructions for all your traits are
located on your DNA on small segments
called genes.
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Genes are located on chromosomes
Every species has a unique chromosome
number
Bat
94
squirrel
40 chicken 78
House fly 12
mosquito
6 king crab 208
Apple
34
carp
104 potato
48
Crab eating rat 92 (highest no. for mammals)
Adders tongue –fern – 1260 (highest)
Jack jumper ant – 2 (lowest number)
Humans - 46
Sexual Reproduction and Genetics
Chapter
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Our species has 46
chromosomes
• Each parent
contributes half
of its
chromosomes
•
23 from dad, 23
from mom
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Sexual Reproduction and Genetics
Chromosome come in pairs
 Homologous chromosomes—one of two
paired chromosomes, one from each
parent
 Same length
 Same centromere position
 Carry genes that
control the same
inherited traits
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Sexual Reproduction and Genetics
Haploid and Diploid
Cells
An organism produces gametes (sex Cells) to
maintain the same number of chromosomes
from generation to generation.
 Human gametes contain 23 chromosomes.
 A cell (sex cells) with n chromosomes is called
a haploid cell.
 A cell (body cells) that contains 2n
chromosomes is called a diploid cell.
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Sexual Reproduction and Genetics
 The sexual life cycle
in animals involves
meiosis.
 Meiosis produces
gametes.
 When gametes
combine in fertilization, the number of
chromosomes is restored.
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What process produces gametes?
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Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis
 Reduces the chromosome number by half
through the separation of homologous
chromosomes
 Involves two consecutive cell divisions
called meiosis I and meiosis II
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Sexual Reproduction and Genetics
 Interphase
 Chromosomes replicate.
 Chromatin condenses.
Interphase
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Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis I
 Prophase I
 Pairing of homologous
chromosomes
Prophase I
 nuclear envelope breaks down.
 Spindles form.
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Sexual Reproduction and Genetics
10.1 Meiosis
 Prophase I
 Crossing over produces exchange of genetic
information.
 chromosomal segments are exchanged
between a pair of homologous
chromosomes.
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Sexual Reproduction and Genetics
10.1 Meiosis
 Metaphase I
Metaphase I
 Homologous chromosomes line up at the
equator.
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Sexual Reproduction and Genetics
10.1 Meiosis
 Anaphase I
 Homologous
chromosomes
separate and move
to opposite poles of the cell.
Anaphase I
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Sexual Reproduction and Genetics
10.1 Meiosis
 Telophase I
 spindles
break down.
Telophase I
 Chromosomes uncoil and form two nuclei.
 The cell divides.
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Sexual Reproduction and Genetics
10.1 Meiosis
 Prophase II
Prophase II
spindle apparatus forms and the
chromosomes condense.
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Sexual Reproduction and Genetics
10.1 Meiosis
 Metaphase II
 A haploid number
of chromosomes
line up at the equator.
Metaphase II
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Sexual Reproduction and Genetics
10.1 Meiosis
 Anaphase II
 The sister
Anaphase II
chromatids are
pulled apart move toward the opposite
poles of the cell.
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Sexual Reproduction and Genetics
10.1 Meiosis
 Telophase II
Telophase II
the nuclear membrane and nuclei reform.
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Sexual Reproduction and Genetics
10.1 Meiosis
Meiosis II
 Cytokinesis results in
four haploid cells,
each with n number
of chromosomes.
Cytokinesis
Meiosis overview
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Sexual Reproduction and Genetics
10.2 Mendelian Genetics
How Genetics Began
 The passing of traits to the next generation
is called inheritance, or heredity.
Mendel – the Father of genetics
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1800s
Austrian monk
Cross bred pea plants
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Why did he choose pea plants?
Collected data over many generations
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Sexual Reproduction and Genetics
10.2 Mendelian Genetics
 Mendel studied seven different traits.
 Seed or pea color
 Flower color
 Seed pod color
 Seed shape or texture
 Seed pod shape
 Stem length
 Flower position
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Sexual Reproduction and Genetics
10.2 Mendelian Genetics
 The parent generation is also known as
the P generation.
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Sexual Reproduction and Genetics
10.2 Mendelian Genetics
 The offspring of
this P cross are
called the first filial
(F1) generation.
 The second filial
(F2) generation is
the offspring from
the F1 cross.
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10.2 Mendelian Genetics
Mendel concluded that there must be 2
forms of the seed traits in the pea plants
 Allele
 An alternative form of a single gene
passed from generation to generation

He also concluded that the 3:1 ratio
observed during his experiments could be
explained if alleles were paired in each of
the plants
 Dominant- trait that is expressed in the F1
generation
 Recessive- trait that is masked in the F2
generation
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Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Dominance
 An organism with two of the same alleles
for a particular trait is homozygous
 Written as BB or bb
 An organism with two different alleles for a
particular trait is heterozygous
 Written as Bb
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10.2 Mendelian Genetics
Genotype and Phenotype
 An organism’s allele pairs are called its
genotype.
 The observable characteristic or outward
expression of an allele pair is called the
phenotype.
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10.2 Mendelian Genetics
Monohybrid Cross
 A cross that
involves hybrids for
a single trait is
called a
monohybrid cross.
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Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Punnett Squares
 Predict the possible
offspring of a cross
between two known
genotypes
Punnett
Squares
Mendel Laws

Law of segregation – two alleles for each
pair separate during meiosis
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Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Law of Independent Assortment
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Random distribution of
alleles occurs during
gamete formation
Genes on separate
chromosomes sort
independently during
meiosis.
Each allele combination
is equally likely to occur.
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Sexual Reproduction and Genetics
Punnett Square—
Dihybrid Cross
Cross involving 2 traits
 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.
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Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Dihybrid Cross
 The simultaneous inheritance of two or
more traits in the same plant is a dihybrid
cross.
 Dihybrids are heterozygous for both traits.
Have you ever had some say they saw your
“twin” or have you seen someone that looked
just like you?
Is this ever possible if they are not related to
you???
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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.
 For us that would be 223 times 2 23 (after
fertilization) or over 70 trillion possible
combinations!!
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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.
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10.3 Gene Linkage and Polyploidy
Polyploidy
 Polyploidy is the occurrence of one or more
extra
sets of all
chromosomes
in an organism.
 A triploid
organism, for
instance, would be
designated 3n,
which means that
it has three complete sets of chromosomes.