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Chapter 5 Key Terms
Gene
Punnett Square
Diploid
Cell cycle
Ovum
Meiosis
Phenotype
Chromosome
Carrier
Haploid
Gamete
Sperm
Allele
Genotype
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Biology Chapter 5
GENETICS
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Characteristics

Species characteristics
 Characteristics
2

eyes, 2 ears, liver, stomach…
Individual Characteristics
 Characteristics
 Hair

that every member of a species possesses
that make a person unique
color, eye color, skin color…
A person is made of species characteristics and individual
characteristics
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Mechanism of Heredity

Genetics
 Study

of heredity
History
 Aristotle’s
Particulate theory of reproduction
 Believed that particles of parent’s blood mixed to form the offspring
 This is where “pure blood” and “blood relative” come from

Gregor Mendel
Performed many experiments that helped advance our understanding
of genetics
 Experimented on peas and their characteristics

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Mechanism of Heredity

Mendel proposed there are pairs of factors in organisms that affect
the offspring

1953, Watson and Crick discovered DNA
 This
opened the way to modern genetics
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Genes

Defined as “a section of DNA that produces a particular
polypeptide chain of amino acids that causes a particular
trait”

Coiled DNA from all cells in person’s body would fit in 1 in. ice
cube

DNA from one cell would stretch out to be 2 yards long

Information contained in DNA of one cell would fill 600,000
pages
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Chromosomes

In an inactive cell, the chromosomes exist in the nucleus as
chromatin material
A
tangled mass of chromosomes
 Chromosomes
them with
do not look like what we normally associate
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Chromosomes

Histones
 Provide
support and protection for DNA
strand
 Help maintain shape of chromosomes

Chromatid
 Two

identical halves of chromosome
Centromere
 Constricted
chromatids
area that joins sister
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Review
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Chromosomes

The number of chromosomes in a cell is a species characteristic
 Horse
 Cat
= 64 chromosomes
= 38 chromosomes

Humans have 46 chromosomes (23 pair) in
each cell nuclei

Karyotype
 Picture
of chromosomes arranged in pairs
and correct order
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Chromosomes

The pairs of chromosomes are called
homologous chromosomes
 Each
member of the pair is called a
homologue

Haploid cell
 One

set of unpaired chromosomes (n)
Diploid cell
 Homologous
pairs of chromosomes (2n)
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Cell Cycle


The repeating cycle of events in the life of a cell
Divided into 3 parts
 Interphase,

mitosis, cytokinesis
Interphase
 Longest
portion of the cell cycle
 Divided into 3 stages: G1, S, G2 phases
 G1 = cell grows, makes new organelles, proteins and other molecules
S
= DNA is replicated, centrosome divides into centrioles
 G2 = cell produces proteins and molecules needed for mitosis
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Cell Division

Mitosis
 Division
of nuclear material to ensure each new nucleus contains
identical copies of genetic information from mother cell

4 phases
 Prophase
 Metaphase
 Anaphase
 Telophase
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Mitosis

Prophase
 Chromosomes
 Centrosomes
fibers

shorten and become visible
migrate to the poles and form spindle
Metaphase
 Chromosomes
 Chromosomes
line up in the middle
look like X’s because the sister
chromatids appear to repel each other
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Mitosis

Anaphase
 Chromatids
separate into daughter chromosomes
 Spindle fibers pull chromosomes toward poles of cell

Telophase
 Chromosomes
reach end of spindle
 Two nuclei form around daughter chromosomes
 Chromosomes uncoil into chromatin
 Spindle

disappears leaving the centrosome
Mitosis is complete when nuclear membrane has
reformed around the nucleus
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Cell Division

Purpose of mitosis
 To
ensure that both daughter cells get an exact copy of the same
information the parent cell contained

Is not important to have equal amounts of cytoplasm and
organelles because the cell will make more

Is important to have correct and complete set of
genes/chromosomes
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Cell Division

Cytokinesis
 Division
of the cytoplasmic content
(organelles, proteins…)
 Cell
completely divides

Different process in plants than in human
and animal cells

Once cytokinesis is complete, the cell cycle
begins all over again
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Meiosis





Edouard van Beneden

Discovered meiosis in 1883 when he noticed the reproductive cells of a worm
only contained half the chromosomes the normal cells contained

Proposed some process occurred to reduce the chromosomes in gametes
As gametes form, the chromosome number is reduced to the haploid
number (23 in humans)
Zygote forms when two gametes (sperm and egg) unite
Each gamete must have 1 of every homologous pair
Meiosis is the reduction of a cell’s chromosomes from diploid to haploid
by two consecutive cell divisions (Meiosis I and Meiosis II)
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Meiosis I

Prophase I
 Chromosomes
 Then
coil, spindles begin to form
duplicated homologous chromosomes pair up, form a tetrad
 Chromatids
are very close together and sometimes exchange
genetic material

Metaphase I
 Tetrads
line up on equatorial plane
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Meiosis I

Anaphase I
 Homologous
pairs separate and move toward
end of spindle

Telophase I
 Chromosomes
arrive at poles of cell, but
chromosomes do NOT uncoil

Cytokinesis
 Cells
completely divide and go directly into
Meiosis II
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Meiosis II

Prophase II
 Mitotic
plane

spindles reform and move chromosomes toward equatorial
Metaphase II
 Chromosomes

Anaphase II
 Sister

align in middle of cell
chromatids separate and move to opposite sides of cell
Telophase II and cytokinesis
 Nuclei
reform and each of the four new cells are haploid
Telophase I
Prophase II
Metaphase II
Anaphase II
Telophase II
Cytokinesis
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Comparing Mitosis and Meiosis

Functions:
 Mitosis
– produce 2 new cells with same number of chromosomes as
parent cell
 Meiosis
– produces four haploid cells

Both go through interphase

All events unique to meiosis occur during meiosis I
Meiosis I Review
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Meiosis II Review
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Genetics

Genetics
 Study

of heredity
Gregor Mendel
 Father
of Modern Genetics
 Experimented
 1865

with how pea plants passed on traits
– published paper on Mendelian Genetics
Mendel’s work on heredity is important to understanding
modern genetic theories
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Genetics

Mendel studied traits of the pea plants that had two variations
 Tall

or short plants; green or yellow pods…
Self-Pollination
 Pollen
(male gamete) fertilizes the pistil (female gamete) of
same plant

Cross-Pollination
 Fertilizing
the pistil of one plant with the pollen from another
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Genetics

P1 = Parent plants/generation
 One
 F1
= First filial generation
 All
 F2
tall parent, one short parent
plants were tall
= Second filial generation
 Out
of 1064 offspring, 787 (74%) plants were tall, 277 (26%)
plants were short
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Genetics

Mendel proposed several concepts
1.
The concept of unit characteristics

2.
An organism’s characteristics are caused by units he called
factors (we call genes)
The concept of dominant and recessive
 Dominant:
expressed trait when two different genes present
 Recessive:
masked trait
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Genetics
3.
The concept of segregation
 Each
 The
gamete contains only 1 gene for each characteristic
gamete would pass on that gene and work with the gene
from the other gamete
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Genetic Terminology

Genotype: the specific genes an organism contains

Phenotype: the physical expression of an organism’s genes

Locus: specific site on chromosome where gene is located

Allele: alternate form of a gene that occupies the same locus
on homologous chromosomes
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Genetic Terminology

Homozygous: both alleles are the same (TT or tt)

Heterozygous: alleles are different (Tt)

Monohybrid cross: cross between individuals that deals with
only one set of alleles

Punnett Squares: determine the probability of the offspring’s
genotype and phenotype
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Punnett Squares

Purpose:
 Visualize
 Predict

genetic crosses
probability of genotype or phenotype of offspring
Rules
 Female
 Male
along top of square
along side of square
 Dominant
Allele written first
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Practice

A father is homozygous for unattached earlobes (dominant)
while the mother is homozygous for attached earlobes
(recessive). What will the genotypes and phenotypes of the
offspring be? (F is dominant, f is recessive)
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Practice

Now, two individuals who are heterozygous for earlobe
attachment cross. What are the possible genotypes and
phenotypes of the offspring?
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Punnett Squares

Test cross
 Mating
an organism with dominant phenotype but unknown
genotype with plant that is homozygous recessive phenotype
 If

all offspring are dominant, parent was homozygous
Pedigree
 Chart
used to trace presence or absence of a trait through a
number of generations
 Used
to predict possibilities of certain traits in offspring
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Variations of Mendelian Genetics

Incomplete Dominance
 Occurs
when two alleles are both expressed
 Phenotype
 Ex.
of offspring is blend or mixture of two parent traits
flower color
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Practice

A cross between a blue bird and a white bird produce silver
offspring. The color is determined by two alleles. A) What are
the genotypes of the parents in the original cross? B) What are
the genotypes of the silver offspring? C) What would the
phenotypic ratios of offspring produced by two silver birds?
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Variations of Mendelian Genetics

Codominance
 Both
alleles for a trait are
expressed
 Colors
are not blended but
are both present
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Variations of Mendelian Genetics

Multiple alleles
 More
than two alleles can be present at a locus
 Only
two possible alleles on the homologous chromosomes
 Ex.
ABO blood type
A
= IAIA or Iai
B
= IBIB or IBi
 AB
O
= IA I B
= ii
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Dihybrid Cross

A cross of two pairs of contrasting traits at the same time

Color of the pod is one pair of genes

Pod characteristics is another pair

Green is dominant, yellow is recessive

Inflated is dominant, constricted is
recessive
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Dihybrid Cross

Independent Assortment
 Segregation
of one set of alleles during meiosis is
not affected by the presence or segregation of
other sets of alleles
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Sex-Linked Inheritance

Normal people have 22 pairs of autosomes
and 1 pairs of sex chromosomes
 Males
= XY
 Females
= XX

Sex-linked inheritance deals with genes
found mostly on the X chromosome

Sex-linked traits
 Colorblindness
and hemophilia
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Colorblindness

The gene for colorblindness is on the
X chromosome and is recessive

If a male receives the colorblindness
gene, he will be colorblind

If a female receives the
colorblindness gene, she may not
express it, depending on the gene of
the other X chromosome
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