Transcript Biology Chapter 6

Section One: Chromosomes and
Meiosis
 Cell Types
 Somatic Cells: cells that make up your body tissues and
organs
 Gametes: sex cells; sperm and eggs
Section One: Chromosomes and
Meiosis
 Chromosomes
 Homologous Chromosomes:
two chromosomes-one from
the mother and one from the
father- that have the same
length and general
appearance
 Humans have 23 pairs of
chromosomes
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Have the same set of genes as
well
Pairs 1-22 are autosomes:
chromosomes that contain
genes not directly related to the
sex of an organism
Pair 23: sex chromosomes:
control the development of
sexual characteristics
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
XX=female
XY=male
Section One: Chromosomes and
Meiosis
 Haploid and Diploid
 Sexual Reproduction: involves the fusion of two gametes that
result in offspring that area genetic mixture of the parents

Fertilization: fusion of the sperm and egg
 Dipolid: the cell has 2 copies of each chromosome
 One copy from the mother and one copy from the father
 Somatic cells are diploid
 Haploid: the cell has only one copy of each chromsome
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Sex chromsomes are haploid
X chromosome is always in the egg
Sperm can contain the X or Y chromosme
Section One: Chromosomes and
Meiosis
 Meiosis
 Maintaining chromosome
numbers is important for
the body to function
correctly
 Meiosis: the form of
nuclear division that
divides the diploid cell
into haploid cells for
formation of gametes
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Produces gametes
Reduces chromosome
number by half
Creates 4 haploid cells
Section Two: Process of Meiosis
 Homologous Chromosomes and Sister Chromatids
 Sister chromatids: duplicated chromosomes that stay
attached to each other
 Homologous Chromosomes: two chromosomes-one
from the mother and one from the father- that have the
same length and general appearance
Section Two: Process of Meiosis
 Meiosis
 Two stages: Meiosis I and Meiosis II
 Meiosis I

Prophase I, Metaphase I, Anaphase I, Telophase I
 MeiosisII

Prophase II, Metaphase II, Anaphase II, Telophase II
Section Two: Process of Meiosis
 Meiosis I
 Prophase I
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Nuclear membrane breaks
down
Centrosomes and
centrioles move
Spindle fibers assemble
Duplicated chromosomes
condense
Homologous
chromosomes pair up
Section Two: Process of Meiosis
 Meiosis I
 Metaphase I

Spindle fibers align the
homologous
chromosomes along cell
equator
Section Two: Process of Meiosis
 Meiosis I
 Anaphase I
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Paired homologous
chromosomes separate
from each other and move
toward opposite ends of
the cell
Sister chromatids stay
attached
Section Two: Process of Meiosis
 Meiosis I
 Telophase I

Spindle fibers disassemble
and the cell undergoes
cytokinesis
Section Two: Process of Meiosis
 Meiosis II
 Prophase II



Nuclear membrane breaks
down
Centrosomes and
centrioles move to
opposite ends of the cell
Spindle fibers form
Section Two: Process of Meiosis
 Meiosis II
 Metaphase II

Spindle fibers align the chromosomes along the center of the
cell
Section Two: Process of Meiosis
 Meiosis II
 Anaphase II

The sister chromatids are pulled apart from each other and
move to opposite ends of the cell
Section Two: Process of Meiosis
 Meiosis II
 Telophase II
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Nuclear membrane forms again
Spindle fibers break apart
Cell undergoes cytokinesis
Section Three: Mendel and
Heredity
 Gregor Mendel and Genetics
 Traits: distinguishing characteristics that are inherited
 Genetics: the study of biological inheritance patterns
and variations in organisms
 Purebred: genetically uniform
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The offspring of the purebred parents inherit all of the parents
characteristics
Cross: the mating of two organsims
 P= parental generation
 F1= first generation of offspring
Section Three: Mendel and
Heredity
 Mendel’s Conclusions
 Law of Segregation
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Organism inherit two copies of each gene, one from each
parent
Organisms donate only one copy of each gene in their
gametes, thus the two copies separate during gamete
formation
Section Four: Traits, Genes, and
Alleles
 Genes
 Gene: a piece of DNA
that provides a set of
instructions to a cell to
make a certain protein
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Consists of two alleles: an
alternate form of a gene
Homozygous: when the
two alleles are the same
Heterozygous: when the
two alleles are different
Section Four: Traits, Genes, and
Alleles
 Genes and Traits
 Genome: all of an
organism’s genetic
material
 Genotype: the genetic
makeup of a specific set
of genes

Codes for phenotype
 Phenotype: physical
traits
Section Four: Traits, Genes, and
Alleles
 Genotype Determination
 Depends on dominant and recessive alleles
 Dominant allele: the allele that is expressed when two
different alleles or two dominant alleles are present
 Recessive allele: the allele that is expressed only when
two copies of it are present
Section Four: Traits, Genes, and
Alleles
 Phenotype
 2 genotypes can produce the dominant phenotype
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Ex: BB and Bb
 Only 1 genotype can produce the recessive phenotype
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Ex: bb
Section Five: Traits and Probability
 Punnett Squares
 A grid system for predicting possible genotypes resulting
from a cross
Section Five: Traits and Probability
 Punnett Squares
 Monohybrid Cross: crosses that examine the inheritance
of only one specific trait
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Homozygous crossed with homozygous
Heterozygous crossed with heterozygous
Homozygous crossed with heterozygous
 Test cross: a cross between an organism with an unknown
genotype and an organism with the recessive phenotype
Section Five: Traits and Probability
 Punnett Squares
 Dihybrid Crosses:
crosses that examine the
inheritance of two
different traits
 Law of Independent
Assortment: the allele
that pairs separate
independently of each
other during gamete
formation
Section Five: Traits and Probability
 Heredity Patterns and Probability
 Probability: the likelihood that a particular event will
happen
Section Six: Meiosis and Genetic
Variation
 Unique Combinations
 Sexual reproduction creates a unique variety of traits

Homologous chromosome pairing
Section Six: Meiosis and Genetic
Diversity
 Crossing Over and Genetic Diversity
 Crossing Over: the exchange of chromosome segements
between homologous chromosomes during prophase I
of meiosis I.
Section Six: Meiosis and Genetic
Variation
 Genetic Linkage
 Genes located close together tend to be inherited
together