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4-1 Notes
Foundations of Genetics
Chapter 4
Lesson 1
Early Ideas About Heredity
• Combined genetic material from a sperm and
an egg determines the traits or features of an
offspring.
Early Ideas About Heredity
• Heredity is the passing of traits from parents
to offspring.
Early Ideas About Heredity
• The idea of blending inheritance is offspring
are a blend of genetic material from both
parents.
+
=
Early Ideas About Heredity
– The genetic material mixed or blended like
colors of paint.
Early Ideas About Heredity
– Over many generations, populations would
eventually look alike.
Early Ideas About Heredity
– Blending inheritance cannot explain why
some traits skip a generation.
Gregor Mendel and His Experiments
• Gregor Mendel was the first to record
evidence that traits are determined by factors
passed from parents to offspring.
• Mendel established the basic laws of heredity.
Gregor Mendel and His Experiments
• Genetics is the study of how traits of
organisms are passed from parents to
offspring.
Mendel’s Experimental Methods
• Mendel conducted breeding experiments by
studying seven traits of pea plants and each
trait had only two variations.
Controlled Experiments
• Mendel controlled fertilization in the pea
plants, allowing him to see how traits pass
from one generation to another.
Controlled Experiments
• Mendel allowed some flowers to
self-fertilize.
Controlled Experiments
• He also performed cross-fertilization by
transferring pollen from one pea flower to
another.
Mendel’s Unique Methods
• Used true-breeding plants for each trait—
plants that always produce offspring with that
trait when they self-pollinate
Mendel’s Unique Methods
• Recorded the inheritance of traits for several
generations
• Used a mathematical approach
Mendel’s Experimental Results
• Mendel concluded that two factors control
each inherited trait.
Plant Height
T (tall)
t (short)
TT
tt
Tt
Mendel’s Experimental Results
• When organisms reproduce, each gamete—
sperm or egg—contributes one factor for each
trait.
T
or
T
TT
t
or
T
or
t
t
t
T
tt
Tt
Tt
Dominant Factors
• A genetic factor that blocks
another genetic factor is called
dominant.
• A dominant trait is observed
when offspring have one or two
dominant factors.
• Indicated by the capital letter
(Y for yellow)
Y
YY or Yy
Recessive Factors
• A genetic factor that is hidden by
the presence of a dominant factor
is recessive.
• A recessive trait can be observed
only when two recessive genetic
factors are present in offspring.
• Indicated by the lowercase letter
(y for green)
y
yy
Modern Definitions of Mendel’s Ideas
• Mendel did not know about DNA or how cells
reproduce, but his ideas about inheritance are
still true today.
Genes and Alleles
• A gene is a section
of DNA that has
information about a
trait in an organism.
Genes and Alleles
• Each form of a gene
with different
information is called
an allele.
Alleles
• A or a
• D or d
• T or t
Genes and Alleles
Phenotype and Genotype
• The observable traits
and all
characteristics of an
organism make up
the organism’s
phenotype.
Phenotype and Genotype
• The alleles that
make up an
organism is the
organism’s
genotype.
• The alleles of a
particular gene is
that gene’s
genotype.
Homozygous and Heterozygous Genotypes
• Because eukaryotes
have pairs of
chromosomes, a
genotype for a gene
has two alleles.
Homozygous and Heterozygous Genotypes
• If the two alleles have the
same information, the
genotype is
homozygous.
Homozygous and Heterozygous Genotypes
• If the two alleles have
different information, the
genotype is
heterozygous.
Homozygous and Heterozygous Genotypes
Symbols
• Y = yellow (dominant)
• y = green (recessive)
Genotype
Phenotype
YY (homozygous dominant)
yellow (purebred)
yy (homozygous recessive)
green (purebred)
Yy (heterozygous)
yellow (hybrid)
3 different genotypes & ___
2 different phenotypes
• ___
Mendel’s Law of Segregation
• During meiosis is
when gametes
(sperm/egg) form.
• The two factors for
each trait segregate
(separate) from each
other during meiosis.
Mendel’s Law of Segregation
• Each set of chromatids separates into different
gametes.
• Each gamete receives only one allele.
Mendel’s Law of Independent Assortment
• The factors for one trait separate
independently of how factors for other traits
separate
Mendel’s Law of Independent Assortment
• A daughter cell might receive the A or a
chromosome from pair 1 and the B or b
chromosome from pair 2.
Mendel’s Law of Independent Assortment
• This results in four possible allele
combinations (for two homologous pairs of
chromosomes).
Importance of Mendel’s Genetic Studies
• In the 1860s, no one knew about
chromosomes or meiosis so it was hard to
understand Mendel’s discoveries.
• All the research of modern genetics is based
on Mendel’s conclusions from his work with
pea plants.
4.1 Foundations of Genetics
What is the passing of traits from
parents to offspring called?
A inheritance
B genetics
C heredity
D allele
4.1 Foundations of Genetics
What are the alleles that make up an
organism called?
A genes
B genotype
C phenotype
D factors
4.1 Foundations of Genetics
If two alleles for a gene have the
same information, what kind of
genotype does that gene have?
A homologous
B recessive
C heterozygous
D homozygous
What is the term for the idea that
offspring are a blend of genetic
material from both parents?
A polygenic inheritance
B sex-linked inheritance
C maternal inheritance
D blending inheritance
What type of alleles can only be
observed in the phenotype when
they are present as a homozygous
genotype?
A dominant
B recessive
C inherited
D heterozygous
What is the term for the idea that
inheritance of one trait is not
influenced by inheritance of another
trait?
A law of independent assortment
B law of heredity
C law of segregation
D maternal inheritance
SCI 2.c
Which pea trait did Mendel not
study?
A seed color
B pod color
C flower position
D flower shape
SCI 2.d
Which does NOT describe Mendel’s
experiments?
A Mendel observed several
generations of plants.
B Mendel chose pea plants because
they reproduce quickly.
C Mendel counted small numbers of
offspring.
D Mendel used true-breeding plants.