Mendelian Genetics

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Mendelian Genetics
Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
How Genetics Began
 Inheritance, or heredity passing traits to
the next generation
 Mendel performed cross-pollination in pea
plants.
 Mendel followed various traits in the pea
plants he bred.
Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
 The parent generation is also known as
the P generation.
Chapter
10
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.
Chapter
10
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
Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Genes in Pairs
 Allele
 An alternative form of a trait
 Ex. Eye color
Chapter
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Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Dominance
 Homozygous 2 of the same alleles for a
particular trait, also called pure bred.
 Heterozygous 2 different alleles for a
particular trait, also called hybrids.
Bb
bb
BB
Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Genotype and Phenotype
 Genotype allele pairs (GENES)
 TT, Tt, BB, bb, Mm
 Phenotype The observable characteristic
or outward expression of an allele pair
(WHAT YOU SEE)
Bb
Dominant vs. Recessive
Dominant
Recessive
• The phenotype of the
• The other allele, has
organism is
no big effect on the
determined completely
organism's phenotype
by one of the alleles
• Written with lowercase
• Written with at least 1
letters (bb)
capital letter (TT or Tt)
Example: Brown eyes is dominant and blue eyes is recessive
Mendel’s Conclusions cont’d…
Ex. Tall plant (T) x short plant (t) = tall offspring (Tt)
What allele was dominant?
Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Mendel’s Law of Segregation
 Two alleles for each trait separate during
meiosis.
 During fertilization, two alleles for that trait unite.
Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Monohybrid Cross
 A cross that
involves hybrids for
a single trait is
called a
monohybrid cross.
Chapter
10
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.
Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Law of Independent Assortment
 Random distribution of alleles occurs during gamete
formation
 Genes on separate chromosomes sort independently
during meiosis.
 Each allele combination is equally likely to occur.
Law of Segregation
 The two alleles for each trait separate during meiosis
(ex: If a parent is Tt, then either T or t can be given to
the offspring)
Chapter
10
Sexual Reproduction and Genetics
10.2 Mendelian Genetics
Punnett Squares
 Predict the possible
offspring of a cross
between two known
genotypes
Monohybrid Crosses
Do this on your paper: Tt X Tt Cross: Give the
genotypes, phenotypes, & percentages
Go to
Section:
Monohybrid Cross Answer…
Go to
Section:
• Probability the chance or
percentage of chance of a trait being
exhibited
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.
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
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
11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Incomplete Dominance
 The heterozygous phenotype is an
intermediate phenotype between the two
homozygous phenotypes.
Chapter
11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Codominance
 Both alleles are expressed in the
heterozygous condition.
Chapter
11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Coat Color of Rabbits
 Multiple alleles can demonstrate a hierarchy
of dominance.
 In rabbits, four alleles code for coat color:
C, cch, ch, and c.
Chapter
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Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Coat Color of Rabbits
Chinchilla
Albino
Light gray
Dark gray
Himalayan
Chapter
11
Complex Inheritance and Human Heredity
11.2 Complex Patterns of Inheritance
Multiple Alleles
 Blood groups in
humans
 ABO blood
groups have
three forms of
alleles.
Human Blood Typing
• Human blood is classified according to the
presence or absence of certain markers
called antigens that are located on the
surface of red blood cells.
• If you have the A antigen, you have type A
blood and antibodies against B blood.
• If you have the B antigen, you have type B
blood and antibodies against A blood.
What about O & AB?
• If you don’t have either the A or B antigen, you
have type O blood.
• In the US, O is the most common blood type.
• You have antibodies against A and B.
• You are also a universal donor. (You can give
blood to anyone)
• If you have both the A and B antigens, you
have type AB blood and this is the rarest form
of blood. No antibodies against either A or B.
Describe sex-linked alleles
• Sex-linked alleles:
controlled by genes located
on sex chromosomes
• Usually carried on X
chromosome
• Since females are XX, they
are usually carriers of the
trait
• Since males are XY, they
have a higher tendency for
inheritance of trait
Recipient’s blood type
AA+
BB+
ABAB+
OO+
Compatible donor’s blood
type
A-, OA-, A+, O-, O+
B-, OB-, B+, O-, O+
A-, B-, AB-, OA-, A+, B-, B+,
AB-, AB+, O-, O+
OO-, O+
Chapter
10
Sexual Reproduction and Genetics
10.3 Gene Linkage and 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.
Chapter
11
Complex Inheritance and Human Heredity
11.3 Chromosomes and Human Heredity
Karyotype Studies
 Karyotype—micrograph in which the pairs
of homologous chromosomes are arranged
in decreasing size.
 Images of chromosomes stained during
metaphase
 Chromosomes are arranged in decreasing
size to produce a micrograph.
Chapter
10
Sexual Reproduction and Genetics
10.3 Gene Linkage and Polyploidy
 Epistasis- is a gene at one location on a
chromosome can affect the expression of a
gene at a second location
A good example of epistasis is the
genetic interactions that produce
coat color in horses and other
mammals. In horses, brown coat
color (B) is dominant over tan (b).
Gene expression is dependent on
a second gene that controls the
deposition of pigment in hair.
Genetics Disorders
Recessive
Cystic Fibrosis
 Affects the mucusproducing glands,
digestive
enzymes, and
sweat glands
Albinism
Caused by altered genes, resulting
in the absence of the skin pigment
melanin in hair and eyes
White Hair
Very pale skin
Pink Pupils
Tay-Sachs
•Causes inflating of
brain nerve cells and
mental deterioration.
•Most common in
Jewish descent
people
Dominant
Huntington’s Disease
•Decline in nervous
system functions &
causes mental
retardation
•Ability to move
deteriorates
Achondroplasia
•small body size
and limbs that are
comparatively
short
Sex-Linked
(On X Chromosome)
Describe sex-linked alleles
• Sex-linked alleles:
controlled by genes located
on sex chromosomes
• Usually carried on X
chromosome
• Since females are XX, they
are usually carriers of the
trait
• Since males are XY, they
have a higher tendency for
inheritance of trait
Hemophilia
Red-Green Color-Blindness
Co-Dominant
Sickle Cell Anemia
Changes in hemoglobin
cause red blood cells to
change to a sickle shape.
Non-Disjunction
Klinefelter Syndrome
•
•
•
•
•
Male
Extra X-chromosome
Genotype: XXY
Sterile
Often mentally
retarded
• Small testes,
enlarged breasts, and
reduced sperm
production
Turner Syndrome
• Only one sex
chromosome (an X).
• X__
• Female
• Short
• Fails to develop
ovaries so become
infertile
Down Syndrome
Chapter
11
Complex Inheritance and Human Heredity
11.1 Basic Patterns of Human Inheritance
Pedigrees
 A diagram that traces the inheritance of a
particular trait through several generations
Interpret pedigrees
• Pedigrees: graphic
representation of family
tree
• Symbols identify sex, if
they are carriers, if they
have a certain trait, etc.
• Follows one trait
• May be used if testcross
cannot be made
Pedigree Symbols
Hemophilia Pedigree
Chapter
11
Complex Inheritance and Human Heredity
11.3 Chromosomes and Human Heredity
Karyotype Studies
 Karyotype—micrograph in which the pairs
of homologous chromosomes are arranged
in decreasing size.
 Images of chromosomes stained during
metaphase
 Chromosomes are arranged in decreasing
size to produce a micrograph.

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