Download mendelian genetics

MENDELIAN
GENETICS
Gregory Mendel – 1822- 1884
•Australian monk
•Afterwards became Father of
modern genetics
•Researched with pea plants
•Developed ideas of dominance
and trait segregation
MENDELIAN GENETICS
How Genetics Began
 The passing of traits to the next generation
is called inheritance, or heredity.
 Mendel performed cross-pollination in pea
plants.
 Mendel followed various traits in the pea
plants he bred.
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
MENDELIAN GENETICS
 Mendel crossed a pure
yellow pea with a pure
green pea
 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.
MENDELIAN GENETICS
Genes in Pairs
 Allele
 An alternative form of a single gene passed
from generation to generation
 They can be Dominant or
 Recessive
MENDELIAN GENETICS
Dominance
 An organism with two of the same alleles for
a particular trait is homozygous.
 An organism with two different alleles for a
particular trait is heterozygous.
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.
 An example of Genotype is Yy
 An example of Phenotype is yellow
MENDELIAN GENETICS
Mendel’s Law of Segregation
 Two alleles for each trait separate during meiosis.
 During fertilization, two alleles for that trait unite.
 Heterozygous organisms are called hybrids.
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.
MENDELIAN GENETICS
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
n
formula 2 , where n is the number of
chromosome pairs.
MENDELIAN GENETICS
Monohybrid Cross
 A cross that involves
hybrids for a single
trait is called a
monohybrid cross.
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.
MENDELIAN GENETICS
Probability
• The likelihood that a particular event will
occur
• Example: What is the probability that a coin
when flipped will be heads? .. ½ X ½ = 50%
• What is the probability that a coin when
flipped will be heads three times in a row?
½ X ½ X ½ = 1/8 or 1 out of 8 chance
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.
Complex Patterns of Inheritance
Codominance
 Both alleles are expressed in the
heterozygous condition.
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.
Complex Patterns of Inheritance
Dosage Compensation
 The X chromosome carries a variety of
genes that are necessary for the
development of both females and males.
 The Y chromosome mainly has genes that
relate to the development of male
characteristics.
Complex Patterns of Inheritance
Sex-Linked Traits
 Genes located on the X chromosome
 Red-green color blindness
 Hemophilia
Complex Patterns of Inheritance
Environmental Influences
 Environmental factors
 Diet and exercise
 Sunlight and water
 Temperature
Pedigrees
 A diagram that traces the inheritance of a
particular trait through several generations
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.
Basic Patterns of Human Inheritance
Cystic Fibrosis
 Affects the mucus-producing glands,
digestive enzymes, and sweat glands
 Chloride ions are not absorbed into the
cells of a person with cystic fibrosis but
are excreted in the sweat.
 Without sufficient chloride ions in the cells,
a thick mucus is secreted.
Basic Patterns of Human Inheritance
Recessive Genetic Disorders
 A recessive
trait is
expressed
when the
individual is
homozygous
recessive for
the trait.
Basic Patterns of Human Inheritance
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
Basic Patterns of Human Inheritance
Tay-Sachs Disease
 Caused by the absence of the enzymes
responsible for breaking down fatty acids
called gangliosides
 Gangliosides accumulate in the brain,
inflating brain nerve cells and causing
mental deterioration.
Basic Patterns of Human Inheritance
Dominant Genetic Disorders
 Huntington’s disease affects the nervous
system.
 Achondroplasia is a genetic condition that
causes small body size and limbs that are
comparatively short.
Basic Patterns of Human Inheritance
Sickle-cell Disease
 Changes in hemoglobin
cause red blood cells to
change to a sickle shape.
 People who are
heterozygous for the trait
have both normal and
sickle-shaped cells.
Chapter Diagnostic
Questions
Which symbol is used to represent the
number of chromosomes in a gamete?
A. #
B. x
C. r
D. n
1.
2.
3.
4.
A
B
C
D
Chapter Diagnostic
Questions
Name the person known as the father of
genetics.
A. Felix Mendelssohn
B. Gregor Mendel
C. Dr. Reginald Punnett
D. Albert Einstein
1.
2.
3.
4.
A
B
C
D
Chapter Diagnostic
Questions
Which term refers to the outward expression
of an allele pair?
A. gamete
B. hybrid
C. phenotype
D. genotype
1.
2.
3.
4.
A
B
C
D
Formative Questions
Segments of DNA that control the production
of proteins are called _______.
A. chromatids
B. chromosomes
C. genes
D. traits
1.
2.
3.
4.
A
B
C
D
Formative Questions
What is the term for a pair of chromosomes
that have the same length, same centromere
position, and carry genes that control the same
traits?
A. diploid
B. heterozygous
C. homozygous
D. homologous
1.
2.
3.
4.
A
B
C
D
Formative Questions
How does the number of chromosomes in gametes
compare with the number of chromosomes in body
cells?
A. Gametes have 1/4 the
number of chromosomes.
B. Gametes have 1/2 the
number of chromosomes.
C. Gametes have the same
number of chromosomes.
D. Gametes have twice as
many chromosomes.
1.
2.
3.
4.
A
B
C
D
Formative Questions
What type of organisms only reproduce
asexually?
A. bacteria
B. protists
C. plants
D. simple animals
1.
2.
3.
4.
A
B
C
D
Formative Questions
What is the name for different forms of a
single gene that are passed from generation
to generation?
A. alleles
B. genotypes
C. phenotypes
D. traits
1.
2.
3.
4.
A
B
C
D
Formative Questions
Which pair of alleles is heterozygous?
A. RR
B. Rr
C. rr
D. yR
1.
2.
3.
4.
A
B
C
D
Formative Questions
In rabbits, gray fur (G) is dominant to black
fur (g). If a heterozygous male is crossed with
a heterozygous female, what is the phenotypic
ratio of the possible offspring?
A. 1:1
B. 1:2:1
C. 2:1
D. 3:1
1.
2.
3.
4.
A
B
C
D
Formative Questions
What is the term for an organism that has one
or more sets of extra chromosomes in its cells?
A. diploid
B. gamete
C. hybrid
D. polyploid
1.
2.
3.
4.
A
B
C
D
Standardized Test
Practice
To which step in this
process does the law
of segregation apply?
A. grows into plant
B. gamete formation
C. fertilization
D. seed development
1.
2.
3.
4.
A
B
C
D