Download 6.3 Mendel and Heredity

6.3 Mendel and Heredity
13.1
EcologistsofStudy
Relationships
Fundamentals
Genetics
Genetics – field of biology devoted to
understanding how characteristics are
transmitted from parents to offspring
6.3 Mendel and Heredity
Father of Genetics
Gregor Mendel
Austrian Monk
• Heredity – transmission of
characteristics from parents to
offspring
• Garden Peas
6.3 Mendel and Heredity
Characteristic
1.
2.
3.
4.
5.
6.
7.
Plant Height
Flower position
Pod appearance
Seed Texture
Seed Color
Flower Color
Pod Color
Traits
Tall
Axial
Inflated
Smooth
Yellow
Purple
Green
Short
Terminal
Constricted
Wrinkled
Green
White
Yellow
6.3 Mendel and Heredity
Mendel’s Methods
• Pollination – pollen produced in the male
reproductive parts of the flower (anther) are
transferred to the female reproductive part of a
flower (stigma)
• Self-pollination – pollen is transferred from an
anther to a stigma on the same plant
• Cross-pollination – involves flowers of two
separate plants
6.3 Mendel and Heredity
Mendel’s Experiments
1. He allowed plants to self-pollinate for several
generations to obtain 14 pure strains: Parental
Generation (P1)
– Pure - always produce offspring with that trait
– Strain - plants that are pure for a trait
2. Cross-pollinated these strains
– one pure for one trait with another pure for
the contrasting trait
– P1 (tall) X P1 (short)  First Filial Generation
(F1)
3. Then allowed F1 to self pollinate  second filial
generation (F2)
6.3 Mendel and Heredity
Mendel controlled the
fertilization of his pea plants
by removing the male parts,
or stamens.
He then fertilized the female
part, or pistil, with pollen from
a different pea plant.
6.3 Mendel and Heredity
Mendel’s Results
• Only one of the two traits in P1 appeared in the
offspring F1
• The trait then reappeared in F2 in a ratio of 3:1
6.3 Mendel and Heredity
Mendel’s Conclusions
• Factor – something is controlling the traits
– Allele
• Pair of factors controls each trait
– Gene
• Recessive & Dominant Traits
- Dominant Allele – masked the other factor
(appeared in F1)
- Recessive Allele – is masked by the presence
of another (reappeared in F2)
6.3 Mendel and Heredity
Chromosomes and Genes
• Molecular genetics – study of the structure and
function of chromosomes and genes
• Gene – segment of DNA on a chromosome that
controls a particular hereditary trait
• Letters are used to represent alleles of genes
- capital letters refer to dominant alleles
T = tall
- lowercase letters refer to recessive alleles
t = short
• Genome - All of an organism’s genetic material
6.4
Genes,
Alleles
6.3 Traits,
Mendel
and and
Heredity
Genotype – genetic makeup of an organism
• TT
Tt
tt
Phenotype – appearance of an organism as a result of
its genotype
• Tall
or
short
Homozygous – both alleles of a pair are alike
• TT
or
tt
Heterozygous – two alleles in the pair are different
• Tt
6.5
Traits and
6.3 Mendel
andProbability
Heredity
• The axes represent
the gametes of each
parent.
– The boxes show the
possible genotypes
of the offspring.
6.5
Traits and
6.3 Mendel
andProbability
Heredity
Genotypic ratio – ratio of the genotypes that
appear in offspring
• 1TT:2Tt:1tt
Phenotypic ratio – ratio of the offspring's
phenotypes
• 3 Tall:1 short
6.5
Traits and
6.3 Mendel
andProbability
Heredity
A monohybrid cross involves one trait (12 points)
Homozygous Dominant
X
Homozygous Recessive
6.5
Traits and
6.3 Mendel
andProbability
Heredity
Heterozygous
X
Heterozygous
6.5
Traits and
6.3 Mendel
andProbability
Heredity
How Mendel's pea plants helped us understand genetics
• http://ed.ted.com/lessons/how-mendel-s-pea-plantshelped-us-understand-genetics-hortensia-jimenez-diaz
6.5
Traits and
6.3 Mendel
andProbability
Heredity
Testcross
• Determine the genotype of an individual whose
Phenotype is dominant
– TT or Tt (?)
• Individual of unknown genotype is crossed with a
homozygous recessive individual
• T? X tt
6.5
Traits and
6.3 Mendel
andProbability
Heredity
Testcross (12 points): Offspring 100% Dom
7.2
Complex
Patterns
of Inheritance
6.3 Mendel
and
Heredity
Complete Dominance – one allele completely
dominant over the other
Incomplete dominance – two or more alleles
influence the phenotype
• results in a phenotype in between the dominant
and recessive
• R = red W = white
• RW  pink
7.2
Complex
Patterns
of Inheritance
6.3 Mendel
and
Heredity
Incomplete Dominance:
Homozygous (1st trait) X
Homozygous (2nd trait)
7.2
Complex
Patterns
of Inheritance
6.3 Mendel
and
Heredity
Codominance – both alleles for a gene are
expressed in a heterozygous offspring
• neither is dominant or recessive
• R = Red
W = White
• RW  red & white polka dots
7.2
Complex
Patterns
of Inheritance
6.3 Mendel
and
Heredity
Codominance:
Heterozygous
X
Heterozygous
7.2
Complex
Patterns
of Inheritance
6.3 Mendel
and
Heredity
Multiple Alleles – 3 or more alleles of the same
gene
•
•
•
•
•
•
•
•
IA or
IB or
i
Blood Types
IAIA
or
IBIB
or
IAIB
ii
IAi
IBi
=
=
=
Blood type A
=
Blood type B
Blood type AB
Blood type O
7.2
Complex
Patterns
of Inheritance
6.3 Mendel
and
Heredity
Blood Type AB
X
Blood Type O
7.1
and Phenotype
6.3 Chromosomes
Mendel and Heredity
Sex-linked Inheritance
• Traits controlled by genes located on the sex
chromosomes (X or Y)
• X-linked traits – found on X chromosome
• Y-linked traits – found on Y chromosome
– X-linked traits more common in males
– Y-linked traits only in males
7.1
and Phenotype
6.3 Chromosomes
Mendel and Heredity
X-Linked
Heterozygous Female
X
Male with recessive trait
7.1
and Phenotype
6.3 Chromosomes
Mendel and Heredity
Y-Linked
Female
X
Male with Dominant trait
7.1
and Phenotype
6.3 Chromosomes
Mendel and Heredity
• Female mammals have an XX genotype
– X-inactivation – one X chromosome is randomly “turned
off” in every cell
– Ex: calico cats
7.1
and Phenotype
6.3 Chromosomes
Mendel and Heredity
Sex-Influenced – traits affected by how much
sex hormones are present
6.5
Traits and
6.3 Mendel
andProbability
Heredity
A dihybrid cross involves two traits (12 points)
Homozygous Recessive/Heterozygous X
Homozygous Dominant for both
6.5
Traits and
6.3 Mendel
andProbability
Heredity
Heredity patterns can be calculated with probability.
• Probability is the likelihood that something will happen
• Predicts an average number of occurrences, not an exact
number of occurrences.
number of ways a specific event can occur
• Probability =
number of total possible outcomes
6.3 Mendel and Heredity
Laws
Law of Segregation – a pair of factors is separated
during the formation of gametes
• 1 trait: Tall from short
Law of Independent Assortment – factors for different
characteristics are distributed to gametes
independently
• All characteristics being separated from each other
• Ex: Tall plant from yellow peas
7.1
and Phenotype
6.3 Chromosomes
Mendel and Heredity
• Autosomal genetic disorders
– Carrier - A heterozygote for a recessive disorder
– Disorders caused by dominant alleles are uncommon.
(dominant)
6.3 Mendel and Heredity
Epigenetics – study of changes in gene activity which
are not caused by changes in the DNA
•
The changes in gene expression or phenotype have
other causes
• Ex: environment, other genes, etc
7.2
of Inheritance
6.3 Complex
MendelPatterns
and Heredity
• Genes can interfere with other genes
• Epistatic genes
7.2
of Inheritance
6.3 Complex
MendelPatterns
and Heredity
Phenotype is a combination of genotype and environment.
• EX: The sex of sea turtles
depends on both genes and
the environment
• EX: Height is another
example of a phenotype
strongly affected by the
environment.
6.3 Mendel and Heredity
Polygenic Inheritance
• Traits controlled by many genes
• ~250 genes have been described to control
human height  up to 700
6.3 Mendel and Heredity
Trihybrid Cross
Hetero/Homo Rec/Homo Dom
X
Homo Rec/Hetero/Homo Dom