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
6.3 Mendel and Heredity
Mendel’s Methods
• Pollination – pollen grains 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 the
anthers of a flower to the stigma on a flower on
the same plant
• Cross-pollination – involves flowers of two
separate plants
6.3 Mendel and Heredity
Mendel’s Experiments
• Grew plants PURE for a trait (always produce
offspring with that trait)
• STRAIN - plants that are pure for a specific trait
• He allowed plants to self-pollinate for several
generations to obtain 14 strains: Parental
Generation (P1)
• 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)
• Then allowed F1 to self pollinate  second filial
generation (F2)
6.3 Mendel and Heredity
interrupted the self-pollination process by removing male
flower parts
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 controlling the traits (allele)
• Pair of factors controls each trait (gene)
• Recessive & Dominant Traits
- Dominant factor – masked the other factor
(appeared in F1)
- Recessive – 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
- capital letters refer to dominant alleles
T = tall
- lowercase letters refer to recessive alleles
t = short
• Genome - All of an organism’s genetic material
6.3 Mendel and Heredity
Genetic Crosses
• Genotype – genetic makeup of an organism
• TT
Tt
tt
• Phenotype – appearance of an organism as a
result of its genotype
TT  Tall
tt  short
• Homozygous – both alleles of a pair are alike TT
or tt
• Heterozygous – two alleles in the pair are
different Tt
6.3 Mendel and 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
Punnett squares illustrate genetic crosses.
• The Punnett square is a grid system for predicting all
possible genotypes resulting from a cross.
– The axes represent
the possible gametes
of each parent.
– The boxes show the
possible genotypes
of the offspring.
• The Punnett square
yields the ratio of
possible genotypes and
phenotypes.
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
6.3 Mendel and Heredity
Testcross
• Individual of unknown genotype is crossed with a
homozygous recessive individual
• Determine the genotype of an individual whose
phenotype is dominant
6.5
Traits and
6.3 Mendel
andProbability
Heredity
Testcross (10 points): Offspring 100% Dom
6.3 Mendel and Heredity
• Complete Dominance – one allele completely
dominant over the other
• Incomplete dominance – two or more alleles
influence the phenotype resulting in a phenotype
intermediate between the dominant and
recessive traits
R=red W=white
RW  pink
6.3 Mendel and Heredity
• Codominance – both alleles for a gene are
expressed in a heterozygous offspring –
neither is dominant or recessive
RW  red & white polka dots
6.3 Mendel and Heredity
Multiple Alleles – 3 or more alleles of the same
gene
•
•
•
•
•
•
Blood Types
IA
IB
IAIA or
IAi
IBIB or
IBi
IAIB
ii
i
=
=
=
=
Blood type A
Blood type B
Blood type AB
Blood type O
• The ABO blood types result from codominant multiple
alleles.
6.3 Mendel and Heredity
Sex-linked Inheritance
• Traits controlled by genes located on the sex
chromosomes
• X-linked gene
• Y-linked gene
• X-linked traits more common in males
Sex-Influenced Inheritance – traits affected by how
much sex hormones are present
7.1
and Phenotype
6.3 Chromosomes
Mendel and Heredity
Punnett Square: Sex-Linked Traits
• Determine Sex of Offspring
• Difference in sex-linked traits.
7.1
and Phenotype
6.3 Chromosomes
Mendel and Heredity
• Male mammals have an XY genotype.
– All of a male’s sexlinked genes are
expressed.
– Males have no
second copies of
sex-linked genes.
7.1
and Phenotype
6.3 Chromosomes
Mendel and Heredity
• Female mammals have an XX genotype.
– X chromosome inactivation randomly “turns off” one X
chromosome.
6.5
Traits and
6.3 Mendel
andProbability
Heredity
A dihybrid cross involves two traits. (12 points)
Homozygous Dominant for both X
Homozygous Recessive 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.
• Probability 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
segregated, or 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)
i.e. Tall plant from yellow peas
7.1
and Phenotype
6.3 Chromosomes
Mendel and Heredity
• Mendel’s rules of inheritance apply to autosomal genetic
disorders.
– A heterozygote for a recessive disorder is a carrier.
– Disorders caused by dominant alleles are uncommon.
(dominant)
6.3 Mendel and Heredity
Polygenic Inheritance
• Traits controlled by many genes
• Multifactorial
• ~180 genes have been described to control
human height  up to 700
• Add the effect of all genes to get the
manifestation of the trait
• ABC – each having their own set of alleles
• AaBbCc
7.2
of Inheritance
6.3 Complex
MendelPatterns
and Heredity
• An epistatic gene can interfere with other genes.
7.2
of Inheritance
6.3 Complex
MendelPatterns
and Heredity
The environment interacts with genotype.
• Phenotype is a combination
of genotype and
environment.
• The sex of sea turtles
depends on both genes
and the environment
• Height is an example of a
phenotype strongly affected
by the environment.
7.2
of Inheritance
6.3 Complex
MendelPatterns
and Heredity
Many genes may interact to produce one trait.
Order of dominance:
brown > green > blue.