Theory of Blending Inheritance
Gametes contain hereditary determinants (genes) that irreversibly blend together when gametes fuse at fertilization
Theory of Particulate Inheritance
Each hereditary determinant or gene has a physically-distinct nature. When gametes fuse, the determinants remain intact and can be recovered
Gamete
a mature haploid male or female germ cell which is able to unite with another of the opposite sex in sexual reproduction to form a zygote.
Pea Flower
Pistil - female organ
Stamen - male organ
Ovule - gamete
Pollen - gamete
Character
an observable physical feature, such as seed shape or seed color
Trait
a particular form of a character (round or wrinkled seeds, green or yellow seeds)
True Breeding Variety
produces the identical character and traits as their parents
Parental Generation
refers to the parents (P); the first filial generation (F1) is their offspring; the second filial generation (F2) is the offspring of the offspring
Hybrid
is the offspring of a cross between two organisms that differ in one or more characters
monohybrid cross
is between organisms that differ in only one character
dihybrid cross
is between organisms that differ in two characters
dominant traits
are more abundant... because they dominate over less abundant recessive traits
Genes
The hereditary determinants
Haploid
Organisms that have one copy of each gene
Diploid
Organisms that have two copies of each gene
Alleles
Different forms of a gene. Different traits arise from these.
Homozygous
a particular gene that has identical alleles on both homologous chromosomes
Heterozygous
having two different alleles of a particular gene or genes.
phenotype
physical appearance of an organism. Determined by interaction genotype and environment.
genotype
genetic constitution of an organism
Mendel's First Law
Two copies of a gene segregate during gamete formation. Exception is when nondisjunction occurs
Probability
can be used to predict inheritance
Gene Segregation during Meiosis I
two alleles of a gene segregate
1. The locus is the location in a chromosome where the allele resides
2. Before Meiosis I, all chromosomes are replicated in S-phase.
3. Homologous chromosome pairs line-up at the metaphase plate of meiosis I, and then chro
Locus
The location in a chromosome where the allele resides
Mendel's Second Law
Different Genes assort/segregate independently. Exception is when two genes are present on the same chromosome.
Independent Assortment of alleles
Occurs during Meiosis I metaphase
Many genes have multiple alleles
New Alleles arise by mutation, which are stable inherited changes in genetic material. Wild type alleles and mutant alleles of a gene occupy the same loci or locus in a chromosome. Because one gene can have multiple alleles, the alleles can display a domi
Wild Type Allele
the allele present in the majority of the population in nature
Mutant Allele
A variant that often produces mutant phenotypes
Example of dominance hierarchy
The color of rabbit coats is determined by multiple alleles of the C gene (C, c^chd, c^h, c) which create four different phenotypes.
Incomplete Dominance
Allele dominance is not always complete. Intermediate phenotype produced.
Co-Dominance
When both alleles of a locus are expressed in the phenotype. e.g is AB blood.
Epistasis
Occurs when the phenotype of one gene depends on the prior function of another.
Example: The function of gene E (pigment delivery and deposition) is required before the function of gene B (pigment synthesis) can be observed in the phenotype.
Hybrid Vigor
Results from new gene combinations and interactions
Inbreeding
produces offspring of 'lower quality' because there is a greater chance for allelic homozygosity... and two recessive (mutant) alleles can be problematic.
Hybrids
show greater vigor in growth due to the advantages of heterozygosity. It reduces the risk of homozygocity which is deleterious in the case of mutant alleles and phenotypes
Environment Influences to Gene Expression
Light, Temperature, and Nutrition are all factors.
Penetrance
The proportion of individuals in a population with a common genotype who show the phenotype
Example: A mutant BRCA breast cancer gene causes cancer but not in all women
Expressivity
The degree or severity of genotype expression in an individual
Example: The mutant BRCA gene affects many tissues on one person, but just one in another
Some Alleles are linked
Independent assortment is not present, and alleles sort together because they are present in the same chromosome
Recombination (crossing over)
the exchange of genetic material between homologous chromosomes during meiosis
Recombination Frequency
How often two linked genes separate from each other during meiosis by chiasmata crossover event. RF of two loci in a chromosome is equal to the number of recombinant progeny divided by the total number of progeny -> expressed in centimorgans (cM), 1% RF =
Genetic Map
Physical distance between two genes in a single chromosome can be calculated from their recombination frequency
Test Cross
A cross of an organism with an unknown genotype (allele composition) with an organism of the same type that has a known allele composition.
Conjugation
In bacteria, the direct transfer of DNA between two cells that are temporarily joined (by sex pilus).
Sex Pilus
extends from one bacteria cell into another, joining their cytoplasm. DNA passes unidirectionally through the conjugation tube in the pilus
Plasmids
small circular DNA molecules that replicate separately from the bacterial chromosome. Encodes genes involved in unique metabolic pathways: antibiotic resistance or sex pilus components.
Key Concepts 1
Key Concepts 2