Lecture 11: Genetics I: Mendel’s Laws of Dominance and Segregation Flashcards
our longest-running genetic experiment: dogs
- people have selected and mated dogs with preferred traits for more than 15,000 years
- such genetic tinkering has led to the incredible variety of body types and behaviors in dogs today
- all domestic dogs were derived originally from a wolf ancestor
heredity
the transmission of traits from one generation to the next
genetics
the scientific study of heredity
Gregor Mendel
- first person to clearly explain the patterns of inheritance
- deduced the fundamental principles of genetics in the 1860s
what Mendel studied and why
garden peas
* easy to grow
* came in many readily distinguishable varieties
* easily manipulated
* can self-fertilize
* had years of experience studying these plants and knowledge from the University of Vienna to prepare him
cross-fertilization in Mendel’s study
- Mendel emasculated the purple plant by taking the stamens off, then used a brush to take the pollen from the white plant off and brushed it on the purple plant
- the resulting flowers would be purple
reciprocal cross in Mendel’s study
- if Mendel emasculated the white plant, the flowers would be purple
- discovered that purple is the dominant color trait
character
a heritable feature that varies among individuals
* e.g. flower color
trait
a variant of a character
* e.g. white flower color vs. purple flower color
characters and traits in Mendel’s study
each of the characters Mendel studied occurred in 2 distinct traits, either dominant (visible) or recessive (not visible)
character: traits (dominant - recessive)
* flower color: purple - white
* flower position: axial - terminal
* seed color: yellow - green
* seed shape: round - wrinkled
* pod shape: inflated - constricted
* pod color: green - yellow
* stem length: tall - dwarf
hybrids
the offspring of 2 different purebred varieties
* P generation: parental plants
* F1 generation: hybrid offspring (“F” stands for filial, so F# denotes the number of generations after the parental generation)
* F2 generation: cross of the F1 plants
monohybrid cross
a cross between purebred plants that differ in only 1 character
law of dominance
when an organism inherits two different alleles for a trait, the dominant allele will be expressed, while the recessive allele will be masked, meaning the offspring will only exhibit the dominant trait in their phenotype
allele
alternative versions of genes
* the dominant allele for flower is represented as a capital letter “P” (purple), while the recessive allele is a lowercase letter “p” (white)
for each inherited character, an organism inherits _____ alleles, _____ from each parent
2; 1
homozygous
an organism is homozygous for a gene if both alleles are identical
* e.g. PP and pp
heterozygous
an organism is heterozygous for a gene if the alleles are different
* e.g. Pp
dominant allele
if 2 alleles of an inherited pair differ, one determines the organism’s appearance, which is called the dominant allele
recessive allele
if 2 alleles of an inherited pair differ, one has no noticeable effect on the organism’s appearance, which is called the recessive allele
law of segregation
gametes only carry one allele for each inherited character. the 2 alleles for a character segregate from each other during the production of gametes.
punnet square
- highlights the four possible combinations of gametes and
- four possible offspring in the F2 generation
phenotype
an organism’s physical appearance
genotype
an organism’s genetic makeup
locus
- a gene locus is a specific location of a gene along a chromosome
- homologous chromosomes have alleles (alternate versions of a gene) at the same locus
