Chapter 18 Flashcards
(25 cards)
Gregor Mendel (1822-1884)
A pioneer of genetics, responsible for the laws governing inheritance of traits. Laws which he developed via studying the inheritance of traits in pea plants
Monohybrid vs Dihybrid
Monohybrid cross is the cross involving a single trait. While Dihybrid cross is the cross involving two traits
Alleles
The two forms of a gene (dominant & recessive)
Ex. R and r
Genotype
Gene combination for a trait
(ex. RR, Rr, rr)
Phenotype
The physical features resulting from a genotype
(ex. Red, white, yellow, etc)
Homozygous genotype
Gene combination involving 2 dominant or 2 recessive genes (ex. RR or rr)
Also called “pure”
Heterozygous genotype
Gene combination of one dominant & one recessive allele (ex. Rr); also called hybrid
Reproduction in flowering plants
Pollen produced by the stamen contains the sperm while the ovaries are found inside the flower. The flowers can either self fertilize or cross fertilize
Mendel’s Laws of Heredity
- Inherited characteristics are controlled by genes that occur in pairs
- Law of Dominance; One factor or gene masks effect of another
- Law of Segregation; the two alleles in gametes separate from eachother during formation then reform at fertilization producing the genotype (During Anaphase 1)
- Law of Independent Assortment; Alleles for different traits are distributed to sex cells (& offspring) independently of one another
Pedigree Charts
A pedigree chart is like a family tree in which the inheritance of a trait can be traced from parents to offspring
Pleiotropy
Pleiotropy is a genetic phenomenon where a single gene or DNA variant influences multiple traits, or phenotypic expressions. (One gene, many effects)
Ex. Dwarfism, gigantism, cystic fibrosis and sickle cell anemia
Sickle-cell anemia
??
Marfan’s syndrome
An inability to produce normal connective tissue, is also associated with a single gene. Symptoms of Marfan’s Syndrome show up as eye skeleton and cardiovascular defects
Co-dominance
or Intermediate Inheritance
Codominance essentially means that no allele can block or mask the expression of the other allele. Causing both genes to be expressed at the same time
Dihybrid Cross
A breeding experiment that tracks the inheritance of two traits
ex. RRYY, RrYY, RrYy
Test Cross
A mating between an individual of unknown genotype and a homozygous recessive individual
Probability
Probability = # of chances for an event
—————————————
# of possible combinations
Polygene
a gene whose individual effect on a phenotype is too small to be observed, but which can act together with others to produce observable variation.
Ex. Skin colour, eye colour and height
Epistasis
When one gene masks another
Complementary Interaction
Occurs when two different genotypes interact to produce a phenotype that neither is capable of producing by itself
Autosomal Traits
Characteristics that are not associated with the sex of the individual
T.H. Morgan’s Experiment
Using fruit flies as a model organism, Morgan discovered a mutant white-eyed male fly and traced its inheritance pattern, revealing a connection between the X sex chromosome and the gene for eye color
Barr Body
Barr body is the inactive X-chromosome in the somatic cells of mammalian females. Made visible by small dark spots of chromatin
Testes Determining Factor (TDF)
Gene on the Y chromosome which makes sure gender male fetus does not differ from a female fetus until 6th or 7th week of pregnancy.
