Module 3—Mendelian Genetics Flashcards
pangenesis
idea that all parts of the body contribute to gamete formation
germ-plasm theory
germline tissues in reproductive organs form gametes
correct replacement for pangenesis
germ replacement theory
inheritance of acquired characteristics
idea that traits acquired in life, like dyeing your hair, are passed on to offspring
preformationism
idea that a miniature adult (homunculus) resides in gametes (especially sperm)
suggests that a person’s traits are inherited from the father
homunculus associated with…
preformationism
blending inheritance
idea that offspring have a blend of parental traits
particulate hypothesis
idea that parents pass on discrete heritable units (genes)
Walter Sutton
chromosomal theory of heredity
chromosomal theory of heredity (3)
genes are located on chromosomes
homologs separate in anaphase I
homologs assort independently
character
heritable feature that varies among individuals; ie color
trait
each variant for a character
true breeding
homozygous crosses - offspring are always same genotype as parent
hybridization
crossing of two true-breeding varieties
testcross
breeding a dominant phenotype organism with unknown genotype to a recessive organism
2 possibilities for a testcross
- If the unknown is homozygous dominant, all offspring will be dominant phenotype
- If the unknown is heterozygous dominant, ½ offspring will be dominant phenotype, and ½ will be recessive
monohybrid cross ratios (genotype & phenotype)
- Genotype ratio—1:2:1
- Phenotype ratio—3:1
law of segregation
the two alleles for a heritable character segregate during gamete formation and end up in different gametes
law of independent assortment
exceptions
two or more genes assort independently during gamete formation
only applies to genes located on different chromosomes, or very far apart on the same chromosome
dihybrid cross ratio
9:3:3:1
Mendel used to discover independent assortment
dihybrid crosses
independent events
outcome of any particular trial is unaffected by what has happened on previous trials
multiplication rule
to determine the probability of one event and the other occurring, we multiply their probabilities
addition rule
to determine the probability of one of two mutually exclusive events occurring, we add their probabilities
complete dominance
heterozygous and homozygous dominant phenotypes are indistinguishable from one another
incomplete dominance
neither allele is completely dominant, resulting in a phenotype that is a mixture/dilution
codominance
two alleles affect phenotype in separate, distinguishable ways - no dilution
levels of dominance in Tay Sachs disease
recessive trait at organismal level
incompletely dominant trait at biochemical level (heterozygous individuals also have some defective enzymes, but functional enzymes are “enough” to keep symptoms from appearing)
codominant at molecular level
penetrance
percentage of individuals having a genotype that expresses the expected phenotype
penetrance is always…
less than the ratios predicted by Mendelian genetics
expressivity
degree to which a character is expressed
yield non-Mendelian ratios in offspring
lethal alleles
pleiotropy
genes with multiple phenotypic effects
a range of phenotypes
continuous traits
epistasis
phenotypic expression of a gene at one locus alters that of a gene at a second locus
epistasis example
black labs, brown labs, yellow labs
epistasis produces ratios which are…
variations on 9:3:3:1
polygenic inheritance
additive effect of 2+ genes on a single phenotypic character
quantitative characters associated with…
polygenic inheritance
most common polygenic traits in population
individuals heterozygous for many or all of the genes involved
used in personalized medicine
polygenic risk score
multifactorial traits
influenced by genetic and environmental factors
phenotypic plasticity
a trait’s reaction to the environment
carriers
heterozygotes carrying a recessive allele for a certain phenotype
