mendelian genetics Flashcards
garden pea study what is it/ why peas
mendel chose garden peas to study genetic inheritance
pea plants inherit flower color
garden peas have both male and female sex organs and can cross pollinate and self-pollinate
inheritance
how genetic info is passed from parents to offspring
generation to generation
character
a heritable feature that varies among individuals
trait
trait in pea study
each variant for a character
in this case the trait was either a purple or white colored flower
mendel’s experiment broken down in generations
p(parent) generation : true breeding parents produce offspring of the same variety over many generations of self pollination —> he fertilized true breeding plants of one trait with true breeding plants of another trait (purple and white flowers)
F1 generation: mono hybrid offspring = all 1 trait which was purple
F2 generation: F1 self-fertilize and recessive trait reappeared (white)
hybridization
crossing of true-breeding variants
parent generation of true breeding variants
conclusions from mendel’s experiment
every individual has 2 genes for a character, and genes have 2 variant forms called alleles
alleles may exist in 2 forms, dominant or recessive
there is a 3:1 ratio between traits in F2 generation
law of segregation and how alleles are separated and recombined
two alleles of a gene separate from each other during gamete formation, so that each sperm and egg end up with only one allele
alleles separate into different haploid cells that eventually give rise to gametes (segregation during meiosis), so that every gamete only receives one allele
during fertilization, male and female gametes randomly combine with each other
genotype
genetic composition on an individual
PP = homozygous dominant
Pp = heterozygous
pp = homozygous recessive
phenotype
physical or behavioral characteristics as a result of gene expression
PP = purple flowers
Pp = purple
pp = white flowers
mono hybrid cross
cross between heterozygotes
punnet square results for mono hybrid cross
3 genotypes PP Pp pp
2 phenotypes 3:1 ratio
two factor cross
observing 2 characters at a time
follows inheritance of two characters
YYRR x yyrr
on punnet square = YR YR. x yr yr
in f1 generation, what do you see after doing a two factor cross
dihybrid
offspring are hybrids with respect to each trait YyRr
in f2 generation what were the two hypothesis proposed for how this generation would look
dependent assortment leading to 3:1 phenotypic ratio
independent assortment leading to 9:3:3:1 phenotypic ratio
what was observed in the f2 generation two factor cross
9:3:3:1 phenotypic ratio
law of independent assortment
alleles of different genes assort independently of each other during the process that gives rise to gametes : meiosis
law of segregation
two alleles of a gene separate from one another during meiosis so every gamete receives only one allele
multiplication rule of probability
probability that 2 or more independent events will occur is equal to the product of their individual probabilities
ex: getting one outcome one time and getting the same outcome another time
addition rule rule of probability
probability that 2 or more mutually exclusive events will occur
getting one outcome one time or getting another outcome
complete dominance
one allele is dominant over another
PP and Pp give rise to same phenotype
non-mendelian genetics
when inheritance of characters deviates from simple mendelian genetics through the following situations
1. incomplete dominance/codominance of alleles
2. multiple alleles
3. pleiotropy
when certain alleles are not completely dominant or recessive
incomplete dominance or codominance
incomplete dominance
neither allele is completely dominant
phenotype of heterozygous individuals is intermediate between the two alleles
purple and white flower —> pink flower
incomplete dominance viewed over generations
P generation: red and white flower
F1 : pink
F2 : red, white, and pink are present
why does incomplete dominance occur
heterozygous dominant genotype is in between the enzyme activity level of homozygous dominant and homozygous recessive
codominance
neither allele is completely dominant but phenotype of heterozygous individuals consists of both the phenotypes of the two alleles
stripes and spots
multiple alleles
most genes exist in populations in more than 2 alleles forms
humans have four blood groups (A,B, AB, or O) are determined by 3 alleles
some genes have more than two alleles that control it
pleiotropy
most genes have multiple phenotypic effects
responsible for multiple symptoms associated with generation hereditary diseases, such as sickle cell disease
2 copies of sickle cell allele
single gene can sometimes produce multiple phenotypes
epistasis
when there are 2 or more genes involved in determining a particular phenotype
when one gene affects the phenotype of another gene because the two gene products interact —> masking of genes
gene at one locus alters that of a gene at a second locus
polygenic inheritance
multiple genes independent affect a single trait
pedigree traits (general)
square = male
circle = female
filled in = affected with trait
offspring are in birth order from left to right
I = parent gen
II = offspring
