LECTURE 3: Gene Segregation and Interaction (Allelic Interaction) Flashcards
2 laws proposed by Gregor Mendel
Law of Independent Segregation
Law of Independent Assortment
Genes exist in 2 or more alternative forms called?
alleles
GENOTYPE vs PHENOTYPE
G: combination of alleles in an individual
P: manifestation of genotype
HOMOZYGOUS vs HETEROZYGOUS genotype
homo: same allele from mother and father found in homologous pair
hetero: mother and father has diff alleles found in homologous pair
Does allele differ from parent chromosome (if from mother or father), or from sister chromatids?
From parent chromosome
so 1 chromosome with 2 sister chromatids have the same allele lagi
Consider heterozygous genotype Rr
what will be the alleles present in:
- anaphase 1
- anaphase 2
- R chromosome in one pole; and r chromosome in another pole
- In R chromosome, sister chromatids, each with R allele, will be separated… same with r chromosome
What does the LAW OF INDEPENDENT SEGREGATION state?
the alleles of a gene pair separate completely and cleanly from each other during meiosis
What does the LAW OF INDEPENDENT ASSORTMENT state?
the alleles of a gene pair separate completely and cleanly from each other AND randomly combine during meiosis
MONOHYBRID CROSS vs DIHYBRID CROSS
MONO: cross between homozygous individuals that are different from each other at ONE GENE LOCUS
DI: cross between 2 homozygous individuals that are different from each other at TWO GENE LOCUS
In mendel’s experiment, what character trait of seeds is DOMINANT and RECESSIVE
Dominant: round
Recessive: wrinkled
DOMINANT vs RECESSIVE allele
D: manifested in a heterozygote
R: masked allele
2 methods of getting the GENOTYPIC RATIO
- Punnett Square/Checkerboard method (confusing when 2 or more genes are crossed)
- Branching Method
What is a testcross?
a breeding experiment that helps determine an organism’s genotype
breed unknown with homo recessive
What is the allele of the ff:
- Parent Generation
- F1 Generation
- F2 Generation
P: RR and rr (basta homozygos)
F1: Rr
F2: Rr and Rr (cross); 1RR 2Rr 1rr
DEFINITION of probability
and formula
the chance an event will occur
Probability of event X = (# of event X in sample)/(sum of event X and Y in sample)
2 types of events in a probability set
- Mutually Exclusive Events (can never take place at the same time)
- Independent Events (events that can occur simultaneously)
How to compute for combined probability on MUTUALLY EXCLUSIVE EVENTS?
and what rule is it based on
*key word in word problem?
SUM RULE OF PROBABILITIES
P [heads, tails] = (P(heads)) + (P(tails))
“Probability of getting P[heads, tails] OR P[tails, tails]?”
2 techniques in branching method
TEGI - take each gene independently
TEPI - take each phenotype independently
How to compute for combined probability on INDEPENDENT EVENTS?
and what rule is it based on
*key word in word problem?
PRODUCT RULE OF PROBABILITIES
P [heads, tails] = (P(heads)) x (P(tails))
“Probability of getting heads AND tails: P[heads, tails]?”
CONDITIONAL PROBABILITY
- definition
- formula
EXAMPLE: “If the flower is red, what is the probability that it is a heterozygote from RrSs x RrSs, with R = red; r = white?”
- probability of an event occurring in the light of another event
P[ X│Y ] = (P X) / (P Y)
(probability of Rr) / (probability of red) = 2/3
BINOMIAL PROBABILITY
- key word?
- formula
- if number of offspring/total events is indicated
ALLELIC INTERACTIONS (5)
- Complete Dominance
- Incomplete Dominance
- Co-dominance
- Lethal Genes
- Overdominance
ALLELIC INTERACTIONS
COMPLETE DOMINANCE
- AA and Aa have the same _____
- the presence of a _____ allele is ______ to express the ______ trait
- F2 phenotypic ratio
- phenotype
- dominant
- enough
- dominant
3:1
ALLELIC INTERACTIONS
INCOMPLETE DOMINANCE
- F1 phenotype is _____
- a ____ between traits in ______ alleles
- F2 phenotypic ratio
- intermediate
- blending
- heterozygous
1:2:1
ALLELIC INTERACTIONS
OVERDOMINANCE
- ______ exhibits a ____ phenotype compared to _____ parents
- shows….?
- F2 phenotypic ratio
- heterozygotes
- superior
- homozyous
“HETEROSIS” (hybrid vigor)
1:2:1
ALLELIC INTERACTIONS
CODOMINANCE
- a _____ of 2 alleles are present (wherein, ______ alleles are expressed at _____ time)
- F2 phenotypic ratio
- mixture
- both
- the same
1:2:1
ALLELIC INTERACTIONS
LETHAL GENES
- definition
- 2 types + definition
- F2 phenotypic ratio
- genes cause death
- Recessive Lethal (1:2:0 1:0:0 3:0:)
- lethal when homozygous recessive is passed to offspring - Dominant Lethal (0:1)
- lethal when homozygous or heterozygous dominant
MODIFIER GENES
- genes that ____ the ______ effect of other genes in a _____ fashion (there is _____ or ____ effect)
- change
- phenotypic
- quantitative
- dilution or enhancement effect
