Mendelian Genetics: Genetic Segregation Flashcards
locus
gene location on chromosome
allele
alternate forms of a gene
dominant
allele/phenotypic trait that’s expressed in heterozygotes
recessive
allele/phenotypic trait that’s expressed only in homozygotes
phenotype
appearance; expressed form of gene(s)
genotype
genetic constitution
heterozygote/heterozygous
inherited different alleles at one of more loci
relates to individuals
ex: Diploid Aa
Tetraploid AAaa
homozygote/homozygous
inherited identical alleles at one or more loci
relates to individuals
ex: diploid AA
tetraploid AAAA
heterogenous
population of individuals with different genotypes
relates to groups/populations
ex: AA, Aa, aa
homogenous
population of individuals with same genotype
relates to groups/populations
ex: Pop.1= AA, AA,AA
Pop. 2= Aa, Aa, Aa
somatic cells
any cell of a living organism other than the reproductive cells
chromosomes in the nuclei of somatic cells usually occur in pairs
Gregor Mendel
examined inheritance of clear-cut alternative traits
Homologous chromosomes
chromosome pairs, one from each parent, that are similar in length, gene position, and centromere location
The position of the genes on each homologous chromosome is the same, however the genes may contain different alleles
true breeding
progeny showed no genetic segregation
Mendel’s Proposed Principles
- Theory of Particulate Inheritance
- Dominance/Recessiveness
- Law of Segregation
- Law of Independent Assortment
Theory of Particulate Inheritance
- Observable traits determined by discrete units of inheritance and different units make up a trait
- 2 particles of heredity (alleles) for each trait (diploid)
Dominance/Recessiveness
When 2 different, but homozygous individuals are crossed their F1 progeny will be uniform
F1: expressed trait= dominant
trait not expressed= recessive allele
Law of Segregation
- during gamete formation, paired alleles of a gene segregate randomly so each gamete receives one allele or another with equal probabilities
- relates directly to what happens in meiosis
- see segregation take place in F2:
- > individual contains pair of identical alleles= all gametes receive same allele
- > individual contains pair of unlike alleles= each gamete has 50% chance of receiving one vs. the other)
Law of Independent Assortment
Random separation of chromosomes; during gamete formation, segregation of alleles at one locus is independent of segregation of alleles at another locus (exception: linked genes)
- relates directly to what happens in meiosis
- dihybrid cross
gametes
a mature haploid male or female reproductive cell that is able to unite with another of the opposite sex in sexual reproduction to form a zygote
Testcross
cross an individual expressing a dominant phenotype and with one expressing a recessive phenotype
-used to determine genotype of dominant plant (homozygous or heterozygous)
determine the number of possible gametes
2^n = # of gametes produced
where n is the number of heterozygous genes
product/multiplication law
taking into account a possibility in different events
probability of 2+ events occurring simultaneously is equal to the product of their individual probabilities; events are mutually exclusive if the outcome of one does not affect the outcome of other events
sum law
different possibilities, same event
probability of independent events being accomplished in more than one-way
Binomial distribution
(p+q)^n where n= sample size or # of progeny utilizes both the multiplication and sum rule exponents of p decrease from n to 0 exponents of q increase from 0 to n coefficients given by Pascal’s triangle
can calculate frequency of families with certain proportion of individuals showing a certain genotype
steps:
(1) assign initial probabilities to each outcome p=# & q=#
(2) locate appropriate term based on n
(3) plug in #s p and q and calculate
monohybrid cross
one trait – occur in fourths
F1 generation→ dominant phenotype for one trait
Each trait can be treated independently
Looking for a 1/4th distribution
(One trait but multiple phenotypic categories → epistasis!)
dihybrid cross
two traits – occur in sixteenths
independent assortment
F1 generation→ dominant phenotype for each trait
4 combinations of an F2 generation for a dihybrid cross 9:3:3:1 phenotypic ratio
(Determined 1/16th but not 9:3:3:1 → epistasis)
2^n= # of gametes (n= number of heterozygous genes)
Chi-squared test
Evaluation of the fitness of observed results to theoretical expectation
(o-e)^2/e
Reject null hypothesis: deviation from the expected ratio is due to more than chance alone
Fail to reject: deviation can be attributed to chance, therefore observed values fit the expected ratio
Use p=0.05 to determine reject (p 0.05) null hypothesis
multihybrid cross
each trait can be treated independently because of independent assortment
3:1 ratio in the F2
use branch diagram/forked line
multiplication rule to determine proportions of trait combos
