[BIOL 110] - Midterm Exam Guide - Everything you need to know! (48 pages long)

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BIOL 110
MIDTERM EXAM
STUDY GUIDE
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Chapter 14: Mendel and the Gene Idea
Thursday, October 20, 2016
6:12 PM
Concept 14.1 Mendel used the scientific approach to identify two laws of inheritance
Mendel's Experimental, Quantitative Approach
o Character - a heritable feature that varies among individuals
o Trait - each variant for a character
o Pea advantages
Short generation time
Large number of offspring
Cross- pollination
o True-breeding
o Hybridization - the mating or crossing of two true-breeding varieties
P, F1, F2
The Law of Segregation
o Ratio of 3:1
o Purple was the dominant trait, white was the recessive
Proven by the white flowers reappearing in the F2 generation
o Seed shape also follows this dominance pattern
Mendel's Model
o Alternative versions of genes account for variations in inherited characteristics
Alternative versions are called alleles
DNA sequence variations
o For each character, an organism inherits two copies of a gene, one from each parent
Alleles of that gene
Genetic locus is represented twice in a diploid cell
o If the two alleles at a locus differ, then one, the dominant allele, determines the organism's
appearance; the other, the recessive allele, has no noticeable effect on the organism's
appearance
Purple was dominant
o Law of segregation - the two alleles for a heritable character segregate (separate from each
other) during gamete formation and end up in different gametes
Egg/sperm get only one of the two alleles in the somatic cell
True-breeding means the allele will be present in all gametes
Useful genetic vocabulary
The Testcross
o Mystery pea plant that has purple flowers
o Is it PP or Pp?
o Cross with true breeding rr plant
o This will reveal the genotype of that organism '
The Law of Independent Assortment
o In segregation, all the F1 progeny were monohybrids (heterozygous)
Cross between heterozygotes is a monohybrid cross
o Independent assortment was discovered by examining two characters at the same time;
seed shape and color
o F1 plants will be dihybrids (individuals heterozygous for the two characters)
o Two pairs of alleles segregate independently from each other
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o Four phenotypic categories: 9:3:3:1
o Sorted into gametes independently of each other
o Law of independent assortment therefore; each pair of alleles segregates independently of
each other pair of alleles during gamete formation
Only applies to genes located on different chromosomes!!
(or very far apart on the same chromosome)
Concept 14.2 the laws of probability govern Mendelian Inheritance
The multiplication and addition rules applied to monohybrid crosses
o Multiplication
Independent events
Multiply the probability of one event by the probability of the other event
o Addition
Probability that any one of two or more mutually exclusive events will occur is
calculated by adding their individual probabilities
Solving complex genetics problems with the rules of probability
o Dihybrid or other multicharacter cross is equivalent to two or more independent
monohybrid crosses occurring simultaneously
o Give us the chance of various outcomes
Concept 14..3 Inheritance Patterns are often more complex than predicted by Simple mendelian
genetics
Extending Mendelian Genetics for a single gene
Degrees of Dominance
o Alleles can show different degrees of dominance
o Complete dominance
Heterozygote and homozygote dominant are indistinguishable
o Incomplete dominance
Neither allele is completely dominance
Red and white snapdragons make pink heterozygotes
Maintain identity; inheritance is particulate
o Codominance
Two alleles each affect the phenotype in separate, distinguishable ways
Human MN blood group
The relationship between dominance and phenotypes
o Dominant means it is seen in the phenotype
o Alleles are simply variations in a gene's nucleotide sequence
o Whe a doiat allele coeists ith a recessie the do’t actuall iteract
o For any character, the observed dominant/recessive relationship of alleles depends on the
level at which we examine phenotype
o Tay Sachs disease
Inherited disorder in humans
Only children with two copies of the allele get the disease
At the organismal level the allele is recessive
Intermediate phenotype at biochemical level shows incomplete dominance
At the molecular level normal allele they are codominant
Frequency of dominant alleles
o The dominant allele being more common is not a given
o Polydactyl is an example of this
Multiple Alleles
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