ARCH 131 Lecture Notes - Lecture 3: Gregor Mendel, Quantitative Genetics, Endoplasmic Reticulum
19 Feb 2017
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ARCH 131 Lecture 3 Notes:
3.1 Inheritance and Mendel’s Principles
Mechanisms of Inheritance of Traits
● 19th century view of inheritance:
○ blending of traits
○ breeding, or Artificial Selection (i.e corn, cows, dogs, plants)
Gregor Mendel (1822-1884)
● “Research on Plant Hybridization” (1850s)
● experimented on the common garden bean, examined 7 different traits of the common pea (seed
form, seed cotyledons/flower colour/pod form etc.)
● Second Generation: 25% of the peas will demonstrate the recessive trait (wrinkly pea)
● Hypothesis:
○ Each second generation parent contains both a dominant and recessive particle for the
trait in question.
○ They randomly pass on one OR the other to each offspring.
○ Each parent’s contribution has a 50:50 that each particle will be passed on, which means
four possible combination.
○ Sw + Sw = SS or Sw or wS or w
● Today, we refer to the “particles” for each trait as alleles. An allele is an alternate
form of a specific gene
○ Homozygous dominant: Having 2 of the dominant form of an allele
○ Heterozygous: having 1 dominant and 1 recessive
○ Homozygous recessive: Having 2 recessive form
● Monohybrid: crossing 2 plants that differ in only one characteristic
● Dihybrid: crosses where the parent plants different in 2 different
Mendel’s Principles
1. Segregation: offspring inherit one discrete particle for a trait from each parent,
those particles maintain their unique integrity from generation to generation
2. Dominance and Recessiveness: some expressions of a specific trait were
dominant over others
3. Independent Assortment: different traits were not inherited together as packages.
They passed from generation to generation as independent particles. (monogenic, polygenic
traits)
● BUT Some of Mendel’s principles were contrary to his principle of independent
assortment
● Mendel examined only discrete traits.
3.2 The Cell and Genetics
Cells
● Somatic + gametes
● Basic Animal Cell Structures
○ Know: mitochondria, nucleus, cytoplasm, plasma membrane, ribosomes,
endoplasmic reticulum
Genes
● Basic DNA structure, double helix inside Gametes
○ Crick + Watson: discovered the structure of DNA, Nobel Prize winners
find more resources at oneclass.com
find more resources at oneclass.com
○ Rosalind Franklin: microscopic photographer, integral to research
● Rails of DNA: 1 phosphate + 1 sugar + 1 nitrogenous base = a nucleotide (A/T, G/C), we have 3.2 billion
base pairs
● Gene: is a set sequence of nitrogenous bases that code for a specific protein
○ Dna unzips, daughter strands are formed
● Chromosomes: different sections of the entire DNA sequence
● Single stranded chromosomes (chromatid) > compacted chromatid > replicated chromatids
○ Humans have 46 chromosomes (diploid)
○ The last set are sex chromosomes, which determine the sex. XX, female, XY
male
● Locus: the area of a gene that refers to a specific location (i.e. earwax type), gene location
● Alleles: different versions of a specific trait, slightly different coding at the same gene location
○ Different alleles may code for conflicting traits (i.e. blood type)
○ Physical expression comes down to which allele is dominant/recessive, whether
it’s monogenic or polygenic trait
○ Each gene location has two alleles one from each parent’s gene contributions
Cell Replication
Mitosis
● Sex cells have haploid chromosomes (23)
Meiosis 1 & 2
● Tetrad stage: where they split apart (3)
● In men: spermatogenesis results in 4 spermatids
● in women: oogenesis results in 1 mature ovum and 3 nonfunctional polar bodies
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Breeding, or artificial selection (i. e corn, cows, dogs, plants) Experimented on the common garden bean, examined 7 different traits of the common pea (seed form, seed cotyledons/flower colour/pod form etc. ) Second generation: 25% of the peas will demonstrate the recessive trait (wrinkly pea) Each second generation parent contains both a dominant and recessive particle for the trait in question. They randomly pass on one or the other to each offspring. Each parent"s contribution has a 50:50 that each particle will be passed on, which means four possible combination. Sw + sw = ss or sw or ws or w. Today, we refer to the particles for each trait as alleles. An allele is an alternate form of a specific gene. Homozygous dominant: having 2 of the dominant form of an allele. Heterozygous: having 1 dominant and 1 recessive. Monohybrid: crossing 2 plants that differ in only one characteristic. Dihybrid: crosses where the parent plants different in 2 different.
