5. Chapter 4: Genetics, Neo-Darwinism and Modern Synthesis Flashcards
Who is Gregor Mendel?
Gregor Mendel was an Austrian monk who is the founder of genetics. He formulated laws on the creation of hybrids (laws of heredity) of how progeny get genetic information from their parents or transmission of hereditary particles from parents to offspring.
How did Mendel distinguish his work?
Through exemplary scientific rigour:
- a judicious experimental material of peas as there are: many varieties available, possibility of crossbreeding, fairly cheap, generation time is short, descendants are plentiful.
- Abundant data and use of mathematical analysis to verify his hypotheses
- Mendel refers to not yet discovered genes as hereditary factors
How is the variation of genetic traits explained?
Variation of genetic traits is explained by the different shapes genes (through different alleles) can have. Each gene occupies a specific locus on a given chromosome. The DNA sequence of the locus can show variants called alleles
What are the modern additions to mendel’s laws? Examples?
- Incomplete dominance: an intermediate or blended inheritance in which one allele for a specific trait is not completely expressed over its paired allele. (this results in a third phenotype in which the expressed physical trait is a combination of the phenotypes of both alleles)
Ex. Snapdragon complete dominance are (RR)red and (WW)white incomplete dominance is (WR)pink or horses cream, and chestnut incomplete dominance horse has cream(cc) mane and chestnut(CC) body called palomino(Cc) - Codominance: a form of dominance wherein the alleles of a gene pair in a heterozygote are fully expressed. (this results in offspring with a phenotype that is neither dominant nor recessive)
Ex. Black chicken (BB), white chicken (WW) and BW chicken is checkered (black and white) - Polygenism: When a phenotypic trait is under the combined action of two or MULTIPLE GENES (very common)
Ex. Up to 20 genes are associated with Skin colour or eye colour - Epistasis: When the effect of a gene hides or blocks the expression of another gene. Certain pleiotropic genes are lethal when homozygous.
Ex. Dog colour, lowercase bb and ee is always chocolate and golden regardless of combination with other genes present as it does not get expressed - Pleiotropy: When a gene influence more than one trait. It’s a very common phenomenon in regards to gene expression
Ex. Manx cat, Manx gene SHOWS INCOMPLETE dominance compared with normal present tail gene, when Manx gene is homozygous it is lethal as the gene is responsible for the lack of tail, heterozygous cats have no tail or have a short tail
What impact did Mendel’s work have when rediscovered?
The discovery of Mendel’s work had, initially, a negative impact on the theory of natural selection. As the first geneticists put the emphasis on the discrete or discontinuitious aspects of the traits associated with Mendel’s ratios and rejected the continued variation observed in nature by claiming that it was non-Mendelian and without any evolutionary importance. Furthermore, Hugo de Vries formulated a “Theory of Mutations” which indicated that new species can be formed in one or multiple steps (saltationism) through mutations that would caused substantial morphological modifications. During the 1920s, it was discovered that mutations are generally harmful or neutral and that only a few seemed to influence, although lightly, an organism traits.
Who resurfaced Mendel’s work?
Coreens
Tschermack
Hugo De Vries
How was “Darwinism” created? (Another name)
Darwinism or the modern evolutionary synthesis were created when genetics and the theory of natural selection were reconciled through mathematics
What were the main impacts of new-Darwinism?
- Lamarckism was finally refuted.
- We started to understand the effect of chance in the transmission of alleles from generation to generation (genetic drift).
- The genetic basis of evolutionary changes was established.
- The study of genetics shows the existence of an important and persistent variation (continuous or discrete) which creates the hereditary material on which evolution can act.
- This continuous variation has a Mendelian basis, that is to say that it implies the segregation of hereditary particles having a minimal phenotypic effect.
What did the emergence of population genetics and micro evolution offer?
It offered a new perspective in regards to the relative significance of the factors producing:
- evolutionary changes in populations
- Speciation: the biological and genetic basis of the formation of species
- Macroevolution: the study of evolution above the species level
- Phylogenies: elaborating the tree of life
What is a phenotype vs genotype?
UNDERSTANDING
phenotype: appearance colour so purple and white flowers
Genotype: genetic makeup: homozygous, heterozygous, PP, Pp, pp
What is the law of segregation?
Two alleles for a heritable character segregate (so separate from each other) during gamete formation and end up in different gametes.
What is the law of independent assortment?
Ex.?
Every pair of allele separates independently from other pairs when the gametes are formed
Ex Peas: yellow/green or smooth/wrinkly
Humans: ear lobes and hairline
What is the phenotypic ratio when alleles do/do not segregate independently?
If does not segregate independently then phenotypic ratio 3:1
If does segregate independently then phenotypic ratio 9:3:3:1
*in terms of peas
What is the law of Uniformity of Hybrids of the first generation?
If both alleles of a locus or hereditary factors are different, one of them, the dominant allele determines the appearance of the organism; whereas the other, recessive allele, has no notable effect on the appearance.
Ex. Ear lobe heterozygous will show dominant trait
What is the hereditary factors in genetics?
We inherit two copies of a gene (different or identical), one from the “father” and the other from the
“mother”. An individual possesses two alleles for one gene (hereditary factor) where human will have 23 pairs of chromosomes.
