Lecture 4 Flashcards
who was a big critic of darwin
Richard Owen
Much attention was paid to the implications for human origins, a topic Darwin was initially reluctant to address directly– why didn’t he address it directly
remember, he was still religious, so he didn’t want to go against everything about god and religion… so he sat back and allowed other to argue for him basically
Darwin defended his work largely through surrogates
what were some critiques of darwins theory
Critiques from the scientific community focused on Darwin’s inability to explain how traits are inherited
why is Genetics important to the study of human origins
Genetics is important to the study of human origins because it addresses the withering criticism Darwin was largely unable to counter in his day
What Didn’t Darwin Know
- What is the source of individual variation?
2. How are characteristics inherited?
What is the source of individual variation?
genes
How are characteristics inherited?
Particulate Inheritance
what is Blending inheritance
was the vaguely-‐defined, yet widespread belief that traits from a mother and a father are ‘mixed’ like liquids
From Classical Greek times to the late 19th century, the concept was the only means of explaining inherited traits
what was a limit of blending inheritance
Blending inheritance could not account for outliers exhibiting traits beyond the limits of, or not found in, the two parents
what are gemmules
All cells in the body are infused with part-‐specific particles that determine physical traits called gemmules
can gemmules be altered
Importantly, gemmules can be altered over the course of an individual’s lifetime
what is Pangenesis
darwin’s theory of how blended inheritance worked
Pangenesis basically provided a blueprint for what
Lamarckian inheritance
how did Pangenesis work
All cells in the body are infused with part-‐specific particles that determine physical traits called gemmules.
Importantly, gemmules can be altered over the course of an individual’s lifetime
Gemmules migrate from their home cells and are collected in the reproductive organs
Parent gemmules are then traded through sexual reproduction
did Pangenesis support or go against natural selection
Ultimately, Pangenesis undermined natural selection because it incorporated into it a competing theory of development of new traits
There are two types of cells, and two ways in which cells divide, what are the ways
somatic cells
germ cells
how do somatic cells work and wha are they
- somatic cells, which compose the body (liver cells, lung cells, skin cells, bone cells, etc.), divide in a clonal process called mitosis, in which the cell material doubles within the cell forcing it to split in two. The result is two identical diploid cells
how do germ cells work and what are they
- germ cells, which are found in the reproductive organs/ systems, divide into 4 haploid cells, which have half the genetic information of a somatic cell. This process is called meiosis
what is mitosis
mitosis is cell division through a cloning process,
what is meiosis
is associated with gametes and there is a splitting of the chromosomes
what are in Chromosomes
Hold DNA
Contains hundreds to thousands of genes
what is Locus
specific location of a gene
what are chromosomes always like In humans
Always in pairs
23 pairs of chromosomes
22 pairs of autosomes (homologous)
1 pair of sex chromosomes (X or Y)
what are genes
are the functional units of heredity; they are found along a stretch of DNA
what is a locus
The specific location of a gene or DNA sequence on a chromosome is called a locus
what are alleles
are different types of the same gene. They can be either homozygous or heterozygous
what are Dominant alleles
(represented by a capital letter) are “expressed”
what are Recessive alleles
(represented by a lowercase letter) are “covered up”
what are Genotypes,
which are the specific gene/ allele combinations
what are Phenotypes,
which are physical, observable characteristics made possible by the genotype
what is the difference between haploid and diploid cells
The main difference between haploid and diploid cells is the number of chromosome sets found in the nucleus. Ploidy is the area of biology that refers to the number of chromosomes in a cell. Therefore, cells with two sets are diploid, and those with one set are haploid
Within the nucleus is contained paired chromosomes, bundled into which are strands of what
DNA
what did GREGOR MENDEL (1822-1884) do
Mendel tracked the following “characters” or traits of the pea plant (Pisum sativum); through hybridization, he hoped to track changes from one generation to the next
how did Mendel conduct his experiment
Within the flower of the plant, pollen from the anther (♂) is deposited on the stigma (♀) either through self-‐pollination or cross-‐ pollination. Fertilization then occurs
The peas themselves are seeds of the plant; pea- ‐pods grow from the flower itself
what were the results of menders experiments
The parent plants are “purebred” specimens
The offspring of the parent generation consistently produced purple flowers
One quarter of the second generation plants had white flowers (of a combined 920 or so flowers…)
what did mendel conclude
Mendel found the 3:1 ratio repeating in succeeding generations. Importantly, the same result was obtained for all of the observed pea plant traits, not only flower color! From all of this, he drew three initial conclusions
what were menders 3 conclusions
- Inheritance is not the result of a mixing of traits, but of inheritable elements (later called genes) from both mom and dad, and that each trait is a product of two genes
- A gene can be passed along to succeeding generations by an individual not exhibiting the corresponding allele (even if it does express the phenotype, but it still has the genotype)
- Parental elements (alleles of genes) must separate (segregate) during germ cell division; otherwise, our genetic material would be compounding exponentially every generation! This is known as the Law of Segregation, and was eventually validated with the observation of meiosis
what are Mendel’s 3 “Laws”
The Law of Segregation
The Law of Independent Assortment
The Law of Dominance
what is the Law of Segregation
states that for every trait, there are two alleles (one from mom, one from dad); each of the post-‐meiosis haploid cells contains one of these alleles
what is the Law of Independent Assortment
states that genes for different traits assort independently of one another in the formation of germ cells
Mendel was curious to know if the traits were codependent on each other… were the traits linked with each other?
he looked at the traits 2 at a type, and there was a result was far more complex… he concluded that traits are independent of each other
e.g. hair colour does not impact height… traits are located on different chromosomes for the most part
what is the Law of Dominance
states that dominant alleles will mask recessive alleles
there are two sources of genetic variation that would facilitate natural selection , what are they
mutation
genetic recombination
what is mutation,
which is the only source of truly new genetic variation, is the alteration or damage to a gene sequence on DNA. Somatic mutations will not be passed on, but germ-‐line mutations will
what is genetic recombination,
which is the result of independent assortment and crossing over during meiosis. This exchange is crucial, because it allows for varying degrees of change within a generation
what are The 2 implications of genetic change for whole populations of organisms
microevolution
macroevolution
what is microevolution
is the change in allele frequency and distribution over time within a population of a species
what is macroevolution
is the same change at or beyond the species level and across multiple populations
what is the study of change called
population genetics
What factors influence the distribution and frequency of alleles in a population
mutation natural selection sexual reproduction genetic drift gene flow (migration)
what is a Gene Pool
A gene pool is a ‘pooled’ combination of the different alleles (B and b) in a given population of a species
Pooling genotypes helps us more easily compare genetic populations of varying sizes
The genotype proportion is represented as a fraction of the total number of alleles
ex. B=7/14, 0.5; b=7/14, 0.5
what is a species
The most common (and practical) definition is a population of individuals capable of mating and producing fertile offspring
what are evolutionary isolating mechanisms
sterility and inviability may be an evolutionary isolating mechanism, meant to preserve species integrity
what is a hybrid
cross between species that are not fertile
what is a Common evolution myth
Species hybridization is an important factor in natural selection
what is a A species complex
is a grouping of very closely-‐related species. The classification of the constituent species may be controversial
