Lecture 5 Flashcards
what are Mendel’s Three “Laws”
The Law of Segregation states that for every trait, there are two alleles (one from mom, one from dad); each of the four post-‐meiosis haploid cells contains one of these alleles.
The Law of Independent Assortment states that genes for different traits assort independently of one another in the formation of germ cells
The Law of Dominance states that dominant alleles will mask recessive alleles
what is the Law of independent Assortment
Each gene at a single location (locus) on a pair of chromosomes (one from dad, other from mom) is equally likely to be transmitted when sex cells are formed
true only for genes on different chromosomes, or those far enough apart on the same chromosome to be separated by recombination…
What is a species?
The most common (and practical) definition is a population of individuals capable of mating and producing fertile offspring
what are the 2 types of mating
random and non-random
what is Random mating
(theoretically) occurs when there are no restrictions (either genetic or behavioral) to sexual reproduction within a species population in a given area
what is the The Hardy-‐Weinberg equilibrium
imagines that allele/gene frequencies will remain constant if random mating alone is at work. It’s used to test the impacts of the factors it doesn’t take into account (e.g., natural selection, mutation, genetic drift and gene flow).
The vast majority of sexual reproduction in the animal kingdom is the result of what
non-‐random mating
what is non-‐random mating
whereby we choose—or are limited by—available partners within our population
what is assortative mating
When choice and desirability are factors in mate selection, we call this assortative mating, which can be either ‘positive’ or ‘negative.’
what is Positive assortative mating
is when individuals mate with partners having similar phenotypes (and, by extension, genotypes).
what does Positive assortative mating result in
This tends to result in more homozygous alleles (AA, aa) in descendent generations
what is Consanguinious mating
(inbreeding) could be considered a form of positive assortative mating.
It results in more homozygous alleles in future generations because close family members share a large number of genes.
It can result in a greater incidence of negative mutations being passed along, as well as increased transmission of beneficial mutations
Example: Haemophilia (recessive trait among European Royal Families)
what is Negative assortative mating
is the result of a preference for mates with differing phenotypes/genotypes.
what does Negative assortative mating result in
This results in more heterozygous alleles (Aa) in descendent generations
what is Sexual selection
is one part of the natural selection process. It favors any adaptation that increases an individual’s chance of
1) Attracting mates
2) Having as many couplings as possible
what are the typical key movers of sexual selection
1) male competition
2) female choice
what is Sexual dimorphism
the differences in appearance between males and females of the same species, such as in colour, shape, size, and structure, that are caused by the inheritance of one or the other sexual pattern in the genetic material
Does monogamy make evolutionary sense?
Many bird species are monogamous (lasts for one nesting)
Social monogamy seems to be more common than sexual monogamy
Males invest their time to ensure their offspring (and, by extension, their genes) survive
what is Genetic Drift
is the action of random changes in the allele frequencies in a population over time. The changes are the result of the inherent chance in sexual reproduction and mutation, and cannot be predicted with any degree of certainty
How significant is the impact of genetic drift on evolution?
Within a very small population, likely very significant. Two separate processes are related to genetic drift.
what are the 2 types of genetic drift
a population bottleneck
The founder effect
what is population bottleneck
is a reduction in genetic stock due to a natural or artificial disaster
what is the founder effect
occurs when a breakaway subset of a population of a species becomes isolated from the original group
what is Gene flow
is the transfer of alleles/genes into or out of a population within a species. This is the result of individuals moving into a population (immigration) or out of one (emigration).
Typically, barriers to gene flow are physical (oceans, mountain ranges, etc.)
Today, humans comprise only one species, what is it
Homo sapiens
was humans as one species always the case
This wasn’t always the case! At various points in the recent past we were divided into several species
Why isn’t our genus currently divided into multiple species?
There are two possibilities:
1) all of us are descended from one sub-‐population that evolved into our modern form recently; or
2) gene flow has always been occurring among the earth’s dispersed human populations
what is a Phylogeny
an evolutionary tree indicating relatedness and divergence of taxonomic groups
A strand of DNA is composed of what
A strand of DNA is composed of base pairs of interlocking nucleobases: adenine, thymine, guanine and cytosine
what was the Human genome project— (1990-2003)
was a multi year endeavour to create a reference genome
a mosaic, not representing any one individual
If our genomes are so similar, why do humans and great apes appear so distinct and behave so differently?
Relatively small genetic changes can produce major phenotypic changes. Long stretches (~98%) of seemingly “junk” DNA may actually initiate (or ‘trigger’) different responses in otherwise identical genes.
There exist two basic sources of variation in human beings, what are they
1) Genetic
2) Environmental
Natural selection occasionally favours specific environmental adaptations strong enough to overcome the homogenizing effects of gene flow, what is an example of this
The ability to tolerate lactose is a good example of such an adaptation
is race a biological category
Today, most biologists and social scientists understand that race is a social construct, not a valid biological category.
There is no ‘natural’ classification system for human races; they’re all somewhat arbitrary
what is a folk taxonomy
A folk taxonomy is a customary, unscientific means of categorizing things. Many cultures have well-‐developed and culture-‐specific folk taxonomies for living things.
Since Linnean classification for human races is impossible, folk taxonomies for race are the only means of classification
Some have suggested practical medical benefits to establishing race as a biological category, what are these
Sickle-‐cell anemia is a homozygous recessive blood disorder affecting mainly West African-‐descended people.
Inheritance of disease stems from genes and ancestry, not race
