Midterm 2 Flashcards
What cells are totipotent and what does it mean to be differentiated?
Embryonic stem cells are totipotent (all powerful). They are able to transform into any type of cell depending on the right signals.
A cell is differentiated once it receives it’s programming to express only the genes that are necessary to support it’s purpose.
What is the Central Dogma of Biology?
All living organisms are made up of proteins. The Central Dogma of Biology describes how we get proteins from the DNA in our cells:
DNA is transcribed into messenger RNA (mRNA) which leaves the cell nucleus and meets up with ribosomes to synthesize proteins.
What happens during translation and transcription? Where do they occur?
Watch:
http://www.youtube.com/watch?v=41_Ne5mS2ls
During TRANSCRIPTION a DNA segment encounters a RNA polymerase in the nucleus and splits temporarily to create mRNA.
The mRNA then leaves the nucleus to meet up with a ribosome in the cytoplasm where TRANSLATION creates proteins from amino acids introduced by tRNA.
The tRNA is then discarded and the resulting chain of amino acids (polypeptide chain) is a protein which will fold into its final shape to determine the protein’s function.
NOTE: In prokaryotes, translation occurs immediately following transcription. In eukaryotes the mRNA is altered first.
What is the significance of the genetic code being nearly universal among all organisms?
A universal genetic code among all organisms means that we all descended from a common ancestor.
What were the prevailing viewpoints before Mendel’s research?
1600s - pre-made human contained in every sperm cell.
Theory of Blended Inheritance - offspring a blend of father/mother traits (white + red = pink).
Why did Mendel choose the pea plant to use in his experiements?
Mendel chose to use pea plants because they:
- were easy to grow
- were quick to reproduce
- could be cross-pollinated by hand
- had easy to observe traits
Why does each somatic cell have 2 alleles per gene?
Because one allele comes from mom, the other from dad. During meiosis, each gamete gets one copy of each gene, so when two gametes combine, there are two alleles in the resulting diploid cell (Law of Segregation).
Describe Mendel’s system of crossing plants. What are monohybrid crosses?
Mendel first looked for traits the expressed two forms such as height. He then crossed plants that expressed the same trait, so short with short and tall with tall. Finally he crossed a short and tall plant.
For the short pair, the offspring were always short. For the tall pair and the short-tall pair, the offspring were sometimes tall and sometimes short.
This led Mendel to conculde that tall trait was DOMINANT and the short trait was RECESSIVE. Mendel uses a capital letter to denote dominant traits and lowercase for recessive.
A monohybrid cross is a mating between two individuals that are heterozygous (Tt) for one gene
Be familiar with how to use a Punnett Square to predict genotypic and phenotypic ratios
Male parent: Tt
Femail parent: Tt
T t T Tt Tt t Tt tt
Phenotypic Ratio:
3 tall : 1 short OR 75% tall : 25% short
Genotypic Ratio:
1 TT : 2 Tt : 1 tt OR 25% TT : 50% Tt : 25% tt
What is an allele?
An allele is a variant (alternative form) of a gene
What does it mean to be dominant?
Dominant alleles are those that obscure other alleles. Dominant alleles occur most often in nature and are often considered the “normal” form of a gene.
What does it mean to be recessive?
Recessive alleles are often masked by dominant alleles and do not appear as often. Recessive alleles are often mutated versions of the dominant allele.
What does it mean to be homozygous?
Homozygous means both alleles are the same. Organisms can be homozygous dominant (TT) or homozygous recessive (tt) for a trait.
What does it mean to be heterozygous?
Heterozygous means an organism has both a dominant and recessive allele for a gene (Tt).
What is a genotype?
A genotype tells us what alleles (genetic makeup) the individual has [e.g. TT, tt, or Tt]
What is a phenotype?
A phtenotype is the outward expression of the allele, it is what we see (e.g. tall or short)
What is a Punnett Square?
A Punnett Square allows us to see the probability of which alleles offspring might inherit from its parents.
What are the exceptions to Mendel’s Laws and what do each of them mean?
Incomplete dominance - occurs when offspring is heterozygous and has parents who are homozygous for two alleles. The single dominant allele does not code for enough of the dominant trait to be fully expressed, therefore appearing “blended”.
To test, simply cross heterozygous offspring again, which can yield the original homozygous dominant and recessive offspring.
Polygenic Traits - Traits that depend on more than one gene. Most human traits are polygenic (e.g. eye color).
Sex-linked Traits - Traits that are carried on the X-chromosome. Because males only have one X-chromosome, males only require one recessive gene to express a recessive phenotype. Females would require two since they have two X-chromosomes, therefore males are more likely to show recessive allele.
Environmental Influence - Traits that are influenced by the environment (e.g. skin color)
How did people believe species arose before Darwin’s Theory of Natural Selection?
People believed that a set number of species was created at the same time the earth was and did not change or die out; the species were perfect.
What is evolution?
Evolution is the genetic change in a population over time.
What is evolution by natural selection and what are the three conditions necessary for natural selection?
Natural selection is a mechanism of evolution where the individuals with the best adaptations for the current, local environment as able to survive and reproduce, passing on the adaptations.
Natural selection requires:
- Variation for a trait (ex: fast vs. slow)
- Heritability (can be passed down to offspring)
- Differential Reproductive Success (more offspring produced than can survive, the best competitors win!)
How does genetic variation arise and how does it contribute to differential reproductive success?
Genetic variation arises from random mutations and natural selection. Individuals that possess a certain variation of a gene may be better adapted to survive in current conditions and therefore able to reproduce successfully, passing on the same variation.
What is meant by evolutionary fitness?
Evolutionary fitness is a measure of reproductive success, the ability to pass on genes to the next generation in a particular environment.
What is the result of evolution by natural selection?
Populations become well-adapted to their current, local environment
Why doesn’t natural selection produce “perfect” organisms?
Because as the environment changes, the traits that were once favored can become useless.
What are the three modes of natural selection?
Directional - one extreme is selected/most fit (e.g. light OR dark coloration: Pepper Moths).
Disruptive - both extremes are selected/most fit (e.g. large AND small: Coho Salmon)
Stabilizing - intermediate phenotype is selected/most fit (e.g. medium weight) - Birth weight
