Chapter 6 Flashcards
Law of Independent Assortment
This law states that which allele is passed down to the next generation at one locus (for example, the locus associated with seed shape) is independent of which allele is passed down to the next generation at another locus (for example, the locus associated with flower color). Today, we know that this holds true only for what are called unlinked loci.
Law of Segregation
Each individual has two gene copies at each locus (the physical location of gene copies on the chromosome) and that these gene copies segregate during gamete production, so that only one gene copy goes into each gamete.
Why does selection reduce variation?
If you select among the possible alternatives, you get less variation. Desired traits are favored among a small population, which will become the dominant group over time, so reducing the gene pool.
Purines
AG; Nitrogenous bases that contain 6 and 5 sided rings
Pyrimidines
CT; Nitrogenous bases that contain sided rings only
DNA definition/ what it’s made of (4)
- chemical basis for life on earth
- macromolecule composed of repeating units inked together in a chain
- four nucleotides (AGCT)
- composed of a pentose sugar, phosphate group, and a nitrogen base
Characteristics of DNA (6)
- double stranded
- 5’ end with terminal PHOSPHATE group
- 3’ end with terminal HYDROXYL group
- strands oriented in antiparallel fashion
- Nitrogenous bases oriented toward the INTERIOR part of each strand
- Pairing is AT and GC
How many copies of chromosomes in diploid and haploid organisms? What protein is DNA usually wrapped around? (3)
- diploid organisms have 2 copies
- HAPLOID organisms have a SINGLE copy of each chromosome
- DNA usually wrapped around the proteing: HISTONES (most heavily conserved protein)
Eukaryotic cells (2)
- Contain nucleus and organelles
- Some organelles have their own genomes (mitochondria, chlorplasts)
Prokaryotic cells (3)
- Lack nucleus and most lack membrane bound organelles
- usually have SINGLE CIRCULAR chromosome
- Some DNA is also located in plasmids
Endosymbiosis hypothesis (2)
- Organelles such as mitochondria were once independent prokaryotic life-forms that entered into a mutually beneficial relationship with other organisms. Over evolutionary time, these cells were incorporated into other cells, which eventually became organelles. These relationships became obligate.
- Proposed by Lynn Margulis
Transcription process
DNA in unwounded and portions are copied into RNA
RNA polymerase (2)
- Binds to the PROMOTER (short sequence before transcribed part of gene) which serves as a signal to BEGIN TRANSCRIPTION
- Unwinds the DNA by breaking the hydrogen bonds
Which strand is used to synthesize the complimentary RNA strand? What base replaces Thymine in RNA?
TEMPLATE strand
Uracil (U) replaces T in RNA
Translation process (2)
mRNA directs protein synthesis
base pair sequences of three (codons) specify specific amino acids
Ribosomal RNA (rRNA)
component of RIBOSOMES which function in protein production by making the covalent bonds that link the amino acids together
tRNA
TRANSPORT amino acids to ribosomes
microRNA
responsible for gene regulation- when genes are turned ON or OFF
Protein functions (5)
- enzymes that initiate and regulate chemical reactions
- chemical signals for cell to cell communication
- bind DNA and regulate when it’s expressed
- structural function
- transport
Degeneracy of genetic code
Redundancy in genetic code often results in amino acid conservation if there are mutations in the 3rd codon position
Stop codons (3)
UAA
UGA
UAG
Gene (4)
- A sequence of DNA that specifies a functional product
- most often a PROTEIN but may ALSO be RNAs’s
- eukaryotic genes are often broken into different regions: exons and introns
- genes can be spliced in MULTIPLE ways
Exons
Stretches of DNA that code for protein products
Introns (3; process)
- Stretches of DNA that DO NOT normally encode proteins
- Introns are spliced out by a RNA-protein complex called SPLICEOSOME & exons are then linked together resulting in mRNA
- mRNA is then TRANSLATED into a chain of amino acids
From DNA to proteins (3-steps)
- Transcription
- Splicing
- Translation
Alleles
variants of the same gene
Locus
physical location of a gene on a chromosome
Genotype
combination of alleles that an individual has at a given locus
Homozygote
DIPLOID species that has TWO COPIES of the SAME allele at a locus
Heterozygote
DIPLOID species that has DIFFERENT alleles at a locus
Regulatory elements
- CONTROL the RATE at which RNA molecules are transcribed from the DNA
- Influence gene expression and phenotype
- process referred to as transcriptional regulation
Enhancers
-regulatory elements that INCREASE the RATE of transcription
Cis regulatory elements
Regulatory elements that affect genes at NEARBY sites on the SAME chromosome
Trans regulatory elements (2)
- Regulatory elements that modify expression or activity of genes on different chromosomes
- Often encode soluble proteins that can act at remote locations on DNA
what are the 4 sources of genetic variation? (in natural selection)
Recombination
Mutation
Migration
Lateral gene transfer
Diploid organisms (3)
- Have paired HOMOLOGOUS chromosomes
- homologous because they contain the same genes, but often have different alleles
- each of the homologous chromosomes come from a different parent during meiosis
Gamete (2)
- Haploid sex cells that have ONE set of chromosomes
- In mammals: egg and sperm
Meiosis (2)
- diploid cells undergo a round of DNA duplication followed by two cell divisions
- Results in 4 haploid gametes
Syngamy
Fertilization gametes from each parent fuse
Crossing-over (4)
- physical exchange of segments of DNA
- generates huge amounts of genetic variability
- occurs AFTER homologous chromosomes have duplicated
- occurs very early in the prophase 1 stage of meiosis
Crossing Over and Independent Assortment is the basis for what?
Gregor Mendel’s Laws of Genetics
Mutation (4)
- change to DNA sequence of organism
- ULTIMATE source of all variation
- in order to be passed on to the next generation the mutation must occur in the germ line cells (sex cells) and NOT on the somatic cells (body cells)
Base substitution (point mutation) (2)
- Transition: purine to purine, pyrimidine to pyrimidine
- Tranversion: purine to pyrimidine, and vice versa, “tranny”
Synonymous
Silent mutation; base substitution does not change the amino acid
Missense mutation (2)
- base substitution changes the amino acid
- can be harmful or beneficial
Nonsense mutation
-base substitution creates a STOP codon = premature termination of translation
“STOP talking NONSENSE”
Frameshift mutation
An insertion or deletion that doesn’t occur in a multiple of 3 nucleotides; pushes it downstream
Chromosomal duplication
- section of a chromosome is duplicated
- results in changes in ploidy (over-expression of a gene due to multiple copies)
Chromosomal deletion
Loss of large section of a chromosome
Inversion
180 degree flip in a section of a chromosome
Translocation
A section of one chromosome moving to another chromosome
Chromosomal fission
Chromosome breaking apart and forming a {new stable configuration}
chromosomal fusion
chromosome breaks apart to form new chromosome
What is an example of a neutral mutation?
Synonymous mutation
Mutations are undirected, due to what two factors?
- mutations are generated at random
- differential replication of certain variants {not all copies occur at the same time, and some more than others}
*only filtering mechanism is death
