Genetics Flashcards
What are DNA and RNA? (Types, building blocks, structure, differences)
RNA: messenger, transfer, ribosomal
Both made of nucleotides: pentose sugar, phosphate group, nitrogenous base
DNA: [deoxy]ribose, double stranded with covalent bonds between sugar and phosphate, hydrogen bonds between bases, anti-parallel
RNA: C-G, A-U
DNA: C-G, A-T
What is DNA replication? When does it occur? What are the 3 steps?
Happens in synthesis (S) phase of interphase
DNA copies for replication
Occurs in nucleus with presence of enzymes (helicase and DNA polymerases) and free nucleotides
1) helicase initiates separation between 2 strands by breaking hydrogen bond
2) free floating nucleotides find complementary partners on open strands polymerase catalyzes covalent bond between nucleotides; both sides happen simultaneously in different directions
3) other polymerase proofread each nucleotide for the template and correct if needed
Catch most mistakes, others are mutations (usually harmless)
Semi-conservative because new strands are 1/2 old DNA (1/2 is conserved)
What are the cell cycle and mitosis basics?
Cell cycle: interphase (G1, S, G2), miotic phase (mitosis, cytokinesis)
Mitosis is in somatic cells
Phases: prophase, metaphase, anaphase, telophase
2 Genetically identical cells that are diploid (two copies of each chromosome)
What is meiosis? How is it different from mitosis?
Meiosis makes sex cells (egg and sperm) or gametes
Have 1/2 the number of chromosomes when done (haploid)
Has homologous chromosome pairing and crossing over
Produces cells with variable genetics
What are the steps of meiosis?
Prophase 1: cell has 2n chromosomes (double chromatid), homologous chromosomes pair in synapsis, crossing over and swapping occurs further from centromere
Metaphase 1: chromosomes line up on metaphase plate in pairs independently assorted
Anaphase 1: sister chromosomes separate from pairs and move to poles
Telophase 1: chromosomes uncoils, cytokenisis divides cell on equator, haploid
Meiosis 2: non-identical sister chromatids line up (single file), cytokinesis creates 4 haploid cells, in females only 1 egg is used
What causes genetic variation and disorders in meiosis?
Genetic variation: swapping between chromosomes, independent assortment, random fertilization
Non-disjunction: homologous chromosomes don’t separate in anaphase 1, usually lethal or down syndrome, intersex
Translocation and deletion: incorrectly transfer or delete fragment of chromosome
What is a gene? codon? anti-codon? protein bond? DNA to RNA translation?
Gene: sequence of bases coding for a trait, found on a locus
Codon: 3 base pairs which code for 1/20 amino acids (triplet)
Anti-codon: tRNA bases that compliment the amino acid it has
Protein bond: condensation reaction → covalent peptide bond
DNA [CAGT] → RNA [GUCA]
What is the process of protein synthesis?
Transcription: DNA into RNA. Gene in DNA is unzipped by RNA polymerase, RNA nucleotides float in, attach via RNA polymerase, stop at stop codon → complementary mRNA of gene which leaves nucleus through pore
Only 1 side of DNA is transcribed, polymerase re-zips
Translation: tRNA is a single strand with complementary anti-codons on the bottom culd-e-suc, other end has corresponding amino acid found in cytoplasm. tRNA and mRNA go to ribosome, 2 tRNAs at once which match the RNA codon. Peptide bond between the amino acids, then moves to next codon. tRNA floats away, stop codon allows amino acids to break off and morph into a protein
What is the one gene / one polypeptide hypothesis?
Belief that every gene coded for 1 enzyme, amended to include all proteins because many proteins are polypeptides
Recent understanding that 1 gene may lead to a single mRNA molecule, but mRNA may be modified by spliceosomes, resulting in many different polypeptides
What are gene mutations? Sickle cell anemia?
Mutation: change in sequence of bases in gene, most mistakes are caught
Usually don’t have an impact, but can be good/bad
Creates genetic variability → if mutation happens in meiosis it can be inherited
Sickle cell anemia: angular red blood cells that clog capillaries, developmental problems, pain. Primarily in black folks and Hispanics. Heterozygotes don’t have sickle cell but are more resistant to malaria. Caused by base substitution in hemoglobin (GAG → GUG)
Genetics vocabulary: Gene? Allele? Genotype? Phenotype? Dominant allele? Recessive allele? Homozygous? Heterozygous?
Gene: heritable factor that controls a specific characteristic (length of DNA occupying a position on a chromosome known as a locus)
Allele: specific form of version of a gene that differs from others by 1 or a few bases, occupies the same gene locus as other alleles
Genotype: alleles passed down by an organism (AA or Aa)
Phenotype: outward expression or characteristics of an organism
Dominant allele: same affect on phenotype whether homo- or hetero- (capitalized)
Recessive allele: only affects phenotype if homo- (lowercase)
Homozygous: 2 identical alleles of a gene
Heterozygous: 2 different alleles of a gene
What is complete dominance?
Dominant allele carries code for protein, recessive doesn’t on its own
Capital / lowercase letters
What is codominance?
More than 1 dominant allele: partial phenotypic affect when hetero- more when homo-
Capital letter same for an alleles with differing capitalized superscript
What is multiple alleles?
Genes with > 2 alleles (blood type)
Similar to codominance notation but recessive (O blood type) is lowercase
What is sex-linked inheritance?
Alleles carried on X chromosome (females have 2, males have 1)
Notation with capital X and / or Y, superscript on X with capital or lowercase
Ex: hemophilia, colorblindness
