Lecture 1 Flashcards
How many base pairs are in the haploid human genome
3 billion in haploid, 6 billion in genome
How related are the genomes of 2 unrelated people
99.5%
How many chromosomes in the human
46 chromosomes, 23 paired in females (22 X and 1 Y chromosome in males)
What percent of the genes are protein-coding genes
2%
How long is DNA if stretched out from single cell
2 meters long
What is a gene
a basic unit of hereditary material
- A segment of DNA that produces a polypeptide chain
How are genes usually defined
commonly defined by the linkage they have to disorders (i.e. BRCA causes breast cancer)
Genetic information is carried in units called
genes
Diploid vs haploid cells in the human body
Diploid: 2 copies of genetic material (i.e most cells in the body)
haplid: cell with a single set of unpaired chromosomes (sex cells)
What is an allele
a different form of a gene
- Variation in nucleic acid sequence of genes leads to 2 different alleles
How many alleles can a diploid organism have
2 copies of the same allele or 2 different alleles
Homozogote vs heterozygote
Homozygote: 2 copies of same allele
Heterozygote: 2 different alleles
Comparison of genotype vs phenotype
Genotype: the alleles someone has (i.e. Aa)
Phenotype: visible expression of genotype (i.e. green eyes with Aa and blue eyes with aa)
What are polygenic and monogenic related to and waht do they mean
related to phenotypes
Polygenic: many genes influence a trait (most human characteristics)
Monogenic: Phenotype influenced by only 1 gene
What is the backbone of DNA
Sugar-phosphate backbone
Central dogma of genetics
DNA transcribes into RNA(transcription, DNA and RNA same language) , RNA is translated into proteins (different languages so must translate)
How do retroviruses work?
use reverse transcriptase, turn RNA to DNA (backwards)
What are autosomes
non-sex chromosomes
What are chromosomes made of
proteins and nucleic acids. Nucleic acid chain wrapped tightly around a histone protein
Which organelle is maternal?
Mitochondria- all have small circular chromosome and have multiple copies
What do helicases do
unwind the dna helix, seperate the strands
What does Primase do
build RNA primers on DNA strands to give DNA polymerase place to build new DNA strand
What does polymerase do
add base to new DNA strands. Catalyzes the covalent addition of free nucleotides to new DNA strands
Which enzyme do chemotherapy drugs target commonly
polymerase, inhibits cancerous dna transcription
How is DNA replication considered semiconservative?
Open up DNA, keep one old strand and make one new strand (2 new strands from one DNA strand since it’s split)
Where are covalent bonds in DNA and RNA
between phosphate and nucleotides
Functions of RNA
-Sending transcription messages
-Form ribosomes to synthesize proteins
-Translate from nucleic acid to amino acid sequence
What are amatoxins? What are they related to?
-Deadly inhibitors of human RNA polymerase
- Cause of death from mushroom poisoning
- Can’t make proteins we need, so we can’t transcribe the proteins we need
Which antibiotic inhibits RNA polymerase?
Rifampin
Is the sense or antisense strand used to make RNA transcript?
Antisense- made sense strand
What 2 regions does RNA polymerase work between
Promotor and terminator
Describe the process of DNA to mRNA
DNA is transcribed, has introns removed, exons spliced together, and is then mRNA
What is tRNA’s relationship to mRNA
complementary
What percent of mutations are replication errors vs chemical or environmental damage
65% are replication errors
35% are chemical or environmental damage
Are mutations usually harmful?
Very few are harmful, most don’t have much effect because cells have enzymes to repair DNA
What do RNA viruses like coronavirus rely on?
RNA dependent RNA polymerases to do retrovirus things (go from rna to dna)
What is the only way we get new alleles created?
mutations
What are germinal mutations vs somatic mutations
Germinal mutation: in sperm or egg
Somatic mutation: in somatic cell (i.e. skin cancer)
What is a point mutation?
Base substitutions (Supposed to be T, puts in G instead).
Results in: transitions(purine to purine (just different letters for same amino acid)) or transversion (purine to prymidene)
What are insertion and deletion mutatoins
Frameshift mutations (add or remove entire nucleic acids)
What is a duplication mutation
gene or segment of DNA is copied or stuck
What is aneuploidy
additional chromosomal copies or deleted copies
Purines vs prymidines
Purine: A/G
Pyrimidines: T/C
What is a strand slippage
one nucleotide strand forms a loop, base pair falls out of strand
Do insertions/deletions or base substitutions occur more frequently?
Insertions and deletions
What mutation leads to unequal crossing over
Deletions and insertions
Describe the 3 phenotypic effects of mutations
- Missense mutation: new codon encodes different amino acid, change in amino acid sequence
- Nonsense mutation: New codon is stop codon
- Silent mutation: New codon encodes same amino acid, no change in aa sequence
What is aneuploidy
one extra single chromosome (23+1 chromosome)
What is polyploidy
all chromosomes have an extra pair (usually no birth)
Describe metacentric, sub-metacentric, acrocentric, and telocentric for centromeres
Metacentric: centromere in middle of chromosomes
Sub-metacentric: almost at the middle
Acrocentric: to one side of the chromosomes
Telocentric: Centromere at the very end of the chromosomes
4 different Chromosome rearrangements during replication
Duplication: chromosome segment duplicated
Deletion: chromosome segment deleted
Inversion: segment turned 180 degrees
Translocation: segment moved elsewhere on different chromosome
Nonreciprocal vs reciprocal translocation
Nonreciprocol: Segment from one chromosome to another, no exchange back
reciprocol: two chromosomes swap (balanced)
Robertsonian: One chromosome is attached to another (considered type of balanced reciprocol)
Common examples of robertsonian translocation
13 and 14,
14 and 21
Tandem duplication vs displaced duplication vs reverse
Tandem: immediately adjacent duplication
Displaced: somewhere else on the same chromosome or on another chromosome
Reverse: inverted (180 degrees) duplicated
What are ring chromosomes
deletion of both chromosomal arms in duplication, sticky ends form a ring.
Ring 14 is common
How do polyploidy fetuses occur
when 2 sperm fertilize an egg at the same time- entire extra set of genes. Do not make it to birth
What is nondisjunction
homologous chromosomes or sister chromatids fail to seperate
- Lead to aneuploidy (abnormal number) or trisomy(3 copies of given chromosome)
What are the 4 types of aneuploidy
Nullisomy- loss of both chromosome pairs
monosomy: loss of 1 chromosome
trisomy: gain single chromosome
Tetrasomy: gain 2 homologous chromosomes
Why are some chromosomes able to have viable trisomys?
They have a smaller number of genes per chromosome so an extra copy makes it possible, a smaller number of genes makes less of an effect (i.e. chromosome 21 has 300 genes to be duplicated instead of the 2544 genes on chromosome 1)
What is associated with maternal age
aneuploidy
What is down syndrome related to (chromosome)
Trisomy 21, extra 21 chromosome
What are some of the key features of Down syndrome?
- Most common chromosomal disorder
- short neck, heart and respiratory defects, delayed or reduced mental development, increased risk of lukemia and alzheimers
What increases risk of down syndrome
mother’s age/paternal age
What gene rearrangement can cause down syndrome
An extra part of chromosome 21 is attached to another chromosome in the parent. When the parent reproduces, it leads to 3 chromosomes for 21 (down syndrome)
Caused by robertsonian translocation
Edward’s syndrome pathology
Extra chromosome 18
1/5 born can live to 1 month
born usually with organs outside of the body
Patau syndrome pathology
Extra chromosome 13
Median survival is 10 days
Low birth weight, major brain development problems
Turner’s syndrome pathology
Only one X chromosome in sex chromosome (X monosomy)
- Hypogonadism, short stature, webbed neck.
- Not able to reproduce, or have menstrual cycle
1/3000 females
Poly X syndrome pathology
No syndrome defined
Tall and thin women, normal intelligence (4 or more X and decreased intelligence)
XYY male syndromes
No syndrome defined
learning difficulties, tall stature possible
Klinefelter syndrome pathology
Male with extra X chromosome (XXY)
- Delayed puberty, tall stature, hypogonadism, obesity
- Decreased testosterone, elevated estrogen
- Usually sterile
1/1000 people
What is X inactivation
One x chromosome is turned off, so one x produces most gene products.
What is a barr body
inactive X forms barr body in females (have 2 x’s so one doesn’t matter)
What is mosaicism caused from
nondisjunction in miotic division generates cells with chromosome abnormality
What is a chimera
2 different cell lines fuse (2 twins conjoin and you get 1 person with different traits). Double fertilization.
