theme 5: modules 1 and 2 Flashcards
Different Sequences lead to Genetic Variation and Overall outcome depends on…
the nature of the change & where in the genome these changes occur.
Single nucleotide polymorphism (SNP)
most common type of genetic variation
- by single nucleotide base changes/substitutions in a DNA sequence that can occur in a significant portion of a population
-often found scattered throughout genome, in both coding and noncoding regions
-if found close enough or linked to gene of interest, SNP will be passed on from parent to child
SNP’s can be used as:
DNA markers if found close to particular gene
Tandem nucleotide repeats (CTA) (VNTR)
patterns of one or more nucleotides that are repeated
-repetitors are directly adjacent each other and can be found in various lengths between diff individuals across populations
DNA sequence variations
commonly occurring within a population, where a single nucleotide differs between diff individuals or paired chromosomes or have variable number of tandem nucleotide repeats
Sequence polymorphism
The {c}at is in the hat
The {r}at is in the hat
Length polymorphism
The cat ran {very} fast
The cat ran {very very} fast
Linked SNPs
located not within genes (outside of genes) and do not affect protein function, they can still serve as “markers”
Causative SNPs
(in genes) affect the way a protein functions correlating with a disease (in coding or regulatory regions).
-noncoding (changes amount of protein produced) or coding (changes amino acid sequence)
Sickle Cell Anemia (inherited, genetic disease)
-variation in A allele of the Beta globin protein gene
Genotype HbA / HbA
-Homozygous Two alleles are the same
- Phenotype, No symptoms of sickle cell anemia, biconcave rbc’s
Genotype HbS / HbS
- Homozygous Two alleles are the
same
- Phenotype Symptoms of sickle cell anemia; no functional Beta-globin proteins
Genotype HbA / HbS
- Heterozygous Two alleles are different
- Phenotype No symptoms of sickle cell anemia, though cells exhibit both protein variants
Detecting SNPs
By looking at a number of SNPs, individuals can be grouped into haplotypes, same SNPs = same haplotype group
SNP genotyping
a) microarray
G,C,A,T: Nucleotides that match one strand of one allele of the SNP
X,Y: deliberate mismatches adjacent to SNP
(oligonucleotides attached to a microarray)
b)DNA from a homozygous C-G/C-G individual (pattern of fluorescence CG/CG)
c) DNA from heterozygous C-G/T-A individual (pattern of fluorescence CG/TA)
d) DNA from homozygous T-A/T-A individual (pattern of fluorescence TA/TA)
SNPs & VNTRs are variations in DNA sequences that contribute to
various DNA polymorphisms
Genetic variations can be detected using:
microarray analysis, gel electrophoresis, & DNA sequencing
DNA polymorphisms may be:
harmless or detrimental or give selective advantages in populations
Tandem Repeat sequence vs Simple Sequence Repeat:
Tandem: repeated nucleotide sequence ( up to several 1000 nucleotides in length and can be present next to each other in multiple identical/near identical copies)
Simple: repeats as short as 2 nucleotides, repeated over and over throughout a DNA sequence stretch
variations in noncoding regions
no observed effect
DNA microarray to detect SNP genotypes
-oligonucleotides that match the common allele and all possible variant SNP alleles, are attached to glass on microarray chip
-millions of short, single-stranded oligonucleotides of known sequence are attached to the chip
-fragments of single stranded DNA are being hybridized to the chip
-possible to match emergent fluorescent pattern based on which SNP each individual has, obtain info on whether they are homozygous or heterozygous
PCR and gel electrophoresis to detect variable # of tandem repeats
-tandem repeat sites are targeted and amplified w/sequence specific primers that target flanking regions of the variable repeats
-resulting amplified DNA fragments can be separated + detected w/gel electrophoresis (crime scene identification)
advantages of sickle cell anemia
heterozygous individuals have a resistance to malaria
Mendel’s 2nd law of independent assortment
-Dominant allele of one gene segregates to the same pole of the cell as the chromosome with the dominant allele of the other gene.
-Dominant allele of one gene can segregate to the same pole as the recessive allele of the other gene on a
different chromosome
Nonhomologous chromosomes sort into:
gametes via independent assortment
Chromosomes are inherited by:
offspring from the parental gametes that are produced during meiosis
