D1.3. Mutations and Gene Editing

State the two reasons why mutations in DNA are rare/ DNA is stable.

• noticing errors and correcting them are possible in the synthesis of DNA strands

• complementary base pairing allows the proper nucleotides to be added

State the characteristics of mutations.

• rare

• random

• happens in individuals unless occurred in reproductive cells

• likelihood of happening does not depend on its benefits or harms

• No natural method of creating mutations

• can be harmful

• can be beneficial

• can have no effect on organism

• can affect coding and non-coding regions

State the three types of point mutations.

1. substitution

2. insertion

3. deletion

Define substitution mutation

Replacement of a base of a nucleotide.

Define insertion mutation

Adding of extra nucleotide

Define deletion mutation

Removal of nucleotide

State the three consequences of base substitutions in coding regions (molecular level).

1. Same-sense mutation

2. nonsense mutation

3. mis-sense mutation

• protein does not function properly

• whether it is beneficial or harmful depends on what protein is affected

Describe same-sense mutation (silent mutation)

• substitution mutation occurs

• no change in amino acid sequence

  • codons are different but they still code for the same amino acid due to degenerate genetic code

  • does not affect the phenotype

Define degenerate genetic code

Different sets of codons (group of 3 nucleotides) can code for the same amino acid

Describe nonsense mutation

• substitution of the base in nucleotide leads to the creation of STOP-CODON (UAG, UAA, UGA)

  • results in a shorter polypeptide

Describe mis-sense mutation

• substitution of base leads to the creation of a different amino acid

  • polypeptide combination is different

State an example of mis-sense mutation

sickle cell anemia

• in hemoglobin gene of red blood cells

• amino acid changes from glutamic acid → valine

  • CTC → CAC

  • GAG → GUG

    • Adenine substituted by Thymine

    • shape of hemoglobin molecule changes from plate → sickle

State the reason behind different base sequences in the genetic code

Mutations

Define single nucleotide polymorphism (SNP)

• Areas in genetic code with possibilities of different nucleotides across individuals due to accumulation of base substitutions over time.

  • Change in the structural level

    • because it affects phenotypes

  • A consequence of a substitution

State the cause of SNP

several base substitutions over time

Define reading frame

Method of dividing base sequences into codons to read the amino acid

State the effects of insertion or deletion mutation

• change reading frame

  • more/ less amino acids in polypeptides

• the original coded for amino acid is not coded for anymore

State the two substitution mutations that are harmful

insertion and deletion

State the two major causes of mutations.

1. error in replication

   • wrong nucleotide in the genetic sequence

   • Rare

2. Mutagens

   • chemically cause different bases in the DNA sequence

   • example:

     • radiation

State the effects of mutations in somatic cells

not passed down to offspring

State the effects of mutations in germ cells (gamete-producing cell)

• passed to offspring

• most harmful

Define alleles

Different forms of a gene

State the role of an allele

Expresses a trait

ex: brown, green, or blue eye color

Define gene

• section or fragment of a DNA that represents a trait

• refers to the location of a DNA (locus)

State the characteristic of a gene

• same locus for same trait in same species

• ex: same location of gene that codes for eye color in humans

Explain the difference between genes and alleles

Genes represent a certain trait (ex. eye color) and alleles express them in different ways (ex. blue, green, or brown).

Genes are certain locations in a DNA strand while alleles are unique base sequences within that gene/ fragment of DNA

State the difference between different alleles

Different base sequences

State how new alleles arise.

from mutations

State the two information necessary to edit genes

• location of gene within genome

• what gene does

Describe the use of Open Reading Frame (ORF)

to locate genes using characteristic base sequences

Define the function of characteristic base sequences

usually starts a gene

help in identifying patterns

Define Gene Knockout

A technique to determine the function of a gene

Define Point Mutation

gene mutation where the base sequence of a codon is changed

Chromosomal Mutation

Changes in the chromosomal level (research more)

Trisomy 21

Extra chromosome (research more)

Define gene mutation

change in the base sequence of a gene; happens randomly

Define codon

sequence of three nitrogenous bases that code for an amino acid

State where the codon is found

mRNA

Explain why genetic mutation is beneficial

source of genetic variation → helps us survive better

State when mutations are passed onto offsprings

Mutations in gametes (egg and sperm)

State the two types of point mutations in frame shift mutation

• deletion

• insertion

Define frameshift mutation

shift in the reading of the codon
(can say that the DNA strand got longer or shorter)

Define phenotype

physical traits

Define BRCA1 gene

tumor suppressor gene by which the actual function includes DNA repair

• mends double stranded breaks

• correct mismatch in base pairing

Explain BRCA1 gene mutation

• insertion or deletion

  • higher chance of cancer due to:

    • lack of DNA repair

State the example of mutations in somatic cell

oncogene mutation that causes cancer

Define Open Reading Frame (ORF)

• characteristic base sequences that help identify where genes are located

• basically the base sequence of the gene itself

State the name of the allele: BB

homozygous dominant

State the name of the allele: bb

homozygous recessive

State the name of the allele: Bb

heterozygous

Explain the process of gene knockout

• Use embryo

• Delete one copy of the target gene

• Grow cells into adult

• Get two of the grown adults with the missing gene

• Breed the two grown adults

  • B₀ xB₀ → BB, B₀, B_o, none

  • By checking what the offspring is missing, you can check what the gene was expressed for.

Explain how embryos are made

Egg cell + sperm cell

egg cell fertilized

egg cell mitosis

Explain why gene knockout uses embryos

ADD LATER, RESEARCH

Define highly conserved sequences

• base sequences that are identical over long periods of time and across a wider range of species

Examples of highly conserved sequences

• tRNA

• rRNA

  (Function is same for all species, rarely mutate)

Hypothesis for highly conserved sequence examples

RESEARCH MORE, ADD MORE

Define Cas 9

protein that cuts sequence

Define CRISPR (clustered regularly interspaced short palindromic repeats)

sequence where the nitrogenous bases are palindromic (same sequence whether read backward or forward)

Define CRISPR Cas 9 System

Bacteria’s method that protects itself from virus
ADD MORE, RESERACH MORE

Explain how CRISPR Cas 9 System works

ADD MORE RESEARCH MORE

State the use of the CRISPR Cas 9 system

• method of finding and altering gene (search + replace)

• Eliminating genetic disease