MedBio Unit 6 Essentials

2 causes of mutations

1. Gene

2. Chromosomal

Gene mutations

Changes in DNA sequence of a single gene

Occurs during DNA replication

Errors build up over time, affecting cell function

Mutagens

Environmental agents that can change DNA or increase frequencies of mutations

3 Types of Mutagens

1. Radiation

2. Chemical

3. Infectious agents

Mutations caused by radiation cause ___

cancer

this type of mutation is not passed on to offspring

Mutations caused by infectious agents can also result in ___

cancer

2 types of gene mutations

1. Point Mutations

2. Frameshift Mutations

3 Types of Point Mutations

1. Silent mutations

2. Missense mutations

3. Nonsense mutations

Silent mutations

A mutation that changes the codon but does not affect the amino acid sequence

Missense mutations

a mutation that changes the codon and produces a new amino acid

Nonsense mutations

a mutation that results in a stop codon

Frameshift Mutations

Throws off the reading frame which results in different amino acids that are produced

Types of Frameshift Mutations

1. Insertion

2. Deletion

3. Trinucleotide Repeat Expansions

Frameshift mutation (insertion)

When one or more nucleotides (bases) are added into the codon

Frameshift mutation (deletion)

When one or more bases are deleted from the DNA sequence

Trinucleotide Repeat Expansions

during DNA replication, DNA polymerase may make duplicate copies of DNA sequence that are repeated

when cells divide and DNA is replicated, the expansion continues

Chromosomal Mutations

Changes in chromosome segments or the whole chromosome

mutations are passed down to offspring

Crossing Over can result in. . .

One chromosome getting more genetic material and the other less

4 types of Chromosomal Mutations

1. Gene Deletion/Gene Duplication

2. Genome Duplication

3. Gene Translocation

4. Nondisjunction Mutations

Gene Duplication or Gene Deletion

prophase 1 of meiosis 1, crossing over may result in unequal exchange of gene segments

one chromosome having 3 copies of a gene is gene duplication

one chromosome missing a copy of a gene is gene deletion

Gene Duplication

Occurs during Anaphase of mitosis, one cell gets both sister chromatids

scientists use chemicals to induce “polyploidy” in plants to control crop production

Gene Translocation

A segment of one chromosome moves to a nonhomologous chromosome

balance translocation: when the exchange is reciprocated and there is no gain/loss in genetic material

Nondisjunction Mutations

When one or more homologous chromosomes do not separate during Anaphase 1 of Meiosis 1

example: Trisomy 21 (3 copies of chromosome 21)

Good Mutations

mutations that enhance the organism’s survival

leads to successful mutations

Mutations that occur in germ cells are. . .

passed on

Mutations that occur within somatic cells are. . .

not passed on

Promoter

a site at the beginning of a DNA that initiates description

Enhancer

short segment of DNA that makes transcription go faster

TATA Box

DNA sequence that indicates where genetic sequence is read and decoded

Located within the promoter site

RNA Polymerase

enzyme that is responsible for copying DNA into RNA during transcription

Ultimate source of genetic diversity occurs in . . .

sexual reproduction

Genetic diversity is essential for. . .

natural selection

phenotypes that allow the organism to survive and reproduce will be selected for

phenotypes that do not are “selected against”

Gene pool

Collection of alleles found in all the individuals of a population

Different alleles in a gene pool ultimately result from ___

mutations

Genetic variation is the result of . . .

crossing over and recombination

chromosomes condense and homologous chromosomes align

Allele frequency

proportion of one allele, compared with all the alleles for that trait, in the gene pool

used to track genetic variation and detect changes in alleles

Hardy-Weinberg Equation

p²+2pq+q²=1