Topic 3.1 GenesIB Biology

R. Price

v. 1 2015

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#1: A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic

Genes• Made of DNA• Influences specific characteristic

(height, eye color, blood type)• Can be passed on to offspring

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#2: A gene occupies a specific position on one type of chromosome

Chromosomes• Genes are linked in groups• Each group is a type of

chromosome• Most plants & animals have two

copies of each chromosome• Locus = specific place on the

chromosome where a specific gene is located

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#3: The various specific forms of a gene are alleles

Alleles• Alternative forms of the same

gene• Cause for wide variation in

characteristics such as eye color, hair color, fur color, blood type• Only one allele per chromosome• Have a pair of each type of

chromosome, so may have two different alleles

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#4: Alleles differ from each other by one or a few bases only

• Genes can be hundreds or thousands of bases long• Alleles are different by only one

or a few bases• Positions in a gene where more

than one base may be present are called single nucleotide polymorphisms (SNPs)

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#5: New alleles are formed by mutation

Base Substitution• One base in sequence of a

gene is replaced by a different base• Most mutations are neutral

or harmful• Body cell mutation gone

when individual dies• Sperm or egg mutation may

be passed onto offspring

#6: The genome is the whole of the genetic information of an organism

Entire base sequence of each of the DNA molecules• In animals• DNA in chromosomes• DNA in mitochondria

• In plants • DNA in chromosomes,

mitochondria, & chloroplasts

• In prokaryotes• DNA in circular chromosome +

plastids

#7: The entire base sequence of human genes was sequenced in the Human Genome Project

Human Genome Project• 1990-2003• One set of chromosomes• Not total understanding of

genetics, but great data• Using this data

• can predict which base sequences are protein coding genes

• Found satellite DNA• “junk” DNA affects gene expression

First printout of Human Genome Project

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Sources

Content Allott, Andrew, and David Mindorff. Biology: Course Companion. 2014 ed. Oxford: Oxford UP, 2014. Print. Oxford IB Diploma Programme.

Walpole, Brenda. Biology for the IB Diploma. 2nd ed. Cambridge: Cambridge UP, 2014. Print.

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