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Lecture 12

Anthropology 2235A/B Lecture Notes - Lecture 12: Null Allele, Product Rule, Population Genetics


Department
Anthropology
Course Code
ANTH 2235A/B
Professor
Eldon Molto
Lecture
12

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Lecture 12 DNA in Forensic Science: Cytogenetics
Cytogenetics
o Cyto = cell
o Cytogenetics refers to the study of genetic mechanisms that
operate within the cell
o In a human cell there are 23 pairs of chromosomes in the nucleus
o In the cytoplasm another hereditary structure exists called the
mitochondrion
o Both chromosomes and the mitochondria are made of DNA
DNA in the nucleus is called nuclear DNA
o Because all the mtDNA is the same often called the 47th
chromosome
Human Nuclear Karotype
o Karotype: number and arrangement of chromosomes
o When a new individual is formed by an egg being fertilized by a
sperm, the new individual (zygote) receives 23 chromosomes from
each parent
o Females have two X chromosomes (receive an X from each parent)
and a male has an X and a Y
o The new individual has 46 chromosomes and eventually has to
transmit his or her DNA to the next generation, the 46 is reduced to
23 by a cell division process called meiosis
o The y- chromosome is smaller and has fewer genes (called exons)
Involved in determining maleness
Medel’s Laws
o 1865: Austrian Cleric Gregor Mendel publishes the 2 key laws of
genetics
o Law 1: Segregation
States that a simple genetic trait is determined by a pair of
separate factors (now called alleles)
One inherited from each parents intact from generation to
generation factors do not blend
o Law 2: Independent Assortment
Deals with the inheritance of two or more traits and states
that each pair of alleles behaves independently of other pairs
Makes it possible to predict the statistical probabilities of
matings
Provides basis for the product rule
o These laws are fundamental to forensic DNA analysis and form the
basis for determining “Random Match Probabilities”
Homozygosity vs. Heterozygosity
o The dominance recessive traits studied by Mendel resulted in the
recessive alleles not showing up in the heterozygous state
Called the null allele
o Loss of an allele is called allelic dropout
Hardy-Weinberg Genetics
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