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1.1 Impacts/IssuesHere Kitty, Kitty, Kitty, Kitty, Kitty
Making clones (exact genetic copies) of adult animals is now a common practice in research and animal husbandry
6.2 Chromosomes
A eukaryotic chromosome is a molecule of DNA together with associated proteins
Chromosome• Structure made of DNA and associated proteins• Carries part or all of a cell’s genetic information
Chromosome Structure
Sister chromatid• One of two attached members of a duplicated
eukaryotic chromosome
Centromere• Constricted region in a eukaryotic chromosome
where sister chromatids are attached
Chromosome Structure
Proteins organize DNA structurally• Allow chromosomes to pack tightly
Histone• Type of protein that structurally organizes
eukaryotic chromosomes
Nucleosome• A length of DNA wound around a spool of histone
proteins
Chromosome Number
A eukaryotic cell’s DNA is divided into a characteristic number of chromosomes
Chromosome number• Sum of all chromosomes in a cell of a given type• A human body cell has 23 pairs of chromosomes
Diploid• Cells having two of each type of chromosome
characteristic of the species (2n)
Types of Chromosomes
There are two types of eukaryotic chromosomes: autosomes and sex chromosomes
Autosomes• Paired chromosomes with the same length,
shape, centromere location, and genes • Any chromosome other than a sex chromosome
Sex chromosomes• Members of a pair of chromosomes that differ
between males and females
Fig. 6-3a, p. 104
diploid reproductive cell in female
diploid reproductive cell in male
X X X Y
eggs sperm
X X X Y
X Y
X
X
XX XY
XX XY
union of sperm and egg at fertilization Stepped Art
Karyotype
Karyotyping reveals characteristics of an individual’s chromosomes
Karyotype• Image of an individual’s complement of
chromosomes arranged by size, length, shape, and centromere location
6.3 Fame and Glory
Erwin Chargaff• Discovered the relationships between DNA bases
Rosalind Franklin• Discovered the basic structure of DNA by x-ray
crystallography
James Watson and Francis Crick• Built the first accurate model of a DNA molecule
The Double Helix
A DNA molecule consists of two strands of nucleotide monomers running in opposite directions and coiled into a double helix
DNA nucleotide• A five-carbon sugar (deoxyribose)• Three phosphate groups• One nitrogen-containing base (adenine, thymine,
guanine, or cytosine)
The Double Helix
Two double-helix strands are held together by hydrogen bonds between nucleotide bases
Chargaff’s rules • Bases of the two DNA strands in a double helix
pair in a consistent way: A = T and C = G• Proportions of A and G vary among species
Patterns of Base Pairing
The order of bases (DNA sequence) varies among species and among individuals• Each species has characteristic DNA sequences
DNA sequence• The order of nucleotide bases in a strand of DNA
6.4 DNA Replication and Repair
A cell replicates its DNA before it divides
Each strand of the double helix serves as a template for synthesis of a new, complementary strand of DNA
DNA replication results in two double-stranded DNA molecules identical to the parent
DNA Replication and Repair
During DNA replication, the double-helix unwinds
DNA polymerase uses each strand as a template to assemble new, complementary strands of DNA from free nucleotides
DNA ligase seals any gaps to form a continuous strand
DNA Replication and Repair
DNA replication• Duplication of a cell’s DNA before cell division
DNA polymerase• DNA replication enzyme; assembles a new strand
of DNA based on sequence of a DNA template
DNA ligase• Enzyme that seals breaks in double-stranded DNA
Fig. 6-8, p. 108
Stepped Art
4) DNA ligase seals any gaps that remain between bases of the “new” DNA, so a continuous strand forms. The base sequence of each half-old, half-new DNA molecule is identical to that of the parent.
3) Each parent strand serves as a template for assembly of a new DNA strand from nucleotides, according to base-pairing rules.
2) As replication starts, the two strands of DNA unwind at many sites along the length of the molecule.
1) The two strands of a DNA molecule are complementary: their nucleotides match up according to base-pairing rules (G to C, T to A).
Checking for Mistakes
DNA repair mechanisms fix damaged DNA• Proofreading by DNA polymerase corrects most
base-pairing errors
DNA repair mechanisms• Any of several processes by which enzymes
repair DNA damage
Mutations
Uncorrected errors in DNA replication may become mutations
Mutation• A permanent change in DNA sequence
6.5 Cloning Adult Animals
Reproductive cloning technologies produce an exact genetic copy of an individual (clone)
Reproductive cloning• Technology that produces genetically identical
individuals
Somatic Cell Nuclear Transfer
Somatic cell nuclear transfer (SCNT)• Method of reproductive cloning in which nuclear
DNA from an adult somatic cell is transferred into an unfertilized, enucleated egg
Therapeutic cloning• Using SCNT to produce human embryos for
research
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