DP Bio Topic 3-2 Chromosomes
Transcript of DP Bio Topic 3-2 Chromosomes
#1: Prokaryotes have one chromosome consisting of a circular DNA molecule
• One chromosome• Circular DNA• Not associated w/ proteins, so
“naked”
Allott 150
#2: Some prokaryotes also have plasmids but eukaryotes do not
• Extra DNA not in the chromosome• May/may not replicate when
chromosome’s replicated• May/may not be passed on during cell
replication• Can be transferred to other cells• Can be transferred to other species• Natural method of gene transfer
between species• Researchers use to transfer genes
artificiallyAllott 150
#3: Eukaryote chromosomes are linear DNA molecules associated with histone proteins
Chromosomes in eukaryotes• DNA + histone protein• Histones = globular proteins• Many histones in a chromosome• DNA wind around histone
#4: In a eukaryote species there are different chromosomes that carry different genes
In eukaryotes:• At least two different types of
chromosomes• In humans -> 23 types of
chromosomes• Genes are found on a specific
position on a specific type of chromosome (locus)• Each chromosome carries specific
sequence of genes along linear DNA molecule
#5: Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes
• Two chromosomes carry same sequence of genes = homologous genes• Same sequence, but not
identical -> alleles
#6: Haploid nuclei have one chromosome of each pair
• Haploid nuclei have one full set of chromosomes• Has only one
chromosome of each type• Some plant life cycles
have a haploid phase (ferns)• Gametes (sex cells) are
haploid
#7: Diploid nuclei have pairs of homologous chromosomes
• Diploid nuclei have two full sets of chromosomes• Has two chromosomes of each
type• Except for sex chromosomes,
has two copies of each gene• Advantage: dominant allele may
protect from a damaging allele• Advantage: hybrid vigor
#8: The number of chromosomes is a characteristic feature of members of a species
• Fundamental characteristic• Organisms with different
number of chromosomes are unlikely to interbreed• # can change, but rare. Can
occur during evolution of species• Decrease if chromosome fuse• Increase if chromosomes split
#9: A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length
• Cell in metaphase gives clearest view of chromosomes• Chromosomes treated with a stain• Micrograph taken of chromosomes• Computer used to sort chromosomes• Chromosomes sorted by size,
position of centromere, and banding after staining• Usually in homologous pairs• Arranged longest to smallest
#10: Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex
Humans (rules may change for other species)• X chromosome large, centromere
near middle• Y chromosome smaller, centromere
near end• One Y chromosome (SRY or TDF)
starts development of male features• XX = female• XY = male
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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