Unit 3
Module 2:Heredity:Inheritance and Variation *DNA is a double helix molecule composed of complementary strands of deoxyribonucleotides units.The complementary base pairs of the DNA are held by hydrogen bonds. *RNA is a single stranded,examples are mRNA,rRNA,tRNA. *In DNA,adenine always bonds with thymine,and cytosine bonds with guanine. *In RNA,adenine bonds with uracil,and cytosine bonds with guanine.
Replication James Watson and Francis Crick wor!ed out that DNA is double helix li!e a twisted staircase in "#$%.The structure of the DNA pro&ides a mechanism for ma!ing accurate copies of the molecule.'hen DNA replicates,( identical copies of DNA molecules are produced,which are exactly the same as the original.
3 types o R!" that help #uild proteins$ *mRNA brings information from the DNA in the nucleus to the protein manufacturing area,the cytoplasm,in that the mRNA becomes the template of information to ma!e proteins. *Ribosomes,rRNA and ribosomal proteins hold tightly into the mRNA using its information to assemble the amino acids in the correct order. *Transfer RNA,tRNA supplies amino acids to the ribosome to be assembled as protein. %ranslation DNA directs the production of proteins and determines the formation of mRNA. )roteins control the acti&ities of the cell,as well as so the life of the entire organism. ach set of % nucleotides in an mRNA molecule codes for one amino acid in a protein.This is why each set of % nucleotides in the mRNA is called a codon.ach codon speci+es a particular amino acid.
MU%"%I&!:Chan'es in the (enetic Code$ Is a change in the base seuence of DNA.It may a-ect only one gene,or they may a-ect whole chromosomes. utation in eggs or sperm may a-ect future generations by transmitting these changes in the o-spring.utations in nonsex /somatic0cells only are not hereditary. *1ene mutation is a permanent change in the DNA seuence that ma!es up a gene. *2hromosomal mutation occurs at the chromosome le&el resulting in gene deletion,duplication or rearrangement that may occur during the cell cycle and meiosis.It maybe caused by parts of chromosomes brea!ing o- or re3oining incorrectly. 2hanges in the seuences of bases in normal hemoglobin and the one a-ected by mutation.A recessi&e gene causes sic!lecell anemia,where most of the red blood cells sti-en and become sic!le shape in a-ected people.Theses diseased cells carry less oxygen than normal cells.)eople a-ected by the diseases e&entually die.
Abnormalities in chromosomal structure may occur during meiosis.The normal process of crossingo&er and recombination may be a-ected,such that chromosomes brea! and reunite the wrong segments.If there is a lose or gain of chromosomal material,there can be signi+cant clinical conseuences. 2hanges that a-ect the structure of chromosomes can cause problems with growth,de&elppment,and function of the body4s systems.These changes can a-ect many genes.5tructural changes can occur druing the formation of egg or sperm cells in fetal de&elopment,or in any cell after birth.)ieces of DNA
can be rearranged within one chromosome or transferred between ( or more chromosomes. 2ri du chat caused by the deletion of part of the short arm of chromosome.It is 6rench and the condition is so named because a-ected babies ma!e highpitched cries that sound li!e a cat.A-ected indi&iduals ha&e wideset eyes,a small head and 3aw,are moderately to se&erely mentally retarded,and &ery short.
*Down4s syndromeusually caused by an extra copy of chromosome (" /trisomy ("0.2haracteristics include decreases muscle tone,stoc!ier build ,asymmetrical s!ull,slanting eyes and mild to moderate mental retardation.
*dwards syndromewhich is the second most common trisomy after Down4s syndrome,is a trisomy of chromosome "7.5ymptoms include mental and motor retardation and numerous congenital anomalies causing serious health problems.About ##8 die in infancy.9owe&er those who li&e past their +rst birthday,usually are uite healthy therafter.They ha&e a characteristic hand appearance with clenched hands and o&erlapping +ngers. *:acobsen syndromeis also called terminal "" deletion disorder.This is a &ery rare disorder.Those a-ected ha&e normal intelligence or mild mental retardation,with poor or excessi&e language s!ills.ost ha&e a bleeding disorder called )aris Trousseau syndrome.
*;linefelter4s syndrome/<<=0.en with this condition are usually sterile and tend to ha&e longer arms and legs and to be taller than their peers.They are often shy and uiet and ha&e a higher incidence of speech delay. *Turner4s syndrome/< instead of << or <=0.6emale sexual characteristics are present but underde&eloped.They often ha&e a short stature,low hairline,abnormal eye feature and > ?
Human )aryotypin' @ccasionally,chromosomal material is lost or rearranged during the formation of gametes or during cell di&ision of the early embryo.5uch changes,primarily the result of nondis3unction or translocation,are so se&ere that the pregnancy ends in miscarriagemeaning loss of an embryo or fetus before the (th wee! of pregnancy or fertiliBation does not occur at all.It is estimated that one in "$C births has some !ind of chromosomal abnormality. ;aryotypeis an image of the full set of chromosomes of an indi&idual that displays the normal number,siBe, and shape.This can re&eal the gender of a fetus or test for certain defects through examination of cells from uterine uida procedure called amniocentesisor through sampling of placental membranes.
(enetic *n'ineerin' A modern biotechnology called genetic engineering produces transgenic or 1 crops of organisms.5cientists ha&e de&eloped methods to mo&e genes from one species into another.'hen DNA from ( di-erent species are 3oined
together,it is called recom#inant +!"$ This prrocess uses restriction enBymes to clea&e one organism4s DNA into fragments and other enBymes to splice the DNA fragment into plasmid foreign DNA.Transgenic organisms are able to manufactre genetic products foreign to them using recombinant DNA.
