Gene Genetic material Instructions or code for a particular trait or characteristic http://www.accessexcellence.org/AB/GG/genes.html

Allele One of the possible options for a given characteristic or trait Pea Plant Examples: flower color is purple or white height is tall or short Flowers are terminal or axial

Homologous pair Two chromosomes that contain genes for the same traits at the same locations One comes from mom, the other from dad Humans have 22 pairs of homologous and 1 pair of non-homologous chromosomes

Probability Chance that a given event will take place Multiplication rule = to calculate the odds of two or more events occurring at the same time, multiply the probabilities for each independent event

Dominant An allele that can mask or hide the expression of another allele for the same trait Is represented by a capital (big) letter

http://www.accessexcellence.org/AB/GG/recessive.html

Recessive An allele that is masked or hidden when present with another allele for the same trait Is only expressed when two are inherited Is represented by a lower case (little) letter

http://www.accessexcellence.org/AB/GG/recessive.html

Homozygous When the two alleles inherited are the same Homozygous dominant Both are dominant alleles TT = tall tall = a tall plant Homozygous recessive Both are recessive alleles tt = short short = a short plant

Heterozygous When the two alleles inherited are different Only the dominant allele is expressed or visible Tt = tall short = a tall plant

Phenotype The actual expression of the genes What you see

Genotype The actual alleles present What genes they inherited for that trait

Law of Segregation Each pair of alleles separate during the formation of the gamete (egg or sperm) Example: If parent is Tt, the offspring will get either the T or the t- not both Tt T t

Law of Independent Assortment Each pair of alleles separate independent from other pairs of alleles during the formation of the gamete Which chromosome goes into a gamete is random TtPp TP or Tp or tP or tp

Gregor Mendel 19th century Austrian monk Experimented in breeding pea plants The father of genetics Developed terminology used Stated laws

http://www.accessexcellence.org/AB/GG/mendel.html

Types of Crosses Individuals Purebred = have only one allele for a trait TT, tt, PP,pp Hybrid = have different alleles for a trait Tt or Pp Crosses Monohybrid = differ for one trait, TT x tt Dihybrid = differ for two traits, TTpp x ttPP

Punnett Squares An easy (non-mathematical) way to calculate the probability of the traits for the offspring of two specific individuals

Terminology for Crosses P1 = parent generation F1 = first generation of children F2 = second generation of children F stands for filial, or sons and daughters

Monohybrid A cross between two individuals Examines only one trait Parents have contrasting traits P1 = Pp x Pp F1 = 3:1 phenotypic ratio = 1:2:1 genotypic ratio

Test Cross A cross used to determine what genes a parent has Gametes P ? p Pp ?p Test Cross A cross used to determine what genes a parent has The unknown individual (PP or Pp) is mated with an individual that is homozygous recessive (pp) Children show the second unknown gene

Dihybrid Cross A cross between two individuals Examines only two traits at the same time Parents have contrasting traits P1 = SSYY x ssyy F1 = SsYy x SsYy F2 = 9:3:3:1 phenotypic ratio

Incomplete Dominance Alleles are not dominant or recessive Both alleles are expressed, or blended Capital letters are used for both alleles, or the same letter with a prime or subscript is used H and H1 Examples: R = red H = straight hair r = white H1 = curly hair Rr = pink HH1 = wavy hair

Codominance Both alleles are completely expressed Neither hides the other Example: Blood Type M and N proteins LM LM produces protein M LN LN produces protein N LM LN produces both protein M and N

Multiple Alleles Three or more alleles for a given trait exist Example: A,B,AB and O blood types result from which 2 of 3 genes you inherit Type A blood results from IAIA or IAi Type B blood results from IBIB or IBi Type AB blood results from IAIB Type O blood results from ii

Pleiotropy One gene influences more than 1 trait Example in peas: One gene determines whether seeds are round or wrinkled Same gene affects starch metabolism and water absorption

http://fig.cox.miami.edu/~cmallery/150/gene/14x15sickle.jpg

Polygenic Inheritance Results from the interaction of many genes to determine a single phenotype- in other words, many genes work to produce appearance of one trait Not just 2 or 3 varieties, but a continuous variation or range of phenotypes The opposite of pleiotropy

http://sun. menloschool http://sun.menloschool.org/~dspence/biology/chapter12/images/eye_color.jpg

http://fig.cox.miami.edu/~cmallery/150/mendel/polygenic.jpg

http://www. specialedprep http://www.specialedprep.net/MSAT%20SCIENCE/Images/PleiotropyPolygenic.jpg

Linked Genes Are on the same chromosome Are inherited together because they come as a package

Sex-linked Sex chromosomes the last pair, X & Y Autosomes pairs 1-22

http://www.accessexcellence.org/AB/GG/sex.html

Sex-linked Examples of human disorders that are sex-linked are: Hemophilia Red-green color blindness Duchennes’s muscular dystrophy These disorders occur more frequently in men than women, because men only inherit 1 gene for the trait, while women inherit 2

Recessive Autosomal Disorders Phenylketonuria = unable to break down phenylalanine, results in mental retardation Sickle-cell anemia = abnormal hemoglobin, unable to transport oxygen Tay-Sachs disease = unable to break down some lipids, causing nerve damage and ultimately death

Dominant Autosomal Disorders Huntington’s disease = mental illness begins in middle age, affecting brain and motor control and leading to total mental and physical incapacity

Fraternal Twins Fraternal twins are the result when two different eggs (ova) are fertilized by two different sperm. This leads to the development of two separate placentas, each with its own chorion and amnion. Fraternal twins are more common than identical twins and account for about 2/3 of twin pregnancies.

Identical Twins Identical twins develop when a fertilized egg splits. Depending on when the split occurs will determine if the twins share a placenta, with either one or two chorions and amnions, or if they each develop their own placentas. In general, the later the spit occurs, the more likely that the twins will share one placenta.

Fraternal vs. Identical Twinning Even after they are born, it is sometimes difficult to know whether twins are identical or fraternal. It can be easier if they: share one placenta (identical) are different sexes (fraternal) have different blood types (fraternal)