GENETICSI. GREGOR MENDEL (1822-1884) General Monk Worked with pea plants Self-fertilization Simple traits Used Statistics Looked at 1 trait at a time
A. Experiment – example Parents purple flower x white flower F1 100% purple F2 75% purple 25% whiteWHAT HAPPENED?
II. MENDELIAN GENETICSA. . DEFINITIONSGene – a segment of DNA that codes for a specific trait. It is found at a specific locus (location) on a chromosome
Chromosome – A condensed structure made of one or two DNA molecules with genes. 2 chromatids 1 chromatidAllele – A form of a gene. T or t
Dominant – Allele that T is expressed when present.Recessive – Allele t expressed when the dominant is not present.
Co-dominant – Alleles for ABO Blood the same gene that both express themselves when present.Incomplete dominance – RR Rr rr The heterozygous Red Pink White genotype results in a phenotype between the two homozygous genotypes.
Genotype – The alleles TT Tt tt an organism/cell has.Phenotype – The Tall Tall Short physical expression of a gene.
Homozygous – The TT or tt homologous pair has the same alleles for the same gene.Heterozygous – The Tt homologous pair has different alleles for the same gene.
DiagramGene – Coat ColorChromosomeAlleleDominantRecessiveGenotype BbPhenotype black
B. Monohybrid Cross – Look at one gene at a time 1. Principle of Segregation Every individual (diploid) has 2 copies (alleles) of a gene (one from the female and one from the male) for every trait. In the production of gametes (by Meiosis) these alleles are separated randomly and come back together in the formation of a zygote (fertilization).
2. Example – Coat Color in Labrador B = black (dominant) b = brown (recessive) Phenotype: Black Black Brown Parent Genotype: BB Bb bb Parent gametes: B B B b b b
Example of the cross Male Female Bb Bbgametes B b B b B b GenotypePunnett B BB Bb 1BB:2Bb:1bbsquare Phenotype b Bb bb 3black:1brown
C. DIHYBRID CROSS – When look at two genes at a time. Linked genes are when genes are on the same chromosome. Example
1. PRINCIPLE OF INDEPENDENT ASSORTMENTGenes on different chromosomes (so are not linked)randomly assort into gametes during Meiosis and have anequal chance for any combination.Meiosis I or Meiosis I
2. Example Gene Alleles ear lobes E=free e=attached freckles F=have f=noneParent Genotypes EeFf EeFfGametes EF Ef eF ef EF Ef eF efEACH GAMETE MUST CONTAIN ONE COPY OF EACH GENE (inthis case each must have an E/e and a F/f)
Free earlobes, freckles EF Ef eF efFree earlobe, none EEFF EEFf EeFF EeFf EFAttached, frecklesAttached, none EEFf EEff EeFf Eeff Ef EeFF EeFf eeFF eeFf eF EeFf Eeff eeFf eeff ef
SEX-LINKED• Gene is on the X chromosome (usually).Male XY Ex. Recessive trait - XHY or X hYFemale XX Ex. Recessive trait – XHXH or XHXh or X hX h
Co-dominantWhen more than one allele for any given gene areboth dominant and express themselves if present.Example:ABO Blood Phenotype Genotype A blood IAIA or IAi B blood IBIB or IBi AB blood IAIB O blood ii
ABO are sugar antigens on the surface ofthe red blood cells (rbc)Rh factors are proteins on the surface of rbc.
Incomplete dominanceThe heterozygote has a phenotype betweenthe two homozygous genotypesGENOTYPES RR RR’ R’R’PHENOTYPES red pink white
III. PedigreeA tool used to track a genetic history. Usedfor a family for some specific trait. without trait with traitFemaleMale mated offspring
GENETIC PROBLEMSMONOHYBRIDIn silkworms yellow cocoon is dominant to white cocoon.Two silkworms are mated (one heterozygous and theother homozygous recessive).Find the: parent genotype and phenotype gametes produced Punnett Square Offspring genotype Offspring phenotype
Albinism is inherited as a recessive trait.a. A heterozygous female has children by a homozygous normal male. What % of their offspring will be carriers for albinism?b. A normally pigmented man whose mother was albino marries a homozygous normal woman. What % of their offspring will be homozygous normal?c. A heterozygous male marries an albino female. What percentage of their offspring will be albino?
DIHYBRIDIn hogs, a gene that produces a white belt around theanimal’s body is dominant over its allele for a uniformlycolored body. Another independent gene produces fusionof the two hooves on each foot (an instance of syndactyly).It is dominant over its allele, which produces normalhooves.Supposed a uniformly colored male hoghomozygous for syndactyly is mated with anormal-footed female hog homozygous for thebelted character.
CO-DOMINANCEIn cattle, red is not dominant to white. When thetwo colors are crossed, the claves have both redand white hairs, called roan.A rancher mates a red bull and white cow.Show Punnett Square and label phenotypes.
INCOMPLETE DOMINANCEIn four o’ clock flowers there are red, white and pink petal colors. Pink petals is a heterozygous condition resulting from a cross of red and white.Cross two pink plants
BLOOD TYPE AND SEX-LINKEDA normal visioned female has type A blood.Her father was colorblind with type O bloodand her mother had AB blood. She marriesa man who is colorblind and has type Bblood (whose mother had normal vision andO blood and whose father had normal visionand B blood).
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