the work of gregor mendel. question have you ever wondered why everyone in your family is tall, but...
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The Work of Gregor MendelThe Work of Gregor Mendel
QuestionQuestion
Have you ever wondered why Have you ever wondered why everyone in your family is tall, but everyone in your family is tall, but you are short? you are short?
Have you ever wondered why Have you ever wondered why brothers and sisters can look brothers and sisters can look different, or look so much alike?different, or look so much alike?
MendelMendel Called the “Father of Genetics”Called the “Father of Genetics” Studied patterns of heredity of pea Studied patterns of heredity of pea
plants.plants. Genetics – the study of heredityGenetics – the study of heredity
Three Conclusions to His Three Conclusions to His ResearchResearch
Principle of Dominance and RecessivenessPrinciple of Dominance and RecessivenessOne allele in a pair may mask the effect of the otherOne allele in a pair may mask the effect of the other
Principle of SegregationPrinciple of SegregationThe two alleles for a characteristic separate during the The two alleles for a characteristic separate during the
formation of eggs and spermformation of eggs and sperm
Principle of Independent AssortmentPrinciple of Independent AssortmentThe alleles for different characteristics are distributed to The alleles for different characteristics are distributed to
reproductive cells independently.reproductive cells independently.
Mendelian geneticsMendelian genetics
Character Character (heritable feature, i.e., fur color)(heritable feature, i.e., fur color)
Trait Trait (variant (variant for a character, i.e., brown)for a character, i.e., brown)
True-bred True-bred (all offspring of same variety) (all offspring of same variety)
Hybridization Hybridization
(crossing of 2 different true-(crossing of 2 different true-breds)breds)
P generationP generation (parents) (parents) FF11 generation generation (first filial (first filial
generation)generation)
Genetic vocabulary…….Genetic vocabulary…….
Punnett square:Punnett square: Gene:Gene: point on a point on a
chromosome that controls the chromosome that controls the traittrait
AlleleAllele: an alternate form of a : an alternate form of a gene gene A or aA or a
Homozygous:Homozygous: identical identical alleles for a characteralleles for a character
Heterozygous:Heterozygous: different different alleles for a genealleles for a gene
Phenotype:Phenotype: physical traits physical traits Genotype:Genotype: genetic makeup genetic makeup Testcross:Testcross: breeding of a breeding of a
recessive homozygote X recessive homozygote X dominate phenotype (but dominate phenotype (but unknown genotype)unknown genotype)
How can the Chances of an Offspring’s How can the Chances of an Offspring’s Traits be Determined?Traits be Determined?
BY USING A BY USING A PUNNETT SQUAREPUNNETT SQUARE Get out your Punnett Squares Get out your Punnett Squares
ProblemsProblems
BbBb X X BbBbPhenotypic RatioPhenotypic Ratio
3:13:1Genotypic RatioGenotypic Ratio
1:2:11:2:1
B b
B
b
B B B b
b B b b
What about two traits?What about two traits? Complete the second half of your Complete the second half of your
Punnett Square ProblemsPunnett Square Problems
Dihybrid CrossDihybrid Cross
BbTtBbTt x x BbTtBbTt
BTBT BtBt bTbT btbt
BTBT BBBBTTTT BBTtBBTt BbTTBbTT BbTtBbTt
BtBt BBTtBBTt BBttBBtt BbTtBbTt BbttBbtt
bTbT BbTTBbTT BbTtBbTt bbbbTTTT bbTtbbTt
btbt BbTtBbTt BbttBbtt bbTtbbTt bbttbbtt
Exceptions to Mendel’s Exceptions to Mendel’s RuleRule
Incomplete DominanceIncomplete Dominance
The phenotype of The phenotype of the heterozygote the heterozygote is intermediate is intermediate between those of between those of the two the two homozygotes.homozygotes.
Ex) Snap Dragon Ex) Snap Dragon ColorColor
Red, Pink, WhiteRed, Pink, White
Co-dominanceCo-dominance
Phenotype of both Phenotype of both homozygotes are homozygotes are produced in produced in heterozygotes heterozygotes individuals.individuals.
Both alleles are Both alleles are expressed equally.expressed equally.
Ex)Roan Cattle Ex)Roan Cattle White-feathered White-feathered birds are both birds are both homozygotes for homozygotes for both B and W both B and W allelesalleles
Multiple AllelesMultiple Alleles
Ex )Blood typeEx )Blood type Blood type A and B are Blood type A and B are co-co-
dominantdominant, while O is , while O is recessiverecessive.. Forms possible blood types of A, B, Forms possible blood types of A, B,
AB, and O.AB, and O.
Blood Also Shows Blood Also Shows CodominanceCodominance
Sex-DeterminationSex-Determination
Chromosome pairs 1-22 are Chromosome pairs 1-22 are autosomesautosomes
Chromosome pair 23 are Chromosome pair 23 are sex sex chromosomeschromosomes
They determine the sex of an They determine the sex of an individualindividual
XX = femaleXX = female XY = maleXY = male
Sex-Linked InheritanceSex-Linked Inheritance
Traits that are only found on the X Traits that are only found on the X chromosomechromosome
Colorblindness and Hemophilia are Colorblindness and Hemophilia are examples of sex-linked traits. examples of sex-linked traits.
These genes are recessive and found These genes are recessive and found only on the X chromosome.only on the X chromosome.
Polygenic InheritancePolygenic Inheritance Inheritance pattern of a Inheritance pattern of a
trait that is controlled trait that is controlled by by two or more two or more genes.genes.
Gene may be on the Gene may be on the same chromosome or same chromosome or on different on different chromosomes.chromosomes.
Ex) Skin color and Ex) Skin color and HeightHeight
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