Unit 7 Genetics

Gregor Mendel Genetics – the study of how characteristics are transmitted from parents to offspring.Genetics – the study of how characteristics are transmitted from parents to offspring. Gregor Mendel was an Austrian monkGregor Mendel was an Austrian monk –Chore: Gardening –Observed plants and then started experimenting with them

He observed 7 characteristics Plant height – short vs. long stemPlant height – short vs. long stem Flower position – Axial vs. terminalFlower position – Axial vs. terminal Pod color – (green vs. yellow)Pod color – (green vs. yellow) Pod appearance (inflated vs. constricted)Pod appearance (inflated vs. constricted) Seed texture (smooth vs. wrinkled)Seed texture (smooth vs. wrinkled) Seed color (yellow vs. green)Seed color (yellow vs. green) Flower color (purple vs. white)Flower color (purple vs. white) These 7 characteristics are called traits. Traits are genetically determined variants of a characteristic. Each Characteristic occurs in two contrasting traits

Mendel and Cross Pollination Mendel used cross-pollination in order to study his plantsMendel used cross-pollination in order to study his plants –Cross pollination – pollination in which pollen is transferred between flowers of two different plants –Plants were bred for several generations that were true-breeding for specific traits (like pure bred dogs) and called those the “P generation)

Offspring of the P generation were called F1Offspring of the P generation were called F1 Offspring of the F1 generation were called F2.Offspring of the F1 generation were called F2.

Recessive vs. Dominant Traits Mendel concluded that inherited characteristics are controlled by factors that occur in pairsMendel concluded that inherited characteristics are controlled by factors that occur in pairs He found that on factor in the pair masked the other.He found that on factor in the pair masked the other. –Dominant – the trait that could be observed –Recessive – the trait that was masked

Laws Law of segregationLaw of segregation –A pair of factors is segregated, or separated, during the formation of gametes. Law of Independent AssortmentLaw of Independent Assortment –Factors for individual characteristics are distributed to gametes independent of one another –This only happens for genes that are located on separate chromosomes or are far apart on the same chromosome

Mendel and his traits We no know that the factors (yellow vs. green pea color, for example) that Mendel studied are called allelesWe no know that the factors (yellow vs. green pea color, for example) that Mendel studied are called alleles –Alleles are alternative forms of the same gene –One allele for each trait is passed from each parent to the offspring

Genotype vs. phenotype GenotypeGenotype –Genetic makeup of an organism (think: genes) –It will be symbolized by a pair of letters TT, Tt, tt …TT, Tt, tt … PhenotypePhenotype –The physical appearance of the organism –Which trait it has Tall vs. shortTall vs. short

Probability The likelihood that a specific event will occur.The likelihood that a specific event will occur. A probability may be expressed as a decimal, percentage, or fraction.A probability may be expressed as a decimal, percentage, or fraction. Probability = # times and event is expected to happenProbability = # times and event is expected to happen # of opportunities for an event to happen

Punnett squares are used to predict the outcome of genetic crossesPunnett squares are used to predict the outcome of genetic crosses –monohybrid cross - cross in which one characteristic is tracked –Test cross – an individual of unknown genotype X homozygous recessive individual It is used to determine the genotype of the unknown individualIt is used to determine the genotype of the unknown individual Examples of genotypes that you will find in a Punnett’s squareExamples of genotypes that you will find in a Punnett’s square –Pure breeding –Hybrid –Heterozygous –homozygous

Types of dominance Complete dominanceComplete dominance –When a heterozygous individuals and dominant homozygous individuals are indistinguishable in phenotype Ex. Gg (heterozygous genotype) = black (phenotype)Ex. Gg (heterozygous genotype) = black (phenotype) GG (dominant homozygous genotype) = black (phenotype)

Incomplete dominanceIncomplete dominance –Two or more alleles influence the phenotype and results in a phenotype intermediate (between) the dominant and the recessive trait Ex. When red four o’clock flowers are crossed with white four o’clock flowers, the offspring produced are pink four o’clock flowersEx. When red four o’clock flowers are crossed with white four o’clock flowers, the offspring produced are pink four o’clock flowers CodominanceCodominance –When both alleles are for a gene are expressed in heterozygous offspring Ex. Blood typingEx. Blood typing

Inheritance Polygenic inheritancePolygenic inheritance –When a characteristic, such as eye color, is controlled by two or more genes Complex characteristicsComplex characteristics –Polygenic traits that are influenced by both genes and the environment Marking of a siamese catMarking of a siamese cat Multiple allelesMultiple alleles –Characteristics, such as ABO blood groups, that are controlled by three or more alleles (forms) of a single gene

Genes and sex Genes reside on chromosomesGenes reside on chromosomes Sex chromosomes vs. autosomeSex chromosomes vs. autosome –Sex chromosomes contain genes that determine an organism’s gender (2 of them). –The rest of the chromosomes that are not involved in determining the sex of an individual are autosomes (44 of them). Sex determinationSex determination –XX female –XY male

Genes and linkage Linked genesLinked genes –Pairs of genes that tend to be inherited together Chromosome mappingChromosome mapping –The farther apart two genes are located in chromosome, the more likely a cross-over will occur –Researchers use recombinant percentages to construct chromosome maps that show relative gene positions

Sex-Linked Genes Sex linkedSex linked –Genes found on the X chromosome are “X-linked genes”. –A sex-linked trait is a trait whose allele is located on the sex chromosome. –Males have only 1 X chromosome. So, a male who carries a recessive allele on the x chromosome will exhibit the sex linked trait. Ex. colorblindnessEx. colorblindness

Sex-Influenced Trait A trait that is expressed differently in men than in women, even if the gene is on an autosome and both sexes have the same genotypeA trait that is expressed differently in men than in women, even if the gene is on an autosome and both sexes have the same genotype –Ex. Male pattern baldness

Pedigree A diagram the reveals inheritance patterns of genesA diagram the reveals inheritance patterns of genes Geneticists use pedigrees to trace diseases or traits through familiesGeneticists use pedigrees to trace diseases or traits through families

Hemophilia – Offspring of Dueen Victoria

Genetic screening and counseling Genetic screening examines a person’s genetic makeup and potential risks of passing disorders to their offspringGenetic screening examines a person’s genetic makeup and potential risks of passing disorders to their offspring Genetic counseling informs the screened individuals about problems that might affect their childrenGenetic counseling informs the screened individuals about problems that might affect their children