Intro to GENETICS GENETICS : The field of biology devoted to understanding how traits are transferred (inherited) from parent to offspring Gregor MENDEL ( ) - Austrian monk - Left his monastery to study science and mathematics at the University of Vienna Upon return to the monastery, Mendel taught high school and experimented with pea plants in his garden “The Father of Genetics”

Mendel’s Observations Trait - a possible appearance of a characteristic in an organism Mendel observed 7 characteristics in his pea plants, each with 2 distinct traits Mendel saw that “Tall” seeds produced “Tall” plants, but also some “Short” plants He also saw that “Purple-flowered” seeds produced “Purple-flowered” plants, but also some “White-flowered” plants

Mendel’s Experiments Mendel could control the pollination (sexual reproduction) of his plants Mendel began with PURE plants (offspring always showed same trait as parent) Cross of Pea Color P (Pure Parents) Cross : Yellow X Green F 1 (Filial) Generation : All Yellow F 2 Generation : Yellow and Green (3:1 ratio) In re-doing this experiment, he obtained the same results for each characteristic !

Mendel’s Conclusions Some “FACTOR” within the plant must be controlling each trait DOMINANT/RECESSIVE TRAITS Factors exist in pairs, and one factor may dominate/mask/hide the other LAW OF SEGREGATION Paired factors segregate (separate) during the formation of gametes QUESTION: What process does this refer to? LAW OF INDEPENDENT ASSORTMENT Factors for different characteristics are distributed to gametes independently

Molecular Genetics Mendel’s findings weren’t appreciated until much later, when new technology revealed the existence of CHROMOSOMES and GENES GENE : a segment on a strand of DNA that controls a particular hereditary trait ALLELE : each of several alternative forms of a gene (these are Mendel’s “factors”)

Genetic Crosses Dominant Allele = capital letter Recessive Allele = lower-case letter Example : Yellow seeds are dominant to green seeds Y = yellow (dominant) y = green (recessive) Genotype: the pair of alleles that an individual possesses YY Yy yy Phenotype: the appearance of a trait as a result of its genotype Genetic Makeup of an Individual Homozygous – both alleles in a pair are alike (YY or yy) Heterozygous – the alleles in a pair are different (Yy) … will show a dominant phenotype

Intro to: Genetic Disorders GENETIC DISORDERS : Diseases or debilitating conditions that have a genetic basis * They are in-born (inherited) * EXAMPLES: - Huntington’s disease - Hemophilia - Duchenne muscular dystrophy - Down syndrome A person with a family history of genetic disorders may wish to undergo genetic screening before becoming a parent

Detecting Human Genetic Disorders AMNIOCENTESIS is a technique used to analyze the genome of a fetus before birth KARYOTYPING BLOOD TESTING can yield some information Couples at risk may wish to undergo… GENETIC COUNSELING The job of a genetic counselor is to: –Administer and analyze genetic tests –Determine risk of inheritance of a disorder –Advise the involved parties of potential consequences and their options

Test-Cross FACT: We don’t always know the genotype of a particular individual (even if we know its phenotype) TESTCROSS: A breeding test in which an individual of unknown genotype is crossed with a homozygous recessive individual

Incomplete Dominance When two or more alleles influence the phenotype of an individual The phenotype of a heterozygous individual is an intermediate (in-between) the dominant and recessive phenotypes Codominance: fully When both alleles are fully expressed in a heterozygote (neither is recessive)

Sex-Linked Traits REMEMBER: humans have 22 pairs of autosomes and 1 pair of sex chromosomes XX = female XY = male SEX-LINKED TRAIT: a trait for which the allele is carried on a sex chromosome In this way, the phenotype of the individual may vary with the sex Examples: Hemophilia Duchenne muscular dystrophy Colorblindness

Pedigree Chart