Chapter 9 Notes 9.1-9.4 Heredity: the transmission of traits from one generation to the next Genetics: study of heredity Gregor Mendel- Found genetics via pea plants He found parents pass discrete genes to offspring He used pea plants to study genetics because they have short gen times, large offspring, many varieties, easily controlled Character: heritiable feature that varies among individuals Ex: flower color Trait: each variant for a character true-breeding an organism that always passes down certain phenotypic traits to its offspring of many generations. Hybrids Offspring of crosses between parents with different traits cross mating of 2 organisms P generation Parental generation, the first two individuals that mate in a genetic cross F1 generation the first generation of offspring obtained from an experimental cross of two organisms F2 generation offspring of the F1 generation Alleles Different forms of a gene Homozygous An organism that has two identical alleles for a trait Heterozygous An organism that has two different alleles for a trait dominant allele An allele whose trait always shows up in the organism when the allele is present. recessive allele An allele that is masked when a dominant allele is present Genotype The genetic makeup of an organism Dominant alleles are assigned uppercase letters while recessive alleles are assigned lowercase letters (Punnet Square) Law of Segregation Mendel's law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete Phenotype An organism's physical appearance, or visible traits. 9.5-9.8 Monohybrid cross A cross between 2 individuals that are heterozygous for one character “A cross between two individuals, concentrating on only one definable trait” dihybrid cross Cross or mating between organisms involving two pairs of different traits A dihybrid is heterozygous for 2 characters Mendel used dihybrid crosses He performed was for seed color and shape traits R=round seed shape, dominate r= wrinkled shape, recessive Y= yellow, dominate y= green seed color, recessive Thus, a dihybrid cross with these characters/raits has the genotype RrYy and a phenotype of round and yellow seeds law of independent assortment Each member of a pair of homologous chromosomes separates independently of the members of other pairs so the results are random testcross cross between an organism with an unknown genotype and an organism with a homozygous recessive phenotype The rule of multiplication A statistical rule stating that the probability of two independent events occurring together is the product(multiply) of their individual probabilities. For instance, consider the monohybrid cross of the BB genotype (Bb x Bb) Each heterozygous parent has a ½ chance of donating the B or b allele The father has ½ chance donating the B allele, same with the mother The father multiplied by the mother = ¼ The rule of addition the probability that an event can occur in two or more alternative ways is the sum of the separate probabilities of the different ways (Bb x Bb Cross) You do ¼ + ¼ to get ½ Pedigree A diagram that shows the occurrence of a genetic trait in several generations of a family. Horizontal lines represent mating events and vertical lines represent offspring 9.9 to 9.11 Many recessive phenotypes are more common that dominate ones Carriers heterozygous individuals who carry the recessive allele but are phenotypically normal Question assuming H is the dominate allele and h is recessive, what genotype can person with Huntington’s disease have Answer: homozygous dominate (HH) or heterozygous (Hh) Question: if an individual is heterozygous for Huntington’s and mates with a healthy individual, what are the chances their offspring will be affected? Answer: 50% (2/4) complete dominance a relationship in which one allele is completely dominant over another, the phenotype is the same for both homozygous dominate (RR) and heterozygous (Rr) genotypes incomplete dominance Situation in which one allele is not completely dominant over another allele Incomplete dominance can be observed for genetic hypercholesterolemia Healthy people are homozygous dominate (HH) Homozygous recesive (hh) = bad 12-14 Codominant Inheritance pattern in which a heterozygote expresses the distinct trait of both alleles. Pleiotropy A single gene having multiple effects on an individuals phenotype The sickle-cell agene gives rise to multiple characters throughout the body polygenic inheritance combined effect of two or more genes on a single character Ex= skin color tone 16-17 chromosome theory of inheritance A basic principle in biology stating that genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns. Segregation occurs durine metaphase 1 and anaphase 1 Independent assortment follows the 2^n rule linked genes Genes located on the same chromosome that tend to be inherited together in genetic crosses. These do not follow independent assortment 9.18-9.20 The recombination frequency is the percentage of recombaint offspring among the total Genetic map an ordered list of the genetic loci along a particular chromosome The farther apart two genes are, the higher the probability that a crossover will occur between them and therefore the higher the recombination frequency linkage map genetic map of a chromosome based on recombination frequencies sex chromosomes Chromosomes that determine the sex of an individual The diploid number for a human is 46, 23 from the mom and 23 from the dad 22 of those chromosomes are autosomal, only 1 is a sex chromosome Male = XY, female= XX sex-linked gene gene located on a sex chromosome X-linked genes Genes found on the X chromosome.
