Bio Exam 4

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Inheritance

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-The transfer of traits from parent to offspring

dna(genotype)→rna→protein→trait→phenotype

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Trait

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A measurable or observable characteristic of a cell/organism, result of the expression of different alleles

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Alleles

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Alternative forms of a gene; most genes have 2 types, dominant and recessive

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Locus

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Segment of dna that has information controlling some aspect of the structure or function of an organism

-alleles govern variations of the same characteristic and occupy corresponding loci (locations) on homologous chromosomes

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Genotype

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Genetic makeup of an organism, often expressed as symbols

-dominant homozygous, AA, always observed in the form of a trait

-dominant heterozygous, Aa, dominant trait is expressed

-recessive homozygous, aa, only time recessive trait is expressed

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Phenotype

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Physical appearance of an organism, determined by genotype

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Multiple genes on one chromosome

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Genes must be at the same location on a pair of homologous chromosomes to be considered alleles

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Mendel's principles of inheritance

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Principle of segregation: alleles separate before gametes are formed; alleles remain intact during meiosis and recessive alleles are not "lost" and can reappear in subsequent generations

-one allele per gametes

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Mendel's principles of inheritance

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Independent assortment: alleles on nonhomologous (different) chromosomes are randomly distributed into gametes

-gametes receive alleles based on where the chromosomes are located during separation

-contributes to genetic recombination

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Linked genes

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Genes on the same chromosome that tend to be inherited together in successive generations

-an exception to the principle of independent assortment

-some genetic recombination occurs as a result of crossing over events as well

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Dominant traits

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Always expressed, represented by capital letters

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Recessive traits

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Only observed if both alleles code for the same trait, represented by lower case letters

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Types of genotypes

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Homozygous- both alleles for a trait are the same

Heterozygous- alleles for a trait are different

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Punnett square

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Predicts the ratios of offspring with a particular genotype or phenotype resulting from the combinations of gametes from two parents; predicts the outcome of a cross

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Monohybrid (parental) cross

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Homozygous dominant alleles x homozygous recessive alleles = 4/4 heterozygous genotype, 4/4 dominant phenotype

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Heterozygous (F1) cross

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Heterozygous alleles x heterozygous alleles = 1/4 homozygous dominant genotype, 2/4 heterozygous genotype, 1/4 homozygous recessive genotype, 3/4 dominant phenotype, 1/4 recessive phenotype

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Test cross

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Determines the genotype of an individual who has a dominant trait by mating the individual with one who has the recessive trait then looking for a recessive offspring

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Dihybrid cross

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Mating between individuals with different alleles at two loci (on homologous or nonhomologous chromosomes)

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Independent events

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One event does not affect the outcome of the other event; chance has no memory

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Product rule

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Probabilities of independent events are multiplied

Ex: if the offspring of two individuals has a 1/4 chance of having hazel eyes, there is a 1/16 chance for them to have two children with hazel eyes since 1/4 * 1/4 = 1/16

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X-linked genes

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Found on the x chromosome, express unusual inheritance patterns with abnormal alleles more frequently expressed in male offspring; y chromosome is smaller than x chromosome and does not have corresponding alleles for some traits, so a female will have one dominant allele that will mask the recessive allele, but if the male only has a recessive allele that will be expressed

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Incomplete dominance

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Heterozygote has a phenotype intermediate between those of its parents

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Codominance

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Heterozygote simultaneously expressed the phenotypes of both types of homozygotes

Ex: speckled chickens

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Multiple alleles

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Three of more alleles for a given locus may exist within a population

Ex: blood type

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Pleiotrophy

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Ability of a single gene to have multiple effects of an organisms phenotype; single gene affects multiple traits

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Polygenic inheritance

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Multiple independent pairs of genes may have similar and additive effects on the same characteristic (height, body shape, etc); multiple genes work together to affect one trait

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mutation

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change in the nucleotide sequence

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spontaneous mutations

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result from errors in base pairing during dna replication