GENETICS - NOTES-

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1 GENETICS - NOTES- Warm Up Exercise Using your previous knowledge of genetics, determine what maternal genotype would most likely yield offspring with such characteristics. Use the genotype that you came up with for the mother, to complete a punnett square. DEFINING KEY TERMS - the transmission of traits from one generation to the next. - differences between members of the same species. - the scientific study of heredity and hereditary variation. Meiosis- a modified type of cell division in reproducing organism consisting of rounds of cell division but only round of DNA replication. It results in cells with the number of chromosome sets as the original cell. Gene- a unit of hereditary information consisting of a in DNA (or RNA in some viruses). o A gene s specific location along the chromosome is called the gene s. - reproductive cells that transmit genes from one generation to the next. SEXUAL VS. ASEXUAL REPRODUCTION Reproduction- a single individual is the sole parent and passes copies of all its genes to its offspring. As a result, the offspring are an exact copy of themselves (a ). Reproduction- two parents give rise to offspring that have unique combinations of genes inherited from two parents. Offspring of sexual reproduction vary genetically to their siblings and both parents.

2 KARYOTYPES - a display of the chromosome pairs of a cell arranged by size and shape. o 22 pairs of o 1 pair of THE HUMAN LIFE CYCLE Fertilization- the union of haploid gametes to produce a. o Meiosis- (sex cells) reproduce by meiosis

3 SOURCES OF GENETIC VARIATION of Chromosomes- allele pairs separate independently during the formation of gametes. Crossing Over- the exchange of genetic material between nonsister chromatids during of meiosis. Random Fertilization- there are over 70 trillion possible diploid combinations of a zygote during fertilization. This makes each individual truly. Mutations-. MENDEL AND THE GENE IDEA Particulate Hypothesis- parents pass on discrete heritable units, called, that retain their separate identities in offspring. Alternative versions of genes account for variations in inherited characters. These alternative versions of a gene are called. - the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes. MENDEL S TERMINOLOGY - the genetic makeup - the appearance of observable traits Monohybrid Cross- of a character Dihybrid Cross- with characters - each pair of alleles segregates independently of each other pair of alleles during gamete formation. (This applies only to genes located on different, non- homologous chromosomes).

4 Punnett Square Practice A brown dog is homozygous for the gene that controls coat color. The brown dog is mated with an albino (all white) dog. The dogs have many puppies. All of the puppies have brown coat color. o Draw a punnett square for this cross and give the expected genotypic and phenotypic outcomes. o What are the dominant and recessive alleles? Provide symbols for both alleles. o What would be the results if these offspring mated with an albino dog? A homozygous brown dog? A heterozygote? About 70% of Americans perceive a bitter taste from the chemical phenylthiocarbamide (PTC). The ability to taste this chemical results from a dominant allele (T) and not being able to taste PTC is the result of having two recessive alleles (t). Albinism is also a single locus trait with normal pigment being dominant (A) and the lack of pigment being recessive (a). A normally pigmented woman who is heterozygous for PTC tasting, has a father who is homozygous for both albinism and PTC tasting. She marries a heterozygous, normally pigmented man who is a taster but who has a mother that does not taste PTC o Give the phenotypic and genotypic ratios of the offspring. A blue- eyed, left- handed woman marries a brown- eyed, right handed man who is heterozygous for both traits. Blue eyes and left- handedness are recessive. o Give the phenotypic and genotypic ratios of the offspring.

5 THE LAWS OF PROBABILITY - used to determine the probability that two or more independent events will occur together in some specific combination. o Multiply the probability of one event by the probability of the other event. - used to determine the probability that any one of two or more mutually exclusive events will occur. o Calculated by adding their individual probabilities. DEGREES OF DOMINANCE - the phenotypes of the heterozygote and the dominant homozygote are indistinguishable. - neither allele is completely dominant and the F1 hybrids have a phenotype somewhere between those of the two parental varieties. - the two alleles both affect the phenotype in separate, distinguishable ways. ADDITIONAL INHERITANCE PATTERNS - most genes exist in populations in more than two allelic forms. Ex: blood type BLOOD CHART

6 Blood Problem Identification bracelets were accidentally removed from three newborn babies. Blood typings were taken to help in the identification procedures. The blood types for the babies and their parents were: Baby 1- type A, Baby 2- type O, Baby 3- type AB o Mr. Black = type A Mr. Black = type B o Mr. Green = type AB Mrs. Green = type O o Mr. White = type O Mrs. White = type O Which baby could belong to Mr. and Mrs. Black? Which baby could belong to Mr. and Mrs. Green? Which baby could belong to Mr. and Mrs. White? ADDITIONAL INHERITANCE PATTERNS - multiple phenotypic effects (exhibited by most genes). - a gene at one locus alters the phenotypic expression of a gene at a second locus. Ex: albinism - an additive effect of two or more genes on a single phenotypic character, which produces quantitative characters that exist on a continuum. PEDIGREES Jane and Joe Smith have dimples, their daughter, Clarissa, does not. Joe s dad has dimples, but his mother and his sister do not. Jane s dad, Mr. Renaldo; her brother, Jorge; and her sister, Emily, do not have dimples, but her mother does.

7 GENETIC DISORDERS Inherited Disorders - show up only in individuals homozygous for the allele Inherited Disorders- Dominant alleles that cause a lethal disease are rare and arise by mutations. GENETIC TESTING AND COUNSELING Tests for identifying carriers Fetal testing o Amniocentesis o Chronic villus sampling (CVS) o Ultrasound o Fetoscopy Newborn screening THE CHROMOSOMAL THEORY OF INHERITANCE Mendelian genes have specific (positions) along chromosomes. It is the chromsomes that undergo segregation and independent assortment.

8 THOMAS HUNT MORGAN - the phenotype for a character most commonly observed in natural populations. - traits that alternatives to the wild type. A student at UK THE CHROMOSOMAL BASIS OF INHERITANCE - Sex determining Region of Y o The presence of this gene on the Y chromosome codes for the development of. In the absence of this gene, the gonads develop into SEX LINKED GENES A gene located on either sex chromosome is called a In humans, sex- linked usually refers to a gene on the larger chromosome For a recessive sex- linked trait to be expressed o A female needs copies of the allele o A male needs only copy of the allele Sex- linked recessive disorders are much more common in than in females

9 MORGAN S EXPERIMENTS - genes located on the same chromosome that tend to be inherited together in genetic crosses. - the production of offspring with combinations of traits that differ from those found in either parent. - offspring that inherit a phenotype that matches one of the parental phenotypes. Recombinant Types or - offspring that have new combinations of phenotypes. RECOMBINATION - accounts for the recombination of linked genes. - an ordered list of the genetic loci along a particular chromosome. - a genetic map based on recombination frequencies. Displays order but not precise location. o Distances are expressed in map units- equivalent to recombination frequency. ( )

10 ALTERATION OF CHROMOSOME NUMBER - pairs of homologous chromosomes do not separate normally during meiosis o As a result, one gamete receives two of the same type of chromosome and the other gamete doesn t receive a copy. - a chromosomal aberration in which one or more chromosomes are present in extra copies or deficient in number. - a chromosomal alteration in which the organism possesses more than two complete chromosome sets. ALTERATION OF CHROMOSOME STRUCTURE - removes a chromosomal segment - repeats a segment - reverses a segment within a chromosome - moves a segment from one chromosome to another

11 EXCEPTIONS TO THE STANDARD CHROMOSOME THEORY - a variation in phenotype depending on whether an allele is inherited from the male or female parent. - genes outside of the nucleus. Some are located in organelles in the cytoplasm.