* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Mendelian Genetics
Hybrid (biology) wikipedia , lookup
Genetically modified crops wikipedia , lookup
Gene expression programming wikipedia , lookup
Ridge (biology) wikipedia , lookup
Polymorphism (biology) wikipedia , lookup
Inbreeding avoidance wikipedia , lookup
Genome evolution wikipedia , lookup
Medical genetics wikipedia , lookup
Genetic engineering wikipedia , lookup
Gene expression profiling wikipedia , lookup
Heritability of IQ wikipedia , lookup
Minimal genome wikipedia , lookup
Behavioural genetics wikipedia , lookup
Genetic drift wikipedia , lookup
Population genetics wikipedia , lookup
X-inactivation wikipedia , lookup
Biology and consumer behaviour wikipedia , lookup
Genome (book) wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Genomic imprinting wikipedia , lookup
History of genetic engineering wikipedia , lookup
Hardy–Weinberg principle wikipedia , lookup
Designer baby wikipedia , lookup
Microevolution wikipedia , lookup
Chapter 11: sec 11-1, 11-2, & 11-3 Genetics Genetics (sec 11-1 & 11-2) • Genetics – The study of heredity • Genes – The chemical factors of inheritance located on chromosomes, made of DNA Mendelian Genetics How Are Traits Inherited? Gregor Mendel • Raised on farm and understood the value of plant breeding. • At 21, entered priesthood and studied plant breeding in a monastery in the Czech Republic. • Loved to read especially about natural sciences and was aware of Darwin’s findings. • Studied the inheritance of traits in pea plants. Gregor Mendel • Studied traits that occur in distinct forms. • Developed true-breeding varieties – When bred amongst themselves these plants produced offspring identical to the parent for that trait. • Used mathematical analysis in his studies. Definitions • Gametes: reproductive cells produced by sexually reproducing organisms. – Two types: • male gametes = sperm – In plants: contained in pollen • Female gametes = eggs – In plants: contained in ovules – Ovules contained in carpels Fertilization • Fertilization: fusion of egg and sperm – Self-fertilized: fusion of sperm and egg from same plant – Cross fertilized: fusion of egg and sperm from two different plants • Produced hybrids • F1: first generation • F2: second generation True-breeding: -Plants allowed to self pollinate -Produced offspring identical to parents Mendel’s Interpretations • Modified to incorporate today’s vocabulary – Genes: the hereditary information that determines a single trait – Alleles: alternate forms of a gene • Homozygous/purebred - When an organism inherits two of the same alleles for a trait. • Heterozygous/hybrid - When an organism inherits two different alleles for one trait. Homozygous Alleles Heterozygous Alleles Why were all the seeds in the F1 generation round? • Dominant vs. Recessive Allele – Dominant: an allele that is expressed whenever it is present • Symbolized by a upper case letter (R) – Recessive: an allele that is masked whenever the dominant allele is present. • Symbolized by a lower case letter (r) • Dominant and recessive alleles influence an organism’s phenotype Genotype and Phenotype • Genotype: Genetic makeup of an individual. It is determined by the alleles present for each trait. The type of genes an individual has. • Phenotype: Physical appearance of a trait. It is the expression of the genotype. Monohybrid Cross (One Factor Cross) Mother contributes: True Breeding A or A A AA AA A AA AA Mother contributes: Cross Breeding a or a A Aa Aa A Aa Aa Can you look at someone and determine their genotype? • Testcross is used to determine the genotype of an individual – Testcross: crossing an organism with unknown genotype with one that is homozygous recessive for the trait. – Example: • Plant that has round (R) seeds crossed with one that is homozygous recessive (rr) for wrinkled seeds R? x rr Test Cross Genetics (sec 11-3) • Mendel performed experiments designed to follow 2 different genes in pea plants – Called a two factor cross (Dihybrid Cross) Mendel’s Laws • Based on Mendel’s data, he formulated two laws: – Law of Segregation: A parent contributes only one of its alleles for a trait to each offspring. – If parent is heterozygous for a trait, the particular allele donated to the offspring is random. • Law of Independent Assortment: Alleles of one gene are passed to offspring independently of the alleles of other genes. – Applies to the inheritance of two or more genes simultaneously. Law of Independent Assortment • Allows for new gene combinations or genetic recombination Why Aren’t Members of the Same Species Identical? • Sources of Genetic Variation – Law of Independent Assortment – Mutation – Crossing over Mutations • Definition = change in DNA sequence resulting the appearance of a new allele • Can occur at any time, but not always beneficial • Some can be harmful and result in death • Some can result in the organism having traits that make them better suited to the environment Do Mendel’s Laws Always Apply? Incomplete dominance – Some alleles (traits) are neither dominant or recessive – Controlled by more than one allele • The heterozygous phenotype is between the homozygous dominant or recessive. Both alleles are expressed. Example of Incomplete Dominance Another example • Shorthorn Cattle: Red male mated to a White female = Roan calf • RR X rr = Rr If a red bull (RR) is mated to a roan (Rr) cow, what color will the calves be? Shorthorn: Red X Roan R R R RR RR r Rr Rr What if Both Parents are Roan? R r R RR Rr r Rr rr I.E. Incomplete dominance – Roan Codominance • Both alleles share dominance and are expressed • I.E. speckled chickens – Black feathers dominant – White feathers dominant Codominance • Two alleles are expressed (multiple alleles) in heterozygous individuals. • Example: human blood type 1. 2. 3. 4. type A type B type AB type O = = = = IAIA or IAi IBIB or IBi I A IB ii Polygenic Traits • Interaction of several genes – Human skin color • More than four genes control this trait – Human eye color – Human hair color Recombination and crossing-over • Recombination- offspring which have traits in a different combination from parents. • Two kinds of recombination – Independent assortment of genes on different chromosomes – Crossing-over of genes on same chromosome Crossing-Over (sec 11-4) • Meiosis I – Starts with tetrads • 4 chromatids (paired homologous chromosomes) – At this point crossing over can occur – Gives us even more variation in living organisms Determination of Sex • Drosophilia - fruit fly – – – – XX - female XY - male XXY - female XO - male • Humans – – – – XX - female XY - male XXY - male XO - female • Non-X or Y chromosomes are known as Autosomes diploid germ cells in female diploid germ cells in male eggs Meiosis, gamete formation in both female and male: sperm X x Y X x X Fertilization: XY X X X XX XX Y XY XY sex chromosome combinations possible in new individual XX Fig. 12.4, p. 196 Slide 4 Sex linkage We have 2 sex chromosomes choices: – X and Y • Females have XX chromosomes, males XY • Sex-linked genes located on X, not Y • To show recessive trait, female needs 2 copies, male only needs 1. Sex Linked Traits • Color blindness (recessive) – Cannot distinguish between certain colors • Most common form red-green colorblindness • Hemophilia (recessive) – A protein needed for blood clotting is missing • Duchenne Muscular Dystrophy (recessive) – Progressive weakening and loss of skeletal muscle