13 Genetics. parents. children. Who are the parents of these children?. Heredity = Continuity of biological traits from one generation to the next. Variation = Inherited differences among individuals of the same species. Genetics = The scientific study of heredity and hereditary variation.
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Who are the parents of these children?
Heredity= Continuity of biological traits from one generation to the next
Variation= Inherited differences among individuals of the same species
Genetics= The scientific study of heredity and hereditary variation
DNA double helix of nucleotides
DNA = Type of nucleic acid that is a polymer of four different kinds of nucleotides.
wound on histon peptide
Chromosomes = Organizational unit of heredity material in the nucleus of eukaryoticorganisms
Gene = Unit of hereditary information that is made of DNA and is located onchromosomes
Locus = Specific location on a chromosome that contains a gene
In a dividing cell, the mitotic (M) phase alternates with interphase, a growth period. The first part of interphase, called G1, is followed by the S phase, when the chromosomes replicate; the last part of interphase is called G2. In the M phase, mitosis divides the nucleus and distributes its chromosomes to the daughter nuclei, and cytokinesis divides the cytoplasm, producing two daughter cells.
Diploid = Condition in which cells contain two sets (2n) of chromosomes
Haploid = Condition in which cells contain one set (1n) of chromosomes
Gamete = A haploid reproductive cell (sperm cells and ova)
The diploid number is restored when two haploid gametes unite
Fertilization = The union of two gametes to form a zygote
Zygote = A diploid cell that results from the union of two gametes
In animalsgametes are the only haploid cells
b. Fungi and some protists
In many fungi and some protists, theonly diploid stage is the zygote
c. Plants and some algae
Plants and some species of algaealternate between multicellularhaploid and diploid generations
What happens during meiosis?
1. Independent assortment of chromosomes
Independent assortment = the random distribution of maternal and paternalhomologues to the gametes
Theprocess produces 2npossible combinations of maternal and paternalchromosomes in gametes
Theories of heredity
Blending theory of heredity = Pre-Mendelian theory of heredity proposing thathereditary material from each parent mixes in the offspring; once blended the hereditary material is inseparable and the offspring's traits aresome intermediate between the parental types
Particulate theory of heredity = Gregor Mendel's theory that parents transmit to theiroffspring discrete inheritable factors (now called genes) that remain as separate factorsfrom one generation to the next
O E |O–E|
705 696.75 8.25
224 232.25 8.25
2 = +
The correction for continuity of
0.5 is only applied when DF=1
2 = 0.086 + 0.259 = 0.345
At DF=1 0.345 lies between 0.016
and 0.455 with 0.900>p>0.500,
so accept hypothesis
Question: In a Mendelian cross between pea plants that are heterozygous forflower color (Pp), what is the probability that the offspring will be homozygousrecessive?
Question: In a Mendelian cross between pea plants that are heterozygous forflower color (Pp), what is the probability of the offspring being a heterozygote?
Complete dominance = an allele is fully expressedin the phenotype of a heterozygote and masks the phenotypic expression ofthe recessive allele; the phenotypes of the heterozygote anddominant homozygote are indistinguishable
Codominance = full expression of both alleles in theheterozygote
Epistasis = Interaction between two nonallelic genes in which one modifies the phenotypic expression of the other (9:3:4)
Recombination is result of crossing over and independant assortment
The farther apart two genes are, the higher the probability that a crossover will occur between them and therefore a higher recombination frequency
Map distance: 1 unit is 1% recombination
This results from multiple crossing over:the further loci are apart, the greater the change for multiple crossing over events
Some genes on a chromosome are so far apart that a crossover between them is virtually certain: independent inheritance, no linkage
TMV particle consists of nucleic acid enclosed by a protein coat
The Current Classification of Plant Virus Genera*
Potato spindle tuber viroid
Discovered by Griffith in 1928.