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1

genetics

is the study of how traits are inherited from one generation to the next

2

gene

the basic unit of heredity

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alleles

when a gene exists in more than one form

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genotype

the genetic makeup of an individual

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phenotype

the physical manifestation of the genetic makeup

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dominant

expressed allele

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recessive

the silent allele

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homozygous

organisms that contain two copies of the same allele

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heterozygous

organisms that carry two different alleles

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monohybrid cross

only one trait is being studied in this particular mating

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testcross

an organism with a dominant phenotype of unknown genotype (Ax) is crossed with a phenotypically recessive organism (genotype aa)

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dihybrid cross

parents differ in two traits, as long as the genes are on separate chromosomes and assort independently during meiosis

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crossing over

exchanges information between chromosomes and may break the linkage of certain patterns

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codominance

occurs when multiple alleles exist for a given gene and more than one of them is dominant

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sex linked

genes that are located on the X or Y chromosome

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nondisjunction

is either the failure of homologous chromosomes to separate properly during meiosis I, or the failure of sister chromatids to separate properly during meiosis II

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trisomy

three copies of that chromosome

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monosomy

a single copy of that chromosome

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mutagenic agents

include cosmic rays, x-rays, ultraviolet rays, and radioactivity as well as chemical compounds such as colchicine or mustard gas

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colchicine

inhibits spindle formation, thereby causing polyploidy

21

phenylketonuria (PKU)

is a molecular disease caused by the inability to produce the proper enzyme for the metabolism of phenylalanine. A degradation product (phenylpyruvic acid) accumulates

22

sickle cell anemia

is a disease in which red blood cells become crescent shaped because they contain defective hemoglobin. The sickle cell hemoglobin carries less oxygen. Caused by a substitution of valine for glutamic acid because of a single base pair substitution in the gene coding for hemoglobin

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nucleotide

which is composed of deoxyribose ( a sugar) bonded to both a phosphate group and a nitrogenous base

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semiconservative

each new daughter helix contains an intact strand from the parent helix and a newly synthesized strand

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RNA

ribonucleic acid, is a polynucleotide structurally similar to DNA except that its sugar is ribose, it contains uracil (U) instead of thymine, and it is usually single stranded

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mRNA

carries the complement of a DNA sequence and transports it from the nucleus to the ribosomes, where protein synthesis occurs

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monocistronic

one mRNA strand codes for one polypeptide

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tRNA

is a small RNA found in the cytoplasm which aids in the translation of mRNA's nucleotide code into a sequence of amino acids. Brings amino acids to the ribosomes during protein synthesis

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rRNA

is a structural component of ribosomes and is the most abundant of all RNA types. rRNA is synthesiszed in the nucleolus

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transcription

is the process whereby information coded in the base sequence of DNA is transcribed into a strand of mRNA which leaves the nucleus through nuclear pores. The remaining events of protein synthesis occur in the cytoplasm