Chapter 10 Nature Of The Gene And The Genome

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The collective body of genetic information in an organism is called the

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genome

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Characteristics of organisms are governed by units of inheritance called

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genes

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Each trait is controlled by two forms of a gene called

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alleles

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When alleles are nonidentical, the _______ allele masks the _____ allele

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dominant masks the recessive

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A ____________________ contains one gene for each trait

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reproductive cell (gamete)

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Somatic cells arise by the union of _____ and ______ gametes

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male and female

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Two alleles controlling each trait are inheritied;

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one from each parent

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The pairs of genes are separated during _______________________

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gamete formation

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Genes controlling different traits segregate independently of eachother

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independent assortment

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Chromosomes are divided equally between the two _____________ during __________

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daughter cells during cell division

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Chromosomes are __________ prior to cell division

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doubled

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Chromosomes are present as pairs of ______________ chromosomes

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homologous

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During meiosis, homologous chromosomes associate and form a ___________; then separate into different cells

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bivalent

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Genes that are on the same chromosome:

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-do not sort independently

-are part of the same linkage group

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Maternal and paternal chromosomes can exchange pieces during _______________ or ___________________

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crossing over or genetic recombination

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Nucleotide

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The building block of DNA

Consists of a phosphate, a sugar, and either a pyrimidine or purine nitrogen base

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Pyrimidines

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Thymine and Cytosine

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Purines

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Adenine and Guanine

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DNA that is more compact than its relaxed counterpart is called

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supercoiled

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Underwound DNA is ____________ supercoiled

Overwound DNA is ____________ supercoiled

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negatively

positively

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Enzymes called _______________ change the level of DNA supercoiling

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topoisomerases

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Type 1 topoisomerases

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change the supercoiled state by creating a transient break in one strand of the duplex

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Type 2 topoisomerases

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makes a transient break in both strands of the DNA duplex

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Renaturation or reanneling is

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when single-stranded DNA molecules are capable of reassociating

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Reanneling of eukaryotic genomes shows three classes of DNA:

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highly repeated

moderately repeated

nonrepeated

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Satellite DNAs

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short sequences that tend to evolve very rapidly

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minisatellite DNAs

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unstable and tend to be variable in the population

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microsatellite DNAs

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shortest sequences and typically found in small clusters

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Moderately repeated DNA sequences:

Repeated DNA sequences with coding functions

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include genes that code for ribosomal RNA and histones

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Moderately repeated DNA sequences:

Repeated DNA sequences that lack coding functions

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do not include any type of gene product; can be grouped into 2 classes: SINEs or LINEs

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Nonrepeated DNA sequences

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code for the majority of proteins

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Polyploidization (whole genome duplication) occurs when

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offspring receive more than 2 sets of chromosomes from their parents

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Gene duplication occurs

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-within a portion of a single chromosome

-may occur by unequal crossing over between misaligned homologous chromosomes

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The globin gene family includes

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hemoglobin, myoglobin, and plant leghemoglobin

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Pseudogenes

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resemble globin genes but are nonfunctional

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Genetic elements are capable of moving within a chromosome

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transposition

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Mobile elements are called

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transposable elements

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Only certain sequences can act as __________, but these insert into target sites randomly

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transposons

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Retrotransposons

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use an RNA intermediate which produces a complementary DNA via reverse transcriptase

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reverse transcriptase

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viruses such as HIV use this mechanism to replicate their genome

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Some moderately repeated sequences are transposable elements

Possible evolutionary roles:

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Rearrangement of the genome

Regulation of gene expression

Production of new genes