Biology Chapter 15

Front 1

Chromosome theory of inheritance

Back 1

a theory that says, mendelian genes have specific loci(positions) along chromosomes, and it is the chromosomes that undergo segregation and independent assortment. A specific gene is carried on a specific chromosome.

Front 2

wild type

Back 2

the phenotype for a character most commonly observed in natural populations (ex. red eyes in fruit flies).

Front 3

mutant phenotype

Back 3

traits that are alternatives to the wild type. (ex. white eyes for the fruit flies). Due to alleles assumed to have originated as changes, or mutations, in teh wild-type allele.

Front 4

SRY gene(sex-determining region of Y)

Back 4

in the absence of this the gonads turn into ovaries, codes for a protein tha regulates other genes.

Front 5

sex-linked gene

Back 5

any gene located on either sex chromosome.(usually the x chromosome).

Front 6

hemizygous

Back 6

any male recieving the recessive allele from his mother expresses this trait

Front 7

Barr body

Back 7

the inactive X chromosome of the female condenses into a compact object called this, which lies on the inside of the nuclear envelope

Front 8

XIST (X-inactive specific transcript)

Back 8

an X chromosome gene, that is active only on the Barr-body chromosome.

Front 9

linked genes

Back 9

genes located on teh same chromosome that tend to be inherited together in genetic crosses.

Front 10

genetic recombination

Back 10

the production of offspring with combinations of traits that differ from those found in either parent.

Front 11

parental types

Back 11

offspring that inherit a phenotype that matches one of the parental phenotypes.

Front 12

recombinant types(recombinants)

Back 12

offspring with new combinations of phenotypes.

Front 13

crossing over

Back 13

the reciprocal exchange of genetic material between nonsister chromatids during prophase during prophase I of meiosis. Accounts for the recombination of linked genes. A set of proteins orchestrates an exchange of one maternal and one paternal chromatid, in effect end portions of the two nonsister chromatids trade places each time this occurs.

Front 14

recombination frequency

Back 14

the percentage fo recombinant offspring is related to the distance between linked genes.

Front 15

genetic map

Back 15

an ordered list of the geneti loci along a particular chromosome.

Front 16

to map genes

Back 16

to assign relative positions to genes on teh same chromosomes.

Front 17

linkage map

Back 17

the genetic map based on recombination frequencies

Front 18

map units(centimorgans)

Back 18

the distances between genes, one is equivalent to a 1% recombination frequency

Front 19

genetically unlinked

Back 19

alleles of these genes are sorted independently, as if they were on different chromosomes.

Front 20

cytogenic maps

Back 20

locate genes with respect to chromosomal features, such as stained bonds that can be seen in the microscope

Front 21

nondisjunction

Back 21

a mishap in which the members of a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids fail to seperate during meiosis II. One gamete recieves two of the same type of chromosome and another gamete recieves no copy, the other chromosomes are usually distributed normally.

Front 22

aneuploidy

Back 22

if either aberrant gametes units with a normal one at fertilization, the zygote will also have an abnormal number of a chromosome, may involve more than one chromosome.

Front 23

monosomic

Back 23

the aneuploid zygote is said to be this for that chromosome, if it is missing a chromosome(caused by fertilization involving a gamete that has no copy of a particular chromosome)(the cell has 2n-1 chromosomes)

Front 24

trisomic

Back 24

an aneuploid cell is this for that chromosome, when a chromosome is present in triplicate in the zygote.(the cell has 2n+1 chromosomes)

Front 25

polyploidy

Back 25

some organisms have more than two complete chromosome sets in all somatic cell.

Front 26

triploidy

Back 26

a type of polyploidy, indicates three chromosomal sets, may arise by the fertilization of an abnormal diploid egg produced by nondijunction of all its chromosomes.

Front 27

tetraploidy

Back 27

a type of polyploidy indicates four chromosomal sets. Could result from the failure of a 2n zygote to divide after replicating its chromosomes.

Front 28

deletion

Back 28

occurs whena chromosomal fragment is lost, teh affected chromosome is then missing certain genes

Front 29

duplication

Back 29

the "deleted" fragment of a chromosome may become attached as an extra segment to a sister chromatid, producing this. Or it can attach to a nonsister chromatid of a homologous chromosome.

Front 30

inversion

Back 30

when a chromosomal fragment reattaches to the original chromosome in hte reverse orientation.

Front 31

translocation

Back 31

the fragment of chromosomal breakage joins a nonhomologous chromosome, a rearrangement.

Front 32

nonreciprocal crossover

Back 32

in crossing over, nonsister chromatids sometimes exchange unequal-sized segments of DNA, so that noe partner gives up more genes than it recieves, the products are one chromosome iwth a deletion and one with a duplication.

Front 33

syndrome

Back 33

genetic disorders with a set of traits characteristic of the type of aneuploidy, can survive birth and beyond.

Front 34

genomic imprinting

Back 34

variation in phenotype depending on whether an allele is inherited from the male or female parent, different from sex-linkage, most genes are autosomes. Occurs during the formation of gametes and results in the silencing of one allele of certain genes, because these genes are imprinted differently in sperm and eggs, a zygote expresses only one allel of an imprinted gene, either the allele inherited from the feamle parent or the male.

Front 35

extranuclear genes(cytoplasmic genes)

Back 35

genes located outside of the nucleus( can be carried in mitochondria or chloroplasts)