AP Bio Vocab - Unit 5

chromatid

one of the two identical halves of a chromosome that has been replicated in preparation for cell division

diploid

(2n) cell condition in which two of each type of chromosome are present

haploid

(n) cell condition in which only one of each type of chromosome is present

meiosis

type of nuclear division that reduces the chromosome number from 2n to n; daughter cells receive the haploid number of chromosomes in varied combinations

gametes

haploid sex cell; ex. egg or sperm

homologous chromosomes

member of a pair of chromosomes that are alike and come together in synapsis during prophase of the first meiotic division; a homologue

crossing over

exchange of segments between nonsister chromatids of a bivalent during meiosis

Law of Independent Assortment

mendelian principle that explains how combinations of traits appear in gametes

nondisjunction

failure of the homologous chromosomes or sister chromatids to separate during either mitosis or meiosis; produces cells with abnormal chromosome numbers

trisomy

chromosome condition in which a diploid cell has one more chromosome than normal; designated as 2n + 1

polyploidy

having a chromosome number that is a multiple greater than twice that of the monoploid number

dihybrid cross

cross between parents that differ in two traits

alleles

alternative form of a gene; alleles occur at the same locus on homologous chromosomes

fertilization

fusion of sperm and egg nuclei, producing a zygote that develops into a new individual

karyotype

chromosomes arranged by pairs according to their size, shape, and general appearance in mitotic metaphase

Barr body

dark-staining body in the cell nuclei of female mammals that contains a condensed, inactive X chromosome; named after its discoverer, Murray Barr

monohybrid cross

cross between parents that differ in only one trait

genotype

genes of an organism for a particular trait or traits; often designated by letters—for example, BB or Aa

phenotype

visible expression of a genotype—ex. Brown eyes or attached earlobes

X-linked inheritance

a way a genetic trait or condition can be passed down from parent to child through mutations (changes) in a gene on the X chromosome

spermatogenesis

production of sperm in males by the process of meiosis and maturation

oogenesis

production of eggs in females by the process of meiosis and maturation

polar body

nonfunctional product of oogenesis produced by the unequal division of cytoplasm in females during meiosis; in humans three of the four cells produced by meiosis are polar bodies

deletion (of chromosome)

change in chromosome structure in which the end of a chromosome breaks off or two simultaneous breaks lead to the loss of an internal segment; often causes abnormalities—ex. Cri du chat syndrome

duplication (of chromosome)

change in chromosome structure in which a particular segment is present more than once in the same chromosome

translocation (of chromosome)

movement of a chromosomal segment from one chromosome to another non homologous chromosome, leading to abnormalities—ex. Down syndrome

inversion (of chromosome)

change in chromosome structure in which a segment of a chromosome is turned around 180°; this reversed sequence of genes can lead to altered gene activity and abnormalities

Law of Segregation

mendelian principle that explains how, in a diploid organism, alleles separate during the formation of the gametes

null hypothesis

the statistical hypothesis that states that there will be no differences observed and expected data

experimental hypothesis

an educated guess or a prediction about the outcome of an experiment

genetically linked genes

genes located close together on the same chromosome

dominant allele

allele that exerts its phenotypic effect in the heterozygote; it masks the expression of the recessive allele

recessive allele

allele that exerts its phenotypic effect only in the homozygote; its expression is masked by a dominant allele

testcross

cross between an individual with a dominant phenotype and an individual with a recessive phenotype to determine whether the dominant individual is homozygous or heterozygous

autosome

chromosome pairs that are the same between the sexes; in humans, all but the X and Y chromosomes

sex chromosome

chromosomes that carry the genes that determine the sex of an individual; ex. Human sex chromosomes X and Y

multiple allelic trait

inheritance pattern in which there are more than two alleles for a particular trait; each individual has only two of all possible alleles

incomplete dominance

inheritance pattern in which an offspring has an intermediate phenotype, as when a red-flowered plant and a white-flowered plant produce pink-flowered offspring

pleiotropic effects

a single gene affecting multiple systems or determining more than one phenotype; the phenomenon in which a single locus affects two or more distinct phenotypic traits

polygenic inheritance

pattern of inheritance in which a trait is controlled by several allelic pairs

codominance

inheritance pattern in which both alleles of a gene are equally expressed in a heterozygote

gene locus

physical location of a trait (or gene) on a chromosome

hemizygous

possessing only one allele for a gene in a diploid organism; males are hemizygous for genes on the X chromosome

homozygous

possessing two identical alleles for a particular trait

heterozygous

possessing unlike allele for a particular trait