genetics lab - midterm 2

allele

one of a group of alternative forms of a gene that may occur at a given site (locus) on a chromosome

cell cycle

stages a cell passes through in the process of cell division

chromosome

a structure composed of DNA and proteins that contains genetic information; made up of genes

co-dominant

phenotype of heterozygote exhibits individual characteristics of each allele

diploid

a chromosome number twice that found in gametes; containing two sets of chromosomes; 2n

dominant

an allele whose phenotypic effect is the same in both the heterozygous and homozygous conditions

gamete

a reproductive, or germ, cell; either egg or sperm

gene

the biological unit of genetic information; containing the information for the synthesis of a single protein; located in a definite position on a chromosome

gene flow

the exchange of genes between different populations

gene pool

all of the alleles of all the genes of all individuals in a population

genotype

the fundamental genetic makeup of an organism

haploid

having a single set of chromosomes as normally present in a mature gamete; n

heterozygous

possessing two different alleles for a given character at the corresponding loci of homologous chromosomes

homozygous

having identical alleles at the same locus on a pair of homologous chromosomes

incomplete dominance

phenotype of a heterozygote is intermediate to that of either homozygote

locus (pl = loci)

position of a gene on a chromosome

mutation

an inheritable change in the DNA sequence of a chromosome not resulting from recombination

overdominance

phenotype of heterozygote is more extreme than either homozygote and typically confers an improvement in fitness

phenotype

the actual appearance of an individual; the physical expression of the genotype

recessive

the opposite of a dominant character; expressed phenotypically only when homozygous (or haploid)

sister chromatids

identical copies of chromosomal DNA held together by a common functional centromere

test cross

breeding an organism of unknown genotype with a homozygous recessive individual

interphase

the preparatory phase of the cell cycle consisting of G1, S, and G2. cell growth happens and replicates DNA before division

prophase (mitosis)

the first phase of mitosis. chromatin condenses into chromosomes. nuclear envelope breaks and mitotic spindle forms

prometaphase (mitosis)

spindle fibers attach to kinetochores of chromosomes. chromosomes begin to move towards center of the cell

metaphase (mitosis)

all chromosomes align single file along the equator of the cell

anaphase (mitosis)

sister chromatids are pulled apart by shortening spindle fibers and move toward the opposite poles of the cell

telophase (mitosis)

final stage of mitosis. two new nuclear envelopes reform around the separated sets of chromosomes which begin to condense

cytokinesis

the division of the cytoplasm that follows mitosis/meiosis. this results in two distinct daughter cells (cleavage furrow in animals, cell plate in plants)

prophase 1 (meiosis)

the longest phase of meiosis 1. homologous chromosomes pair up (synapsis) and exchange genetic material (crossing over)

synapsis

the close pairing of homologous chromosomes that take place during prophase 1 of meiosis

crossing over

the physical exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase 1. increases genetic diversity

chiasmata

the x-shaped structural regions where crossing over has occurred between non-sister chromatids

metaphase 1 (meiosis)

pairs of homologous chromosomes (tetrads) align along the metaphase plate, rather than individual chromosomes

anaphase 1 (meiosis)

whole homologous chromosomes are pulled apart to opposite poles, while sister chromatids remain attached at their centromeres

telophase 1 and cytokinesis (meiosis)

two haploid daughter cells are formed, each containing one set of duplicated homologous chromosomes

interkinesis

a short rest period between meiosis 1/meiosis 2 where no DNA replication takes place

prophase 2 (meiosis)

chromosomes condense again and new spindle apparatuses form in the two haploid cells

metaphase 2 (meiosis)

individual chromosomes align single file along the metaphase plate, similar to mitotic metaphase

anaphase 2 (meiosis)

sister chromatids are finally pulled apart toward opposite poles by the spindle fibers

telophase 2 and cytokinesis (meiosis)

the final stage of meiosis resulting in four genetically different haploid daughter cells

wild-type phenotype

the most common form of a trait as it occurs in nature, often written with (+)

mutant phenotype

an alternative form of a trait resulting from a permanent alteration (mutation) in the DNA sequence of a gene

four stages of Drosophila life cycle

egg, larva (instar I, II, III), pupa, adult

male Drosophila

heavily pigmented, fused dark bands at tip of abdomen, round abdomen, sex combs on front legs, visible external genitalia

female Drosophila

lighter, separate stripes down abdomen, pointed abdomen

wild-type Drosophila

red eyes, long wings, brown body (y+w+m+)