Biology Holt McDougal Chapter 6

Somatic Cell

body cell

Gamete

a haploid reproductive cell that unites with another haploid reproductive cell to form a zygote; sex cell

Homologous Chromosome

chromosomes that have the same sequence of genes, that have the same structure, and that pair during meiosis

Autosome

Any chromosome that is not a sex chromosome

Sex Chromosome

one of the pair of chromosomes that determine the sex of an individual (either X or Y)

Sexual Reproduction

reproduction in which gametes from two parents unite

Fertilization

the union of a male and female gamete to form a zygote

Diploid

a cell that contains two haploid sets of chromosomes

Haploid

describes a cell, nucleus, or organism that has only one set of unpaired chromosomes

Meiosis

a process in cell division during which the number of chromosomes decreases to half the original number by two divisions of the nucleus, which results in the production of sex cells (gametes or spores)

Gametogenesis

process by which gametes are produced through the combination of meiosis and other maturational changes

Sperm

the male gamete (sex cell)

Egg

a sex cell produced by a female

Polar Body

one of the small cells that separates from an oocyte during meiosis, that have little cytoplasm and eventually get discarded

Trait

a genetically determined characteristic

Genetics

the science of heredity and of the mechanisms by which traits are passed from parents to offspring

truebreeding (purebred)

type of organism whose ancestors are genetically uniform; Homozygous dominant or Homozygous recessive

Cross

mating of two organisms

Law of Segregation

Mendel's law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete

Gene

a segment of DNA that is located in a chromosome and that codes for a specific hereditary trait

Allele

one of the alternative forms of a gene that governs a characteristic, such as hair color

Homozygous

describes an individual that has identical alleles for a trait on both homologous chromosomes

Heterozygous

describes an individual that has two different alleles for a trait

Genome

The complete genetic material contained in an individual or species;the entire genetic makeup of an organism

Genotype

the combination of genes for one or more specific traits

Phenotype

an organism's appearance or other detectable characteristic that results from the organism's genotype and the environment

Dominant

describes the allele that is fully expressed when carried by only one of a pair of homologous chromosomes

Recessive

describes a trait or an allele that is expressed only when two recessive alleles for the same characteristic are inherited

Punnett Square

a graphic tool used to predict the results of a genetic cross

Monohybrid Cross

a cross between individuals that involves one pair of contrasting traits

Testcross

the crossing of an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype

Dihybrid Cross

a cross between individuals that have different alleles for the same gene

Law of Independent Assortment

the law that states that genes separate independently of one another in meiosis

Probability

the likelihood that a possible future event will occur in any given instance of the event

Crossing Over

the exchange of genetic material between homologous chromosomes during meiosis; can result in genetic recombination

Genetic Linkage

tendency for genes located close together on the same chromosome to be inherited together

Why did Mendel use pure breeding plants?

so he could be sure of the offspring results