Genetics: Heredity, Variation, and Meiosis

Reproduction

Ability of organisms to produce offspring.

Genetics

Scientific study of heredity and variation.

Heredity

Transmission of traits across generations.

Variation

Differences in appearance among offspring.

Genes

Units of heredity made of DNA segments.

Gametes

Reproductive cells: sperm and eggs.

Locus

Specific location of a gene on a chromosome.

Chromosomes

DNA packaged into structures within cells.

Asexual reproduction

Single individual reproduces without gamete fusion.

Clone

Genetically identical individuals from one parent.

Sexual reproduction

Offspring from two parents with unique genes.

Life cycle

Generation-to-generation sequence of reproductive stages.

Somatic cells

Non-gamete cells in humans, 23 chromosome pairs.

Karyotype

Ordered display of chromosome pairs from a cell.

Homologous chromosomes

Chromosomes in a pair with same genes.

Sex chromosomes

Determine individual sex; X and Y chromosomes.

Diploid cell

Cell with two sets of chromosomes (2n).

Haploid cell

Cell with one set of chromosomes (n).

Fertilization

Union of sperm and egg gametes.

Zygote

Fertilized egg with chromosomes from both parents.

Meiosis

Cell division producing haploid gametes.

Meiosis I

Reductional division separating homologous chromosomes.

Meiosis II

Equational division separating sister chromatids.

Crossing over

Exchange of DNA segments between nonsister chromatids.

Tetrad

Group of four chromatids formed during meiosis.

Microtubules

Cytoskeletal structures that separate chromosomes during meiosis.

Kinetochore

Protein structure where microtubules attach to chromosomes.

Anaphase I

Homologous chromosomes separate to opposite poles.

Sister chromatids

Identical copies of a chromosome joined at the centromere.

Telophase I

Chromosomes decondense; nuclei form at cell poles.

Cytokinesis

Division of cytoplasm into two daughter cells.

Punnet Square

a diagram used to predict the possible genotypes and phenotypes of offspring in a cross, based on the genotypes of the parents

Pedigree

a diagram that visually represents the inheritance of a specific trait or genetic condition through multiple generations of a family

Prophase II

Spindle apparatus forms; sister chromatids prepare for division.

Metaphase II

Sister chromatids align at the metaphase plate.

Crossing over

Exchange of genetic material between homologous chromosomes.

Genetic variation

Diversity in gene frequencies within a population.

Independent assortment

Random distribution of maternal and paternal chromosomes.

Recombinant chromosomes

Chromosomes with mixed genetic material from parents.

Haploid

Cell with one set of chromosomes (n).

Diploid

Cell with two sets of chromosomes (2n).

Cohesins

Proteins that hold sister chromatids together.

Mutations

Changes in DNA that create genetic diversity.

Alleles

Different versions of a gene.

Random fertilization

Combination of gametes from different parents.

Tetrads

Paired homologous chromosomes during meiosis I.

2n combinations

Possible combinations of chromosomes during independent assortment.

Nonsister chromatids

Chromatids from different homologous chromosomes.

Genetic diversity

Variation in genetic traits within a population.

Genetic variation

Diversity in gene combinations from two parents.

Random fertilization

Any sperm can fuse with any ovum.

Zygote

Cell formed by the fusion of gametes.

Diploid combinations

Approximately 70 trillion combinations in zygotes.

Crossing over

Exchange of chromosome segments during meiosis.

Natural selection

Environment favors certain genetic variations.

Sexual reproduction

Combines genetic material from two parents.

Hybridization

Mating of two true-breeding varieties.

P generation

True-breeding parents in Mendel's experiments.

F1 generation

Hybrid offspring from the P generation.

F2 generation

Offspring from self-pollination of F1 hybrids.

Law of segregation

Alleles for a trait separate during gamete formation.

True-breeding

Plants produce identical offspring when self-pollinated.

Homozygous

Two identical alleles for a trait.

Heterozygous

Two different alleles for a trait.

Phenotype

Physical appearance of an organism.

Genotype

Genetic makeup of an organism.

Monohybrid cross

Cross between two heterozygotes for one trait.

Dihybrid cross

Cross between F1 dihybrids for two traits.

Law of independent assortment

Alleles segregate independently during gamete formation.

Complete dominance

Heterozygote phenotype matches dominant homozygote.

Incomplete dominance

F1 hybrids show intermediate phenotypes.

Codominance

Both dominant alleles expressed distinctly in phenotype.

Sex-linked gene

Gene located on a sex chromosome.

Barr body

Inactive X chromosome in mammalian females.

Linked genes

Genes inherited together due to proximity.

Nondisjunction

Failure of homologous chromosomes to separate.

Monosomic zygote

Zygote with one copy of a chromosome.

Trisomic zygote

Zygote with three copies of a chromosome.

Chromosome breakage

Can lead to deletion, duplication, inversion, translocation.