Meiosis, Genetic Variation, and Mendelian Inheritance

Asexual Reproduction

Single parent passes all genes to offspring.

Sexual Reproduction

Two parents contribute genes, increasing genetic variation.

Meiosis

Cell division reducing chromosome number from diploid to haploid.

Fertilization

Fusion of sperm and egg to form zygote.

Homologous Chromosomes

Pairs of similar chromosomes inherited from each parent.

Gametes

Reproductive cells transmitting genes across generations.

Locus

Specific location of a gene on a chromosome.

Somatic Cells

All body cells except gametes, humans have 46 chromosomes.

Clone

Group of genetically identical individuals from asexual reproduction.

Karyotype

Picture of complete set of chromosomes arranged in pairs.

Autosomes

Nonsex chromosomes, excluding X and Y chromosomes.

Haploid Cells

Cells with half the number of chromosomes, n.

Diploid Cells

Cells with two sets of chromosomes, 2n.

Crossing Over

Exchange of genetic material between homologous chromosomes.

Independent Assortment

Random distribution of homologous chromosomes during meiosis.

Random Fertilization

Combination of any sperm and egg increases diversity.

Sister Chromatids

Identical copies of a chromosome connected at the centromere.

Centromere

Region where sister chromatids are joined together.

Metaphase Chromosome

Chromosome aligned at the cell's equatorial plane during meiosis.

Zygote

Fertilized egg formed from sperm and egg fusion.

Maternal Chromosomes

Chromosomes inherited from the mother.

Paternal Chromosomes

Chromosomes inherited from the father.

Chromosome Number

Total count of chromosomes in a cell, 46 in humans.

Meiosis

Process reducing diploid to haploid chromosome sets.

Mitosis

Cell division producing two identical daughter cells.

Diploid

Cell with two chromosome sets (2n).

Haploid

Cell with one chromosome set (n).

Meiosis I

First division stage separating homologous chromosomes.

Meiosis II

Second division stage separating sister chromatids.

Interphase

Phase where DNA replication occurs before meiosis.

Prophase I

Stage where homologous chromosomes undergo synapsis.

Synapsis

Joining of homologous chromosomes during prophase I.

Tetrad

Structure formed by paired homologous chromosomes.

Crossing Over

Exchange of DNA between homologous chromosomes.

Chiasmata

Regions where crossing over occurs between homologs.

Metaphase I

Homologous chromosomes align at the metaphase plate.

Anaphase I

Homologous chromosomes separate to opposite poles.

Telophase I

Homologous chromosomes reach poles; cytokinesis occurs.

Cytokinesis

Division of cytoplasm following nuclear division.

Sister Chromatids

Identical copies of a chromosome connected at centromere.

Metaphase II

Sister chromatids align at the metaphase plate.

Anaphase II

Sister chromatids finally separate to opposite poles.

Telophase II

Final stage resulting in four haploid daughter cells.

Genetic Variation

Diversity in offspring due to crossing over.

Spindle Apparatus

Structure that moves chromosomes during cell division.

Homologous Chromosomes

Chromosome pairs, one from each parent.

Sister chromatids

Identical copies of a chromosome joined together.

Haploid daughter cells

Cells with one chromosome set after meiosis.

Homologous pairs

Chromosome pairs, one from each parent.

Anaphase I

Homologous chromosomes are pulled to opposite poles.

Independent assortment

Random sorting of maternal and paternal chromosomes.

Genetic variation

Differences in genetic makeup among individuals.

Synapsis

Pairing of homologous chromosomes during meiosis.

Tetrads

Paired homologous chromosomes during meiosis I.

Meiosis II

Second division of meiosis resulting in haploid cells.

Prophase II

Spindle apparatus forms in haploid cells.

Metaphase II

Haploid chromosomes align at the metaphase plate.

Anaphase II

Sister chromatids separate and move to opposite ends.

Telophase II

Nuclei reappear as chromosomes reach cell poles.

Cytokinesis

Division of cytoplasm resulting in daughter cells.

Chromosome number reduction

Chromosome count decreases during meiosis I.

Genetic diversity

Variety of genetic combinations in offspring.

Maternal chromosome

Chromosome inherited from the mother.

Paternal chromosome

Chromosome inherited from the father.

Random fertilization

Unique combinations of egg and sperm.

Possible combinations

8.4 million from independent assortment in humans.

Unique chromatids

Chromatids that differ due to crossing over.

Mendel's Law of Segregation

Alleles separate during gamete formation.

Mendel's Law of Independent Assortment

Alleles segregate independently during gamete formation.

P Generation

True-breeding parents in genetic crosses.

F₁ Generation

First filial generation from P generation.

F₂ Generation

Second filial generation from F₁ generation.

Alleles

Alternative versions of a gene.

Dominant Allele

Expressed allele in heterozygous individuals.

Recessive Allele

Not expressed in the presence of a dominant allele.

Homozygous

Two identical alleles for a trait.

Heterozygous

Two different alleles for a trait.

Phenotype

Observable traits of an organism.

Genotype

Genetic makeup of an organism.

Gametes

Reproductive cells containing one allele.

Punnett Square

Diagram showing allele combinations in offspring.

Pedigree Analysis

Chart tracking inheritance patterns across generations.

3:1 Ratio

Observed ratio of dominant to recessive traits in F₂.

Meiosis

Cell division producing gametes with half chromosome number.

Anaphase I

Stage in meiosis where homologous chromosomes separate.

True-breeding

Organisms that produce identical offspring when self-fertilized.

Cross-pollination

Mating between different plants to produce hybrids.

Genetic Cross

Mating of two organisms to study inheritance.

Offspring

Descendants resulting from a genetic cross.

Probability Rules

Mathematical principles used to predict genetic outcomes.

Dominant allele

Allele expressed in heterozygous condition.

Recessive allele

Allele expressed only in homozygous condition.

Homozygous

Having identical alleles for a trait.

Heterozygous

Having two different alleles for a trait.

Phenotype

Observable physical traits of an organism.

Testcross

Cross to determine unknown genotype.

Monohybrid cross

Cross studying one trait only.

Dihybrid cross

Cross studying two traits simultaneously.

Gamete

Reproductive cell carrying alleles.

F₁ generation

First filial generation from parental cross.