Genetics Overview

Gene

Basic functional unit of heredity, a section of DNA sequence that codes proteins.

Allele

Alternative form of a gene in a DNA sequence, can be dominant or recessive.

DNA

Double-stranded nucleic acid chain made of nucleotides carrying instructions for proteins.

Chromosome

Threadlike structure made of DNA and histone proteins, circular in prokaryotes and linear in eukaryotes.

Genome

Total organism DNA measured in base pairs in a haploid set of chromosomes.

Nucleic Acid

Macromolecules like DNA and RNA, composed of nucleotide polymers.

Nucleotide

Monomer unit of nucleic acid with a nitrogen base, phosphate group, and sugar molecule.

Double Helix

DNA structure with two anti-parallel polynucleotide chains forming a helix.

Antiparallel

Two DNA strands running in opposite directions.

Complementary Base Pairing

Specific pairing of nitrogenous bases (A-T, C-G for DNA; A-U, C-G for RNA).

Hydrogen Bonds

Bonds holding nitrogenous bases together in DNA and RNA.

Mitochondria

Organelles containing DNA in cells.

Chloroplasts

Organelles containing DNA in plant cells.

Homologous Chromosomes

Chromosomes with same genes, different alleles, same size, and gene loci.

Sister Chromatids

Identical copies of a chromosome connected by a centromere.

Somatic Cells

Cells responsible for bodily functions excluding reproduction.

Gametes

Sex cells responsible for reproduction.

Autosomes

Chromosomes coding for bodily functions excluding sex determination.

Sex Chromosomes

Chromosomes determining biological sex and coding for gametes.

Karyotype

Visual representation of an organism's chromosomal makeup.

Trisomy 21

Down Syndrome - extra chromosome in autosomal pair 21.

Trisomy 13

Kleinfelter's Syndrome - extra chromosome in pair 13

Haploid

One complete set of chromosomes, e.g., gametes (n)

Diploid

Two sets of chromosomes, e.g., somatic cells (2n)

Monoploid

One chromosome per homologous pair, complete set

Polyploidy

Three or more sets of chromosomes (3n, 4n)

Aneuploidy

Addition or loss of one chromosome in a cell

Non-disjunction

Failure of chromosomes to separate properly during cell division

Meiosis I

Reduction division resulting in two haploid cells

Meiosis II

Division of haploid cells into daughter cells

Independent Assortment

Random alignment of homologous chromosomes in meiosis

Crossing Over

Exchange of genetic material between homologous chromosomes

Somatic Cell

Body cell with two sets of chromosomes (2n)

Gamete

Sex cell with one set of chromosomes (n)

Centromere

DNA region holding sister chromatids together

Spindle Fibres

Protein structures separating chromosomes during cell division

Centrioles

Organelles aiding chromosome movement in cell division

Homologous chromosomes

Chromosomes with same genes, different alleles, same size, from maternal and paternal copies

Sister chromatids

Identical daughter strands of replicated chromosome, same genes, alleles, size, gene loci

Meiosis

Process creating genetically distinct gametes for sexual reproduction

Double nuclear division

Process in meiosis forming 4 haploid daughter cells with unique DNA

Independent assortment

Random alignment of homologous pairs in meiosis, increasing genetic variation

Crossing over

Exchange of genetic material between homologous chromosomes in Prophase I of meiosis

Genetic diversity

Variability in genetic makeup due to crossing over and independent assortment

Mitosis

Cell division for growth, repair, asexual reproduction, creating identical daughter cells

Genotype

Genetic composition at a gene locus, represented by letter symbols

Phenotype

Physical or biochemical traits resulting from gene expression and environment

Homozygous

Having identical alleles at a gene locus

Heterozygous

Having different alleles at a gene locus

Dominant inheritance

Trait expressed from a variant gene, masking recessive allele effects

Recessive inheritance

Trait expressed only in homozygous state, masked by dominant allele

Codominant inheritance

Both alleles fully expressed in phenotype of heterozygote, no masking

Incomplete dominance

Heterozygous genotype where both alleles are expressed in an intermediate phenotype

X-linked inheritance

Trait inheritance exclusively on the X chromosome, can be recessive or dominant

Dominant Phenotype Expression

Knowing when a dominant or recessive phenotype will be expressed.

Codominance

Both alleles in a heterozygous individual are dominant and expressed.

Incomplete Dominance

Neither allele in a heterozygous individual is dominant, resulting in an intermediate phenotype.

Genotype Determination

Determining if dominant, recessive, codominant, or incomplete dominant phenotype will be expressed.

Genotype vs. Environment

Phenotypes are influenced by genotype and environmental factors.

Environmental Impact on Traits

Example of a human trait affected by the environment.

Epigenetics

Study of heritable changes in gene expression without altering DNA sequence.

Epigenetic Phenotype Impact

Example of how epigenetic factors influence phenotypes.

Autosomal vs. Sex-linked Genes

Difference between genes on chromosomes 1-22 and the sex chromosomes.

Pedigree Symbols

Understanding symbols used when reading a pedigree chart.

Interpreting Pedigree Charts

Analyzing and drawing conclusions from pedigree diagrams.

Modes of Inheritance

Determining autosomal vs. X-linked and dominant vs. recessive inheritance patterns.

Punnett Squares in Pedigrees

Assigning genotypes in pedigrees and predicting phenotypes using Punnett squares.

Monohybrid Cross

Cross involving one trait, showing parent genotypes, phenotypes, gametes, and F1 generation outcomes.

Co-dominance Punnett Square

Completing Punnett squares for co-dominant inheritance patterns.

Incomplete Dominance Punnett Square

Using Punnett squares to predict outcomes in incomplete dominance scenarios.

Complete Dominance Punnett Square

Predicting genotypes and phenotypes in complete dominance using Punnett squares.

Offspring Phenotype Ratios

Determining predicted ratios or percentages of offspring phenotypes from Punnett squares.

Monohybrid Test Cross

Purpose and process of determining unknown dominant genotypes.

Dihybrid Cross

Inheritance of two different genes controlling two traits.

Dihybrid Genotypes and Gametes

Writing dihybrid genotypes and determining parent gametes.

Dihybrid Cross Phenotypic Ratios

Completing dihybrid crosses to identify phenotypic ratios of offspring.

Linked Genes vs. Independent Assortment

Understanding gene linkage on the same chromosome and independent assortment.

Dihybrid Test Cross

Determining if genes are linked or independently assorting through test crosses.

Law of Independent Assortment

Homologous chromosomes align randomly during cell division, leading to genetic variation.