Meiosis and Genetics Vocabulary Flashcards
Meiosis and Gamete Formation
Purpose: create haploid gametes from a diploid organism so that fertilization restores diploidy in the zygote.
Haploid vs. diploid:
Diploid cells in humans have 23 pairs of chromosomes (46 total). 2n = 46
Haploid cells have one copy of each chromosome (23 total). n = 23
How haploid cells are produced: Meiosis (two rounds of cell division following DNA replication in S phase).
Start with a typical diploid cell, duplicate chromosomes in S phase, then proceed through meiosis I and meiosis II.
Meiosis I and II each have prophase, metaphase, anaphase, and telophase. Prophase I includes synapsis and crossing over; Meiosis II resembles mitosis but starts with haploid cells.
Gamete, germline, and fertilization:
Gametes are haploid cells produced by germline cells via meiosis.
When two gametes unite (fertilization), a genetically unique diploid zygote forms and grows into an embryo and then an adult.
Germline cells are the cells that undergo meiosis to produce gametes; somatic cells are diploid but not used for reproduction.
Stages of meiosis I vs meiosis II:
Meiosis I: Prophase I, Metaphase I, Anaphase I, Telophase I (followed by cytokinesis) -> two haploid daughter cells.
Meiosis II: Prophase II, Metaphase II, Anaphase II, Telophase II (cytokinesis) -> four unique haploid gametes.
Prophase I features: chromosome condensation, homologous chromosomes paired as tetrads (two homologs, each with two sister chromatids), synapsis, and crossing over (recombination).
Synapsis creates a tetrad (four chromatids). Crossing over exchanges corresponding segments between homologous chromosomes, producing new allele combinations.
After crossing over, sister chromatids are no longer identical.
Random orientation of tetrads during Metaphase I leads to independent assortment (each pair’s alignment is random with respect to maternal/paternal origin).
Anaphase I: homologous chromosomes separate to opposite poles; sister chromatids remain attached at the centromeres.
Telophase I and Cytokinesis: two haploid cells form.
Meiosis II (no crossing over): sister chromatids separate; results in four unique haploid gametes.
Key features that increase genetic diversity:
Independent assortment during Metaphase I and Anaphase I (random alignment of homologous chromosomes).
Crossing over (synapsis) during Prophase I exchanges genetic material between homologous chromosomes.
Random fertilization further increases diversity by producing many possible zygotes.
Terminology and definitions:
Gamete: a non-identical haploid cell (sperm or egg) formed by meiosis.
Germline cells: cells that undergo meiosis to produce gametes.
Zygote: diploid sperm-egg fusion product; genetically unique from both parents.
Interphase prior to meiosis: G1, S, G2 stages (same as mitosis).
Sister chromatids: identical copies of a chromosome held together at the centromere until meiosis II.
Visual overview (video reference): two gametes unite to form an embryo that grows into an adult; meiosis produces haploid gametes; germline cells undergo meiosis; karyotypes show chromosomes; meiosis ensures genetic diversity.
Genotype vs Phenotype; Alleles; and Basic Inheritance
Definitions:
Genotype: the genetic makeup; the specific alleles an individual has for a given gene.
Phenotype: the observable or measurable traits produced by the genotype (and environment).
Allele terminology:
Allele: a version of a gene.
Each person has two copies of a gene (two alleles for each gene).
Homozygous: two identical alleles for a gene (e.g., AA or aa).
Heterozygous: two different alleles for a gene (e.g., Aa).
Genotype examples for earlobe shape: uppercase and lowercase letters used to denote dominant/recessive alleles.
Dominance patterns (basic Mendelian genetics):
Strict (simple) dominance: one allele (dominant) masks the other (recessive) in heterozygotes.
Dominant allele represented with an uppercase letter; recessive with the same letter lowercase.
Genotype possibilities:
Homozygous dominant: AA
Homozygous recessive: aa
Heterozygous: Aa
Phenotype mapping:
Dominant phenotype corresponding to presence of at least one dominant allele (A-).
Recessive phenotype only when both alleles are recessive (aa).
Punnett squares (example: two heterozygous parents Aa x Aa):
Genotypes: AA, Aa, Aa, aa
Genotype ratio: 1:2:1 = rac{1}{4}: rac{1}{2}: rac{1}{4}
Phenotype ratio (dominant vs recessive): 3:1
Conclusion: a 25% chance for homozygous dominant, 50% heterozygous, 25% homozygous recessive; 75% show dominant trait, 25% show recessive trait.
Monogenic vs polygenic traits:
Many traits are polygenic (influenced by more than one gene) and show a spectrum (not just discrete categories).
Examples often misused in intro genetics: eye color, hair color, skin color, height, body size; these are polygenic.
Incomplete dominance vs codominance (patterns of heterozygotes):
Incomplete dominance: heterozygote phenotype is intermediate between two homozygotes (e.g., red + white flowers yield pink in the heterozygote).
Codominance: both alleles are fully expressed in the phenotype of the heterozygote (e.g., AB blood type expresses both A and B antigens).
Blood type and multiple alleles (ABO system):
Alleles: IA, IB, i (IA, IB, i).
Dominance relationships: IA and IB are codominant with each other; IA and IB are both dominant over i.
Genotypes and phenotypes:
IAIA or IAi -> Type A
IBIB or IBi -> Type B
IAIB -> Type AB (codominance)
ii -> Type O
Multiple alleles: there are more than two alleles in the population (three ABO alleles: IA, IB, i).
Example genotypes: IAIA, IAi, IBIB, IBi, IAIB, ii (six possible genotypes).
Protein expression on red blood cells differs by genotype, producing A, B, AB, or O surface profiles.
Sex-linked (X-linked) inheritance:
Genes on the X chromosome can show different patterns in males (XY) vs females (XX).
Males: only one X allele to express (no second X to mask a recessive allele); this increases expression of X-linked traits in males.
Color blindness is a common X-linked trait; red-green color blindness is more common in males because the Y chromosome carries no equivalent allele to compensate.
Examples of notation:
Normal color vision: X^C
Color blindness allele: X^c
Female genotypes: XX, X^C X^c, X^c X^c; male genotypes: X^C Y, X^c Y.
Karyotyping and chromosomal content:
Karyotype: visual inspection of chromosomes, used to assess number and structure, not gene function.
Humans: somatic cells are diploid with 46 chromosomes (23 pairs).
Sex chromosomes: XX indicates genetically female; XY indicates genetically male.
Homologous chromosomes: the two copies of each autosome (e.g., chromosome 1, 2, …, 22) that are similar in shape and gene content but may carry different alleles.
Homozygous vs heterozygous for a gene refers to the two alleles on homologous chromosomes at a given locus.
Common chromosomal abnormalities (examples mentioned):
Trisomy 21 (Down syndrome): three copies of chromosome 21; most survivable trisomy; associated with intellectual disability and congenital anomalies; shorter lifespan (historically ~40 years, now longer with medical advances).
Turner syndrome (Monosomy X, XO): females with a single X chromosome; infertility and underdeveloped secondary sexual characteristics are common.
Klinefelter syndrome (XXY): males with an extra X chromosome; reduced testosterone, incomplete penis/testicle development, breast development; usually infertile.
Trisomies involving other chromosomes (e.g., trisomy 13) often lead to severe malformations and early death.
Aneuploidy generally results in developmental failure and often early embryonic loss; some cases survive depending on chromosome involved.
Monogenic disorders (single-gene defects) discussed:
Sickle cell disease: single base change in hemoglobin gene; altered hemoglobin shape leads to red blood cell sickling, hemolysis, and systemic complications.
Cystic fibrosis: mutation in a gene encoding a chloride channel protein; thick secretions in mucus, sweat, digestive, and reproductive systems; infection risk and reduced lifespan.
Genome and epigenetics:
Genome: all genetic material of a species or individual; humans have ~
genes: about 20,000
proteins: a bit more than 20,000 encoded by genes
many single-gene disorders exist; most are rare
roughly ~1 in 200 people may carry some kind of genetic abnormality (as stated in the lecture).
Epigenome and epigenetics: study of functional groups and chemical modifications attached to DNA or histones that regulate gene expression without changing the DNA sequence.
Inheritance of epigenetic marks: some epigenetic states can be inherited across generations, influenced by parental/grandparental environments and life experiences.
Practical genetics concepts for the exam:
Genotype-phenotype relationships; how alleles influence trait expression.
How to set up and interpret Punnett squares for simple dominance, including two-trait crosses where appropriate.
Distinctions among autosomal vs sex-linked traits; how sex chromosomes influence inheritance patterns in males vs females.
Recognition of polygenic traits and non-Mendelian patterns (incomplete dominance, codominance).
Understanding karyotypes and what they reveal about chromosome number and sex determination (XX vs XY).
Basic awareness of common genetic disorders and their underlying genetic mechanisms.
Epigenetics as a layer of regulation and its potential heritability in some contexts.
Exam logistics (summary from the lecture):
The exam will be multiple-choice with around 80 questions.
Time: about 85 minutes; pencils and erasers recommended.
Review questions at the end of modules and chapter-specific practice questions are available for study.
Connections to foundational principles and real-world relevance
Meiosis provides genetic diversity via recombination and independent assortment, which underpins evolution and species adaptation.
Mendelian genetics (dominance, segregation, independent assortment) forms the basis for predicting trait inheritance in simple cases; deviations (incomplete/codominance, polygenic inheritance, and linked traits) explain the complexity of real-world traits.
Karyotyping and chromosomal abnormalities illustrate how numerical and structural chromosomal changes can profoundly affect development and health, guiding prenatal diagnosis and clinical management.
ABO blood types demonstrate multiple alleles and codominance in a human system with clear medical and social relevance (transfusion compatibility, immunology).
Sex-linked inheritance highlights the importance of chromosomal context in trait expression and explains why certain conditions (like color blindness) are more prevalent in one sex.
Epigenetics broadens the view of heredity beyond DNA sequence, showing how environment and life history can shape gene expression and potentially be inherited, with implications for disease risk and aging.
Real-world examples (Down syndrome, Turner syndrome, Klinefelter syndrome, sickle cell disease, cystic fibrosis) illustrate how different genetic mechanisms (trisomy, monosomy, single-gene mutations) translate to phenotypes and clinical outcomes.
The genome and epigenome concepts connect to modern genetics research, personalized medicine, and genome-wide analyses, highlighting how small variations can have wide-ranging effects on health and development.
Key numerical references and formulas to remember
Human chromosome count and structure:
Diploid human cells: 2n = 46
Chromosome pairs in humans: 23 pairs (1–22 autosomes, plus sex chromosomes)
Meiosis outcome:
Meiosis I yields two haploid cells; meiosis II yields four haploid cells: total 4 haploid gametes per original diploid germ cell.
Mendelian cross (two heterozygotes) genotype/phenotype ratios:
Genotype ratio: 1:2:1 ( rac{1}{4}: rac{1}{2}: rac{1}{4} )
Phenotype ratio for complete dominance: 3:1 (dominant:recessive)
ABO blood type genotypes (six possibilities) and phenotypes:
Genotypes: IAIA,\, IAi,\, IBIB,\, IBi,\, IAIB,\, ii
Phenotypes: Type A, Type B, Type AB, Type O
Sex-linked inheritance notation examples:
X^C = normal color vision, X^c = color blindness; male genotype examples: X^C Y, X^c Y; female: X^C X^C, X^C X^c, X^c X^c
Common aneuploidies discussed:
Down syndrome: trisomy 21 (three copies of chromosome 21)
Turner syndrome: monosomy X (X0)
Klinefelter syndrome: XXY
Major monogenic conditions mentioned:
Sickle cell disease: mutation in the hemoglobin gene affecting Hb conformation and function
Cystic fibrosis: mutation in chloride channel protein affecting secretions across multiple organ systems
Notes on terminology and study cues
Remember the difference between genotype vs phenotype and how dominance patterns affect phenotype in heterozygotes.
Distinguish autosomal inheritance from sex-linked (X-linked) inheritance when solving problems.
Practice with Punnett squares for simple dominant/recessive traits, and expand to ABO or color-blindness examples to reinforce codominance and monogenic vs polygenic contexts.
Distinguish polygenic traits (often showing a spectrum) from single-gene traits (clear Mendelian patterns).
Understand what a karyotype shows (structure/number of chromosomes) vs what it cannot show (gene function or expression).
Be able to identify the clinical implications of major chromosomal abnormalities and recognize that some combinations are incompatible with life, while others are survivable with varying phenotypes.
Appreciate epigenetics as a layer of gene regulation that can influence disease risk and inheritance patterns beyond DNA sequence.
If you want, I can convert these into a printable study sheet with a compact set of flashcards for the key terms, definitions, and genotype/phenotype rules.