Genetics Flashcards
DNA
Nucleic acid found in cells; the genetic material that specifies protein synthesis in cells.
Gene
Unit of heredity existing as alleles on the chromosomes
Allele
Alternate form of a gene
Chromatin
Network of fibrils consisting of DNA and associated proteins within a nucleus
Chromosome
Composed of chromatin and contains the hereditary units, or genes.
Homologous Chromosomes (homologues)
Similarly constructed chromosomes that have the same shape and contain genes for the same traits.
Chromatid
each of the two threadlike strands into which a chromosome divides longitudinally during cell division.
Diploid cell
Twice the number of chromosomes found in gametes
Haploid cell
Half the diploid number; the number characteristic of gametes that contain only one set of chromosomes
Fertilization
Union of a sperm nucleus and an oocyte nucleus to create a zygote
Phenotype
Outward appearance of an organism caused by the genotype and environmental influences
Dihybrid
Individual that is heterozygous for two traits.
Multiple Alleles
Inheritance pattern in which there are more than two alleles for a particular trait
Genotype
Combinations of alleles
Homologues
Similarly constructed chromosomes that have the same shape and contain genes for the same traits.
Gametes
Haploid sex cell; an oocyte or a sperm that joins during fertilization to form a zygote
Genetic Variation
Due to crossing over and independent assortment during meiosis , off-spring do not have the same genetic makeup as either parent.
Crossing Over
Exchange of corresponding segments of genetic material between non-sister chromatids of homologous chromosomes during synapsis ( the connection of chromosome pairs during meiosis) of meiosis
Independent assortment
Alleles of unlinked genes segregate independently of each other during meiosis so that the gametes contain all possible combinations of alleles.
Prophase I
Homologous chromosomes pair during synapsis
Metaphase I
Homologous chromosome pairs align at the metaphase plate
Anaphase I
Homologous chromosomes separate, pulled to opposite poles by the centromeric spindle fibres.
Telophase I
Daughter cells ave one chromosome from each homologous pair
Interkinesis
Period of time between meiosis I and meiosis II during which no DNA replications takes place.
Prophase II
Cells have one chromosome from each homologous pair
Metaphase II
Chromosomes align at the metaphase plate
Anaphase II
Daughter chromosomes move toward the poles
Telophase II
Spindle disappears, nuclei form, and cytokinesis takes place
Daughter Cells
Meiosis results in four haploid daughter cells
Recessive allele
Hereditary factor that expresses itself in the phenotype only when the genotype is homozygous
Dominant allele
Allele that exerts its phenotypic effect in the heterozygote; it masks the expression of the recessive allele
homozygous
Having identical alleles, which could be AA or aa for a given trait; pure breeding.
heterozygous
Having two different alleles for a given trait, Aa
Monohybrids
Individual that is heterozygous for one trait
Co-dominance
Three phenotypes (one per genotype) and the third one is a combination of the other two ex. roan cow
Epistasis
More than one pair of genes for ONE trait
Incomplete dominance
Three phenotypes (one per genotype) and the third one looks like a blend ex. skin colour
Multi-allelic genes
One pair of genes with more than 2 alleles
Carrier
Heterozygous woman who has no apparent abnormality but can pass on an allele for a recessively inherited genetic disorder
Autosomes
Any chromosome other than the sex chromosomes
Sex chromosomes
Chromosome that determines the sex of an individual; in humans, females have two X chromosomes, and males have an X and Y chromosome
Sex-linked
Allele that occurs on the sex chromosomes but may control a trait having nothing to do with the sexual characteristics of an individual
Difference between Meiosis and Mitosis
Mitosis: Cell division to produce more cell growth
Meiosis: Is the process as part of sexual reproduction in which the gametes (23 chromosomes from each parent) to form a zygote
Difference between Meiosis I and Meiosis II
Meiosis I: During Telophase the daughter cells form
Meiosis II: This is where the sister chromatids separate
A-sexual reproduction:
- One parent is needed
- Cell division by mitosis produces cells
Sexual reproduction:
- Two parents (46 chromosomes - diploid)
- Cell division by meiosis
- Sex cells (gametes) produce half the number of chromosomes (23)
Tetrad
A grouping of four chromatids that have similar genes. This is where crossing over may occur
Principle of Segregation:
genes exist in pairs, which segregate randomly when gametes are formed and then recombine into pairs at fertilization
Principle of Dominance:
heterozygous, then one version will dominate and the other will disappear. The recessive version of the gene will only show up as a trait when an individual inherits two copies of the recessive, or is homozygous recessive.
