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Genetics
| Term | Definition |
|---|---|
| Allele | One of the alternative versions of a gene located at a given location in a chromosome. They are responsible for genetic variation. |
| Gene | Genes are strings of DNA that hold the information that determines an organism's traits. |
| Genome | The total set of genetic material of an organism. This is the information held in a complete set of RNA and DNA in a chromosome. |
| Locus | The specific location of a gene or genetic sequence on a chromosome. |
| Dominant Allele | An allele that, when present, expresses its observable trait whether it is paired with an identical allele or recessive allele. |
| Recessive Allele | An allele that only expresses its observable trait when paired with an identical allele. |
| Diploid | A cell or organism that contains two sets of chromosomes. |
| Haploid | The amount of chromosomes in a gamete cell of an organism. Or, half the number of chromosomes contained in an organism's somatic cells. |
| Homologous Chromosomes | Two identical sets of chromosomes, one maternal and one paternal, that come together during meiosis. |
| Autosome | Any chromosome that does not determine the sex of an organism. |
| Sex Chromosome | A chromosome that is responsible for determining the sex and sexual characteristics of an organism. |
| Genotype | The whole set of genes in an organism. The information that determines what an organism's traits are. |
| Phenotype | How an organism expresses traits described in its genotype. |
| Sex Linked Trait | A trait that is determined by an allele only located within a sex chromosome. |
| Homozygous | A trait whose associated alleles are identical. |
| Heterozygous | A trait whose associated alleles are different. |
| Codominant Allele | A pair of alleles that can both exhibit their associated traits when present. |
| Carrier | An organism that holds a recessive trait (usually defective), but does not display it. |
| Test Cross | An organism displaying a dominant trait is bred with an organism displaying a recessive trait in order to determine the zygosity of the organism with the dominant trait. |
| Multiple Alleles | At times, more than two alleles can be associated with the same gene. |
| Linkage Group | Two or more loci that have been shown to be close in the genome but have not been determined as being on the same chromosome. |
| What is the difference between a chromosome and a chromatid? | A chromatid is one of a pair of duplicated chromosomes. They are generally linked by a centromere |
| How can you tell the difference between single and duplicated chromosomes? | Duplicated chromosomes will be composed of chromatids and appear to be two closely paired objects, while a single chromosome is just a single chromosome. |
| Bivalent | Bivalents are a pair of homologous chromosomes that are held together by a complex. They are formed through synapsis during Prophase 1 of meiosis. |
| Synapsis | The process of pairing homologous chromosomes during Prophase 1 of meiosis. It occurs before they are segregated and allows the possible crossing-over of genetic material between the two chromosomes. |
| Random Orientation | When homologous pairs arrange on the equatorial plate, either the maternal or paternal chromosome can be oriented towards either pole. This occurs randomly and contributes to genetic variation. |
| Gamete | A sex cell that contains haploid chromosomal information. |
| What occurs during interphase? Why does this phase occur only once in meiosis? | The DNA in a cell is replicated. This only occurs once as the DNA is duplicated until the final stages of meiosis 2 and is ultimately split into 4 haploid cells. |
| Prophase 1 | Centromeres begin to move to the poles of a cell and produce spindle. The chromatid within the cell begins to condense to form chromosomes with two chromatids. Homologous chromosomes pair in synapsis. These chromosomes will then exchange genetic material. |
| Metaphase 1 | The bivalents created in prophase 1 arrange themselves in random orientation at the equatorial plate. Spindle fibers attach to the centromeres of the chromosomes. The nuclear envelope is dissolved at this point. |
| Anaphase 1 | The spindle fibers pull the homologous chromosomes to opposite ends of the cell. |
| Telophase 1 | The spindle fibers retract and the chromosomes they were attached to become uncoiled. A new nuclear envelope develops around the DNA and cytokinesis occurs. |
| Prophase 2 | DNA condenses again and centromeres start producing more spindle once more. |
| Metaphase 2 | The nuclear envelopes disappear and the chromosomes contained within arrange along the equatorial plate in random orientation. Spindle fibers attach to the centromeres of each sister chromatid. |
| Anaphase 2 | Spindle fibers pull the sister chromatids apart and drag them to opposite poles of the cell. |
| Telophase 2 | Spindle fibers retract and the chromosomes (now singular) uncoil into DNA strands. New nuclear envelopes develop around the DNA at each pole of each cell. Cytokinesis occurs. The end product is four haploid cells with non-duplicated DNA. |
| Why is meiosis a reduction division? | Meiosis is a reduction division because it results in a reduced amount of chromosomes. It goes from diploid to haploid. |
| Stages of meiosis | Interphase, Prophase 1, Metaphase 1, Anaphase 1, Telophase 1, Prophase 2, Metaphase 2, Anaphase 2, Telophase 2. |
| Crossing Over | Crossing over is the exchange of genetic material between two homologous chromosomes in prophase 1 of meiosis. It results in genetic variation between organisms. |
| How is a chiasma formed? | They are formed in prophase 1 of meiosis and are the points at which crossing over between homologous chromosomes takes place. They are formed between the exact same spot on the two chromosomes. |
| How does crossing over result in an exchange of alleles? | Homologous chromosomes exchange genetic material with each other during crossing over in the form of shuffling alleles between the chromosomes. It results in a new combination of maternal and paternal alleles in each homologous chromosome. |
| End product of meiosis | The end product of meiosis is four daughter cells each with a haploid number of chromosomes. |
| Which two phases of meiosis create the most genetic variation in offspring? | Prophase 1: As crossing over occurs in this phase, which ensures that the genetic information of offspring is always different than that of the parents. Metaphase 1: As random orientation results in the random position of maternal and paternal chromosomes |
| Mendel's Law of independent assortment | The transmission of traits from parent to offspring are completely independent of one another. |
| Mendel's second law in meiosis | During random orientation of metaphase 1, homologous chromosomes line up along the equator and face a different side independently of one another. This means that the genetic information they are carrying will sort without connection to any other info. |
| How does nondisjunction cause down-syndrome? | Nondisjunction is the failure of chromosomes or chromatids to separate properly during cell division. Because a chromosome does not separate it winds up as an extra chromosome in the resulting organism. Down syndrome is contracted in this way. |
| Trisomy 21 | Trisomy 21, commonly referred to as Down's Syndrome, is a genetic condition where an organism contains an extra chromosome 21. This is caused by nondisjunction during cell division. |
| Chromosomes in a karyotype | In karyotyping, chromosomes are arranged in pairs according to their size and structure. |
| Why conduct a karyotype? | It can help in pre-natal diagnosis of chromosomal abnormalities. |
| Cell collection for a karyotype | Cells are collected for a karyotype through amniocentesis or chorionic villus sampling. |
| Determining nondisjunction through a karyotype. | If there are extra chromosomes detected in a karyotype, this means that non-disjunction has occurred. |
| Key for ABO blood types | A = IA IA, IA Ii B = IB IB, IB Ii AB = IA IB O = ii |
| ABO and odominance | Codominant alleles are alleles that both affect the phenotype when present in genotype. The AB blood type is an example of a codominant trait because it contains two codominant alleles, A and B. |
| ABO and multiple alleles | There are three alleles associated with the ABO blood group. IA, IB, and i. Whenever there are more than two alleles that affect a certain gene, they are referred to as multiple alleles. Therefore, multiple alleles are associated with the ABO blood group. |
| Which chromosomes determine gender? | The sex chromosomes (X and Y) of an organism determine that organism's gender. XX = Female. XY = Male |
| X and Y chromosomes | Not all genes present on the X chromosome are present on the shorter Y chromosome. |
| Color blindness | The X chromosome holds the gene that codes for color blindness. |
| Hemophilia | The X chromosome hold the gene that codes for hemophilia. |
| Color blindness & Hemophilia: sex linked | Hemophilia and color blindness are sex-linked traits because the gene that codes for the two diseases lies on the X chromosome, which is a sex chromosome. |
| Key for Color blindness | Normal = Female: XB XB, XB Xb. Male: XB Y Color blind = Female: Xb Xb. Male: Xb Y |
| Key for Hemophilia | Normal = Female: XH XH, XH Xh. Male: XH Y Hemophilic = Female: Xh Xh. Male: Xh Y |
| Female sex-linked zygosity | Females can be homo- and heterozygous with respect to sex-linked traits because they carry two of the same sex chromosomes. Having two possibilities is necessary for something to be considered Homo/heterozygous. |
| Male sex-linked zygosity | Males contain one of each sex chromosome and can therefore only inherit one of a pair of alleles. Having two alleles is necessary for determining zygosity, so males cannot be zygous |
| Female carriers and x-linked traits | Female carriers are always heterozygous because they contain one dominant allele and one recessive allele in their sex chromosomes. |
| Example of liked genes | Hair color and skin color. |
| Identifying offspring as recombinants | Recombinant offspring contain the genotypes that are not represented by either parent. If the parents were XxYy and XXYy, the recombinant offspring could be XXYY, XxYY, xxYY, XxYY |
| Polygenetic Inheritance | The kind of inheritance where a particular trait is produced from the interactions of many genes. Non-mendelian inheritance |
| Continuous variation | Variants cannot be grouped into any one group because there are almost an infinite number of possible groups. Measurements are on a complete range from the maximum and minimum of a continuously variable trait. Body weight and Height. |
| Discontinuous variation | Variants can be grouped into distinct groups, as the trait is measured discretely. Blood type and |
Created by:
BenSchulz
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