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genetics midterm
| Question | Answer |
|---|---|
| What is a gene? | A unit of heredity transferred from parent to offspring. |
| What is an allele? | Different, alternate forms of a gene: for example, a gene for a seed color might have two alleles, one for yellow and one for green. |
| What is the difference between a phenotype and a genotype? | A genotype is the combination of genetic alleles, and a phenotype is the observable characteristic |
| What is the difference between 'homozygous' and 'heterozygous'? | Homozygous means an individual has 2 copies of a gene which are the same allele (ex. AA, aa). Heterozygous means they have two different alleles (ex. Aa) |
| What is a dihybrid cross? | A dihybrid cross predicts the ratios of the combination of two different traits passed down by parents (ie nose shape and hair color) to offspring. |
| How do you set up a dihybrid cross of two traits? | A parent has two alleles for each trait (ex Aa and Ff), and pass down one allele for each trait. There are 4 possible combinations (ex. AF, Af, aF, af). Cross each parent's possible combos against each other to get punnett square results (ex. AAff, etc) |
| What is a test cross? | A cross of an f1 generation hybrid to a homozygous recessive type; this helps determine whether an F1 hybrid with a dominant trait was homozygous or heterozygous, based on the results of the offspring. |
| What is a back cross? | A cross of an f1 generation hybrid to either one of its parents. |
| Explain Mendel's First Law (The Law of Segregation) | Every organism contains two alleles for each trait-- one inherited by each parent, whose two alleles from THEIR parents have been separated during meiosis into haploid gametes. The separated alleles are randomly distributed to the offspring. |
| Explain Mendel's Second Law (Law of Dominance) | In a pair of alleles for a trait, one allele (dominant) may conceal the presence of the other (recessive) but both are transmitted to the offspring. |
| What is an autosome? | A chromosome that is not a sex chromosome. |
| What is polymorphism? | When there are two or more possible alleles for a specific gene |
| What is the equation for a chi-square test? | x^2 = sum of [(observed-expected)^2 ] / expected |
| What is the chi-square test used for [in genetics]? | It helps determine whether the observed proportions of a cross are following our expectations of Mendelian genetics, or of non-Mendelian inheritance might be involved. |
| Do we reject the null hypothesis if a p-value is greater than, or less than 0.5? What does it mean to reject the null? | We reject the null if the p-value is less than 0.5. Rejecting the null hypothesis means that we are seeing a value outside of the expected proportions— so something outside of Mendelian inheritance is the cause of the pattern. |
| How do you determine degrees of freedom for a chi-square test? | df = n-1 (where n is the number of independent variables) |
| What is sex-linked single gene inheritance? | When a gene is present on a sex-chromosome (X or Y) and is passed down to the offspring with sex-specific patterns of inheritance. |
| What are some characteristics of x-linked inheritance vs y-linked inheritance? | Because males are XY and females are XX, only males will get traits from Y-linked inheritance. In X-linked inheritance, females can either display traits or be carriers, but affected males will always show the trait because they only have one X-chromosome |
| Name three extensions to Mendel's Laws of Inheritance, and describe them. | Incomplete Dominance (ex. red+white flower=pink flower); Codominance (red+white flower = red and white flower petals); Polygenic Inheritance ( Phenotype controlled by many genes, receive 'doses' that add up) |
| Define 'penetrance' | The proportion of individuals with a specific genotype that manifest that genotype at the phenotype level |
| Define 'expressivity'. What factors might contribute to a level of expressivity? | Expressivity is the degree to which a particular genotype is expressed in the phenotype. The environment, interacting genes, etc, can all effect it (ex: the color of a fruit's skin based on sunlight it receives!) |
| What is variable expressivity? | Expressivity can have variation, such as a piebald dog whose spots might differ in shape, pattern and location compared to another dog with the same genes |
| What are the four organic bases of DNA? Which ones pair together, and how many bonds do they share? | Adenine pairs with Thymine with 2 hydrogen bonds. Guanine pairs with Cytosine with 3 hydrogen bonds. (A-T, G-C) |
| What are the four organic bases of RNA? Which ones pair together? | Adenine pairs with Uracil. Guanine pairs with Cytosine. (A-U, G-C) |
| What is a 'reverse complement' of a DNA sequence? | Looking at a DNA sequence, you can find the sequence of its other strand. Write down the complementary bases, and then write that sequence in reverse order. This is the reverse complement. |
| Describe the central dogma of biology. | DNA is in the nucleus of a cell. RNA unzips the DNA, transcribes its information, and then goes to relay that to the ribosomes. The information is translated, and proteins are created from the provided information. |
| Describe the structure of DNA. | DNA is in the shape of a double helix, with a sugar-phosphate backbone on the outside, and nucleic bases paired on the inside. |
| What are the differences in replication between Eukaryotes and Bacteria? | In Eukaryotes, replication initiates from multiple origins bi-directionally. In Bacteria, it begins at one site and spreads bi-directionally by means of 2 replication forks; genes are organized in sets of operons and everything happens at once |
| What are nucleosomes, and why are they important? | They are structural units composed of DNA wrapped around an octamer of histone proteins. The way they're coiled is responsible for accessibility to the DNA-- turning on/off genes and determining which ones are expressed! |
| What is the difference between somatic and germline mutations? | Somatic mutations occur in the body cells, and are not heritable (can cause cancer though). Germline mutations occur in the germ cells, alter the genetic sequence of cells, and are inheritable (basis of evolution!) |
| What are codons? | Codons are a sequence of three nucleotides that code for an amino acid. They are non-overlapping, and have to be read in their set of three. They have redundancy; one amino acid may have multiple codons that can create it. |
| What is the direction of synthesis for a mature RNA strand doing its work? | In the direction of the 3' end (mature RNA is ordered from 5'-->3') The 3' end can be identified by the poly A tail. |
| What is the difference between an exon and an intron? | An exon is the nucleotide sequence that codes for a protein. An intron is the non-coding section of the DNA. (remember: exons 'express!' and introns look like loops during transcription because they're out of the loop/not being coded...) |
| Name four types of mutations that can happen to genetic code, and their consequences. | Synonymous (last letter of codon changed, creates same amino acid, no consequence); Non-synonymous (point mutation; changes amino acid); Nonsense (creates a premature STOP codon); Frame Shift (insertion/deletion causes rest of code to be misread) |
| What is the difference between a haplo-sufficient and haplo-insufficient gene? | Haplo-sufficient means that 1 good copy in a diploid is enough to result in a normal phenotype (loss of 1 copy is tolerated). Haplo-insufficient means that the loss of even one copy will lead to a mutant phenotype. |
| If all cells in an organism contain the same DNA, why do a liver cell and a neuron have different shapes and functions? | Certain genes are expressed/repressed (turned on/off) to create the type of cell needed for a certain function. |
| What is structural variation? Is it more or less consequential than a point mutation? | Structural variations are DNA rearrangements that involve at least 50 nucleotides; they have a greater effect on a genetic code than a point mutation, which changes much less in comparison. |
Created by:
clownestate