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Description
Flashcards by Licole Woo, updated more than 1 year ago
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Created by Licole Woo
over 7 years ago
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| Question | Answer |
| Study of heredity | = passing on characteristics from one generation to the next |
| Gene | = a segment of DNA that controls a specific characteristic / trait -> there are 2 copies of each gene in diploid cells (paternal + maternal) |
| Allele | = specific form of a gene -> Homozygous: when 2 alleles are the same -> Heterozygous: when 2 alleles are different |
| Locus | = particular position of gene on homologous chromosomes -> homologous chromosomes carry the same genes on the same loci |
| Genotype | = the combination of alleles of an organism, usually represented by 2 letters (e.g. BB, Pp, tt) |
| Phenotype | : observable characteristics of an organism (e.g. blue eyes, type O blood) |
| Types of Alleles | 1. Dominant allele = an allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state 2. Recessive allele = an allele that only has an effect on the phenotype when present in the homozygous state 3. Co-dominant alleles = pairs of alleles that both affect the phenotype when present in a heterozygote -> combined phenotype |
| Mendel and the Principles of Inheritance | - discovered the Principles of Inheritance through experiments in which large number of pea plants were crossed -> transfer male pollen from one variety to female parts in flowers of another variety -> grew the pea seeds that were resulted to test for characteristics -> Repeated trials shows reliability in Mendel's experiments (large # of replicates in quantitative results) |
| Results of Mendel's Experiments | - All of the offspring showed the characteristic of one of their parents, not the other -> the common characteristic has the dominant allele (e.g. TT) which masks the effect of the recessive allele (e.g. tt) - Example of co-dominant alleles: -> if a red-coloured flower (C^R) crosses with a white-coloured flower (C^W), the offspring have pink flowers (C^RC^W) |
| Gametes | - Parents pass genes onto their offspring in gametes - Contains one chromosome of each type -> gamete is haploid, which contains only one allele of each gene -> each parent makes an equal genetic contribution to their offspring |
| Law of Segregation (first rule of Mendel's Principle) | - when pairs of alleles of a gene segregates during gamete formation - the haploid nucleus only receives one of the alleles of the diploid cell -> two copies of the allele are present (e.g. PP), the haploid nucleus will receive P -> two different alleles are present (e.g. Pp), there is a 50-50% chance of receiving either alleles P or p |
| Law of Independent Assortment (Second rule of Mendel's principle) | - Occurs at metaphase I - Orientation of chromosomes (paternal / maternal) on either side of the equator is random and independent of other chromosomes - refers to 2 or more unlinked genes |
| Monohybrid cross | = crossing two organisms that differ in one characteristic (single gene -> single characteristic) |
| Test cross | = testing a suspected heterozygote - to find out the genotype of an organism with a dominant character (homozygous dominant / heterozygous?) - How? Cross it with a homozygous recessive individual |
| Inheritance with Multiple Alleles | - Some genes have more than 2 alleles EXAMPLE: HUMAN BLOOD GROUP = determined by the type of cell surface protein of RBCs - has 3 alleles in human blood group -> Co-dominant alleles: I^A, I^B -> recessive allele: i |
| Human Blood Group (Genotypes & Phenotypes) | |
| Many genetic diseases in humans are due to recessive alleles of autosomal genes | - when an individual has 2 copies of the recessive allele - when an individual has one dominant allele and one recessive allele = CARRIER -> has a recessive allele of a gene that does not have an effect on their phenotype -> allele can be passed onto offspring EXAMPLE: CYSTIC FIBROSIS -> causes lung infections and limits the ability to breathe over time -> C allele: normal -> c allele: affected |
| Some genetic diseases are due to dominant alleles of autosomal genes | EXAMPLE: HUNTINGTON'S DISEASE -> H allele = affected -> h allele = normal -> only takes one allele to cause the condition |
| Sex Determination in Human | - X and Y chromosomes control gender -> XY = boy; XX= girl - Sex-linkage = genes that are located on sex chromosomes -> expression and inheritance patterns differ between females and males - Sex-linked inheritance of genetic diseases are usually due to the genes on the X chromosome (because the Y chromosome is smaller, there are fewer genes / loci) - Females have two genes for a trait (2 chromosomes); males have one gene for a trait and one X chromosome passed on from the mother (less likely to be affected by sex-linked diseases) |
| Some genetic diseases are sex-linked | EXAMPLE: RED-GREEN COLOUR BLINDNESS -> X-linked recessive -> Alleles: X^C (normal), X^c (affected) EXAMPLE: HEMOPHILIA -> results from a recessive sex-linked allele on X chromosome -> Alleles: X^H (normal), X^h (affected) ** Only females can be carriers / heterozygous for x-linked recessive traits (e.g. X^C X^c) |
| Some genetic diseases are due to co-dominant alleles | EXAMPLE: SICKLE CELL ANEMIA -> normal allele for hemoglobin: HB^A -> allele for sickle-cell: HB^S Phenotypes of different genotypes: -> HB^A HB^A: susceptible to malaria, not anemic -> HB^S HB^S: susceptible to malaria, severely anemic -> HB^A HB^S: increased resistance to malaria, mildly anemic (due to the altered shape of RBC) |
| Dihybrid Cross | - examines 2 genes (2 different characteristics) together |
| Linked V.S. Unlinked Genes | - Mendel's Law of Independent Assortment and Law of Segregation only applies to UNLINKED GENES (genes located on different chromosomes) -> segregate independently during meiosis - LINKED GENES (genes on the same chromosome) do not segregate independently -> travel together during meiosis |
| Linked Genes | Linkage group = a group of genes who loci are on the same chromosome -> their alleles can't be separated independently during anaphase I - linked genes tend to be inherited together - A dihybrid cross between two hybrids usually produces a phenotypic ratio of 9:3:3:1 (MENDELIAN RATIO) -> applies to unlinked genes - A dihybrid cross that do not produce 9:3:3:1 ratio = NON-MENDELIAN RATIO -> applies to linked genes |
| Recombination | Recombination can occur in chromosomes with linked genes via. crossing-over Example: Parental gametes = PL and pl After crossing-over occurs, 4 different types of gametes are formed (PL, Pl, pL, pl) -> Pl and pL = recombinants (that vary from parental gametes) -> relatively few in # Recombination = offspring whose genotype and phenotype are different from their parents |
| Example of Crossing-Over of Linked Genes | |
| How to represent recombinants in terms of notation? | |
| Chi-Squared Test | = a statistical test to compare observed results with expected results and determine whether or not the difference is significant or not |
| Equation of Chi-Square | |
| Types of Variations | 1. Discontinuous / Discrete variations -> no intermediates -> determined by genes only -> e.g. eye colour, blood type 2. Continuous variations -> continuous range of intermediates between 2 extremes -> affected by both genes + environment -> follows bell-shape curve (normal dist.) -> e.g. weight, height |
| Polygenic Inheritance | = a characteristic affected by multiple genes (2 or more) -> produces many possible combination of alleles -> producing a broad range of phenotypes -> cumulative effect: as # of genes increase, phenotypic variation increases -> resulting in continuous variation |
| Example of Polygenic Variation | EXAMPLE: HUMAN SKIN COLOUR -> multiple genes influence skin colour -> skin colour depends on the amount of MELANIN (pigment) being produced -> Each gene codes for melanin production -> more dominant alleles = the darker the skin (for every dominant allele in genotype, one "unit" of melanin is added to skin) -> results in a great variety of skin colour |
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