AP Biology: Genetics – Flashcards
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Gregor Mendel
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Austrian monk who conducted a quantitative study of inheritance using garden peas Why garden peas? alternate traits, true breeders, small and easy to grow, fertilization
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How did Mendel conduct his experiments?
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*1.* allowed plants to self fertilize for several generations- produced true breeders *2.* crossed true breeders *3.* allowed F1 generation to self fertilize *4.* counted numbers of offspring
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What did Mendel reason for his experiments?
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*--*"factors" caused the traits *--*each organism had two factors for a trait *--*two factors for a trait came from parents *--*gametes contain only one factor from a parent *--*gametes have equal chance of having either factor
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allele
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alternate form of a gene Ex. gene = flower color allele = purple or white
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character
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heritable feature that varies among individuals
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trait
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variant of a character
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locus
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location of gene on chromosome
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dominant
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allele that is expressed if present Ex. RR, Rr, rR
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recessive
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allele that is "masked" by dominant **only seen if dominant is NOT present Ex. rr
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genotype
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an organism's genetic make-up for a trait Ex. RR, Rr, rR, rr
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homozygous
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having two identical alleles for a trait; purebred Ex. RR, rr
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heterozygous
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having two different alleles for a trait; hybrid Ex. Rr, rR
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phenotype
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a physical trait on an organism that can be "seen" Ex. blue eyes, green eyes
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How do gametes play a role in genetics?
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Each gamete carries one allele. **Alleles come from parents' sex cells.
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law of segregation
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alleles separate in meiosis so that only one allele from each pair is present in each gamete **random chance which allele goes into a gamete **results in genetic variation in gametes and offspring **ON DIFFERENT CHROMOSOMES
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law of independent assortment
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alleles of one trait sort independently of the alleles of other traits **Exception: if genes are on the same chromosome, then they'll always be found together. **results in genetic variation in gametes and offspring **ON DIFFERENT CHROMOSOMES
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law of dominance
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one of the alleles for a pair of inherited traits will be dominant and the other recessive
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Punnett Square
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device used to predict possible outcome of a genetic cross *1.* List parents' genotypes *2.* Draw box *3.* Write allele(s) parents could donate to a gamete along top and side *4.* Combine alleles (gametes) into individual boxes
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Multiplication Rule
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("AND" rule) - use when trying to find probability of 2 or more separate events occurring together.
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Addition Rule
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("OR" rule) - use when trying to find probability of ONE of two or more mutually exclusive events occurring together.
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monohybrid cross
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cross dealing with one trait
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dihybrid cross
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cross dealing with two traits
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Ratio for a dihybrid cross between 2 heterozygous parents
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9:3:3:1
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test cross
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process used to determine the genotype of an unknown parent *1.* cross "unknown" parent with a recessive parent *2.* examine results >If any offspring show recessive trait, unknown parent was heterozygous.
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incomplete dominance
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neither allele is completely dominant over the other **results in mixing *--*R = red, W = white *--*RR = red, WW = white *--*RW = pink
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codominance
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more than one dominant allele **both expressed if present *--*B = black stripes, Br = brown stripes *--*BB = black stripes, BrBr = brown stripes *--*BBr = black and brown stripes
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multiple alleles
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more than two alleles possible for a trait **organism only contains 2 Ex: human hair color Ex: blood type >AA or Ao = Type A >BB or Bo = Type B >AB = Type AB >oo = Type O
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polygenic inheritance
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traits influenced by more than one gene Ex. human skin color, human height **occurs when multiple genes determine the phenotype of a trait
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multifactorial
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when one or more genes + environmental factors influence a trait or disease **diabetes
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pedigree
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family history tracing a particular trait Used to determine the pattern of inheritance: 1. Dominant/recessive 2. Autosomal/sex-linked 3. Monogenic or polygenic
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sex linked genes
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genes carried on the sex chromosomes **usually the X chromosome Ex. colorblindness, hemophilia
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glycoproteins
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on the surface determine blood type and is important in transfusions and transplants
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codominant blood types?
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type AB
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universial donor
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O negative
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universal recipiant
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AB +
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Rh factor
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another type of antigen which can be either present (+) or absent ( - ) on RBCs... **In general, Rh- blood is given to Rh- patients and Rh+ blood or Rh- blood may be given to Rh+ patients.
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X-INACTIVATION...
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IN FEMALE MAMMALS **Most of one X chromosome in each cell is randomly inactivated by addition of methyl groups to DNA. **Becomes a condensed structure called a BARR BODY • **Thus males and females have same effective dose of most X-linked genes
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EXTRANUCLEAR GENES
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**Exhibit a non-Mendelian pattern of inheritance **Extranuclear genes are found in cytoplasmic organelles (plastids and mitochondria) **Inherited from mother (in egg's cytoplasm)
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Barr bodies
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inactivated X chromosomes found only in females (kind of like a "back-up" X chromosome) XX
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sex linked traits
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traits determined by genes on the sex chromosomes **most are recessive
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autosomes
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the 22 pairs of "non-sex" chromosomes
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sex chromosomes
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the one pair of chromosomes that determine gender **two types: X and Y XX = female XY = male
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Why does the almighty Y chromosome determine gender?
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contains SRY gene which causes testosterone to develop, creates a male
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Why do sex linked traits show up in males much more often than females?
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males have only one X-sex chromosome, so they show the allele they have, and females have 2 X-sex chromosomes, so they have to be homozygous to show the trait
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karyotype
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a picture of matched chromosomes (arranged in pairs by size and shape) 1. use blood cells 2. add chemicals to begin division and then stop in metaphase 3. chromosomes isolated and stained 4. chromosomes photographed, cut out, arranged in homologous pairs
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genetic disorders
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these are due to either a "disease" gene or an incorrect number of chromosomes
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genetic diseases
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these are caused by alleles but the chromosome number is correct
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Autosomal genetic diseases:
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cystic fibrosis sickle cell anemia Huntington's
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Sex-linked genetic diseases:
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hemophilia color-blindness muscular dystrophy
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non-disjunction
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failure of chromosomes to separate during meiosis **results in abnormal chromosome # in egg or sperm, causes genetic disorders
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How are autosomal genetic disorders caused?
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when autosomes fail to separate
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trisomy
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genetic disorder in which there are extra autosomes Ex. Trisomy 21 (Down Syndrome)
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monosomy
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genetic disorder in which there are missing autosomes **does not occur because you need all autosomes to develop properly
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How are sex-linked genetic disorders caused?
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when sex chromosomes fail to separate
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Sex chromosome disorders:
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Turner's Syndrome >sexually immature female Klinefelter's Syndrome >male w/ female characteristics XXX - normal female XYY - normal male OY - does not exist
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linked genes
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genes found on the same chromosome usually inherited as a linked unit and associated with genes on the autosomes
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Some traits are usually seen together (blonde hair, blue eyes). Why do variations of the expected combination occur?
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Variations of this expected combination occur due to crossing-over during meiosis.
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How do you determine whether traits are linked?
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*--*Perform a cross with a parent recessive for both traits *--*Examine offspring *--*Examine the ratio of observed versus expected offspring
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parental dominant
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offspring with same dominant traits as one of the parents
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parental recessive
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offspring with same recessive traits as one of the parents
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non-parental
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trait combination not seen in either parent
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What affects how often genes cross-over?
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the distance the genes are from each other *--*genes closer together cross over less frequently *--*genes farther apart cross over more frequently **Crossing over frequency also affected by how close gene is to centromere
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recombination frequency
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frequency in which a single chromosomal crossover takes place between two genes during meiosis **measure of genetic linkage used in the creation of a genetic linkage map (genes occurring together)
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recombination mapping
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mapping of linkage groups with one map unit representing 1% recombination
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null hypothesis
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there is no statistically significant difference between observed and expected results
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autosomal dominant
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only need one dominant allele to be affected
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autosomal recessive
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need two recessive alleles to be affected
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x linked recessive
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females need two recessive alleles, males only need one allele to be affected
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linked genes
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Genes located near each other on the same chromosome tend to be inherited together in genetic crosses
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Genetic Recombination
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Production of offspring with combinations of traits that differ from those found in either parent.
