Bio Unit 3 Part 1 Test
Aneuploidy of Sex Chromosomes
-Nondisjunction of sex chromosomes produces a variety of aneuploid conditions -Klinefelter syndrome is the result of an extra chromosome in a male, producing XXY individuals -Monosomy X, called Turner syndrome, produces X0 females, who are sterile; it is the only known viable monosomy in humans
How are traits transmitted from parents to offspring
1. Each parent has two alleles for each character 2. two alleles segregate (separate) during gamete formation 3. offspring inherit one allele from each parent 4. When offspring reproduces, alleles segregate
Epistasis
In epistasis, expression of a gene at one Locus alters the phenotypic expression of a gene at a second locus. For example, and Labrador retrievers and many other mammals, coat color depends on two genes. One gene determines the pigment color (with alleles B for black and b for brown) The other Gene (with alleles E for color and e for no color) determines whether the pigment will be deposited in the hair. If heterozygous black labs (genotype BbEe) are mated, we might expect the dihybrid F2 ratio of 9:3:3:1 However, a punnets square shows that the phenotypic ratio will be nine black to three chocolate to four yellow labs Epistatic interactions produce a variety of ratios, all of which are modified versions of 9:3:3:1.
pedigree analysis
In human genetics, geneticist, analyze the results of human matings that have already occurred. a PEDIGREE is a family tree that describes the inheritance of a family across generations.
X in activation in female mammals
In mammalian females, one of the 2X chromosomes in each cell is randomly in activated during embryonic development The inactive X condenses into Barr body If a female is heterozygous for a particular gene located on the X chromosome she will be a mosaic for that character Inactivation of an X-chromosome involves modification of the DNA and proteins, bound to it, called histones A part of the chromosome contains several genes involved in the inactivation process One of the genes there becomes active only on the chromosome that will be inactive The gene is called XIST x-inactive specific transcript
Coraline behavior of a genes alleles with behavior of a chromosome pair
In one experiment, Morgan needed male flies with white eyes mutant with female flies with red eyes wild type - the F1 generation all had red eyes - The F2 generation showed a 3 to 1 red to white eye ratio, but only males had white eyes Reason that white eye mutant alleles must be located on the X chromosome Female flies have 2X chromosomes. Do males. Have one X one Y
Useful Genetic Vocabulary
An organism with two identical alleles for a gene is called Homozygote -They have a homozygous genotype. Genotype describes your genetic make up for that character. - it is said to be homozygous for the gene controlling that character An organism with two different alleles for a gene is a heterozygote and is said to be heterozygous for the gene controlling that character - unlike homozygotes, heterozygotes are not true breeding. in organisms traits do not always reveal it's genetic composition Therefore, we distinguish between organisms phenotype, physical appearance, and its genotype, genetic make up. - For example: flower color in pea plants, PP and app have the same phenotype (purple) but different genotypes (PP & Pp)
Other abnormalities from abnormal chromosome number
Aneuplodiy - results from fertilization of gametes in which nondisjunction occurs (offspring with his condition have abnormal number of particular chromosomes) a MONOSOMIC ZYGOTE - has only one copy of a particular chromosome a TRISOMIC ZYGOTE - has three copies of a particular chromosome POLYPLOIDY is a condition in which an organism has more than two complete sets of chromosomes Triploidy (3n) - is 3 sets of chromosomes Tertaploidy (4n) - is four sets of chromosomes Polyploidy is common plants but not animals and are normal in appearance unlike a aneuploids
Nature and nurture: the environment impact on phenotype
Another departure from simple Mendelian genetics arises when the phenotype for a character depends on environment, as well as genotype The phenotypic range is broadest for polygenic characters Traits that depend on multiple genes combined with environmental influences are called MULTIFACTORIAL. cause there's multiple factors controlling the expression of that trait. The genes and environment.
extending mendelian genetics for a single gene
Inheritance of characters by a single gene may deviate from simple Mendelian patterns in these situations: -when alleles are not completely dominant or recessive - when a particular gene has more than two alleles - when a single gene produces multiple phenotypes
cystic fibrosis
Is the most common lethal genetic disease in the United States, striking one out of every 2500 people of European descent The cystic fibrosis allele results in defective or absent chloride, transport channels in plasma membranes leading to a buildup of chloride ions outside the cell Symptoms include mucus, build up in some internal organs and abnormal absorption of nutrients in the small intestines. untreated, cystic fibrosis can cause death by the of 5. Daily doses of antibiotics to stop infection in physical therapies can prolong life. In the United States, more than half of those with cystic fibrosis survive into their 40s
Mendelian inheritance has its physical basis in the behavior of chromosomes
Biologist saw parallels between chromosome behavior in the behavior of proposed factors Sutton in Boveri and others independently noted that these parallels, and begin to develop the chromosomal theory of inheritance First evidence associated with a specific gene with a specific chromosome Evidence provided convincing that Chromosomes are the location of Mendels heritable factors
altercations of chromosome structure
Breakage of a chromosome can lead to four types of changes in chromosome structure: Deletion -removes a chromosomal fragment Duplication- repeats a segment Inversion- reverses orientation of a segment within a chromosome Translocation - move the segment from one chromosome to another
Using a dihybrid cross, Mendel develop the law of independent assortment
It states that each pair of alleles segregate independently of any other pair of alleles during gamete formation. - This law applies only to genes on different non-homologous chromosomes, or those far apart on the same chromosome. - Genes located near each other on the same chromosome tend to be inherited together (basically saying, sometimes some genes are linked together like freckles and red hair) if they are far apart enough on a gene you will see the law of independent assortment.
Altercations of chromosome number structure, cause some genetic disorder
Large scale, chromosomal alterations in humans and other mammals lead to spontaneous abortion (miscarriages) or cause a variety of developmental disorders Plants tolerate such a genetic change better than animals do
Mendel was —— pollinating plants. Hybridization. (And meaning of P; F1; & F2)
Manually in a typical experiment, Mendel, mated two contrasting, true-breeding varieties, a process called HYBIRDIZATION. The true breeding parents are called the P generation - Parental generation; The hybrid offspring of the P generation are called the F1 generation - first generation; When F1 individuals self-pollinate or cross-pollinate with other F1 hybrids, the F2 generation is produced - second generation... continues F3, etc.
multifactoral disorders
Many diseases, such as heart, disease, cancer, alcoholism and mental illnesses, have both genetic and environmental components. No matter what our genotype our lifestyle has a tremendous effect on phenotype
Mendels model
Mendel developed a model to explain the 3:1 inheritance pattern, he observed in F2 offspring - possible combinations of sperm and egg can be shown using a punnets square - A capital letter represents a dominant allele, and a lowercase letter represents a recessive allele - four related concepts make up this model (these concepts can be related to what we now know about genes and chromosomes)
Mendel used the scientific approach to identify two laws of inheritance
Mendel discovered the basic principles of heredity by breeding garden peas in carefully planned experiments - his fresh approach to the study of heredity allowed him to deduce principles that had remained elusive to others /peas were available to Mendel in many different varieties/ Advantages of using peas: - Short generation time - Large numbers of offspring - Mating could be controlled; plants could be allowed to self pollinate, or could be cross pollinated
Degrees of Dominance
Complete dominance: occurs when phenotypes of the heterozygote and dominant homozygote are identical, (normal situation) Incomplete dominance: the phenotype of F1 hybrids is somewhere between the phenotypes of two parental varieties. For example; if you mix red with white, you get pink. Codominance: two dominant alleles affect the phenotype in separate, distinguishable ways. See both variations at the same time (cat that's black and white)
Frequency of dominant alleles
Dominant alleles are not necessarily more common in populations than recessive alleles - one baby out of 400 in the United States is born with extra fingers or toes (polydactyl) This condition is caused by a dominant allele found much less frequently in the population than the recessive allele
Linked genes tend to be inherited together because they are located near each other on the same chromosome
Each chromosome has hundreds of thousands of genes except the Y Jeans that are located on the same chromosome tend to be inherited together and are called linked genes
Test for identifying carriers
For growing number of diseases test are available that identify carriers, and help to find the odds of having an affected child more accurately The test enable people to make more informed decisions about having children However, they raise other issues such as weather affected individuals, fully understand their genetic test results, and how the test results are used
What is the relationship between genes and chromosomes
Genes are located on chromosomes - chromosomes duplicate before cell division - during meiosis 1, homologous chromosomes separate and allele segregate. I'm meiosis 2 sister chromatids separate. - each chromosome has one version of a gene (one allele) - offspring inherit one allele from each parent
Genetic testing and counseling
Genetic counselors can provide information to perspective. Parents concerned about a family history for a specific disease. Fatal and newborn testing can also reveal genetic disorders
Many human traits follow Mendelian patterns of inheritance
Humans are not good subjects for genetic research - Generation time is too long - Parents produce relatively few offspring - Breeding experiments are unacceptable However, basic Mendelian genetics endures as the foundation of human genetics.
More on behavior of recessive alleles
If a recessive allele that causes a disease is rare, it is unlikely that two carriers will meet and mate Consanguineous matings (that is, between close relatives) increases the chance that both parents of the child carry the same rare allele. Most societies and cultures have laws or taboos against marriages between close relatives
Third concept of Mendels model
If the two alleles at a locus differ, then one, the dominant allele, determines the organisms appearance The other, the recessive allele, has no noticeable effect on appearance - in the flower color example, the F1 plants had purple flowers because the allele for that trait is dominant.
Results of genomic imprinting
Imprinting is the result of methylation (addition of -CH3 groups) of cysteine nucleotides Genomic imprinting may affect only a small fraction of mammalian genes Most imprinted genes are critical for embryonic development
abnormal chromosome number
In NONDISJUNCTION pairs of homologous chromosomes, do not separate normally during meiosis As a result, one gamete received two of the same type of chromosome another gamete receives no copy
fetal testing
In aminocentesis the liquid that beat the fetus is removed and tested for certain genetic disorders in chlorotic villus sampling (CVS) a sample of the placenta is removed and tested Other techniques, such as ultrasound, allow, fetal health to be assessed, visually in utero
Mendels crosses on flower color
Mendel reasoned that only the purple flower factor was affecting flower color in F1 hybrids - Mendel called the purple flower color, a dominant trait in the white flower color, a recessive trait - The factor for white flowers was not diluted or destroyed because it reappeared in the F2 generation - Mendel observed the same pattern of inheritance in six other pea plant characters, each represented by two traits - What Mendel called a " heritable factor" is what we now call a Gene
Probability laws govern Mendelian inheritance
Mendel's laws of segregation and independent assortment reflect the rules of probability that apply to tossing a coin or rolling a dice. - When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss - In the same way, the alleles of one gene segregate into gametes independently of another gene's alleles
Morgan's choice of experimental organisms
Morgan chose to study Drosophila melon gaster, a common species of fruit fly Convenient for genetic studies: - Produce many offspring - Generation can be bread every two weeks - Have four pairs of chromosomes noted, wild type, or normal, phenotypes that were common in fly populations traits alternative to the wild type or called mutant phenotypes The first mutant, Morgan discovered was a fly with white eyes instead of wild type red eyes
Sex, linked genes exhibit unique patterns of inheritance
Morgan's discovery of a trait that correlated with the sex of lies with key to the development of chromosome theory of inheritance
Pleiotropy
Most genes have multiple phenotypic effects, a property called pleiotropy For example, pleiotropy alleles are responsible for the multiple symptoms of certain hereditary diseases, such as cystic fibrosis and sickle-cell disease.
Multiple locations and addition rules for momo hybrid crosses
Multiplication rule: The probability that two or more independent events will occur together at the same time is the product of their individual properties - Probability in an F1 mono hybrid cross can be determined using this - Segregation in a heterozygous plant is like flipping a coin: each gamete has a 1/2 chance of carrying the dominant allele and 1/2 chance of carrying the recessive allele Addition rule: The probability that any one of two or more mutually exclusive events will occur, is calculated by adding together their individual probabilities - Mutually exclusive events do not have to occur at the same time - The rule of addition can be used to figure out the probability that an F2 plant from a mono hybrid cross will be heterozygous rather than homozygous.
Alleles result from —-.
Mutations come in recessive and dominant
Recombination of Unlinked Genes: Independent Assortment of Chromosomes
Offspring with phenotype, matching one of the parental PE phenotypes are called parental types Offspring with nonparental phenotypes you combinations of traits are called recombinant, types or recombinants A 50% frequency of recombination is observed for any two genes on different chromosomes.
Mapping the Distance Between Genes Using Recombination Data
One of Morgan's students constructed a genetic map, an ordered list of the genetic loci along a particular chromosome Predicted that the farther apart the two genes are the higher, the probability that the crossover will occur between them, and therefore the higher, the recombinant frequency
Sickle cell disease genetic disorder with evolutionarily implications
affects one out of 400 African-Americans. Caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells. In homozygous individuals all hemoglobin is abnormal (sickle cell) Symptoms include physical, weakness, pain, organ, damage, and even paralysis Heterozygotes said to have the sickle cell trait are usually healthy, but may suffer some symptoms About one out of 10 African-Americans has the sickle cell trait Heterozygotes are less susceptible to the malaria parasite, so there is an advantage to being heterozygous and regions, where malaria is common
A Mendelian view of heredity and variation (Hydrangeas are—-.)
an organisms phenotype includes all aspects of it's a physical appearance, internal anatomy, physiology, and behavior. your personality traits are still considered physical expressions of information in your genes. Behavior is a phenotype. an organisms phenotype reflects its overall genotype but also unique environmental history. (Nurture) ;multifactorial
Trait
each variant for a character (such as purple or white color for flowers)
Relationship among two or more genes
Photo of epistasis and polygenic inheritance
polygenic inheritance
QUANTITATIVE CHARACTERS are those that vary in the population along a continuum. Quantitative variation usually indicates POLYGENIC INHERITANCE an additive affect of two or more genes on a single phenotype. Height is a good example of polygenic inheritance; over 180 genes affect height Skin pigmentation in humans is also controlled by many separately inherited genes.
behavior of recessive alleles
Recessively inherited disorders show up only in individuals homozygous for the allele CARRIERS are heterozygous individuals who carry the recessive allele, but our phenotypically normal. Most individuals with recessive disorders are born to carrier parents Albinism is a recessive condition, characterized by a lack of pigmentation in skin and hair
New combination of alleles: variation for natural selection
Recombinant chromosomes, bring alleles together, and you combinations in gametes Random fertilization increases even further, the number of variant combinations that can be produced This abundance of genetic variation is the raw material upon which natural selection works
Newborn screening
Some genetic disorders can be detected at birth by simple test that are now routinely performed in most hospitals in the US One common test is for PKU, a recessive we inherited disorder that occurs in one of every 10,000 to 15,000 births in the us The number of conditions that can be tested in newborns is over 100 and ever increasing
Dominantly inherited disorders
Some human disorders are caused by dominant alleles Dominant alleles that cause a lethal disease are rare and arise by mutation Achondroplasia is a form of dwarfism caused by a rare dominant allele The timing of onset of a disease significantly affects its inheritance Huntington's disease is a degenerative disease of the nervous system The disease has no obvious phenotypic affect until the individual is about 35 or 40 and once the deterioration of the nervous system begins, the condition is irreversible and fatal
Counseling based on Mendelian genetics and probability rules
Suppose a couple both have a brother who died from the same recessivly inherited disease A genetic counselor can help determine the risk that this couple will have a child with a disease It is important to remember that each child represents an independent event, in the sense that its genotype is unaffected by the genotypes of older siblings If both members of a couple had a sibling with the recessive, we inherited illness, both of the parents were carriers Does each has a 2/3 chance of being a carrier themselves If both are carriers, there's one for chance of each child having a recessive illness The overall probability of them having a child with the illness is 2/3×2/3×1/4 = 1/9
genomic imprinting
Variation in phenotype is called genomic imprinting for a few mammalian traits the phenotype depends on which parent passed along the alleles for those traits Genomic printing involves the silencing, of certain genes, depending on which parent passes them on Most imprinted genes are on autosomes The mouse gene for insulin like growth factor 2 (Igf2) was one of the first imprinted genes to be identified -Only the paternal allele of this gene is expressed
Inheritance of X-Linked Genes
X chromosomes have genes for many characters unrelated to sex, whereas the Y chromosome mainly encodes genes related to sex determination x-linked genes follow a specific pattern of inheritance - for recessive X-linked trait to be expressed a female needs two copies of the allele homozygous, and a male needs only one copy hemizygous. X-linked recessive disorders are much more common in males than females Some disorders called by recessive alleles on the X chromosome in humans: color, blindness, hemophilia, and duchenne muscular dystrophy
A sex linked gene
a gene that is located on either sex chromosome. genes on the Y chromosome are called while linked genes Only 78 genes coding for about 25 proteins have been identified on the Y chromosome genes on the X chromosome are called X-linked genes; the human X-chromosome contains about 1,100 genes
recessively inherited disorders
-Many genetic disorders are inherited in a recessive manner -These range from relatively mild to life-threatening
The chromosomal basis of sex
- In humans and other mammals have two types of sex chromosomes: a larger X-chromosome, and a smaller Y-chromosome. A person with 2X chromosomes usually develops in anatomy. We associate as female and associated with the inheritance of one X in one why is a male (XX and XY) - Only the ends of the Y chromosome have regions that are homologous with the X chromosome - the XY system is not the only chromosomal system of sex determination Short segments at the end of the Y chromosome, or homologous with the X. Allowing the two to behave like homologues during meiosis in males. In mammals, a gene on the Y chromosome called SRY (sex determining region on the Y) is responsible for the development of the testes in an embryo
How Linkage Affects Inheritance
- Morgan did other experiments with fruit flies to see how linkage affects inheritance of two characters - Morgan crossed flies that differed in traits of body color and wing size - the first crossed with a P generation cross to generate F1 dihybrid flies - the second was a test cross The resulting flies had a much higher than expected proportion of the combination of traits seen in the P generation flies, parental phenotypes He concluded that the jeans do not assort independently and reasons that they were on the same chromosome Nonparental phenotypes were also produced in the test cross, suggesting that the two traits could be separated sometimes This involves genetic recombination, the production of offspring, with combinations of traits different from either parent
Recombination of Linked Genes: Crossing Over
-Morgan observed that although some genes are linked, nonparental allele combinations are still produced -He proposed that some process must occasionally break the physical connection between genes on the same chromosome -That mechanism was the *crossing over* of homologous chromosomes
The Testcross
An individual with the dominant phenotype could be either homozygous dominant or heterozygous dominant. To determine the genotype, we can carry out a TESTCROSS: breeding the mystery individual with a homozygous recessive individual. If any offspring display the recessive phenotype, the mystery. Parent must be heterozygous.
linkage map
A genetic map of chromosomes based on recombinant frequencies Distance between genes can be expressed as map units one math unit represents one percent recombinant frequency A map unit indicates relative distance in order, not precise location of genes Jeans that are far apart on the same chromosome, have a recombinant frequency near 50%, and such jeans are physically linked the genetically unlinked and behave as they found on different chromosomes Stuart used recombinant frequencies to make linkage maps, a fruit fly jeans and found that jeans clustered into four groups of linked genes are called linkage groups Linkage Mabs, combined with the fact that there are four chromosomes in Joseph philia provided additional evidence that genes are located on chromosomes
character
A heritable feature that varies among individuals (such as flower color)
Segregation law - independent assortment law
Alleles separate - genes separate
Human disorders due to chromosomal altercations
Altercations of chromosome number in structure associate with some serious disorders Some type of an aneuploidy appears to upset the genetic balance, less than others, resulting in individual surviving to birth, and beyond, with a set of symptoms, or syndrome, characteristic of the type of aneuploidy Down syndrome (trisomy, 21) aneuploidy condition that results from three copies of chromosome 21 Frequency of down syndrome increases with the age of a mother, a correlation not explained
First concept of Mendels model
Alternative version of genes account for variations in inherited characters (for example: the gene for flower color in pea plants exist in two variations, one for purple flowers and the other for white) THESE ALTERNATIVE VERSIONS OF A GENE ARE CALLED ALLELES!! They are the variation of the SAME GENE (each gene resides at a specific locus/location on a specific chromosome
Genetic recombination and linkage
The genetic findings of Mendel and Morgan relate to the chromosomal basis of recombination
The first law Mendel created
The law of segregation - in the 1800s the explanation of heredity was the " blending" hypothesis - When Mendel crossed contrasting, true-breeding white and purple flowered pea plants, all of the F1 hybrids were purple - This result was not predicted by the blending hypothesis (half purple, half white) -When Mendel crossed the F1 hybrids, many of the F2 plants had purple flowers, but some had white -Mendel discovered a ratio of about three purple flowers to one white flower in the F2 generation.
Inheritance patterns are often more complex than predicted by simple Mendelian genetics
The relationship between the genotype and phenotype is rarely as simple as in the pea plant character Mendel studied - Many heritable characters are not determined by only one gene with two alleles - However the basic principles of segregation and independent assortment apply even to more complex patterns of inheritance
Disorders caused by structurally alter chromosomes
The syndrome, cri du chat (cry of the cat) resulted from a specific deletion in chromosome 5 A child born with this is severely intellectually disabled, and has a cat like cry, usually die in infancy Certain cancers, including chronic myelogenous leukemia, CML, or caused by trans locations of chromosome
Fourth concept of Mendel's model
The two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes Meiosis one set of chromosomes in each sec cell in your body. Each sex cell will have one allele in the sex cell for each gene character. - thus and egg or sperm gets only one of the two alleles that are present in the organism - this segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis Basically saying: if youre heterozygous for a character and this is what it looks like (As) alleles were separate out into different sex cells. It is entirely random to which of the sex cells appear in the offspring. However if you're homozygous it doesn't matter because all of your sex cells will end up having the same allele. (Like pure bred for that character.)
Some inheritance patterns are exceptions to standard Mendelian inheritance
There to normal occurring exceptions to Mendelian genetics One exception involves genes located in the nucleus in the other involves genes located outside the nucleus In both cases, the sex of the parent contributing an allele is a factor in the pattern of inheritance
more about pedigrees
They can be used to make predictions about future offspring. We can use the multiplication and addition rules to read at the probability a specific phenotypes.
True breeding
Think about when you're breeding a golden retriever and you refer to them as pure bred. Or pure offspring. They look the same as their parent. There is no variety. (Mendel means asexual.)
Characteristics and varieties Mendel chose to track
Tracked characteristics that occur in to distinctive, alternate forms (so peas only came in two colors, purple or white; and tall and short) He also started with varieties that were TRUE BREEDING (plants that could produce offspring of the same variety when they SELF pollinate).
Inheritance of Organelle Genes
extranuclear genes (or cytoplasmic genes) are found in organelles in the cytoplasm. mitochondria, chloroplasts, and other plant plastids carry small circular DNA molecules. extranuclear genes are inherited maternally because the zygote's cytoplasm comes from the egg. the first evidence of extranuclear genes came from studies on the inheritance of yellow or white patches on leaves of an otherwise green plant. some defects in mitochondrial genes prevent cells from making enough ATP and result in diseases that affect the muscular and nervous systems. - for example, mitochondrial myopathy and leber's heredity optic neuropathy it could be possible to avoid passing along mitochondrial disorders - The chromosome from the egg of an affected mother can be transferred to an egg of a healthy donor, generating a two mother egg -This egg can then be fertilized by the sperm from the perspective. Father and transplanted to the womb of the prospective mother.
Second concept of Mendels model
for each character, an organism inherits two alleles, one from each parent - Mendel made this deduction without knowing about chromosomes - the two alleles at a particular locus may be identical, as in the true-breeding plants of Mendels P generation - Or the two alleles at a locus may differ, as in the F1 hybrids
Mendel's Second Law
law of independent assortment Mendel derived the law of segregation by following a single character. (like focusing on plant color at one time) The F1 offspring produced in this cross were MONOHYBRIDS, meaning that they were heterozygous for one character. - A cross between such heterozygotes is called a MONOHYBRID CROSS (Another name for a regular pinnet square) Mendel identified his second law of inheritance by following two characters at the same time. (instead of j tracking color he was tracking maybe color and stem height) - Crossing two true-breeding parents differing in two different characters produces DIHYBRID in the F1 generation, heterozygous for both characters. - A DIHYBRID CROSS, a cross between F1 dihybrids, can determine whether two characters are transmitted to offspring together as a unit or independently. dihybrids (both at same time) He was trying to figure out where there are certain genes inherited together at the same time?
multiple alleles
most genes exist in populations in more than two allelic forms - for example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme that attaches A or B carbohydrates to red blood cells: I^A, I^B, and i. - the enzyme encoded by the I^A allele adds the A carbohydrate, whereas the enzyme encoded by the I^B allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither. A gets a triangle carbohydrate and B gets a circle carbohydrate.
to differentiate incomplete dominance when writing the letters
red is AA and white is also AA. So use C to talk about the trait (color). Red would be C^R C^R and white would be C^W C^W
extending mendelian genetics for two or more genes
some traits may be determined by two or more genes In epistasis, one gene affects the phenotype of another due to interactions of their gene production. In polygenic inheritance, two or more (multiple) genes independently affect a single trait (phenotype) So either one gene is affecting another gene or one gene is working with multiple other genes at the same time to produce a certain phenotype for example, eyecolor or hair color is a polygenic inheritance.
Solving complex genetics problems with the rules of probability
we can apply the rules of probability to predict the outcome of crosses involving multiple characters - A multi character cross (dihybrid, or greater) is equivalent to two or more independent mono hybrid crosses occurring simultaneously - In calculating the chances for various genotypes each character is considered separately, and then the individual probabilities are multiplied For example, you can basically do two separate mono hybrid crosses, and then multiply the probability together.