Every living thing has a set of _____________
Characteristics inherited from its parent or parents
Heredity
The delivery of characteristics from parent to offspring
Genetics is the study of _________ and the key to understanding ___________
Heredity; what makes each organism unique
Who was the modern science of genetics founded by?
An Austrian monk named Gregor Mendel
Give some info on Mendel's life.
Born in Czech Republic in 1822; became a priest then began studying science and math at University of a Vienna; spent 14 years working in a monastery and teaching high school; in charge of monastery garden, where he did work that changed biology forever
Mendel carried out most of his research with __________. Why?
Pea plants; they are small, easy to grow, and produce hundreds of offspring over a short time span
Peas are known as ____________. What does this mean?
Model systems; they are convenient to study and show us how other organisms function (also produce fast results)
When Mendel began experimentation, he was aware of the male and female parts of a flower, called __________, and their locations, which are ______________
Sperm and eggs; in pollen (male) and in flower "ovaries" (female)
During sexual reproduction, what takes place and what does it produce (list general answer and answer specific to pea plants)?
Fertilization (fusion of sperm and egg cell) produces a zygote (in peas, specifically an embryo encased within a seed)
Most pea flowers are self-pollinating, meaning _________________
Sperm cells fertilize egg cells within the same flower; zygote inherits all of its parent's (singular) traits
Mendel's pea plants were _____________, meaning that they _______________
True-breeding"; were self-pollinating and produced offspring identical to themselves - the traits of each successive generation would be the same
Trait
Specific characteristic of an individual- these vary from one organism to the next
How did Mendel determine how traits were inherited?
He cross bred his stocks of true-breeding pea plants (he caused one plant to reproduce with another plant, preventing self-pollination)
How did he cross breed the plants? What is the scientific name for this process? How did it help Mendel?
He cut the male parts out of the flower then dusted pollen from another plant onto the first one; cross pollination (produces plant with two parents); helped Mendel breed plants with different traits then study the results
Mendel studied _____ different traits in pea plants. What were these?
7; seed shape (round vs wrinkled), seed color (yellow vs green), seed coat (gray vs white), pod shape (smooth vs constricted), pod color (green vs yellow), flower position (axial vs terminal), and plant height (tall vs short)
Hybrids
The offspring of crosses between parents with different traits
When doing genetic crosses, P=_________ and F1=__________
Parental generation (original pair of organisms); first filial generation (offspring)
To Mendel's surprise, when he studied the F1 generations of crossed pea plants, what did he discover?
For each trait studied, all of the offspring had the characteristic of only one of its parents; the nature of the other parent seemed to have disappeared
What was Mendel's first conclusion?
An individual's characteristics are determined by factors (called genes) that are passed on from one parental generation to the next
Each of the traits Mendel studied was controlled by ___________
A single gene that occurred in two contrasting varieties
Alleles
The different forms of a gene
What was Mendel's second conclusion?
The principle of dominance, which states that some alleles are dominant while others are recessive
What are dominant and recessive alleles?
Dominant - will exhibit a trait if present in a gene; recessive - will exhibit a trait when dominant allele is not present in a gene
What did Mendel still wonder after cross breeding the P generation? How did he go about finding the answer?
Had the recessive alleles disappeared, or were they still present in the new plants?; he allowed 7 kinds of F1 plants to self-pollinate to produce an F2 (second filial) generation of plants
When Mendel studied the F2 plants, he made an amazing discovery:
The traits controlled by the recessive alleles reappeared in roughly 1/4 of the second generation
T/F: Recessive alleles mask corresponding dominant alleles in the F1 generation
False; other way around
What did the reappearance of recessive alleles suggest?
At some point, the recessive allele separated from the dominant allele - called segregation
Segregation
Separation of alleles
during gamete formation
in F1 generation
Gametes
Sex cells
During gamete formation, ______________
The alleles for each gene segregate from each other, so that each gamete carries only one allele for each gene [ex. either T (tall dominant) or t (short, recessive)] - each organism produces two kinds of gametes (ex. T and T, T and t, or t and t)
Capital letter = _________ allele, lowercase letter = _________ allele
Dominant; recessive
Alleles pair up again _____________
During the F2 generation (ex. TT, Tt, or tt)
According to Mendel's experiment, TT allele would produce a ________ plant, Tt allele would produce a _________ plant, and tt allele would produce a _________ plant
Tall; tall; short
The F2 generation has ______________
A new combination of alleles
Whenever Mendel performed a cross with pea plants, he carefully ______________
Categorized and counted the offspring
Whenever he crossed 2 plant hybrids for stem height (Tt), about ________ of the resulting plants were tall and about _______ were short
3/4; 1/4
What did Mendel realize could be used to explain the results of his genetic crosses?
The principles of probability
Probability
The likelihood that a particular event will occur
What does the multiplication of individual probabilities illustrate?
Past outcomes do not affect future ones
Give an example of the previous question
Flipping a coin 3 times in a row does not mean you are more likely to have a coin tails up on the next flip; the probability remains 1/2
T/F: The way in which alleles segregate during gamete formation is organized and precise
False; it is random
Why is there a 1/4 chance of two crossed heterozygous F1 generation plants producing an F2 generation plant exhibiting a recessive allele?
Since both plants have one dominant and one recessive allele (Tt), there is a 1/2 chance of a gamete carrying a recessive allele after formation. A recessive trait will only be exhibited in an organism if both gametes are recessive (tt). The chances of a
Which ratio consistently showed up in Mendel's experiments?
3/4 offspring in F2 generation exhibiting dominant trait, 1/4 exhibiting recessive trait
T/F: Not all organisms with the same characteristics have the same combinations of alleles. Depending on the answer, provide an example
True; two plants could exhibit the dominant (tall) trait, but one could have a combination TT and the other could have a combination Tt
Homozygous organism
Have two identical alleles for a particular gene (ex. TT or tt)
Heterozygous organism
Have two different alleles for the same gene (ex. Tt)
Probabilities predict ____________
The average outcome of a large number of events
What is true of the probability of genetics?
The larger the number of offspring, the closer the results will be to the predicted values of allele combinations/gametes
What was one of Mendel's most revolutionary insights followed directly from his observations of F1 crosses?
Every organism has a genetic makeup as well as a set of observable characteristics
Phenotype
Physical characteristic of an organism
Genotype
Genetic makeup of an organism
T/F: Two organisms with the same phenotype have the same genotype
False; two organisms may share the same phenotype but have different genotypes
The genotype of an organism is ____________, and the phenotype is largely determined by ___________
Inherited; the genotype
One of the best ways to predict the outcome of a genetic cross is by drawing a simple diagram known as a ________________, which uses ______________ to help predict possible ___________ and _________ combinations of offspring
Punnett Square; mathematical probability; genotype; phenotype
How do you make a Punnett Square?
Begin with a Square; follow the principle of segregation - all possible combinations of alleles in the gametes produced by one parent are written along the top edge of the square, the other parent on the left edge of the square; every possible genotype is
What was Mendel's next question? How did he go about solving it?
Does the segregation of one pair of alleles affect another pair?; Mendel followed two different genes as they passed from one generation to the next
What are two types of crosses (these are not the only types)?
Two-factor/gene (dihybrid) and single-factor/gene (monohybrid) crosses
The Two-Factor Cross
Mendel crosses true-breeding plants that produced ___________ seeds with plants that produced _____________ seeds - ________ x ________
Round, yellow; wrinkled, green; RRYY; rryy
The Two-Factor Cross
All of the F1 generation produced ___________, and their genotypes were all __________
Round, yellow seeds; RrYy - heterozygous
The Two-Factor Cross
Does the F1 generation indicate whether genes assert independently or not? What does it provide?
No; provides the hybrid plants needed to breed the F2 generation
The Two-Factor Cross
Mendel crossed the F1 generation to produce the F2 generation. In doing this, what were the results?
F2 plants produced 556 seeds - 315 were round and yellow, 32 were wrinkled and green, and 209 had combinations of phenotypes, and therefore, combinations of alleles that were not present in either parent
The Two-Factor Cross
What did Mendel's results prove?
Genes that segregate do not influence each other's inheritance
Mendel's results were very close to the _______________ that the Punnett Square for the experiment predicted. He had discovered the principle of _______________.
9:3:3:1 ratio; independent assortment
What is the principle of independent assortment? What does it help account for?
States that genes for different traits can segregate independently during gamete formation; many genetic variations observes in organisms, even when they have the same parents
What did Mendel contribute to our understanding of genetics?
Mendel's principles of heredity, observed through patterns of inheritance, form the basis of modern genetics
What is Mendel's first principle?
The inheritance of biological characteristics is determined by individual units called genes, which are passed from parent to offspring
What is Mendel's second principle?
Where two or more alleles of the gene for a single trait exist, some alleles may be dominant and others may be recessive
What is Mendel's third principle?
In most sexually reproducing organisms, each adult has two copies of each gene � one from each parent. These genes segregate during gamete formation.
What is Mendel's fourth principle?
Alleles for different genes usually segregate independently of each other
In the early 1900s, American geneticist ______________ used a different model organism to advance the study of genetics. What was this organism?
Thomas Hunt Morgan; Drosophila, the common fruit fly
Why was the Drosophila a good model system?
They are small, very easy to find and contain, and produce plenty of offspring in a short time span
T/F: Mendel's principles apply to most organisms
TRUE
Mendel's principles can be used to _________________
Study the inheritance of human traits and to calculate the probability of certain traits appearing in the second generation
T/F: There are no exceptions to Mendel's principles
False; there are a few exceptions that occur when genetic becomes more complicated in certain organisms
What are the four exceptions?
Incomplete dominance, codominance, multiple alleles, and polygenic traits
Incomplete dominance
Neither allele is completely dominant over the other; heterozygous phenotype lies somewhere between two homozygous phenotypes; an allele is neither dominant nor recessive
Give an example of incomplete dominance
In Mirabilis plants, when one red-flowered plant (RR) is crossed with one white-flowered plant (WW), the F1 generation will consist of pink-colored flowers (RW) because neither color allele is dominant over the other - they are both expressed in a mixed c
Codominance
The phenotypes for both alleles are expressed completely
Give one example of codominance
In certain varieties of chicken, the allele for black feathers is codominant with that of white feathers. Heterozygous chickens will express feathers with specks of white and black, called erminette - the two colors appear separately, not blended as in in
Give a second example of codominance, but in humans
A human gene for a protein that controls cholesterol levels in blood shows codominance; people with the heterozygous form of the gene will produce two different forms of the protein, each with a different effect on cholesterol levels
Multiple alleles
Many genes exist in several different forms and are said to have multiple alleles, meaning they have more than two alleles per gene
An individual usually has only ________ copies of each gene, but many different alleles are often found within a _____________
2; population
Give an example of multiple genes
Coat color in rabbits, which is determined by a single gene that has at least 4 different alleles; the four known alleles display a pattern of simple dominance that can produce 4 coat colors
Give a second (short) example of multiple alleles in humans
The human genes for blood type have multiple alleles
Polygenic traits
Many traits are produced by the interaction of several genes; these traits are controlled by 2 or more genes - polygenic means "many genes
Give an example of polygenic traits
At least 3 different genes are involved in making the reddish-brown pigment in the eyes of a fruit fly
Polygenic traits often show a wide range of _____________
Phenotypes
Give another (short) example of polygenic traits in humans
The variety of skin color in humans is controlled by more than 4 different genes
T/F: Phenotypes are controlled only by genotypes
False; genes provide a plan for development, but how that plan unfolds also depends on the environment
Does the environment have a role in how genes determine traits?
Environmental conditions can affect gene expression and influence genetically determined traits
What is an example of an organism whose phenotype is greatly affected by their environment? How does their phenotype change from spring to summer?
The western white butterfly - Pontia occidentalis; butterflies that hatched in the summer had lighter wing color patterns than those that hatched in the spring - difference in wing pigmentation (dark in short days of spring, light in long days of summer);
Why does the western white butterfly's wing pigmentation change dramatically depending on the season of hatching?
In order to fly effectively, the western whites must have a specific body temperature - since spring months are cooler, greater pigmentation helps them reach the body temp needed, and since summer months are warmer, less pigmentation allows the butterflie
Explain the temperatures needed to be met by butterflies for flight vs the average spring and summer temperatures
Temp needed for flight: 28-40 degrees Celsius; Average spring temp: 26.5 degrees Celsius; Average summer temp: 34.8 degrees Celsius
What events must occur in order for Mendel's principles to be true?
(1) an organism with two parents must inherit a single copy of every gene from each parent and (2) when that organism produces gametes, those two sets of genes must be separated so that each gamete contains just one set of genes
Chromosomes are the carriers of __________, which are located ______________
Genes; in specific positions on chromosomes
Homologous chromosomes
Chromosomes in which one set comes from the male parent and one set come from the female parent (corresponding chromosomes from male and female)
Diploid cell
A cell that contains two sets of homologous chromosomes ("two sets"); same number and types of genes
How many sets of genes are found in most adult organisms?
Most contain two complete sets of inherited chromosomes and two complete sets of genes
All body somatic cells are ___________
Diploid cells
Diploid number of chromosomes is represented by ________
2N
N" represents ________________
The single set of chromosomes found in a sperm or egg cell
Haploid cell
A cell that contains a single set of chromosomes and therefore, a single set of genes
Most haploid cells are ____________
Gametes
Haploid number of chromosomes is represented by ______
N
If a cell contains a diploid number of 24, then its haploid number is ______
12
T/F: Usually haploid cells undergo meiosis
False; diploid cells
T/F: Haploid cells are produced from diploid cells during meiosis
TRUE
Meiosis forms ______ haploid cells from one diploid cell
4
Meiosis
A form of sexual reproduction in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell
How many division take place in meiosis? What are they called?
2; Meiosis I and II
Meiosis I __________ and produces ___________
Separates homologous chromosomes; 2 haploid daughter cells with different sets of chromosomes and alleles
Chromosomes undergo ___________ prior to first phase of meiosis
Replication
Prophase I
The cell begins to ________, and each _____________ chromosome pairs with its corresponding ___________ chromosome. This pairing forms a __________, containing __________. As tetrads form, they undergo a process called ____________. A _________
Divide; replicated; homologous; tetras: four chromatids; crossing over; spindle; tetrad
What is crossing over? What does it produce?
When the homologous chromosomes "cross over" each other and exchange crossed sections of chromatids; new combinations of alleles in cells
Metaphase I
_____________ line up across ____________
Paired homologous chromosomes; the center of the cell
Anaphase I
The homologous pairs of chromosomes _____________ and ____________ pull each homologous chromosome pair towards ___________
Separate; spindle fibers; opposite ends of the cell
Telophase I and Cytokinesis
Separated chromosomes ___________ at opposite ends of the cell, and a ___________ forms around each group. Cytokinesis follows, forming _________.
Cluster; nuclear membrane; two new cells
Meiosis II _____________
Separates sister chromatids
What is special about Meiosis II?
DNA is not replicated before the process begins
Prophase II
Chromosomes, each consisting of ___________, become _________, but do not pair to form _________ because ____________. The _________ form and attach to each chromosome ____________.
2 chromatids; visible; tetrads; homologous chromosomes have already been separated; spindle fibers; centromere
Metaphase II
Chromosomes ___________
Line up along the center of the cell
Anaphase II
Chromatids _________ and move ___________
Separate; to opposite ends of the cell
Telophase II and Cytokinesis
____________ form around each cluster of chromosomes. Cytokinesis occurs, producing ____________ each containing ___________.
Nuclear membranes; 4 haploid cells; one set of chromosomes
What are the main differences between mitosis and meiosis?
(1) Mitosis is a form of asexual reproduction while meiosis is the beginning step to sexual reproduction (2) Mitosis - genetic material separates and each daughter cell receives one complete set of chromosomes; meiosis - homologous chromosomes move to sep
Which researcher found many different connected genes in fruit flies and discovered their specific locations on each chromosome
Thomas Hunt Morgan
Drosophila has _________ linkage groups and _________ pairs of chromosomes
4 (both)
Morgan's findings led to 2 remarkable conclusions:
(1) Each chromosome is a group of linked genes (2) Independent assortment was confirmed, but it was discovered that chromosomes assort independently, not individual genes
Alleles of genes tend to be inherited from one generation to the next _____________
When they are located close together on the same chromosome
Alfred Sturtevant reasoned that what affects the frequency of crossing between genes?
The locations of genes on a chromosome: far apart = more likely to cross over, closer together = less likely to cross over
He used the frequency of crossing over between genes to ______________
Determine their distances between each other
What did Sturtevant make that was very important to the study of genetics? Why?
A gene map of the fruit fly showing the relative locations of each known gene; every since, scientists have used his method to construct gene maps
What are the two types of gametes?
Sperm and egg/ova
Spermatogenesis
Production of sperm from meiosis - 4 haploid cells that change shape and grow flagella
Oogenesis
Production of eggs from meiosis - 1 large egg, 3 small polar bodies (that die eventually)
Fertilization
Fusion of an egg and sperm cell to create unique combination of genes
A new cell is called a _________. How does it develop into a full body?
Zygote; by undergoing mitosis repeatedly
To determine what makes us uniquely human, we have to look deeper into _____________________
The genetic instructions that build each individual
Genome
The entire set of genetic information that an organism carries in its DNA
The study of any genome starts with ____________
Chromosomes - the bundles of DNA and protein found in the nuclei of eukaryotic cells
How do biologists see human chromosomes clearly?
By photographing cells in mitosis, when chromosomes are condensed and easy to see, then cutting out the chromosomes from the photos and arranging them in a picture called a karyotype
Karyotype
A micrograph of the complete diploid set of chromosomes grouped together in pairs, arranged in order of decreasing size
A typical human cell contains _________ chromosomes, arranged in _______ pairs
46; 23
Why do our chromosomes come in pairs?
Life begins when a haploid sperm cell with 23 chromosomes fertilizes a haploid egg cell with 23 chromosomes; the resulting diploid cell develops into a new organism and contains 46 chromosomes - 2 sets of 23
Two of the 46 chromosomes in the human genome are known as ______________ because _______________
Sex chromosomes; they determine an individual's sex
Females have ____________ while males have ______________
2 copies of the X chromosome; one X chromosome and one Y chromosome
Males and females are born in a ________ ratio
50:50:00
More than __________ genes are found on the X chromosome, while the Y chromosome contains only about _________ genes, most of which are associated with _______________
1200; 140; male sex determination and sperm development
The remaining 44 human chromosomes are known as ___________ chromosomes, or ____________
Autosomal; autosomes
The complete human genome contains ________ chromosomes, which include _______ autosomal chromosomes and _____ sex chromosomes
46; 44; 2
To summarize the total number of chromosomes present in a human cell, biologists write __________ for females and __________ for males
46, XX; 46, XY
List four genes on the X chromosome, and one on the Y chromosome
Duchenne muscular dystrophy, X-inactivation center, Hemophilia A, and Colorblindness; Testis-determining factor
What have studies of human genetics/DNA using molecular techniques shown?
Human genes follow the same Mendelian patterns of inheritance as the genes of other organisms
Many human traits follow a pattern of ________________
Simple dominance
Give one example of simple dominance in humans
The MC1R gene helps determine skin and hair color; the recessive alleles for this gene produce red hair, while the dominant alleles for this gene produce darker hair colors
Give a second example of simple dominance in humans
The Rhesus, or RH, blood group; the allele for the Rh factor comes in two forms: Rh+ and Rh-; Rh+ is dominant and Rh- is recessive, so individuals with both alleles are said to have Rh positive blood, while individuals with two recessive alleles are said
The alleles for many human genes display _____________ inheritance
Codominant
What is one example of codominant inheritance/multiple alleles in humans?
The ABO blood group, determined by a gene with 3 alleles: IA, IB, and i; IA and IB are codominant and i is recessive
Explain the ABO group
Alleles IA and IB are codominant; they produce molecules known as antigens on the surface of red blood cells; individuals with alleles IA and IB produce both A and B antigens, making them blood type AB; the i allele is recessive; individuals with alleles
Because the X and Y chromosomes determine sex, the genes located on them show a pattern of inheritance called ______________
Sex-linkage
Sex-linked gene
A gene located on a sex chromosome
In regards to sex-linkage, genes on the Y chromosome ________________
Are found only in males and are passed directly from father to son
What leads to some interesting consequences in men?
The fact that males have only one X chromosome
What is one interesting consequence?
Humans have 3 genes responsible for color vision, all located on the X chromosome; since males only have one X chromosome, a defect in one of these genes will result in colorblindness; in order for a recessive allele like colorblindness to be expressed in
What is the most common form of colorblindness in males? What percentage of men have it? How common is colorblindness in women?
Red-green colorblindness; 1/12 men have it; 1/200 women are affected by colorblindness
What is one of the most notable facts about sex-linked inheritance?
The recessive phenotype of a sex-linked genetic disorder tends to be much more common among males than females
If just one X chromosome is enough for cells in males, how does the cell "adjust" to the extra X chromosome in female cells?
In female cells, most of the genes in one of the X chromosomes are randomly switched off, forming a dense region in the nucleus known as a Barr body; Barr bodies are generally not found in males because their single X chromosome is still active
Who discovered X-chromosome inactivation?
British geneticist Mary Lyon
Explain how X-chromosome inactivation affects female Calico cats
In cats, a gene that controls the color of coat spots is located on the X chromosome; one X-chromosome may have an allele for orange spots, while the other has an allele for black spots; in cells in certain areas of the cat's body, one of the X-chromosome
How does this differ in male cats?
Since they have only one X chromosome, they can have spots of only one color; therefore, if a cat expresses 3 different colors in its phenotype, you can be almost certain that it is female
Pedigree chart
Chart that shows the presence or absence of a trait according to relationships within a family across several generations; used to analyze the pattern of inheritance followed by a particular trait
T/F: Pedigrees can only be used for humans
False; they can be used for any species
Pedigree
Circle represents __________
A female
Pedigree
Square represents ___________
A male
Pedigree
Horizontal line connecting male and female represents _____________
A marriage
Pedigree
Vertical line and a bracket connect __________
The parents to their children
Pedigree
Shaded circle/square indicates _______________
That a person expresses the trait
Pedigree
Unshaded circle/square indicates ________________
That a person does not express the trait
By analyzing a pedigree, we can often infer ____________
The genotypes of family members
How can pedigrees be used to analyze human inheritance?
The information gained from pedigree analysis makes it possible to determine the nature of genes and alleles associated with inherited human traits
Based on a pedigree, you can usually determine if a trait is ______________ vs __________________, ______________ vs ______________
Dominant; recessive; autosomal; sex-linked