Gregor Mendel has discovered that biological inheritance is determined by genes, which are passed from one generation to the offspring. Every gene is determined by alleles, which represent different variants of a certain trait.

c. alleles

Homozygous genotype is present when an offspring inherits the same alleles (both dominant or both recessive), while heterozygous genotype means that one recessive and one dominant allele are inherited.

c. homozygous

True-breeding is a process of plant breeding where there is only one parent, which means that an offspring will have the same appearance as the parental generation.

Self-pollination is a process of plant breeding where there is only one parent, which means that an offspring will have the same appearance as the parental generation. Cross-pollination is a process of plant breeding with two different plants, which creates an offspring with different traits than the parental plant. Plants that are produced in this way are known as hybrids. Cross-pollination contributes to the genetic diversity. In order to make a hybrid and prevent self-pollination, Mendel has cut off the male parts of a pea flower and dusted with their pollen female parts of the different plant.

We use the Punnett square to determine the probable outcome of a genetic cross.

a. probable outcome of a cross

The genotype is the genetic inheritance that will cause the creation of certain physical features of an organism, which are known as phenotype.

c. phenotype

Probability represents the odds that a certain situation will happen. It can be calculated. In an example of coin flipping, the probability of getting a head is 50%, or 1/2. If we need to get a head two times in a row, the probability would be 1/2 * 1/2 = 1/4, or 25%.

c. 1/4

Mendel’s contribution to genetics is great because he was the first one to explain and prove the basic principles of heritage.
begin{enumerate} % for numbers
item Biological inheritance is determined by genes, which are passed from one generation to the offspring.
item The segregation law explains the process that occurs in the parental generation, where gametes contain only one, randomly chosen allele.
item Alleles for different traits can be dominant or recessive.
item Alleles for various genes may segregate separately of each other.
end{enumerate}

The dominant allele determines the yellow color of pea seeds, while the recessive allele determines the green color of seeds. When a plant inherits one, or two dominant alleles from its parents, that will define the yellow color. The green color of the offspring will appear only if the recessive allele is inherited from both of the parental plants (yy genotype, green colored in the table). If both parents are heterozygous (Yy genotype), the probability of a green offspring is 25 percent. The Punnett square, where the gametes are blue colored, will look like this:
begin{center}
begin{tabular}{ c c c}
& {color{Blue}Y} & {color{Blue}y}\
{color{Blue}Y} & YY & Yy\
{color{Blue}y} & Yy & {color{Green} yy}
end{tabular}
end{center}

Genes usually have more than two alleles or multiple alleles.

d. multiple alleles

Mendel’s discovered that alleles for different traits can be dominant or recessive. An exception is an incomplete dominance, where neither one of the two alleles is completely dominant over the other. It means that the heterozygous genotype will not appear as the phenotype of homozygous genotype, recessive nor dominant. The color of the Mirabilis plant is an example of incomplete dominance. Dominant homozygous genotype will give red, while the recessive homozygous genotype will give white petals. Heterozygous genotype will produce a pink color of petals. If the gametes, which are blue colored, have the genotypes Rr and rr, we can conclude that there is a 50 percent chance of getting a pink and 50 percent chance of getting a white flower. Therefore, the probability for producing the red flower is zero.

begin{center}
begin{tabular}{ c c c}
& {color{Blue}R} & {color{Blue}r}\
{color{Blue}r} & rR & rr\
{color{Blue}r} & rR & rr\
end{tabular}
end{center}

a. 0

Multiple alleles are referred to a number of possible alleles, which must be higher than two, that can be inherited by one gene. An example is the ABO blood type inheritance, where we have three different alleles – A, B, and O (where we have four possible phenotypes – A, B, AB, and O type of blood). Polygenic traits are some physical characteristics, such as the color of the human skin or eyes, that are controlled by at least two genes.

Multiple alleles are referred to a number of possible alleles, which must be higher than two, that can be inherited by one gene. There is a higher number of potential genotypes in the genes that have multiple alleles. An example is the ABO blood type inheritance, where we have three different alleles – A, B, and O (where we have four possible phenotypes – A, B, AB, and O type of blood).

An organism’s phenotype is determined by its genotype, but gene expression can be affected by environmental factors. These factors can alter the inherited traits of an organism.

We have several stages of meiosis I. In prophase I, chromosomes are paired with the adequate homologous chromosome. In metaphase I, chromosomes are aligned in the center of the cell. In this phase occurs a crossover. During anaphase I, two sets of chromosomes move toward the opposite ends of the cell. In telophase I and cytokinesis, this diploid cell (2N) divides into two haploid cells (N). Meiosis II consists of prophase II, metaphase II, anaphase II, telophase II and cytokinesis. In prophase II, each chromosome contain two chromatids. In metaphase II, chromosomes are aligned in the center of the cell. During anaphase II, paired chromatids are divided and they move toward the opposite ends of the cell. In telophase I and cytokinesis, two haploid cells (N) divide into four haploid cells (N).

d. metaphase I

Meiosis consists of meiosis I and II. In the first meiotic division, a diploid cell is divided into two haploid cells. At the end of the second meiotic division, these two cells are divided without duplication and four haploid cells are made.

d. four haploid gametes

ofGene mapping was studied by Alfred Sturtevant. He has discovered relative gene location of one chromosome of the Drosophila, based on the rate of crossing-over among the genes in a meiotic division.

b. the relative location of genes of a chromosome

This organism has 4 pairs (2N=8, therefore N=4) of homologous chromosomes, which makes a total number of eight chromosomes.

This organism has 4 pairs of homologous chromosomes, which makes a total number of eight chromosomes.

Meiosis consists of meiosis I and II. Meiosis I consists of prophase I, metaphase I, anaphase I, telophase I and cytokinesis. In prophase I, chromosomes are paired with the adequate homologous chromosome. In this phase occurs a crossover, which is an interchange of DNA material within the homologous chromosomes. This process induces genetic diversity. In metaphase I, chromosomes are aligned in the center of the cell. During anaphase I, two sets of chromosomes move toward the opposite ends of the cell. In telophase I and cytokinesis, this cell divides into two cells, while the nucleus is formed around chromosomes of each cell. Therefore, in the first phase, the diploid cell is divided into two haploid cells. Meiosis II consists of prophase II, metaphase II, anaphase II, telophase II and cytokinesis. In prophase II, each chromosome contain two chromatids. In metaphase II, chromosomes are aligned in the center of the cell. During anaphase II, paired chromatids are divided and they move toward the opposite ends of the cell. In telophase I and cytokinesis, this cell divides into two cells. In the second phase, two haploid cells are divided without duplication and make four haploid cells.

The law of independent assortment explains that gamete cell inherits alleles for various genes separately of one another. Meiosis consists of meiosis I and II. At the end of the first phase, the haploid cell is divided into two cells, where each one inherits 23 chromosomes, one of each homolog pair. The process in which one daughter cell inherits one, while the other gets another chromosome is random. Since we have 46 chromosomes, there are about 8 million various possibilities for chromosome arrangement between these cells. The result of the second phase is two cells that are divided without duplication and making of four haploid cells. This is an example of independent assortment, where a child receives 23 chromosomes from a mother and 23 chromosomes from a father, while its phenotype will be determined by alleles inherited from both of its parents.

The dominant alleles (Y and R) determine the yellow color and round shape, while the recessive alleles (y and r) determine the green color and wrinkled shape. In order for the yellow color to appear at least one Y allele must appear in the genotype of an offspring, but its genotype must be yy to express the green color of seed. If the seed is round shaped, that tells us that at least one R allele must appear in the genotype of an offspring, but its genotype must be rr for the wrinkled seed. The Punnett square will look like this:
begin{center}
begin{tabular}{ c c c c c}
& {color{Blue}RY} & {color{Blue}Ry} & {color{Blue}rY}& {color{Blue}ry}\
{color{Blue}RY} & RRYY & RRYy & RrYY & RrYy \
{color{Blue}Ry} & RRyY & RRyy & RrYy & Rryy \
{color{Blue}rY} & RyYY & RrYy & rrYY & rrYy \
{color{Blue}ry} & RrYy & Rryy & rrYy & rryy \
end{tabular}
end{center}

Meiosis I consists of prophase I, metaphase I, anaphase I, telophase I and cytokinesis. One diploid (2N) cell enters the prophase I, where chromosomes are paired with the adequate homologous chromosome. In metaphase I, chromosomes are aligned in the center of the cell. During anaphase I, two sets of chromosomes move toward the opposite ends of the cell. At the end of telophase I and cytokinesis, this cell divides into two cells, each of them contain one set of chromosomes- N. Meiosis II consists of prophase II, metaphase II, anaphase II, telophase II and cytokinesis. In prophase II, each chromosome contain two chromatids. In metaphase II, chromosomes are aligned in the center of the cell. During anaphase II, paired chromatids are divided and they move toward the opposite ends of the cell. In telophase I and cytokinesis, this cell divides into two cells. In the second phase, two haploid cells are divided without duplication and make four haploid cells (N).

The law of independent assortment explains that gamete cell inherits alleles for various genes separately of one another. Meiosis consists of meiosis I and II. At the end of the first phase, the haploid cell is divided into two cells, where each one inherits 23 chromosomes, one of each homolog pair. The process in which one daughter cell inherits one, while the other gets another chromosome is random. Since we have 46 chromosomes, there are about 8 million various possibilities for chromosome arrangement between these cells. The result of the second phase is two cells that are divided without duplication and making of four haploid cells. This is an example of independent assortment, where a child receives 23 chromosomes from a mother and 23 chromosomes from a father, while its phenotype will be determined by alleles inherited from both of its parents.

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If the white color of the wool is determined by dominant allele A and the black by recessive allele a, we can conclude that the genotype of a white sheep can be Aa or AA. If this sheep would cross only with black sheep (genotype aa), we could find out the genotype of the white sheep based on the phenotype of its offspring. If there is a black sheep among the offspring, the genotype of the white sheep must be Aa. If the white and black sheep give only the offspring with white wool, the genotype of the parental white sheep is most likely AA.

The offspring of the same parents can have the same physical characteristics as the offspring with different genotype because of the existence of heterozygous genotype. Since one dominant allele is present, the phenotype will be the same as in an offspring with homozygous dominant genotype.

Gene expression can be affected by environmental factors, which can alter the phenotype of an organism. The ptarmigan is a bird that lives in the Arctic and molts its feathers. They have brown and black feathers during the spring and summer, and greyish in the autumn. However, in the winter, when the snow falls, they are white. This is one example of how an organism evolves and blends into the environment in order to be less visible for the predators.

Mendel discovered that alleles for different traits can be dominant or recessive. An exception is the incomplete dominance, where neither one of the two alleles is completely dominant over the other. It means that the heterozygous genotype will not appear as the phenotype of homozygous genotype, recessive nor dominant. However, if alleles are codominant, then the features that are determined by both dominant and recessive allele appear in the phenotype of a heterozygous offspring. The red and white hairs in the coat of the offspring that is made by red bull and a white cow is an example of codominance. If this physical characteristic was determined by incomplete dominance, the coat of an offspring would appear pink.

Mendel discovered that alleles for different traits can be dominant or recessive. In order for the dominant trait to appear in the offspring, they must have at least one dominant allele in their genotype, but for a recessive physical characteristic, they must be homozygous recessive. If a recessive trait didn’t appear in a parental generation but it was present in their offspring, that tells us that both of the parents are heterozygous (Aa) for that specific trait and they passed on a recessive allele to the next generation.
begin{center}
begin{tabular}{ c c c}
& {color{Blue}A} & {color{Blue}a}\
{color{Blue}A} & AA & Aa\
{color{Blue}a} & Aa & aa\
end{tabular}
end{center}

The scientist knows that dominant allele determines the tallness, while the recessive allele determines shortness. When a plant inherits one, or two dominant alleles from its parents, that will define the tallness. The shortness of the offspring will appear only if the recessive allele is inherited from both of the parental plants (tt genotype, red colored in the table). If both parents are heterozygous (Tt genotype), the Punnett square, where the gametes are blue colored, will look like this:

begin{center}
begin{tabular}{ c c c}
& {color{Blue}T} & {color{Blue}t}\
{color{Blue}T} & TT & Tt\
{color{Blue}t} & Tt & {color{Red} tt}
end{tabular}
end{center}

We can conclude that the probability for a short offspring to appear is 25 percent, while for tall offspring is three times higher, 75 percent.

The ratio of the red-colored eyes compared to the number of flyes with the brown eyes is:

37:14 = x : 1
x = 37/14
x = 2,6

c. 3 : 1

Mendel discovered that alleles for different traits can be dominant or recessive. In order for the dominant red-colored eyes to appear in the offspring of fruit flies, they must have at least one dominant allele in their genotype, but for a recessive physical characteristic, such as brown-colored eyes, they must be homozygous recessive.

Mendel discovered that alleles for different traits can be dominant or recessive. In order for the dominant red-colored eyes to appear in the offspring of fruit flies, they must have at least one dominant allele in their genotype, but for a recessive physical characteristic, such as brown-colored eyes, they must be homozygous recessive. The fly that has brown eyes has aa genotype, while the fly with red eyes can have either AA or Aa genotype. If a recessive trait didn’t appear in an F1 generation but it was present in an F2 generation, that tells us that both of the flies in F1 are heterozygous (Aa) for that specific trait and they passed on a recessive allele to the next generation.
begin{center}
begin{tabular}{ c c c}
& {color{Blue}A} & {color{Blue}a}\
{color{Blue}A} & AA & Aa\
{color{Blue}a} & Aa & aa\
end{tabular}
end{center}

The process that occurs during meiotic division of gametes induces genetic diversity. In prophase I, chromosomes are paired with the adequate homologous chromosome. In this phase occurs a crossover, which is an interchange of DNA material within the homologous chromosomes. It is responsible for the various patterns of fur in puppies.

Mendel tracked down various traits of the pea plant through the offspring of seven crosses. He has discovered that some traits weren’t present in parental generation but they have appeared in the offspring of F1 or F2 generation. He concluded that alleles for a certain trait can be dominant or recessive. For a dominant characteristic to appear, the offspring must be homozygous dominant or heterozygous. If an offspring has a recessive trait, the genotype must be homozygous recessive, therefore, the recessive allele has been inherited from both of the parents. Mendel’s segregation law explains the process that occurs in the parental generation, where gametes contain only one, randomly chosen allele.

Mendel crossed true breeding tall and true breeding short pea plant and he observed the traits that appeared in their offspring. Will the offspring develop traits of the parental generation?
begin{center}
begin{tabular}{ c c c}
& {color{Blue}T} & {color{Blue}T}\
{color{Blue}t} & Tt & Tt\
{color{Blue}t} & Tt & Tt
end{tabular}
end{center}
In the generation of F1, he noticed that all the plants were tall. However, when he crossed two plants from F1 generation, they developed an offspring, both tall and short. The probability in the F2 generation for a tall plant was 75% and for the short one 25%.
begin{center}
begin{tabular}{ c c c}
& {color{Blue}T} & {color{Blue}t}\
{color{Blue}T} & TT & Tt\
{color{Blue}t} & Tt & tt
end{tabular}
end{center}
How could a trait for shortness get lost in F1 and reappear in the F2 generation?
He has discovered that some traits weren’t present in a parental generation but they have appeared in the offspring of F2 generation. He concluded that alleles for a certain trait can be dominant or recessive. For a dominant characteristic to appear, the offspring must be homozygous dominant or heterozygous. If an offspring has a recessive trait, the genotype must be homozygous recessive.

Mendel discovered that alleles for different traits can be dominant or recessive and that alleles for various genes may segregate separately of each other. However, there are several exceptions to these rules:
begin{enumerate} % for numbers
item In incomplete dominance, neither one of the two alleles is completely dominant over the other. It means that the heterozygous genotype will not appear as the phenotype of homozygous genotype, recessive nor dominant. An example is Mirabilis jalapa, where one red and one white plant give rose offspring.
item In codominance, the traits of both alleles will appear in the offspring, so the heterozygous will have characteristics of both inherited alleles, recessive and dominant. An example is an inheritance of a protein that affect cholesterol level in the blood. People that are heterozygous for this trait produce two types of protein, while homozygous produce only one.
item Multiple alleles are referred to a number of possible alleles, which must be higher than two, that can be inherited by one gene. There is a higher number of potential genotypes in the genes that have multiple alleles. An example is the heritage of ABO blood type, where we have three alleles – A, B and O.
item Polygenic traits are some physical characteristics, such as the color of the human skin or eyes, that are controlled by at least two genes.
end{enumerate}