Name: ____________________________ Homework/class-work ...



Name: ____________________________ Homework/class-work Unit#9 Mendel and basic genetics (25 points)

Think and try every question. There is no reason for a blank response or an I don’t know. Any blanks will receive a zero.

Every assignment must be done on a separate piece of paper. Each assignment must be complete, neat, in complete sentences and done on time for full credit. Any assignment may be used as a take home or pop quiz at any time. One missing or late assignment will lose 5 points, 2 will lose 15 points, 3 will be considered incomplete and given a zero.

1. Reading classical (Mendelian) genetics: Date: __________________

Genetics is the study of how genes bring about characteristics, or traits, in living things and how those characteristics are inherited. Genes are portions of DNA molecules that determine characteristics of living things. Thorough the process of meiosis and reproduction, genes are transmitted from one generation to the next.

The Augustinian monk Gregor Mendel developed the science of genetics. Mendel performed his experiments in the 1860s and 1870s, but the scientific community did not accept his work until early in the twentieth century. Because the principles established by Mendel form the basis for genetics, the science is often referred to as Mendelian genetics. It is also called classical genetics to distinguish it from another branch of biology known as molecular genetics.

Mendel believed that factors pass from parents to their offspring, but he did not know the existence of DNA. Modern scientists accept that genes are composed of segments of DNA molecules that control discrete hereditary characteristics.

Most complex organisms have cells that are diploid. Diploid cells have a double set of chromosomes, one from each parent. For example, human cells have a double set of chromosomes consisting of 23 pairs, or a total of 46 chromosomes. In a diploid cell, there are two genes for each characteristic. In preparation for sexual reproduction, the diploid number of chromosomes is reduced to a haploid number. That is, diploid cells are reduced to cells that have a single set of chromosomes. These haploid cells are gametes, or sex cells, and they are formed through meiosis. When gametes come together in sexual reproduction, the diploid state is reestablished.

The offspring of sexual reproduction obtain one gene of each type from each parent. The different forms of a gene are called alleles. In humans for instance, there are two alleles for earlobe construction. One allele is for earlobes that are attached, while the other allele is for earlobes that hang free. The type of earlobe a person has is determined by the alleles inherited from the parents.

The set of all genes that specify an organism’s traits is known as the organism’s genome. The genome for a human consists of about 100,000 genes. The gene composition of a living organism is its genotype. For a person’s earlobe shape, the genotype may consist of two genes for attached earlobes, or two genes for free earlobes, or one gene for attached and one gene for free earlobes.

The expression of the genes is referred to as the phenotype of a living thing. If a person has attached earlobes, the phenotype is “attached earlobes.” If the person has free earlobes, the phenotype is “free earlobes.” Even though three genotypes for earlobe shape are possible, only two phenotypes (attached and free) are possible.

The two paired alleles in an organism’s genotype may be identical, or they may be different. An organism’s condition is said to be homozygous when two identical alleles are present for a particular characteristic. In contrast, the condition is said to be heterozygous when two different alleles are present for a particular characteristic. In a homozygous individual, the alleles express themselves. In a heterozygous individual, the alleles may interact with one another, and in many cases, only one allele is expressed.

When one allele expresses itself and the other does not, the one expressing itself is the dominant allele. The overshadowed allele is the recessive allele. In humans, the allele for free earlobes is the dominant allele. If this allele is present with the allele for attached earlobes, the allele for free earlobes expresses itself, and the phenotype for the individual is “free earlobes.” Dominant alleles always express themselves, while recessive alleles express themselves only when two recessive alleles exist together in an individual. Thus a person having free earlobes can have one dominant allele or two dominant alleles, while a person having attached earlobes must have two recessive alleles.

Inheritance patterns:

Mendel was the first scientist to develop a method for predicting the outcome of inheritance patterns. He preformed his work with pea plants, studying seven traits: plant height, pod shape, pod color, seed shape, seed color, flower color, and flower location. Pea plants pollinate themselves. Therefore, over many generations, pea plants develop individuals that are homozygous for particular characteristics. These populations are known as pure breeding.

In his work, Mendel took pure breeding pea plants and cross pollinated them with the other pure breeding pea plant. He called these the parent generation. When Mendel crossed the pure breeding purple flowering plants with the pure breeding white flowering plants, he discovered that all the plants resulting from the cross were purple flowered. He called this generation the F1 generation (first generation). Next, Mendel crossed the offspring of the F1 generation purple flowering plants among themselves to produce a new generation called the F2 generation (second generation). Among the plants in this generation, Mendel observed that three-fourths of the plants were purple flowered and one-fourth of the plants were white flowered.

Mendel’s laws of genetics:

Mendel conducted similar experiments with other pea plant traits. Over many years, he formulated several principles that are known today as Mendel’s laws of genetics. His laws include the following:

1. Mendel’s law of dominance: When an organism has two different alleles for a trait, one allele dominates.

2. Mendel’s law of segregation: During gamete formation by a diploid organism, the pair of alleles for a particular trait separates, or segregates, during the formation of gametes (as in meiosis).

3. Mendel’s law of independent assortment: The members of a gene pair separate from one another independent of the members of other gene pairs. (These separations occur in the formation of gametes during meiosis.

Mendelian crosses:

An advantage of genetics is that scientists can predict the probability of inherited traits in offspring by performing a genetic cross. To predict the possibility of an individual trait, several steps are followed. First, a symbol is designated for each allele in the gene pair. The dominant allele is represented by a capital letter and the recessive allele by the corresponding lowercase letter, such as A for normal skin pigmentation and a for albinism. For a homozygous dominant individual, the genotype would be AA.

The next step in performing a genetic cross is determining the genotypes of the parents and the genotypes of the gametes. A heterozygous male and a heterozygous female to be crossed have the genotypes of Aa and Aa. During meiosis, the allele pairs separate. A sperm cell contains either an A or an a, while the egg cell also contains either an A or an a.

To continue the genetics problem, a Punnett square is used. A Punnett square is a boxed figure used to determine the probability of genotypes and phenotypes in the offspring of a genetic cross. The possible gametes produced by the female and the male are placed on the outside of the square (one set on top and one set on the left side).

Continuing, all of the possible combinations of alleles are considered. This is done by filling in each square with the alleles above it and to the left.

From the Punnett square, the phenotype of each possible genotype can be determined. For example, the offspring having AA, Aa and Aa will have normal skin pigmentation. Only the offspring with the genotype aa will have albinism. Therefore, the ration of phenotypes is three with normal skin pigmentation to one with albinism (3:1). The ratio of genotypes is 1:2:1 (1 AA: 2 Aa: 1 aa).

Principles of genetics:

Mendel’s studies have provided scientists with the basis for mathematically predicting the probabilities of genotypes and phenotypes in the offspring of a genetic cross. But not all genetic observations can be explained and predicted based on Mendelian genetics. Other complex and distinct genetic phenomena may also occur. Several complex genetic concepts, described in this section, explain such distinct genetic phenomena as blood types and skin color.

Incomplete dominance:

In some allele combinations, dominance does not exist. Instead, the two characteristics seem to blend together. In such a situation, both alleles have the opportunity to express themselves. For instance, snapdragon flowers display incomplete dominance in their color. There are two alleles for flower color: one for white flowers and one for red flowers. When the two alleles for white are present, the plant displays white flowers. When the two alleles for red are present the plant displays red flowers. But when one allele for red is presents with one allele for white, the color of the flowers is pink. However, if two pink snapdragons are crossed, the phenotype ratio of the offspring is one red, two pink, and one white. These results show that the genes themselves remain independent; only the expressions of the genes seem to blend. If the gene for red and the gene for white actually blended, pure red and pure white flowers could not appear in the offspring.

Multiple alleles:

In certain cases, more than two alleles exist for a particular characteristic. Even though an individual has only two alleles, additional alleles maybe present in the population. This condition is multiple alleles.

An example of multiple alleles occurs in blood type. In humans, blood groups are determined by a single gene with three possible alleles: A, B, or O. Red blood cells can contain two antigens, A and B. The presence or absence of these antigens results in four blood types: A, B, AB, and O. If a person’s red blood cells have antigen A, the blood type is A. If a person’s red blood cells have antigen B, the blood type is B. If a person’s red blood cells have neither antigen A or B, the blood type is O.

The allele for type A and type B blood are co-dominant; that is, both alleles are expressed. However, the allele for type O blood is recessive to both type A and type B. Because a person has only two of the three alleles, the blood type varies depending on which two alleles are present. For instance is a person has the A allele and the B allele, the blood type is AB. If a person has two A alleles, or one A and one O allele, the blood type is A. If a person has two B alleles, or one B and one O allele, the blood type is B. If a person has two O alleles, the blood type is O.

Polygenic inheritance:

Although many characteristics are determined by alleles at a single place on the chromosomes, some characteristics are determined by an interaction of genes on several chromosomes of at least several places on one chromosome. This condition is polygenic inheritance.

An example of polygenic inheritance is human skin color. Genes for skin color are located in many places, and skin color is determined by which genes are present at these multiple locations. A person with many genes for dark skin will have very dark skin color, and a person with many genes for light skin will have very light skin. Many people have some genes for light skin and some for dark skin, which explains why so many variations of skin color exist. Height is another characteristic reflecting polygenic characteristics.

Di-hybrid crosses:

The foil method for determining gametes: When geneticists want to look at the occurrence of two traits both showing up in the offspring of a genetic cross the number of genotypes and phenotypes tend to vary more. In order to analyze a di-hybrid cross you must use the FOIL (First, outer, inner, last) method to find out the gametes for each parent and cross them in a 16 square Punnett square.

1. Answer the following based on your reading: Date: _______________________

1. What does it mean to be pure breeding?

2. Describe the difference between phenotype and genotype.

3. What is polygenic inheritance?

4. What is inheritance through multiple alleles? How is this different from classical genetics?

5. What is incomplete dominance? How is this different from classical genetics?

6. In your own words describe Mendel’s laws of genetics.

7. What are alleles? How do they give us genetic variation?

8. What is the difference between homozygous and heterozygous?

9. What are genes?

10. If two parents have a dominate trait, can they have a child that has a recessive trait? Explain.

11. If two parents have a recessive trait, can they have a child that has a dominant trait? Explain.

2. Mendel and basic genetic questions: Date: _______________________

1. What is the name of the organelle that contains the genetic material?

2. What is the full name of DNA?.

3. The passing of traits from one generation to the next is known as what?

4. What is the name of the part of the DNA molecule that represents or codes for a trait?

5. Genes code for what?

6. Different forms of the same gene are known as what?

7. A trait expressed when only one copy is present:

8. A person’s physical characteristics are called a persons what?

9. Name the 3 different genotypes and tell me the letters that represent each.

10. Explain why two heterozygous parents can have offspring that are phenotypically and genotypically far different from themselves.

11. List and analyze the early theories of genetics including who proposed the theories. Use your knowledge of genetics to explain why the early theories are incorrect.

3. One trait Punnett squares: Date: _______________________

In certain species of animals, black fur (B) is dominant over brown fur (b). For each example 1-3 below use a Punnett square to determine the cross and answer questions A-D:

1. Both parents are heterozygous and have black fur.

2. One parent is homozygous black and the other is brown.

3. One parent is heterozygous black and the other is brown.

A. What is the genotypic ratio?

B. What is the phenotypic ratio?

C. How many offspring will have brown fur?

D. How many offspring will have black fur?

In certain species of flowers the flower come in three different colors-Red, pink and white. When red and white flowers are crossed all the offspring are pink. When red and pink flowers are crossed 1/2 of the offspring is red and 1/2 of the offspring is pink. For each example 1-3 below use a Punnett square to determine the cross and answer questions A-E:

1. Cross a plant that has red flowers with a plant that has pink flowers:

2. Cross a plant that has pink flowers with a plant that has white flowers:

3. Cross a plant that has white flowers with a plant that has red flowers:

A. What is the genotypic ratio?

B. What is the phenotypic ratio?

C. How many offspring will be pink?

D. How many offspring will be white?

E. How many offspring will be red?

4. Blood type Punnett Squares: Date: ______________________

In blood typing, the gene for type A and the gene for type B are co-dominant. This means when both genes are present the individuals phenotype will reflect both A and B blood. For each example A-E below use a Punnett square to determine the cross and answer questions 1-6:

Questions:

A. The father is type O, the mother is type O:

B. Father is type A, homozygous, mother is type B, homozygous:

C. Father is type A, heterozygous, mother is type B, heterozygous:

D. Father is type O, mother is type AB:

E. Father and mother are both AB:

1. What is the genotypic ratio?

2. What is the phenotypic ratio?

3. How many offspring will have type AB blood?

4. How many offspring will have type B blood?

5. How many offspring will have type A blood?

6. How many offspring will have type O blood?

Answer the following:

6. What blood type(s) can a person with A blood accept in a transfusion?

7. What Blood type(s) can a person with O blood accept in a transfusion?

8. Blood type O is _______________ to types A &B.

9. When a person has both the A & B gene for blood type they will express both types. What is this referred to as?

10. A confused new mother just gave birth to a beautiful 8 pound 5 ounce baby girl. The only catch is that she is unsure who the father is. The doctors tested her and her daughter to determine their blood type. The mother is type AB and her daughter is type AO. Possible father #1 is type AB, father #2 is heterozygous type A and father #3 is homozygous type A. Who is the father?

5. Advanced genetics: Date: ___________________________

1. During this unit we have discussed four types of inheritance, List them and briefly explain what they are.

2. Look at each graph below and determine which type of inheritance/trait is shown:

A. B. C. D.

3 Mr. Cash died and left all his money to his two children. A young man claiming to be a lost third child sued for his share of the estate. The judge ordered blood tests for all the family members and for the young man. Mr. Cash’s blood type was AB. His wife had type A.

Use a Punnett Square to show the offspring that could be produced by Mr. and Mrs. Cash if Mrs. Cash is homozygous type A.

A. How many possible phenotypes are there?

B. What is the phenotypic ratio?

C. What is the genotypic ratio?

Use a Punnett square to show the offspring that could be produced by Mr. and Mrs. Cash if Mrs. Cash is Heterozygous type A

A. How many possible phenotypes are there?

B. What is the phenotypic ratio?

C. What is the genotypic ratio?

The man claiming to be the long-lost son then went for his blood test. He had type O blood.

A. What is the genotype of the long-lost son?

B. Does he have a right to part of the estate?

6. Punnett squares two traits: Date: __________________________

In a di-hybrid cross, when two traits are considered, the number of possible combinations in the offspring increases. Suppose that brown hair (B) is dominant over blonde hair (b) and brown eyes (E) are dominant over blue eyes (e). Hint: Assume that brown and blue are the only possible eye colors. For each example A-D below use a Punnett square to show the cross and answer questions 1-4.

A. The father has black hair (heterozygous) and brown eyes (heterozygous) and the mother has blonde hair and blue eyes.

B. Both parents have brown hair (heterozygous) and brown eyes (heterozygous).

C. A man that is heterozygous Type A and has blue eyes is having a child with a woman that is Type AB and has heterozygous brown eyes (Ee).

D. A man that is heterozygous type B and heterozygous for brown eyes is having a child with a woman that heterozygous type A and heterozygous for brown eyes.

1. What is the genotypic ratio?

2. What is the phenotypic ratio?

3. How many different genotypes are there?

4. How many different phenotypes are there?

7. One and two factor crosses: Date: ________________________

Part 1: One-Factor Crosses.

Crosses that involve one trait, such as seed coat color, are called one-factor crosses or monohybrid crosses. For the one-factor crosses in this activity, we will use some of the traits Mendel observed in pea plants. The expression of the dominant and recessive allele for the genes controlling these traits are described in the following chart. The chart also assigns letters to represent the different alleles.

Use the chart below for problems 1-10.

|Trait |Dominant allele |Recessive allele |

|Pod shape |Smooth (N) |Constricted (n) |

|Pod color |Green (G) |Yellow (g) |

|Flower position |Axial (A) |Terminal (a) |

|Plant height |Tall (T) |Short (t) |

Problems 1-10: For each problem below, make a Punnett Square and give the phenotypic and genotypic ratios.

1. Nn x NN

2. Aa x aa

3. Tt x Ttz

4. Cross two plants that are heterozygous for green pods.

5. Cross a plant that is heterozygous for axial flowers with a plant that has terminal flowers.

6. Cross a homozygous tall plant with a short plant.

7. Cross a plant that is heterozygous for smooth pods with a plant that has constricted pods.

8. When a tall plant is crossed with a short plant, some of the offspring are short. What are the genotypes of the parents and the offspring? What is the phenotypic ratio in the offspring?

9. Three-fourths (3/4) of the plants produced by a cross between two unknown pea plants have axial flowers and 1/4 have terminal flowers. What are the genotypes of the parent plants?

10. What cross would result in 1/2 of the offspring having green pods and 1/2 of the offspring having yellow pods?

Part 2: Two factor crosses:

Crosses that involve two traits, such as pod color and pod shape are called two factor crosses or dihybrid crosses. Predicting the outcome of two factor crosses requires basically the same procedure as that for crosses involving one trait. Keep in mind that in two factor crosses the genes controlling the two different traits are located on non-homologous chromosomes. During meiosis, non-homologous chromosomes assort independently. This means that each of the chromosomes of any pair of homologous chromosomes has an equal probability of ending up in a gamete with either chromosome form any other pair of homologous chromosomes. Because of independent assortment, a plant that is heterozygous for two traits (genotype AaBb) will produce equal numbers of four types of gametes—AB, Ab, aB and ab.

For problems 1-4 use the following information: In mice, the ability to run normally is a dominant trait. Mice with this trait are called running mice (R). The recessive trait causes mice to run in circles only. Mice with this trait are called waltzing mice (r). Hair color is also inherited in mice. Black hair (B) is dominant over brown hair (b).

For problems 1-4 make a Punnett Square and give the phenotypic and genotypic ratio.

1. Cross a heterozygous running, heterozygous black mouse with a homozygous running, homozygous black mouse.

2. Cross a homozygous running, homozygous black mouse with a heterozygous running, brown mouse.

3. Cross a waltzing brown mouse with a waltzing brown mouse.

4. Cross a heterozygous running, heterozygous black mouse with a heterozygous running, heterozygous black mouse.

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