Topic 7 Lesson 1 and 2 (Genes and Heredity)

What fraction does each box in a Punnet square represent? What percentage does each box represent?

1/4 25% Each box represents the chance of an offspring inheriting a certain trait

Punnett square method

A Punnet square uses the laws of probability to demonstrate why those results occurred - to determine the probability of inheriting alleles 1. Draw a square box divided into four square parts 2. Determine the alleles of each of the parents - One parent's alleles go on the top and other parents alleles go on the left

recessive allele

An allele that is hidden whenever the dominant allele is present. If one parent donates a dominant allele and the other donates a recessive, only the dominant trait will be expressed.

dominant allele

An allele whose trait always shows up in the organism when the allele is present.

heterozygous (hybrid)

An organism that has two different alleles for a trait (ex: Bb)

homozygous (purebred) dominant

An organism that has two dominant alleles for a trait (ex: BB)

Homozygous and Heterozygous

An organism that has two identical alleles for a trait - geneticists refer to an organism has this instead of saying purebred. When the alleles are both dominant, as in the yellow seed plant (GG), the genotype is called homozygous dominant. When the alleles are both recessive, as in the green seed color (gg) the genotype is called homozygous recessive. When it is a hybrid (Gg) as in the yellow seed color, the genotype is called the heterozygous condition (hetero means different)

homozygous (purebred) recessive

An organism that has two recessive alleles for a trait (ex: bb)

genotype

An organism's genetic makeup, or allele combinations. The combination of alleles that are inherited

phenotype

An organism's physical appearance, or visible traits - what we see. The expressions of an organism's genes is called its phenotype. The height, the shape, the color the size the texture - whatever trait is being expressed, is referred to as the phenotype. So a pea plant with the phenotype of yellow seed color could have two possible genotypes , GG or gg

What would happen to the probabilities of yellow and green seed is one parent were homozygous recessive and the other were homozygous dominant?

Because the homozygous dominant parent is guaranteed to provide a dominant allele to the offspring, all of the offspring would be hybrids with yellow seed color

factors

In math a factor is something that is multiplied, in science a factor is something that determines something else - he called the information that carried the traits factors because they determined what was expressed

steps of meiosis in order

1 - chromosome pairs come together and cross over 2-cell divides into 2 daughter cells 3-chromosome splits into two chromatids 4-four daughter cells are formed

A die is a six sided cube with dots representing the numbers 1 through 6. What is the probability of rolling a 3?

1 out of 6 or 1/6

1 - What is the term for each of the long strands that is show in the illustration? (page 363) 2 - what do each of the colored and labeled sections represent? 3-How many genes are present on this pair of chromosome? 4-How many alleles are present? 5-Which of the genes are homozygous? 6-Which of the genes are heterzygous? 7-Which of the genes will result in a recessive trait?

1-chromosome 2-genes and alleles 3-7 4-14 5-bb, EE, FF 6-Aa, Cc, Dd 7-bb

Determine if each of the following are purebred or hybrid: 1-Both parents donate a recessive allele for a trait 2-One parents donates a dominant allele, and the other parents donates a recessive allele for a trait 3-Both parents donate a dominant allele for a trait *Mendel discovered that yellow is the dominant pea seed color while recessive pee seed color is green

1-purebred (gg) 2-hybrid (Gg) 3-purebred (GG)

What is an example of cloning that occurs in nature?

asexual reproduction, where the offspring are genetic copies of their parent

Which process that occurs during meiosis does not occur during mitosis?

crossing over

What is an example of cloning that occurs in humans?

identical twins, which are genetic copies of each other

How did Mendel come to the conclusion that an organism's traits were carried on different alleles?

Mendel's experiments, where traits appeared in the F2 generation that were not in the F1 generation disproved what many people believe prior to his work that all traits in offspring's were a mixture of each parent's traits.

LOOK at page 364 at the Pedigree chart

Sickle cell anemia is a genetic disease that changes the structure of red blood cells. In the pedigree, affected members are shaded. Circle any individuals on the pedigree who are definitely carriers for that trait

What are chromosomes?

Structures within a cell's nucleus that contain genetic material DNA that is passed from one generation to the next

Think of a trait you admire. How can that trait get passed through a family? Create a pedigree that outlines the transmission of this trait through a family. Consider who has the trait, who is a carrier for it, and who does not have it.

Students should show that if an individual expresses a trait, at least one parents must carry the trait, whether or not they express it. If an individual carries a trait without expressing it, then at least one parent must carry the trait.

What controls the traits an organism has?

The alleles it inherits

How is genetic material of the parent cell different from the four cells that are formed?

The cells that were formed have less genetic material and the genetic material inside each cell is different

You have learned that the alleles an offspring receives from its parents depends on probability. How is this similar to the outcome of coin toss?

There are equal chances of an offspring inheriting a specific allele from a parents, just as there are equal chances that a coin will land either heads up or tails up.

What would happen to the offspring if crossing over did not occur during the first part of meiosis?

There would be less genetic variation in the offspring

How would geneticists -people who study genes-know whether an organism is homozygous or heterozygous for a certain trait by examining its chromosomes?

They look at the code on the gene from each inherited chromosome. If each gene has identical codes, the same alleles, the individual is homozygous for the trait. If the genes have difference codes, the individual is herterozygous for the trait.

Did the ducks reproduce sexually or asexually? How do you know?

They reproduce sexually because the offspring are not exact genetic copies of their parents

How will you determine the number of chromosomes in a sex cell in an organism if you know the number of chromosomes in the body cell?

You would divide the number of chromosomes in a body cell by 2, since there are half the number of chromosomes in a sex cell

How will you determine the number of chromosomes in a body cell if you know the number of chromosomes in a sex cell?

You would multiple the number by 2

meiosis and mitosis

2 main types of cell division the majority of our body cells divide to make two genetically identical new cells in the process of MITOSIS - the cells nucleus divides into two new nuclei, and identical copies of the parents cells genetic material are distributed into each daughter cell

A male king crab has 104 chromosomes in a sperm cell. How many chromosomes does it have in each of its body cells?

208 Chromosomes

Example: The probability of a specific allele from one parent being passed on to an offspring is 1 in 2 or 1/2. This is the same probability as predicting a coin toss correctly. How often would you expect a coin to show tails if you flip it 100 times?

50

probability

A number that describes how likely it is that a particular event will occur. The laws of probability predict what is likely to happen and what is not likely to happen. When dealing with genetics and inheritance, it is important to know the laws of probability. Every time two parents produce offspring, the probability of certain traits getting passed on is the same. Ex. A family that has multiple children all of the same sex. According to the laws of probability, a boy should have been born already, but there is no guarantee of that happening. Every time parents have a child, the probability of having a boy remains the same as the probability of having a girl

chromosome

A threadlike structure within a cell's nucleus that contains DNA that is passed from one generation to the next. The genes are segments of code that appears on structures called chromosome. These threadlike strands of genetic material have condensed and wrapped themselves around special proteins. This provides support for the chromosome structure.

pedigree

A tool that geneticists use to map out the inheritance of traits. The diagram shows the presence or absence of a trait according to the relationships within a family across several generations. (it is like a family tree)

Why are there 46 chromosomes in body cells but only 23 chromosomes in sex cells?

Because the sex cells each contribute 23 chromosomes to the offspring during fertilization, for a total of 46. You get 23 chromosomes from your mother and 23 from your father. These chromosomes come in pairs called homologlous chromosomes, that contain the same genes. Two alleles: one from the mother and one from the father - represent each trait. Some of the alleles for how the gene is expressed may be dominant or recessive. Because more that one gene is present on the 23 pairs of chromosomes, there is a wide variety of allele combinations. Other organisms have different numbers of chromosomes, and there is a great variety. Ex. mallard ducks have 80 chromosomes. ALL sexually reproducing organisms form sex cells, which have 1/2 the number of chromosomes that body cells have

Process of Meiosis

Before a cell can divide, the genetic material condenses into chromosomes. This picture shows how meiosis starts with the genetic material being copied and condensing into chromosomes. After crossing over, the chromosomes separate and the cell divides into two cells. Each new cell containing 1/2 the number of chromosomes divides again making a total of 4 daughter cells. Meiosis II shows how the second division occurs. Each chromosome splits into two rod-like structures called chromatids. Each chromatid contains a double helix of DNA. Note that each of the 4 daughter cells has one distinct chromatid.

crossing over

During crossing over, a segment of the gene from the mother changes places with a segment of the same gene from the father.

How can crossing over lead to the expression of new traits?

During crossing over, homologous chromosomes exchange genetic information by swapping alleles. As a result, each of the four new daughter cells has a slightly different combination of genes. This means different traits can form, leading to variation

DUCKLINGS: page 360 question 2 Each duckling came from these parents. They look similar, but they are not exactly the same. Why are they not identical? Explain

Each duckling came from a different egg and a different sperm. When each sex cell is created it is genetically unique.

How would you represent a purebred?

Either two capital letters or two lower case letters (GG or gg)

What do genes do?

Every living thing needs instructions to live. Without these instructions, living things would not be able to grow and function. These instructions are located on genes. Genes are located on chromosomes In humans, between 20,000-25,000 genes are found on the 46 chromosome. Chromosomes are different sizes. Larger ones contain more genes that smaller chromosomes. Each gene contains instructions for coding a particular trait.

Can you use probability to predict that an event will definitely occur?

For most events, probability predicts only what event is likely to occur, not what event will definitely occur. Some events such as a sunrise, have a 100 percent probability of occurring.

Explain how genotypes and phenotypes are different?

Genotype is the genetic makeup while phenotype is the expressed trait (what you see)

For plant stem length, the dominant allele for height is T and the recessive allele is t. What would be the genotypes, phenotypes, and offspring probabilities of a cross between two heterozygous parents for tall stem length>

Genotypes: TT, Tt and tt with probabilities of 1/4 being TT; 1/2 being Tt and 1/4 being tt. Phenotypes are tall and short stem length, with probabilities of 3/4 being tall and 1/4 being short

Homologous chromosomes

Have one chromosome from each parent. While the two chromosomes share the same sequence of genes, they may have different alleles. Before the chromosomes separate and move into separate cells, they undergo a process called crossing over. - where a small segment of one chromosome exchanges place with the corresponding segment on the other chromosome. By exchanging this genetic information, the new cells that form will have a slightly different combination of genes. This allows for minor variations in traits to form, which means there is a higher likelihood that offspring with desirable traits will form within the larger population.

The dominant allele for dimples is D. What genetic condition does an individual with the alleles dd have?

Homozygous recessive purebred, no dimples

You and a friend both roll a die at the same time. On the first roll, the dots on the dice add up to 7. On the second roll they add up to 2. Which do you think was more likely, rolling a total of 2 or a total of 7? Why

It is easier to get a total of 7 because there are more possible combinations of rolls that add up to 7 but only one possible combination of rolling a total of 2 - 1 and 1

During which process does crossing over occur?

Meiosis

Which process results in the greater number of daughter cells? How many?

Meiosis, which results in 4 daughter cells

How would you evaluate the contribution of Mendel's experiments with pea plants to the study of biology? Explain

Mendel's work revolutionized biology by advancing the science of inheritance. He proved that an organism inherits alleles ("factors") that control which traits are expressed and that these alleles could be dominant or recessive. He determined that traits are inherited using pieces of information that he called factors and we call genes. He discovered how genes, such as those in ducks, were transferred from parents to offspring and how they made certain traits appear. However, Mendel did not know what genes actually looked like.

How many cells divisions occur during mitosis and meiosis?

Mitosis - one cell division Meiosis two cells divisions

Mitosis vs. Meiosis

Mitosis: one division forming 2 identical cells (clones) with the same DNA as the parent cell The sex cells produced by Meiosis (two cell divisions) are not genetically identical - why? *crossing over exchanges genetic material between homologous chromosomes and *the two cell divisions that occur in meiosis produce 4 daughter cells and each cell has 1/2 its parent cell's DNA - as a result - each sex cell has different genetic information Mitosis forms body cells Meiosis forms sex cells

Is the chromosome number a good predictor of organism complexity? explain

No

A student claims that for an organism to be called purebred the two alleles for a trait must be the same and that both alleles must be also dominant. Do you agree? Why?

No, the student's claim is incorrect. Purebred means that the two alleles are the same but they may be either dominant or recessive

Do all living things have the same number of genes? Explain

No. The number of genes depends on the number of chromosomes, and not all living things have the same number of chromosomes

Are Mendel's pea plants an example of cloning? Why or Why not?

No. The pea plant he produced were not an exact copy of another plant.

How does the genetic makeup of the daughter cells that result from mitosis and meiosis differ?

The daughter cells that result from mitosis are genetically identical. The daughter cells that result from meiosis are genetically different.

What does probability predict will occur if you toss a coin ten times?

The expected outcome is that the coin will land heads up five times and tales five times

How are traits passed from parents to offspring during the process? (regarding northern cardinals)

The offspring receives half of its genes from one parent and half from the other

What conditions would have to occur for an offspring to express the recessive trait?

The offspring would have to inherit two recessive alleles (one from each parent)

heredity

The passing of traits from parents to offspring.

meiosis

The process that occurs in the formation of sex cells (sperm and egg) by which the number of chromosomes is reduced by half - cell division that forms 4 sex cells with half the amount of genetic information. It is through meiosis that homologous chromosomes separate into two different cells. This creates new cells with 1/2 as many chromosomes as the parent cell.

A domestic cat has 38 chromosomes in its skin cells while a dog has 78 chromosomes. How does this fact help to explain why dogs and cats cannot interbreed?

The sex cells could not easily combine to form the body cells of an offspring because of the different chromosome number

Will the sex of the cardinal's offspring determine any of its traits?

Yes, if it is a male, it will be red. If it is a female, it will be gray

DUCKLINGS: page 360 How were the traits transferred from the parents to the ducklings during reproduction? Where were those traits found?

Traits are transferred to offspring during fertlization when the egg and sperm come together. Traits are found on the genes in the sex cells of the parents (egg and sperm)

zygote

When the sperm and egg fuse, they for a zygote, or fertilized egg. The zygote gets two sets of chromosomes - one set from the sperm and one set from the egg. Human eggs - contain 23 chromosomes in a set and sperm cells contain 23 chromosomes in a set. So, each of your body cells contains one set of chromosomes from your mother and another set from your father for a total of 46 chromosomes.

Geneticists

scientists who study patterns of inheritance

cell cycle

series of events in which a cell grows, prepares for cell division, and divides to form two new daughter cells. During this time the chromosome gets its characteristic X shape.

What is required for sexual reproduction to occur?

sex cells from a mother and a father

Which process do you think cardinals use to reproduce?

sexual reproduction

What is the different between an object's structure and its function?

structure is the form of something, while function is what it does

Allele

the different forms of a gene; could be dominant or recessive Pea plans have one gene that controls the color of the seeds. This gene may express itself as being either yellow or green through a combination of yellow alleles and green alleles. When crossed, each parent donates one of its alleles for seed color to the offspring. The allele that each parents donates is random. An offspring's seed color is determined by the combination of both alleles ALL organism's traits are controlled by the alleles it inherits

What do these cells contain?

they contain genes that will determine the offspring's traits

How would geneticists - people who study genes - know whether the organism in FIGURE 3 (look in book page 363) is homozygosus or heterozygous for a certain trait by examining the chromosome pair?

they look at the code on the gene from each inherited chromosome. If each gene has identical codes, the same alleles, the individual is homozygous for the trait. If the genes have different codes, the individual is herterozygous for the trait

Quantify

to express an amount, to show a complete set of data