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Interest Grabber Section 14-1 A Family Tree

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a family tree

Interest Grabber

Section 14-1

A Family Tree
  • To understand how traits are passed on from generation to generation, a pedigree, or a diagram that shows the relationships within a family, is used. In a pedigree, a circle represents a female, and a square represents a male. A filled-in circle or square shows that the individual has the trait being studied. The horizontal line that connects a circle and a square represents a marriage. The vertical line(s) and brackets below that line show the child(ren) of that couple.
  • 1. This pedigree shows the inheritance of attached ear lobes. Which parent has attached ear lobes?
  • 2. How many children do the parents have? Which child has attached ear lobes?
  • 3. Which child is married? Does this child’s spouse have attached ear lobes? Do any of this child’s children have attached ear lobes?
  • The father
  • Three; the daughter has attached ear lobes.
  • The second son; no; yes, the daughter
slide2

Section Outline

Section 14-1

  • 14–1 Human Heredity
    • Human Chromosomes
    • Human Traits
    • Human Genes
      • Blood Group Genes
      • Recessive Alleles
      • Dominant Alleles
      • Codominant Alleles
    • From Gene to Molecule
      • Cystic Fibrosis
      • Sickle Cell Disease
      • Dominant or Recessive?
slide3

14–1 Human Heredity

    • A. Human Chromosomes-
      • 1. Human chromosomes can be organized so scientist can look at them. This is called a karyotype.
      • 2. There are 46 chromosomes in the human genome. 2 of those are called the sex chromosomes because they determine an individual’s sex.
  • Females have two X chromosomes
  • Males have one X and one Y chromosome
slide4

The other 44 chromosomes that do not determine sex are called the autosomes.

  • A normal female would be written as 46,XX and a normal male would be 46,XY.
video 1

Video 1

Human Sex Determination

Video 1
  • Click the image to play the video segment.
slide6

B. Human Traits

    • 1. Human traits follow the patterns of inheritance shown by Gregor Mendel.
      • a. A pedigree chart can be used to show the relationships of a certain trait within a family. Figure 14-3 page 342.
slide7

Figure 14-3 A Pedigree

Section 14-1

A circle represents a female.

A square represents a male.

A vertical line and a bracket connect the parents to their children.

A horizontal line connecting a male and female represents a marriage.

A half-shaded circle or square indicates that a person is a carrier of the trait.

A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait.

A completely shaded circle or square indicates that a person expresses the trait.

slide8

2. Most traits you see expressed are polygenic. They have more than one gene regulating them.

  • Some traits are not just controlled by environment. Many are strongly influenced by environmental, or non-genetic factors including nutrition and exercise

3. This can also work the other way. Genes we have that might be bad for us cannot be expressed unless we put ourselves in the condition for them to work.

slide9

C. Human Genes – there are certain genes scientist have been able to track down due to their expression is visible or easy to find.

      • 1. Blood Group Genes – The ABO blood typing given labels the antigens that person has on their blood. If a foreign antigen enters the blood it is attack by the immune system. Figure 14-4 page 344.
        • There is also the RH factor that plays a role here. It only comes into play at the birth of a child. Rh is dominant.
        • When figuring the blood type remember that A and B are codominant while O is recessive.
slide10

Figure 14-4 Blood Groups

Section 14-1

Safe Transfusions

Antigen on

Red Blood Cell

Phenotype

(Blood Type

Genotype

From

To

slide11

2. Recessive Alleles – One of the first genetic disorders to be understood with genetics was PKU (phenylketonuria). People with PKU lack the enzyme needed to break down phenylalanine. If this is not broken down in newborns it will build up in tissues and cause severe mental retardation. Figure 14-6 shows other autosomal diseases that we know of.

slide12

Codominant alleles

Recessive alleles

Dominant alleles

Tay-Sachs disease

Huntington’s disease

Sickle cell disease

Galactosemia

Albinism

Cystic fibrosis

Hypercholes-

terolemia

Phenylketonuria

Achondroplasia

Concept Map

Section 14-1

Autosomol

Disorders

caused by

include

include

include

slide13

Dominant Alleles – Examples of dominant genetic diseases are dwarfism and Huntington’s disease.

Codominant Alleles – Sickle cell anemia is an example of a codominant disease. A codominant disease is where both traits are dominant and both will be expressed.

slide14

D. From Gene to Molecule – In both cystic fibrosis and sickle cell disease, a small change in the DNA of a single gene affects the structure of a protein, causing a serious disorder.

slide15

1. Cystic Fibrosis – This disease is more common in people whose descendants are from Northern Europe. It is caused by a recessive allele on chromosome 7. Children who have this disease have serious digestive disorders and produce a thick mucus in their lungs. Figure 14-8 page 347.

slide16

Figure 14-8 The Cause of Cystic Fibrosis

Section 14-1

Chromosome # 7

CFTR gene

The most common allele that causes cystic fibrosis is missing 3 DNA bases. As a result, the amino acid phenylalanine is missing from the CFTR protein.

Normal CFTR is a chloride ion channel in cell membranes. Abnormal CFTR cannot be transported to the cell membrane.

The cells in the person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus.

slide17

2. Sickle Cell Disease- Sickle cell disease is a common genetic disorder found in African Americans. Just one amino acid is changed in the protein. Valine is replaced by glutamic acid. Malaria helped this disorder spread throughout Africa because people who have Sickle Cell are resistant to malaria.

video 3

Video 3

Point Mutations

Video 3
  • Click the image to play the video segment.
slide19

3. Dominant or Recessive? Things change as we learn more. At first Sickle Cell was thought to be recessive. Now we find that it is a codominant gene. Both normal and sickle cell shaped blood can be present in an individual.

gender benders

Interest Grabber

Section 14-2

  • On a sheet of paper, construct a Punnett square for the following cross: XX x XY. Fill in the Punnett square. What does the Punnett square represent? According to the Punnett square, what percentage of the offspring from this genetic cross will be males? What percentage will be females?
  • On a sheet of paper, construct a Punnett square for the following cross: XXX x XY. Fill in the Punnett square. How is this Punnett square different from the first one you constructed? What might have caused this difference?
  • 3. How do the offspring in the two Punnett squares differ?
Gender Benders
  • One half of the offspring will be males; the other half, females.
  • One of the gametes has two X chromosomes instead of just one. This might have resulted from a mistake in meiosis: Instead of separating, the pair of X chromosomes stayed together.
  • Instead of two XX and two XY offspring, there are one XX and one XY (which are normal), plus one XXX and one XXY (which are abnormal).
  • You may remember that in humans, the sperm cells may carry an X chromosome or a Y chromosome, while egg cells have only X chromosomes. Sometimes, errors during meiosis in one of the parents produce offspring with an abnormal number of sex chromosomes.
slide21

Section Outline

Section 14-2

  • 14–2 Human Chromosomes
    • Human Genes and Chromosomes
    • Sex-Linked Genes
      • Colorblindness
      • Hemophilia
      • Duchenne Muscular Dystrophy
    • X-Chromosome Inactivation
    • Chromosomal Disorders
      • Down Syndrome
      • Sex Chromosome Disorders
slide22

14–2 Human Chromosomes – A human diploid cell contains more than 6 billion base pairs of DNA. The average human gene consists of about 3000 base pairs while the largest gene has more than 2 million base pairs.

slide23

Human Genes and Chromosomes – Chromosomes 21 and 22 are the smallest human autosomes. Chromosome 21 has 225 genes and 32 million base pairs in it alone.

Sex-Linked Genes – Because the X and Y chromosome determine sex the other genes on them are said to be sex-linked genes.

slide24

Colorblindness – is a recessive trait on the X chromosome. In males, a defective version of this produces colorblindness. For females it takes two copies of it to express.

    • Males have just one X chromosome. Thus, all X-linked alleles are expressed in males, even it they are recessive.
slide25

Figure 14-13 Colorblindness

Section 14-2

Father

(normal vision)

Normal vision

Colorblind

Male

Female

Daughter

(normal vision)

Son

(normal vision)

Mother (carrier)

Daughter

(carrier)

Son

(colorblind)

slide26

Figure 14-13 Colorblindness

Section 14-2

Father

(normal vision)

Normal vision

Colorblind

Male

Female

Daughter

(normal vision)

Son

(normal vision)

Mother (carrier)

Daughter

(carrier)

Son

(colorblind)

slide27

2. Hemophilia – is a recessive disorder on the X chromosome. The difference here is that there are two genes that control it and a recessive expression in either will produce a form of hemophilia.

slide28

3. Duchenne Muscular Dystrophy – This is a sex-linked disorder that results in the progressive weakening and loss of skeletal muscle.

slide29

C. X-Chromosome Inactivation – In females one of the two X chromosomes is randomly switched off. British geneticist Mary Lyon discovered this.

slide30

D. Chromosomal Disorders – for most genetic diseases the cause is nondisjunction. This occurs during meiosis and is when homologous chromosomes fail to separate. This affects the number of chromosomes a cell will have. Figure 14-15 page 352.

slide31

Nondisjunction

Section 14-2

Homologous chromosomes fail to separate

Meiosis I:

Nondisjunction

Meiosis II

slide32

Nondisjunction

Section 14-2

Homologous chromosomes fail to separate

Meiosis I:

Nondisjunction

Meiosis II

slide33

Nondisjunction

Section 14-2

Homologous chromosomes fail to separate

Meiosis I:

Nondisjunction

Meiosis II

video 2

Video 2

Nondisjunction

Video 2
  • Click the image to play the video segment.
slide35

1. Down Syndrome – this is also called trisomy 21, because it results from having three copies of the 21 chromosomes. Down syndrome produces mild to severe mental retardation and an increased susceptibility to many diseases and birth defects.

slide36

Sex Chromosome Disorders – When there are multiple copies of sex chromosomes it causes these disorders.

    • Turner’s syndrome 45,X here a female receives only one copy of the X chromosome. Women with this are sterile because their sex organs do not develop at puberty.
slide37

b. Klinefelter’s syndrome 47, XXY here a male receives and extra X chromosome. This causes both male and female sex organs to sometimes form. Hermaphroditic.

  • c. There have been no known cases of a baby born without an X chromosome.
bioethics and you

Interest Grabber

Section 14-3

  • Working with a partner, answer the following questions.
  • In what type of situation do you think genetic engineering—changing the genes of organisms—is warranted? Explain your reasoning about your position. If you do not think that genetic engineering is ever warranted, explain your reasons for your position.
  • 2. In what type of situation do you think genetic engineering might be misused? Suggest limits that might be placed on the manipulation of genes to avoid its misuse.
Bioethics and You
  • As you become more aware of scientific advances in genetics, you might realize that with the ability to manipulate genes, there comes responsibility. This ability provides an opportunity to improve the lives of many people. But there is also a potential for errors or intentional misuse of the technology.
  • Students’ answers likely will include medicinal uses of genetic engineering, such as gene therapy for genetic diseases and production of needed substances such as insulin. Some students may object to all genetic manipulations.
  • Students’ answers may include the “designing” of human babies with desirable traits and the cloning of humans. Some students may object to genetically altered foods.
slide39

Section Outline

Section 14-3

  • 14–3 Human Molecular Genetics

A. Human DNA Analysis

1. Testing for Alleles

2. DNA Fingerprinting

B. The Human Genome Project

1. Rapid Sequencing

2. Searching for Genes

3. A Breakthrough for Everyone

C. Gene Therapy

D. Ethical Issues in Human Genetics

slide40
14–3 Human Molecular Genetics
  • Human DNA Analysis-The decoding of DNA has taken years. Figuring out the roughly 6 million base pairs has been done. Now we need to figure out what that means. Scientist look for similarities amongst people with certain disorders to see what genes they have that are different from other people. That is how we have labeled the genetic disorders like we have.
slide41
Testing for Alleles – DNA probes. This is when two parents can have their genetic information checked to see if they have the chance to pass on a known disease.
slide42
DNA Fingerprinting – The great complexity of the human genome ensures that no individual is exactly like any other genetically.
    • DNA fingerprinting analyzes sections of DNA that have little or no known function but vary widely from one individual to another. Figure 14-18 page 356.
    • Restriction enzymes are used to cut the DNA at the end of sections that repeat. The sizes of the sections are then compared to find similarity between the two DNA samples.
    • (CSI Test) this process has continued to improve since the 1980’s. It is now the driving force behind larger crime fighting units.
slide43

Figure 14-18 DNA Fingerprinting

Section 14-3

Restriction enzyme

Chromosomes contain large amounts of DNA called repeats that do not code for proteins. This DNA varies from person to person. Here, one sample has 12 repeats between genes A and B, while the second sample has 9 repeats.

Restriction enzymes are used to cut the DNA into fragments containing genes and repeats. Note that the repeat fragments from these two samples are of different lengths.

The DNA fragments are separated according to size using gel electrophoresis. The fragments containing repeats are then labeled using radioactive probes. This produces a series of bands—the DNA fingerprint.

slide44
The Human Genome Project – despite the large size of the human genome scientist in 1990 began to decode this huge amount of data. This project is still an ongoing effort to analyze the human DNA sequence.
    • Rapid Sequencing – By labeling repeating sections and looking between them for the new gene scientist use this shotgun method to search through DNA.
slide45
Searching for Genes - Actually only a small part of our DNA is actually genes. It is said that humans have around 20,000 genes. The rest of the DNA is unknown for sure it total function.
  • A Breakthrough for Everyone – A very awesome thing about this project is that the scientists that are doing this project are putting their findings on the Internet for anyone to see. This information has been labeled public domain. This means that any discovery from their findings will not make them any money. This will help keep the price of medicines down. Not much but it does help.
slide46
Gene Therapy – in this an absent or faulty gene is replaced by a normal, working gene. The first authorized attempt to cure a human with this was in 1990. Then, in 1999, a young French girl was apparently cured when her bone marrow was removed, genetically modified and put back in. She is still surviving today after the process.
      • Viruses are used to inject the new DNA into the cells of the material being altered. Figure 14-21 page 360.
      • Scientist have tried to cure cystic fibrosis with method with only short gain progress. The disease returns.
slide47

Figure 14-21 Gene Therapy

Section 14-3

Bone marrow cell

Nucleus

Normal hemoglobin gene

Chromosomes

Bone marrow

Genetically engineered virus

slide48
D. Ethical Issues in Human Genetics - here is the catch. If we start curing diseases with this method how long until they start designing how people look? The main thought to keep in our minds as we look at this future medicine is develop a thoughtful and ethical consensus of what should and should not be done with the human genome.
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