Human Heredity

Chapter 14

Human Karyotype

Photograph of cell during mitosis

Shows if individual got the right # of chromosomes

Shows homologous chromosomes paired-up

Number of chromosomes = 46

44 are autosomes

2 are sex chromosomes (XX or XY)

46, XX (female) or 46, XY (male)

Sex Determination

Male to female births = 1:1 ratio

Female sex chromosomes – XX

Gametes (egg cells) have one X chromosome

Females - inherit one copy of every gene located on each of the X chromosomes

Male sex chromosomes - XY

Gametes have either one X or one Y chromosome

½ carry Y chromosome and ½ carry X chromosome

Pedigrees

Traces the pattern of inheritance of human

traits through several generations within

families

Must be traits controlled by a single gene

Can determine whether an allele is dominant

or recessive

Used to infer the genotypes of family

members

Pedigree Chart

A circle represents

a female.

A square represents

a male.

A horizontal line connecting

a male and female

represents a marriage.

A vertical line and a

bracket connect the

parents to their children.

A half-shaded circle

or square indicates

that a person is a

carrier of the trait.

A completely

shaded circle or

square indicates

that a person

expresses 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.

Human Genes

Tens of thousands of genes specify characteristics through proteins

Examples - Blood group genes

ABO blood group – blood type is example of human trait determined by multiple alleles IA, IB, i

IA and IB are codominant but both are dominant over i

IA and IB produce A and B antigens on surface of blood cells

i produces no antigens (ii is type “O”)

Rh blood group – one gene with two allelic forms Positive allele – Rh+ (dominant)

negative allele – Rh- (recessive)

Blood Groups

Phenotype

(Blood Type Genotype Antigen on

Red Blood Cell

Safe Transfusions

To From

Section 14-1

Figure 14-4 Blood Groups

Recessive Allele Disorder

Must inherit two recessive alleles

(homozygous recessive) to have disorder

PKU – phenylketonuria

Autosomal recessive allele disorder

Inhibits production of enzyme needed to

breakdown phenylalanine

an amino acid found in milk and other foods

Causes build-up of phe. in brain

Autosomal allele disorders

Cystic Fibrosis – Recessive allele disorder

Causes defect of CFTR protein causes CF

Caused by Deletion mutation:

3 bases in gene sequence for CFTR protein is missing

Missing codon in mRNA and then a shorter CFTR polypeptide chain

Causes the protein called CFTR to fold improperly and can’t function – leads to absence of CFTR in cell membranes

Result is a build up of mucus in the lungs and digestive tract An individual is more susceptible to infection and liver

problems

Cystic Fibrosis

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.

Section 14-1

Figure 14-8 The Cause of Cystic Fibrosis

Sickle Cell Disease

Sickle Cell Disease – Autosomal Codominant Disorder RBC’s contain abnormal hemoglobin

Caused by Substitution mutation:

diseased allele differs by one DNA base substitutes amino acid valine for glutamic

acid

People heterozygous for sickle cell – healthy because they have some normal hemoglobin.

Dominant Allele Disorders

Autosomal dominant allele disorders

Effects are expressed even when recessive allele is

present (only need one allele for disease)

Huntington’s Disease – nervous system disorder

Progressive loss of muscle control and mental function

No symptoms until thirties or older

Individuals heterozygous for disease – might not pass

allele for disease to offspring

Achondroplasia – form of dwarfism

Autosomal

Disorders

caused by

include include include

Autosomol

Disorders

Recessive

alleles Dominant alleles

Codominant

alleles

Albinism Galactosemia Tay-Sachs

disease

Huntington’s

disease

Sickle cell

disease

Cystic

fibrosis Phenylketonuria Achondroplasia

Hypercholes-

terolemia

Sex Linked Disorders

Sex-linked genes are on the sex chromosomes (X or

Y)

Most are on the X-chromosome

Recessive, sex-linked disorders- more common in males

Males – have one X so all X-linked alleles are

expressed

Hemophilia – proteins for blood clotting are missing

Colorblindness – Inability to distinguish certain

color(s), more common in males because it is a

recessive allele on X chromosome

Females can have hemophilia and/or

colorblindness

Colorblindness Father

(normal vision)

Colorblind

Normal

vision

Mother

(carrier)

Daughter

(normal vision)

Son

(normal vision)

Daughter

(carrier)

Son

(colorblind)

Section 14-2

Male

Female

Figure 14-13 Colorblindness

Colorblindness Father

(normal vision)

Colorblind

Normal

vision

Mother

(carrier)

Daughter

(normal vision)

Son

(normal vision)

Daughter

(carrier)

Son

(colorblind)

Male

Female

25 – both normal vision and red-green colorblind individuals will see this. It is a control test.

45 – a normal individual will see this; red-green color blind individual will see only spots.

29 – a normal individual will see this; red-green color blind individual will see only spots

56 – both normal vision and red-green colorblind individuals will see this.

6 – a normal individual will see this; red-green color blind individual will see only spots.

8 – a normal individual will see this; red-green color blind individual will see only spots.

The individual with normal color vision will see a 5 revealed in the dot pattern.

An individual with Red/Green (the most common) color blindness will see a 2 revealed in the dots

Try to find a circle, a star, and/or a square on this

card in 3 seconds.

Answer: Everyone should be able to see a circle,

star, and square in the demonstration plate

Try to find a circle, a star, and/or a square on this

card in 3 seconds.

Answer: Colorblind individuals should see the

yellow square. Color normal individuals should see

the yellow square and a "faint" brown circle.

Try to find a circle, a star, and/or a square on this

card in 3 seconds.

Answer: Colorblind individuals should see the

yellow circle. Color normal individuals should see

the yellow circle and a "faint" brown square.

Try to find a dog, boat, balloon, or car (as shown in

the above demonstration card) in 3 seconds.

Answer: Colorblind individuals should see nothing.

Color normal individuals should see a "faint" brown

boat.

X-Chromosome Inactivation

Females – One X randomly switched off

Barr body

Example – calico cats

Gene for coat color on X chrom.

Possible female genotype: Xorange Xblack

Some parts of body Xorange is turned off and other

parts Xblack is turned off

Produces mixture of colors in females

Males – single color spots because only have one X

chromosome – Xorange or Xblack

Chromosome Separation

Errors Failure of homologous chromosomes to separate during

meiosis (autosomes or sex-chromosomes)

Causes abnormal numbers of chromosomes in gametes

Causes birth defects such as Down Syndrome

Autosomal Trisomy 21 – Mild to severe mental retardation

Homologous

chromosomes

fail to separate

Meiosis I:

Nondisjunction Meiosis II

Disorders from Nondisjunction

of Sex Chromosome

If Nondisjunction occurs between sex-chromosomes then gametes will have the wrong number of sex chromosomes

Produces Gametes with: 2 X’s, X AND a Y, or NO sex chrom.’s

Role of X chromosome – No human born without an X chromosome – genes vital for development

Turner’s syndrome (1 in 2500)

Karyotype 45,X or 45,X0 - female with only one X chromosome (monosomy X)

Sterile, various physical characteristics, predominantly affected by cardiovascular malformations

Klinefelter’s syndrome (1 in 17,000)

Karyotype 47, XXY – male; sterile

Language impairment, physical characteristics vary

Human DNA analysis

Genetic tests used to detect genetic disorders

DNA Probe method Hybridize persons DNA – breaks H-bonds between DNA strands

to form single strands

Mix DNA probes with the persons single DNA strand DNA probe – known DNA fragments tagged with radioactive markers

Can determine the persons nucleotide sequence depending on which DNA probes base-pair with the single DNA strand Determines if they have the diseased allele mutation

Restriction enzyme Method “chemical scissors” – cuts DNA molecules into fragments at

specific DNA sequences

Detects differences between the lengths of normal and abnormal alleles

DNA Fingerprinting

Analyzes non-coding sections of DNA (not the genes)

No two people have exactly the same DNA except for identical twins

Restriction enzymes -- “cut” DNA into fragments at specific nucleotide sequences

attracted to Repeats - specific patterns of nitrogen bases

Everyone has these but not at the same places along the chromosomes

Because the patterns occur in different places the Length of fragments produced varies from person to person

DNA fragments are analyzed by gel electrophoresis

Separates DNA fragments by size to produce unique banding pattern

bands in each “fingerprint” are analyzed

If banding patterns in gel are the same then DNA had to come from the same person

DNA Fingerprinting

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.

Section 14-3

Gene Therapy

Used to cure genetic disorders by replacing a

faulty gene with a normal, working gene

Faulty gene must be identified

If the gene is successfully replaced and

transcribed by the persons cells the correct

protein or enzyme can be produced

*Genetically engineered viral DNA – contains

normal, healthy allele of a gene and is injected

into persons bone marrow

Normal hemoglobin gene

Bone

marrow cell

Chromosomes

Genetically engineered virus

Nucleus

Bone

marrow

Section 14-3

Figure 14-21 Gene Therapy

Chapter 14 Quiz I

1. What are the two types of chromosome shown in a Karyotype?

2. True or false: A karyotype can determine if an individual inherited an incorrect number of chromosomes.

3.In humans a male has how many X chromosomes and how many Y chromosomes?

4. Human females produce egg cells that have how many X chromosomes?

5. What percentage of human male gametes carries an X chromosome?

6. A human female inherits how many copies of X-linked genes?

7. What can be used to show how a trait is passed from one generation to the next within families.

8. True or False: In a pedigree all of the symbols can be squares.

9. Which of the following is determined by multiple alleles?

a. Rh blood group b. ABO blood group c. PKU disease

10. Which of the following genotypes result in the same phenotype?

a. IAIA and IAIB c. IBIB and IAIB

b. IBIB and IBi d. IBi and ii

14-1 Quiz Answers

1. Autosomes and sex chromosomes

2. True

3. One X, and one Y

4. One

5. 50%

6. Two

7. Pedigrees

8. False

9. B

10. B

Chapter 14 Quiz II

1. If a person has PKU which parent did they have to inherit the recessive allele(s) from?

2. If a man with blood type A and woman with blood type B produce an offspring, what might be the offspring’s blood type?

3. Sickle cell disease is caused by a change in how many DNA bases?

4. In cystic fibrosis, a change in a single gene causes the CFTR protein to

A. become less soluble B. fold improperly C. Destroys cell membranes

5. True or false: A missing codon in the mRNA for the CFTR protein leads to cystic fibrosis

6. True or False: People heterozygous for sickle cell disease are healthy because they are resistant to malaria.

7. Most sex-linked genes are on what chromosome?

8. True or False: The allele for colorblindness is located on the Y chromosome making colorblindness more common in males.

9. True or False: The father of a colorblind boy may be colorblind.

10. Which type of chromosome forms a Barr body?

11. What is the failure of chromosomes to separate during meiosis called?

12. True or false: A baby can be born without an X chromosome.

13. Which combination of sex chromosomes represents a female?

A. XY B. XXY C. XX D. XXXY

14. If nondisjunction occurs during meiosis, some gametes may have too few or extra ____________.

15. True or False: Nondisjunction can involve autosomes, homologous chromosomes, and sex chromosomes.

1. Both parents

2. A, B, AB, or O

3. One

4. B

5. True

6. False

7. X

8. False

9. True

10. X

11. Nondisjunction

12. False

13. C

14. Chromosome

15. true

Chapter 14 Quiz III

1. The process of DNA fingerprinting is based on the fact that no two people, except ______________, have exactly the same DNA.

2. True or False: It can be concluded that if two DNA fingerprints show identical patterns of bands then the DNA came from two different people.

3. True or False: the purpose of gene therapy is to cure genetic disorders.

4. Which is the first step in gene therapy?

A. identify the faulty gene B. splice normal gene to viral DNA C. “cut” out the normal gene from DNA

5. True or False: Gene therapy is successful if the replacement gene is transcribed in the person’s cells.

6. A person who has ________ is unable to break down the amino acid Phenylalanine.

7. True of False: A person who has blood type O can receive a blood transfusion only from a person who has blood type O.

8. A female with the disorder ____________ inherits only one X chromosome and has the genotype XO.

9. Nondisjunction in males can lead to the disorder called ___________________.

10. A boy who has hemophilia inherited the disorder from his ____________.

Chapter 14 Quiz III

1. Identical twins

2. False

3. True

4. A

5. True

6. PKU

7. True

8. Turner’s

9. Klinefelters

10. mother

Chapter 14 Quiz

1. True or False: Males have two X chromsomes.

2. True or False: All of the alleles for the ABO blood group gene are codominant.

3. A change in just one DNA base for the gene that codes for the protein _____________ causes sickle–shaped red blood cells.

4. What is the dense region in the nucleus that is formed by the turned-off X chromosome?

5. True or False: Barr bodies are found only in males.

6. If you saw a white cat with orange and black spots, is it most likely a male or a female?

7. The condition in which an individual has three copies of chromosome is known as _____________.

8. True or False: Labeled DNA probes can be used to detect specific sequences found in disease-causing alleles.

9. What is the method of identification of individuals that analyzes sections of DNA that have little or no know function but vary widely from one individual to another.

10. During what process can an absent or faulty gene be replaced by a normal working gene?