Genetics

The science that relates to the study of genes and the patterns of heredity

Please don’t talk over the lesson….raise your hand if

you have a question to make. Thank You

HeredityA puppy gets its traits from its parents just as we get ours from our parents, but just how are traits inherited?

KARYOTYPE

Each human has 46 chromosomes located in their body cells nucleus of the cell (diploid cells)These are divided into 23 chromosomes- a baby inherits one chromosome from each parent from each pair of chromosomes

Of the 46 total chromosomes, two of them are sex chromosomes.XX- femaleXy- male

A piece of DNA on a chromosome is called a gene. Genes also come in pairs. They determine many of the characteristics of a

baby.

Alleles, are variations of a gene, and they usually come in pairs. Alleles determine the appearance of our characteristicsThere are at least two alleles for every characteristicIf the two alleles are the same then it is said to be homozygous for that geneIf they are different then they are heterozygous

Patterns_of_Inheritance.asf

Gregor MendelGregor Mendel is known as

the father of geneticsHe was born in Austria in

1822He grew up on a farm and

learned a lot about flowers and trees

When he was 21 yrs old he joined a monastery and

became a monk. As a monk he taught science and performed scientific experiments

• Mendel spent most of his time and energy performing experiments with pea plants

• He was very curious as to how offspring inherited their traits

• He used pea plants in his experiments because peas had many desirable traits that made them easy to work with

• Peas were a good choice because • They grow quickly• They come in many varieties with

easy to observe traits: round, wrinkled, yellow, green, smooth bumpy, tall, short

• Some cross pollinate, others self-pollinate

• Self –pollination was important because Mendel was able to grow true- breeding plants for his experiments

GREGOR MENDEL USED PEAS FOR HIS EXPERIMENTs- WHY?

• Mendel noticed that one trait was always present in the first generation and the other one seemed to disappear

• He called the trait that appeared the dominant trait and the trait that seemed to fade away the recessive trait

• To find out what might have happened to the recessive trait, Mendel decided to perform another set of experiments

P stands for the parents of the first generation (purple flower crossed with white flower)

F1 stands for the offspring of the a self of the purebred cross above.

F2 stands for the offspring when an F1 flower is self-fertilized were crossed.

• Brown eyes is a dominant trait, so we would write the genotype for brown eyes as BB, Bb

• Blue eyes is a recessive trait. The only way to show a recessive trait is to have a genotype with two recessive alleles, such as bb

Alleles

• An allele is a variation of a gene:

BB, Bb, CC, Cc, cc, DD, EE, ee

Some alleles are dominant and some alleles are recessive. Dominant alleles are represented by

capital letters in genetics, and recessive alleles are represented by lower case letters

Genotype and Phenotype

• Genotype is the combination of alleles that code for a specific trait

DD for example could be the genotype for having dimples.

• Phenotype is the physical appearance that the genotype codes for.

• Dimples is a phenotype. What is a phenotype that you have?

PHENOTYPES

Your adorable smile, the shape and color of your eyes, and your hair texture are just a few examples of phenotypes

We know that genes determine our smile, but what about personality? Yes, some of our personality is hereditary, but part of it is also a result of the environment we are exposed to as a child

Nature vs. Nurture

Homozygous and Heterozygous Genotypes

• Homozygous genotypes with either all dominant alleles or all recessive alleles (think: the same)

• DD, dd, cc, CC, EE, ee, FF, gg, GG, dd, DD

• Heterozygous genotypes have at least one dominant allele and one recessive allele

• (think: different)• Dd, Ff, Gg, Ee, Ee, Cc,

Gg, Rr...

Punnett Squares predict the possible genotypes of offspring in a particular cross using the genotypes of the

parents

What color feathers will the offspring in the test cross below have?

Gregor_Mendel_s_Rules_of_Heredity__Using_Punnett_Squares - Shortcut.lnk

PTC tasting is a dominant trait

Gregor_Mendel_s_Rules_of_Heredity__Using_Punnett_Squares - Shortcut.lnk

A brown furred rabbit (Bb) mates with a white furred rabbit (bb). What is the probability that they

will have dark-furred offspring?

Answer:

• Approximately 50% of their offspring will be dark-furred, with a heterozygous (Bb) genotype.

• What percent would likely have the recessive phenotype of white fur?

• To show the recessive trait, the offspring must have inherited two recessive alleles (bb), one from each parent. They also have a 50% chance of having white furred bunnies…..

Punnett Square Problem

• Two brown furred rabbits with the genotypes Bb mate and produce ¼ offspring that are light furred with the genotype bb. How is this possible?

Answer

• The ¼ offspring received one recessive allele from each parent giving them a recessive trait

• True or false

A puppy receives half its genes from its mother and half from its father

Incomplete DominanceAn inheritance pattern where neither allele is dominant, but instead the phenotype of the offspring is in between both homozygous genotypes

In this case, the R allele codes for a red color, so the more of this of this protein, the more red the petal color

Codominance

• An inheritance pattern where neither allele is dominant, but rather they share dominance, and thus, the offspring will have traits of both alleles if it inherits one of each

Human blood type is determined by codominanceThere are three alleles for blood type. We inherit two from our parents.IA and IB share dominance and i is recessiveSee chart to the side….A person with alleles A and B is neither A or B blood type, but rather, blood type AB.A person must have two i alleles to have blood type O because O blood type is a recessive trait.

Type A and B individuals can be either homozygous (IA,IA, or IB, IB), or heterozygous (IA i, or IB i)

A person must have two i alleles to have blood type O

• A woman with blood type A and a man with type B blood could potentially have offspring with which of the following blood types?

Multiple Genes

• Some traits, such as hair, eye and skin color are determined by multiple genes, giving a wide variety in the colors produced

Environmental Influences

• Some genes can remain unexpressed until something in the environment influences it

• For example, some people have a gene for developing lung cancer that may not be expressed unless the person is exposed to the chemicals in tobacco

• The Himalayan rabbit has a gene for fur color that produces dark fur, but it is only activated at cooler temperatures, which is why the cooler body parts, like ears and nose are black.

These Rabbits have a gene that causes fur color to be black if exposed to low temperatures

EYE COLOR

• Different eye colors are produced because of the different amounts and patterns of pigments in the iris (colored part of the eye), which is determined by one’s genetic make up

• The DNA inherited from one’s parents determines what color eyes they will have

• Right now there are three known gene pairs that control eye color, and at least two are incompletely dominant

• The bey 2 gene on chromosome 15 has a brown and blue allele

• On chromosome 15 the bey 1 gene contains the central brown gene

• On chromosome pair 19, the gey gene contains a blue allele and a green allele

BB Xbb

All children with Bb genotype

Bb X BbPossible genotypes: BB,Bb,Bb, bb

Can two brown-eyed parents have a blue-eyed child? Explain and show your work.

Yes, if both are heterozygous for brown eyes and the child inherits a recessive allele from

each parent. There is 25% chance…

A green allele is dominant to a blue alleleAnd brown allele is dominant to both a blue and a

green alleleFor the bey 2 gene if a person has a brown allele then

they will have brown eyesIn the gey gene the green allele is dominant to the blue

alleles but still recessive to brownA person will have green eyes if they have a green

allele on chromosome 19 and all or some blue alleles Blue eyes is produced by having only recessive genesSo for a blue eyed person all four alleles have to be

blue

• If two parents have a blue and a brown gene, there eyes are brown, but they can have a blue eyed child if the child inherits a blue gene from each parent

• If the child inherits one blue gene and one brown gene the child will have brown eyes, because brown is dominant to blue

Heterochromia- condition where a person has two different colored eyes

What are the causes of heterochromia?

• Disease or injury to that affects the health of the melanocytes (cells in the eyes that produce eye colors)

• Wardenburg Syndrome- A mutation in certain genes that causes melanocytes to get lost on their way to where they are supposed to go

• Chimarism (very rare!)- when two fertilized eggs fuse to form one egg, each with a different set of DNA

David Bowie

Genetic DisordersA genetic disorder is one that is caused by abnormalities

in the genes or chromosomesWhile some diseases, such as cancer, are caused by

genetic abnormalities in some cells, a “genetic disease” is one that is present in all cells and has been present since conception

When something goes wrong with the chromosomes in processing a new human being, the code cannot be read properly and the child’s brain and body may not develop properly. When a problem results from this genetic mistake, we call is a genetic disorder.

Karyotype A karyotype is a picture

of all the chromosomes in a cell

A normal human karyotype has 46 chromosomes, 22 are identical pairs

The other two are the sex chromosomes.

Is this the karyotype of a male or a female individual?

Turner’s Syndrome XOOccurs 1 in every 2000These women have only

45 chromosomes; they are missing an x chromosome

They are genetically female, but do not mature sexually during puberty and are infertile

They have a short stature 98% of these fetuses die

before birth

Trisomy X

• A condition where a female has an extra copy of an X chromosome, typically inherited from the mother

• It is a random event• Typically diagnosed

later in life, if ever

Trisomy X (XXX)• Sometimes there are no

symptoms and symptoms vary a lot between individuals

• Possible symptoms:• Tall stature• Speech and language

delays• Delayed motor skills• Below average

intelligence

• Occurs 1 in 1000 births• These women are fertile

and capable of having normal (XX) and (XY) children

Super Male XYYThese are males with an

extra Y chromosomeThey tend to be taller

than averageMore prone to acneUsually have a low mental

IQUsed to be thought that

these men were more likely to end up in prison, but no study was able to back this claim

Klinefelter’s Syndrome XXY• A chromosomal condition that affects a male’s

sexual development• Most males with this have an extra copy of the X

chromosome in each cell• Because the testicles of these males do not form

normally, affected males may have low levels of the hormone, testosterone, beginning during puberty

• A lack of this hormone can cause breast development, reduced facial and body hair, and the inability to father children (infertility)

Klinefelter’s Syndrome

Down SyndromeThis individual has an extra # 21

chromosome, instead of two copies, they have three

The extra chromosome causes physical differences in appearance as well as learning challenges

About half of these individuals have heart defects

These children did not used to live very long due to heart defects and other ailments, but today they are able to live in to adulthood, thanks to advances in medicine

Down Syndrome

Amniocentesis

A medical procedure used in prenatal diagnosis of genetic risk factors, in which a small amount of amniotic fluid is extracted from the amnion or the amniotic sac around the fetus, and the fetal DNA is examined for genetic abnormalities

A commonly used test to detect Down Syndrome- has a 99% accuracy rate

Amniocentesis is a risky procedure which can result in harm to the baby

if it is not performed correctly and carefully

Chorionic Villus Sampling• Another diagnostic test to help detect genetic

abnormalities, such as Down Syndrome• Done early in pregnancy (around tenth week)• 1 in 100 chance of miscarriage• Chorionic villi are tiny finger-shaped growths

in the placenta• The DNA in the villus projections are the same

as in the baby’s cells, so in this test, samples of the chorionic villus cells are taken for a biopsy for the chromosomes to be studied

Multiple Sclerosis

• This is a chronic inflammatory disease of the immune system

• Two genes have been found to increase a person’s risk for MS, and they are found in the immune system

• The person’s immune system begins to attack the fatty covering around the axon of a nerve cell, called a myelin sheath, this interrupts the electrical signals necessary in the relaying of impulses from one nerve cell to another

In patients with multiple sclerosis, the axon’s myelin sheath is destroyed by the person’s own immune system

Albinism

An albino is a person or animal who lacks the pigment, melanin, the protein that gives skin, eyes, and hair color. This is due to a recessive inheritance pattern.These people are prone to vision problems and sun burning because of the lack of melanin.

Albinos inherited a recessive allele one from each parent. This recessive gene causes the individual to have no melanin production, and so their skin, hair, and eyes lack

pigmentation (color)

Sickle Cell Anemia-one bad copy of a gene for this disease and the person is a carrier, two bad copies and the person is affected with the disease

One out of 500 African Americans has sickle cell anemia

This disease is caused by a mutation in the alleles for a gene that carries instructions for how the protein hemoglobin in red blood cells should look like

The error causes the protein to come out with the wrong shape

It causes red blood cells to collapse and into sickle shapes that are hard and sticky

Sickle Cell Can Cause Clots in Arteries and Veins

Sickle cells do not carry oxygen as well as normal red blood cells and they sometimes get stuck in the blood vessels causing a clot

It can cause chronic anemia and pain

Anemia means the blood is low in oxygen

Two cures: bone marrow transplant or hydroxyure drug

Cystic fibrosis

Cystic fibrosis is a fatal genetic lung disease caused by a defect in the CFTR gene

This gene makes a protein that controls the movement of salt and water in and out of your cells

This gene does not work right and results in a thick, sticky mucus in lungs and salty sweat

With better treatment, people with CF are living longer-may live into their 30’s

A child must carry two abnormal copies of the CFTR gene, one from each parent to have the disease. If the child has

one copy, he or she is a carrier

If the problem lies on a sex chromosome, we call it a sex-linked

disease or disorder• Hemophilia and Color Blindness are two sex-

linked recessive disorders we will discuss in this class. For both, the problem lies on the X chromosome with a recessive inheritance pattern.

Color blindness is a Sex -linked recessive disorder

This condition is more common in males than in females because the problem lies on the X chromosome (we’ll do pedigree charts on this)

Humans have three color receptors, if one or more are faulty or missing, a person will not see all the colors

Red/green colorblindness is the most common

A color blind person could not see the numbers and letters inside the squares

Hemophilia

• An X linked chromosomal disorder in which a person does not clot blood well

• With hemophilia a person lacks the gene for proper blood clotting.

Pedigree Charts show the patterns of inheritance among families; it is a tool used by geneticists to help council patients who are worried that they might pass down a

faulty gene to their children

Cri du Chat

• A rare genetic disorder which results from the deletion of or loss of a significant portion of the genetic information of the arms of the chromosome #5

• Infants with this disorder have a distinctive high pitched cry which sounds like a cat

• The disorder is also characterized by mental retardation, delayed development, small head size, distinctive facial features, low birth weight, and weak muscle tone

Gene TherapyGene therapy is a technique for correcting defective

genes responsible for disease developmentSeveral approaches are used:A normal gene can be inserted into a nonspecific

location in the genome to replace a nonfunctional gene (using a carrier, vector, to deliver the gene)

An abnormal gene can be repaired through selective reverse mutation

The regulation of a gene (degree to where it is turned on or off) can be altered

Gene therapy is still a new area in science and is considered to be in experimental stages

How Does Gene Therapy work?In most gene therapy cases, a normal gene is inserted

into the genome to replace an abnormal geneA carrier molecule such as a vector is used to deliver

the therapeutic gene to the patient’s target cellCurrently the most common vector is a virus that has

been genetically altered to carry human DNAViruses have evolved a way to encapsulate and deliver

their genes in to human cells to cause disease, so scientists have tried to take advantage of this capability and manipulate the virus by removing disease causing genes and replacing it with therapeutic ones.

Factors that prevent gene therapy from being an effective way to treat genetic

diseases