Genetics Notes

Website to visit

• http://learn.genetics.utah.edu/content/begin/traits/

• What is heredity?• What is a trait?

Trait: a characteristic of an organism

• Examples in peas:

Parent generation: Shows the 2 alleles of the gene for this trait

F 1 generation: Shows which is dominant

2 alleles for Every Trait• Organisms have 2 copies of each gene,

called alleles, for every trait– One from mother

• (piece of DNA in the chromosomes you got from her)

– One from father• ( piece of DNA in the 23 chromosomes you got from him)

http://wwwdelivery.superstock.com/WI/223/1538/PreviewComp/SuperStock_1538R-56651.jpghttp://learn.genetics.utah.edu/content/begin/traits/

Mid-Digital Hair:

Tongue rolling.

Widow’s peak.

Earlobe attachment.

Hitchhiker’s thumb.

Trait: a characteristic of an organism

Mendel’s Law of Segregation

• Each trait is defined by a pair of genes. Each parent can produce two types of gametes: one allele is “randomly separated” into each gamete.

• A Punnett Square is a tool to keep track of the alleles in the gametes and work out the possible combination in offspring

Reginald Punnett

Professor of Genetics at Cambridge

Even Pea plants have parents!

http://activity.ntsec.gov.tw/lifeworld/english/content/images/en_gene_c4c.jpg

P1 generation F1 generation F2 generation

http://library.thinkquest.org/17109/media/mendel2.gif

Parent generation

All Homozygous

F1 generation

All Heterozygous

F2 generation

¼ homozygous dominant, 2/4 heterozygous, ¼

homozygous recessive

Dominant & Recessive Genes

• Dominant genes – capital letter. Overpower recessive genes

• Recessive genes – lowercase letter.

are “masked” in a hybrid and only show up in a purebred with both recessive genes.

Purebred vs. Hybrid

• Purebred = homozygous means there are two alleles of the same type for a trait. – TT (both tall genes)– tt (both short genes)

• Hybrid= heterozygous means there are two different alleles for a trait. – Tt

Phenotype and Genotype

• Phenotype means the appearance of a trait in an organism– For example short/tall, wrinkled/smooth,

yellow/green are all phenotypes• Genotype means the two alleles an

organism has for a trait.– Examples:TT. Tt. tt

Websites for punnett square problems:

• http://www.dnaftb.org/5/index.html “DNA from the beginning

Steps to complete a Punnett Square

Step #1: Read the problem to figure out the phenotypes and genotypes of the parents

Problem: In pea plants, tall plants (T) are dominant to short plants (t). Consider a genetic cross of one short plant and one hybrid plant.

phenotype of parent #1: _____genotype of parent #1: _____

phenotype of parent #2: _____genotype of parent #2: _____

short ttTall Tt

• Step 2. draw a box with 4 squares

• Step 3. Write the genotype of #1 parent across the top lining up one gene above each column below.

• Step 4: write the genotype of the #2 parent along the side of the square with one gene next to each row

• Step #5: fill in the genotypes of the offspring by putting one gene from each box into the squares.

• Step #6: analyze the genotype and phenotype of the offspring shown in the boxes.

t t

T

t

t t t

T T

t t

t

Analyze the results of the punnett square

• What is the genotype and phenotype of the following POSSIBLE offspring?

• #1: tT tall• #2 tT tall• #3 tt short• #4 tt short• What percent of the offspring

are predicted to be tall? 50%• What percent are predicted to

be purebred short?

Tt

tt

Tt

tt

1 2

3 450%

Monohybrid Crosses

• Involve one trait whole allele may be dominant or recessive.

• Example two hybrid pea plants where T: tall and t: short.

• The punnett square for this is:

• Mendel’s Law of Dominance: some alleles are dominant and others are recessive.

• Mendel’s Law of Segregation: two alleles are segregated from each other so that each gamete carries only a single copy of each gene.

• Mendel’s Law of Independent Assortment: genes for different traits can segregate independently during the formation of gametes.

Dihybrid CrossesInvolve 2 traits:

Trait #1 Seed color• Y:Yellow seed• y: green seeds

Trait #2 seed shape• R round seeds• r wrinkled seeds

Dihybrid cross

• http://www.dnaftb.org/5/problem.html “Problem”

Incomplete dominance: The hybrid shows a blending of alleles

4 o’clock flowers• RR: red• WW: white• RW pink

Codominance: The hybrid has both traits

• Example in chickens – DD: dark colored feathers– LL: light colored feathers– DL: where the hybrid has both dark and light

speckled feathers.

Multiple Alleles: Genes that have more then two alleles

Example:

Alleles that determine blood type: A, B, O

Red blood cells

• In some ways, every person's blood is the same they carry oxygen and nutrients to the body’s cells

• But, when analyzed under a microscope, distinct differences are visible.

• Blood can have 2 different markers (antigens) on its surface – Molecule “A” = Type A blood– molecule “B”, = Type B blood– Molecules “A & B”, = Type AB blood– no molecules = Type O blood

The Rh protein

• The Rh factor genetic information is also inherited from our parents, but it is inherited independently of the ABO blood type alleles.

• There are 2 different alleles for the Rh factor known as Rh+ and Rh-. Someone who is "Rh positive" or "Rh+" has at least one Rh+ allele, but could have two. Their genotype could be either Rh+/Rh+ or Rh+/Rh-.

• Someone who Rh- has a genotype of Rh-/Rh-. Rh factor Possible genotypes Rh+ Rh+/Rh+Rh+/Rh- Rh- Rh-/Rh-

Molecules (antigens) on outside of red blood cells

Type A Type B Type AB Type O

Parent’s determine your blood type

• Your mother and father will both pass one allele /genes for blood type to you.

• A and B are co-dominant• O is recessive to both A and B

Genotypes for each blood type What are the possible genotypes of the 4

blood types? A, B, AB, O

–Type A Blood•AA•AO

–Type B Blood•BB•BO

–Type AB Blood•AB

–Type O Blood•OO

2 different styles of notation

Donating Blood

• If two different blood types are mixed together, the blood cells may begin to clump together in the blood vessels, causing a potentially fatal situation.

• Your body makes antibodies to attack blood cells with molecules different then your own.

Antibodies in your blood

• Type A blood has anti-B antibodies to attack type B blood cells

• Type B blood has anti-A antibodies to attack type A blood

• Type O blood has anti-A and anti-B antibodies to attack type A and B blood.

• Type AB blood has no antibodies

Antibodies in blood plasma to attack foreign blood

Type A Type B Type AB Type O

Type A Type B Type AB Type O

No antibodies

Type A Type B Type AB Type O

No marker molecules

Blood Donation

• Go to website: http://www.givelife2.org/aboutblood/bloodtypes.asp

Out of 100 donors . . . . .

84 donors are RH+

16 donors are RH-

38 are O+ 7 are O-

34 are A+ 6 are A-

9 are B+ 2 are B-

3 are AB+ 1 is AB-Source: AABB.ORG

Almost 40% of the population has O+ blood

Only about 7% of all people have Type O negative blood

Type O negative blood is the preferred type for accident victims and babies needing exchange transfusions

There is always a need for Type O donors because their blood may be transfused to a person of any blood type in an emergency

Blood Type

A B AB O

Can donate blood to

A, AB B, AB AB O, A, B, AB

Can receive blood from

A, O B, O AB, A, B, O O

Universal Donor • Type O blood has no molecules on the

outside of the red blood cells therefore anti-A or anti-B antibodies will not attack if they are in the blood of a recipient.

Universal Recipient

• Type AB blood produces no antibodies in it therefore it will not attack any molecules on blood that is mixed with it.

Blood Donation

• Go to website: http://www.givelife2.org/aboutblood/bloodtypes.asp

• O Rh Positive 37.4%

O Rh Negative 6.6%

A Rh Positive 35.7%

A Rh Negative 6.3%

B Rh Positive 8.5%

B Rh Negative 1.5%

AB Rh Positive 3.4%

AB Rh Negative.6%

• Helpful website: http://learn.genetics.utah.edu/content/begin/traits/blood/

Problem #1: Show a punnett square between a mother who is type O and a father that is type AB.

O O

A

B

O O

A AO AO

B BOBO

What are the possible blood types of their children? What are the ratio’s of these genotypes?

Sex chromosomes

• There are two chromosomes out of a persons 46 that have been nicknamed the “x”chromosomes and the “y” chromosome.

• These are “sex chromosomes” because they carry the genes for sexual characteristics– Sexual organs– Body hair– Voice– Muscle mass

• “x” chromosomes carry genes for female characteristics• “y” chromosomes carry genes for male characteristics

Figure 1: Male human chromosomes.X and Y chromosomes are indicated by arrows.

© Nature Reviews Genetics 2, 175-185 (March 2001).

Sex linked traits

• Some genes that affect both males and females are found on the “x” sex chromosomes. – For example the gene for color vision, blood clotting

(or hemophilia=not clotting) • Because women have sex chromosomes XX

women have two copies of the gene and men have one copy.

• For this reason x linked alleles are expressed in males even if they are recessive.

• Notation in punnett squares the alleles are written as a superscript above a Xh or Y chromosome.

Sex linked problem• In flies red eyes is

dominant to white eyes

• A purebred red eyed female is bred with a white eyed male

Question: What color are the male offspring’s eyes?

Question: What color are the female offspring’s eyes?

Colorblindness• The term 'colour blindness' is misleading. People who can't see all colours

can still see things (other than colour) as clearly as people who are not colour blind. The term means that a person can't see some colours, or sees them differently from other people. Very few people who are colour blind are blind to all colours. The usual colours that people have difficulty with are greens, yellows, oranges and reds. Colour blindness is inherited, affecting more boys than girls. Out of 20 boys, it is likely that one or two will have a colour vision problem.

• Color blindness test:

http://colorvisiontesting.com/ishihara.htm • http://colorvisiontesting.com/online

%20test.htm#Test%20Card%20Number%203%20answer

• For more info on seeing color: http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Colour_blindness?OpenDocument

Can you see the numbers?

Using a pedigree

Hemophilia: The Royal Disease

• Queen Victoria of England and her family

http://www.sciencecases.org/hemo/hemo.asp

The royal pedigree

Questions from royal pedigree

• 1.a What is the probability that Alice of Athlone’s other son was hemophilic? – 50%

• 1.b What is the probability that her daughter was a carrier? – 50%

• 1.c What is the chance that both children were normal? – 50%

From royal pedigree

• 2. Would you predict that Juan Carlos was normal, a carrier, or hemophilic? – Normal, because neither his father nor mother

was a hemophiliac. Also males can’t be carriers.

From royal pedigree• 3. a. What was the probability that all 4 of Alix and

Nikolas II of Russia’s daughters were carriers? – 50%

• 3.b If Alexis had lived and married a normal woman, what are the chances that his daughter would be hemophiliac? – 0%

• 3.c What are the chances that Alexis daughters would be carriers? – 100%

• 3.d. What are the chances that his sons would be hemophiliacs? – 0%

websites

• What makes you rhyming presentation: http://www.amnh.org/ology/genetics#features/youYou/youyou.php?TB_iframe=true&height=350&width=600

• What do you know about genetics quiz and answers: http://www.amnh.org/ology/genetics#features/whatdoyouknow_genetics/?TB_iframe=true&height=400&width=600

• Cloning sheep explanation http://www.amnh.org/ology/index.php?channel=genetics#features/cloning/?TB_iframe=true&height=450&width=600

Karyotypes

Using Karyotypes To Diagnose Genetic Disorders http://learn.genetics.utah.edu/content/chromosomes/diagnose/

A picture of a person’s chromosomes organized into

homologous pairs

Chromosomes as seen through a microscope

Chromosomes organized into a karyotype

• Where does a person get their 46 chromosomes? – 23 from mom– 23 from dad

• What is the type of cell division in which a persons 46 chromosomes are divided to produce sex cells with only 23 chromosomes? – MEIOSIS!

How to make a karyotype

1. During Mitosis chromosomes are spread out within a cell and can all be seen.

2. Chromosomes in metaphase are stained to produce a banding pattern of light and dark regions.

– The dye stains regions of chromosomes that are rich in the base pairs Adenine (A) and Thymine (T) producing a dark band. Thin bands contain hundreds of genes.

3. The are photographed4. They are organized into homologous pairs.

Male vs. FemaleFemale: “X” “X” sex chromosomesMale: “X” & “Y” sex chromosomes

Typical Human’s have 46 total chromosomes.

“XX” female / “XY” male• The “x” chromosome is larger

than the “y” chromosomes• “x” chromosomes have

genes resulting in female reproductive systems and other genes that do not have to do with gender like genes to see color.

• “y” chromosome is smaller has fewer genes and they code for male reproductive organs.

Image: http://www.biotechnologyonline.gov.au/images/contentpages/karyotype.jpg

Chromosomal Disorders

• Trisomy: having three copies of a chromosome. The most common is Down’s Syndrome

• Nondisjunction: when chromosomes fail to separate properly in meiosis forming gametes with too many or too few chromosomes.

• Website showing nondisjunction: http://www.biostudio.com/d_%20Meiotic%20Nondisjunction%20Meiosis%20I.htm

2 ways nondisjunction can occur

http://warunee.chs.ac.th/c15x11nondisjunction.jpg

Mark

Steven

Sarah

Lisa

Kevin

Lisa “A” Typical Female

All chromosomes match

Sex chromosomes “x” “x” look identical.

Lisa

Steven “B” MaleTrisomy 21 Down’s Syndrome

• 22 pairs of chromosomes match

• Male: Sex chromosomes “X” “Y”

• 3 chromosomes at #21

Kevin “C” Male Trisomy 18

• sex chromosomes “x” & “y”

• 3 chromosomes at #18

Mark “D” Typical Male

22 pairs of chromosomes match

Sex chromosomes “X” “Y” look different.

Sarah “E” Female Trisomy 21 Down’s Syndrome

• All chromosomes match

• Sex chromosomes “x” “x”

• 3 chromosomes at #21

Sarah

• A genetic disorder is a disease that is caused by an abnormality in an individual's DNA. Abnormalities can range from a small mutation in a single gene to the addition or subtraction of an entire chromosome or set of chromosomes.

(http://learn.genetics.utah.edu/content/disorders/whataregd/)

Disorders

• Due to a change in entire chromosome– Down’s Syndrome /trisomy 21– Edward’s Syndrome Trisomy 18– Patau syndrome Trisomy 13 – Klinefelters syndrome XXY– Turner’s Syndrome XO– XYY

• Most disorders are due to changes within one chromosome not a change to an entire chromosome. – Cystic fibrosis (thick mucus in respiratory system)– Sickle Cell disease (malformed red blood cells that get stuck in capillaries)– Lou Gehrig’s disease/ALS (loss of muscle control)

Genetic Engineering

1. Combining genes from different organisms

2. Genetically modified (GM), Genetically modified organisms (GMO’s), genetically engineered, transgenic