Genetics & Heredity

An overview of the history & principles of genetics

Mitosis/Meiosis• Living things are composed of cells.• Cells are specialized and can be

grouped into 2 main groups. – 1.Somatic cells (body cells)- brain

cells, blood cells, skin cells, etc.– 2.Gametes (sex cells) – Sperm

(male) & Egg (female).

• Mitosis – somatic cell division. A process that takes the original cell, copies the genetic information and ends up with 2 identical cells.

• Meiosis – sex cell division. A process that takes the original cell reproduces the genetic information and divides twice producing 4 cells each with 1\2 the original cells genetic information.

Animations

What is genetics?

• Genetics is the study of how organisms pass on information to their offspring

• It also explains characteristics & certain diseases.

What is a trait?

• A trait is a characteristic that is passed on from parent to offspring.

• Traits include eye color, hair color, metabolism, left or right hand.

• Acquired characteristics like strength & education are not passed on directly as traits.

Who discovered genetics?

• Gregor Mendel was a monk from Austria that is called the “Father of genetics”.

• He worked with pea plants.• He studied several traits in the

peas.– 1.pod shape – 2. Pod color – 3. Seed shape – 4. Seed coat color – 5. Plant height – 6. Flower position

• He was able to predict outcomes & noticed patterns.

Mendel’s Findings• He noticed that there were 2 versions of

many traits.• He noticed that in certain crosses 1 of the

traits showed up more than the other.• He set up experiments to cross plants to

see if he could predict the traits.– Mendel crossed plants with different

traits to create a 2nd generation of plants and all 2nd generation plants looked exactly like the parent plant with the dominant traits.

– Mendel also crossed 2nd generation plants with each other and the recessive trait reappeared with a 3-1 dominant to recessive ratio.

– Finally Mendel did a few backcrosses with the 2nd generation plants and their parent offspring to help predict which traits were dominant & recessive.

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Mendel’s Findings (cont.)• He called the trait that

showed up more a dominant trait. The more hidden trait he called a recessive trait. – Dominant trait – a trait

that seems to hide or mask another trait.

• In a cross a dominant trait is shown with a capital letter.

– Recessive trait – a trait that is masked or hidden by a dominant trait.

• A lower case letter in a cross shows a recessive trait

More of Mendel’s findings

• There are three possible gene combinations.

• 1. Homozygous (pure) dominant – 2 copies of the dominant gene.

• 2. Homozygous recessive – 2 copies of the recessive gene.

• 3. Heterozygous (Hybrid) – 1 copy of the dominant gene & 1 copy of the recessive gene.

What is a pedigree?

• A pedigree is a diagram that shows the history of a trait in a family.

• They are good indicators that certain traits or diseases are possible.

• Males are squares. Females are circles. They are usually in order from oldest to youngest from left to right.

• Colored parts show the trait being looked at.

This pedigree show 3 generations

Punnett squares

• A Punnett square is a method used to predict possible gene combinations.

• Dominant genes are given capital letters.

• Recessive genes are given lower case letters.

– Ex Tall (T) is dominant over short (t)

– Possible combinations TT,Tt,tt.

Genotype and Phenotype

• Phenotype – describes the visible expression of genes. (What you see.)

• Genotype - shows the actual gene combinations. (What you get).

• Online lab

How are traits passed on?

• Traits are passed from parents to offspring.

• They are passed by objects known as chromosomes.

• Chromosomes – structures within the nucleus of a cell that carry genes. – *****Chromosomes

occur in pairs.• Genes are specific locations

on chromosomes.• Organisms receive 1 copy of

each gene for a trait from each parent.

Co dominance and Incomplete Dominance

• Incomplete dominance – a situation where an organism gets 2 genes that are not dominant over each other. Both genes are expressed. – Ex. Cross a red flower & a

white flower & get a pink flower.

– Sickle cell anemia – a genetic disease that curves red blood cells into a sickle shape. It is very painful & often deadly. It shows incomplete dominance.

• Co-dominance – a situation where an organism has 2 dominant genes & both are expressed. – Ex. Two different colored eyes

or alternating white & red flowers. Also blood types.

Web lab Blood type game

Incomplete dominance

Co dominance

Multiple Alleles/Co dominance and Blood Types

• Multiple alleles - Any of a set of three or more alleles, or alternative states of a gene, only two of which can be present in a diploid organism.

• Eye color, Hair color, & blood types are all cases of multiple alleles.

• Blood type is also co dominance with A & B being co dominant and O being recessive.

What is DNA?

• DNA stands for Deoxyribonucleic Acid

• It is a long thread – like material located in the nucleus of cells.

• It has a twisted ladder shape called a double helix.

• The shape was discovered by James Watson & Francis Crick.

The Genetic Code

• DNA is made of 4 nitrogen containing base.

• They are adenine,guanine,cytosine,& thiamine.

• The sequence of these bases in triplet pairs determine an individuals genetic code.

• Example: TAG could make left handed, TTG could make right handed.

Human Genetics

Humans have 46 chromosomes (23 pairs)

1 pair is the sex chromosomes.

Females have XX

Males have XY

Mutations

• Mutations are changes in the genetic structure.

• They can be DNA mutations or chromosome mutations.

• Mutations may be harmful, helpful or neither.

Conjoined twins are caused by a mutation which won’t allow fertilized eggs to split.

Gene Mutations

Gene deletion Gene duplication

Gene inversion Gene translocation

Chromosome Mutations

Trisomy:3 copies where 2 should be.

Monosomy: 1 copy where 2 should be

Genetic diseases

SICKLE CELL ANEMIA TAY SACHS DISEASE CYSTIC FIBROSIS THALASSEMIA DUCHENNE MUSCULAR

DYSTROPHY. PHENYLKETONURIA (PKU) MARFAN SYNDROME PROGERIA TRISOMY 21 OR DOWN

SYNDROME SPINA BIFIDA ACHONDROPLASIA(DWARFISM) HUNTINGTON'S DISEASE

FRAGILE X SYNDROME HEMOPHILIA KLINEFELTER SYNDROME TURNER SYNDROME TRISOMY 18 OR EDWARD

SYNDROME CRI DU CHAT CLEFT LIP/CLEFT PALATE TRISOMY 13 OR PATAU

SYNDROME Blue Rubber Bleb Nevus

Syndrome Prader-Willi Syndrome Waardenburg Syndrome Retinoblastoma

Genetic Counseling

• If couples have a history of genetic diseases they may wish to see a genetic counselor.

• They are specialized doctors who use pedigrees, Punnett squares & genetic screenings to determine probabilities of disorders.

• They then advise the couple of their findings & their options.

Genetic Engineering

• Genetic Engineering involves mapping the genes of organisms & manipulating them.

• Many of the ideas of genetic engineering are controversial because they involve controlling traits.

• Cloning, gene splicing, & gene therapy are part of genetic engineering.

Gene Splicing

• Gene splicing involves “cutting” an undesirable gene out of one organism & replacing it with a desirable gene from another.

• The organisms must be compatible.

• Examples: Frost & insect resistant plants & Beefalos.

• A Beefalo is an angus cow that has the size gene of the American Bison (Buffalo)

The animal in the front is a normal angus cow. The animal in the rear is an 8 month old Beefalo.

Cloning

• Cloning is the process of using DNA to produce a genetic duplicate of an organism.

• Not even identical twins are genetic duplicates.

• Sheep & cows have been cloned.

• Human cloning is illegal in the US.

Click and clone mice