Download ppt - Gregor Mendel Known as the Father of Modern Genetics Austrian monk Studied garden pea plants

Gregor Mendel• Known as the Father of Modern Genetics

• Austrian monk

• Studied garden pea plants

• Heredity: the passing of traits from parents to offspring (kids)

– Can be complicated• Ex: Why does your brother have different features than you?

• Ex: Why do some family members look alike while others look completely different?

• Trait: a distinguishing quality that can be passed from one generation to another.-Ex. Eye color, Hair color, height, weight, skin color, facial features, body structure

• Genes: pieces of DNA that carry hereditary information on them.

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• Dominant trait: a trait observed when at least one dominant gene for a characteristic is inherited.Example: Bb or BB

(capital letters represent dominant)

• Recessive trait: a trait that is apparent only when two recessive genes for the same characteristic are inherited.Example: bb

(lower case letters represent recessive)

• Genotype: inherited combination of

actual genes•Ex. Bb, LL, tt

• Phenotype: the organism’s physical appearance

•Ex. Blue eyes, brown hair

• Purebred: both genes are alike– Also called homozygous– bb, TT, DD

• Hybrid: genes are different– Also called heterozygous– Bb, Tt, Dd

Incomplete Dominance

• When one trait is not completely dominant over another. Each gene has its own degree of influence.

• The hybrid genotype would yield a new phenotype.

• For example, in snapdragons, red flowers are incompletely dominant over white. The hybrid is pink.

• So the genotype RR would yield red flowers, WW would yield white flowers, and RW or WR would yield pink flowers.

Punnett Square

• Square used to visually show all possible gene combinations



•

Tall Plant (Tt) X Short Plant (tt)

T t

t

t

Tt

Tt

tt

tt

50 % Tall

50 % Short

•

Tall Plant (TT) X Short Plant (tt)

T T

t

t

Tt

Tt

Tt

Tt

100 % Tall0 % Short`

• Probability: chance that an event will occur– After solving Punnett squares, questions will often ask you to predict the probability of one of the traits.

– Ex: What’s the chance of a child having blue eyes?

– Expressed as: Percentages0%, 25%, 50%, 75%, or 100%

Ratios(0/4) (1/4) (2/4) (3/4) (4/4)

How are traits passed?

• Sexual Reproduction

• Asexual Reproduction

Sexual Reproduction• Need 2 parent cells to reproduce (1 male and 1 female)

• Ex. Humans and most animals

• Offspring will have a combination of traits from both parents (genetic diversity)

Sexual ReproductionAdvantages

• Adapts to changing environments more quickly

• If parents have a disease there is still a chance the offspring will be healthy

Disadvantages• Parents can be carriers and be healthy but there are no guarantees the offspring will be healthy

• Takes longer (because a mate is required)• Less reliable

Asexual Reproduction

• 1 parent needed to reproduce

• Ex. Earthworms, fungi, many plants, bacteria, body cells

• Offspring is exact clone of parent (genetic continuity)

Asexual ReproductionAdvantages

• Faster and easier to reproduce• If parent is healthy then offspring will be healthy

• If parent has a disease it will likely die before reproducing

Disadvantages• If parent has a disease or mutation then the offspring will have it too

• No genetic variation, so unfavorable conditions in the environment could wipe out an entire population

• Insufficient resources due to quick population growth and overcrowding

Mutations• A substitution or change in DNA• Could be random error or caused by physical or chemical agents

• Occur when there is a change in the order of bases in an organism’s DNA

• A “mutagen” is anything (physical or chemical) that causes a mutation in DNA

• (Ex. High energy radiation from x-rays and ultraviolet radiation, asbestos and chemicals in cigarette smoke)

Mutations cont.• We inherit hundreds of mutations from our parents.

• The human body cell has to have an entire set of 46 chromosomes (or 23 pairs) in order to grow and function.

• When mistakes are made during DNA replication and cell division, most of the time repair enzymes and other proofing mechanisms decrease the error rate in the end.

Genetic Disorders

• Result from an inherited disruption in an organism’s DNA.

• Inherited disruptions can take several forms including a change in the number of chromosomes and the deletion or duplication of entire chromosomes or parts of chromosomes.

• Mainly, alteration of a single specific gene is responsible for a disorder.

• Some genetic disorders result from several genetic alterations occurring simultaneously.

Genetic Disorders• Diseases resulting from gene alterations cause a wide variety of physical malfunctions and developmental problems.

• Ex. hemophilia, cystic fibrosis, sickle cell anemia, Down’s syndrome, Tay-Sachs disease, Huntington’s disease

Down Syndrome



Sex linked traits• If a gene is found only on the X chromosome and not on the Y chromosome, it is said to be a sex linked trait.

• Because the gene controlling the trait is located on the sex chromosome, sex linkage is linked to the gender of the individual.

• The result is that females will have two copies of the gene while males would only have one.

Sex linked traits cont.

• If the gene is recessive, then males only need one such recessive gene to have the sex linked trait rather than the normal two recessive genes for non sex linked traits.

• This is why males exhibit some traits more frequently than females.

Examples of Sex linked traits

• Red-green colorblindness• Male Pattern baldness• Hemophilia• Duchenne Muscular Dystrophy

Human Genome Project• Completed in 2003, the Human Genome

Project (HGP) was a 13-year project coordinated by the U.S. Department of Energy and the National Institutes of Health

Some of the project goals were:• identify all the approximately 20,000-25,000

genes in human DNA• determine the sequences of the 3 billion

chemical base pairs that make up human DNA• store this information in databases



Ethical Issues

• Discussion:What is the line between medical treatment and enhancement?