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