Download Human Genetics 8th Grade Science Think About it…. Observe the

Human Genetics
8th Grade Science
Think About it….
Observe the colors of the kitten in the photo. Look at the kitten’s coat colors
and pattern.
 Observe the mother cat in the photo. Note her coat color and pattern.
 Acquired vs. inherited Traits
 Trait Survey
 Take the trait survey
 What are inherited characteristics?
An inherited trait or characteristic is one that is determined by the organism’s DNA
and was inherited from their parents.
 Inherited Characteristics
 Examples of inherited characteristics in humans:
eye color, handedness, blood type
Can you think of other examples?
 Examples of inherited characteristics in animals:
Patterns of stripes or spots location of eyes, number of limbs.
 Can you think of other examples?
 What are acquired characteristics?
A trait/characteristic that an organism gets or acquires throughout their lifetime
(not related to their DNA).
 Acquired Traits
 Examples of acquired characteristics in humans:
Language spoken, knowledge learned, tastes in food, scratches/scars.
Any other examples?
 Examples of acquired characteristics in animals:
A dog learns to sit on command, an animal learning where to hide from predators.
Any other examples?
 What are acquired characteristics?
A trait/characteristic that an organism gets or acquires throughout their lifetime
(not related to their DNA).
 Acquired Traits
 Examples of acquired characteristics in humans:
Language spoken, knowledge learned, tastes in food, scratches/scars.
Any other examples?
 Examples of acquired characteristics in animals:
A dog learns to sit on command, an animal learning where to hide from predators.
Any other examples?
 History of Genetics
 Gregor Mendal is known as the “father of genetics”
 Before we can study his work, there are some basic ideas that you must
understand
 Basics of Genetics
 Every person has two copies (alleles) for each gene. How those two alleles
interact determines what you see for an organism, their phenotype.
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 Dominant Alleles
 Represented by a CAPITAL LETTER
 Dominant alleles hide recessive alleles when it is present in a genotype with
one dominant allele
 It is expressed when an organism has 1 OR 2 copies of this allele
 The majority of alleles interact in a dominant/recessive relationship.
 Some interact in a co-dominance or incomplete dominance relationship.
 Co-Dominance
 “Co”—think of cooperation, they share the spotlight, you see both
 2 dominant alleles—dominant trait is seen
 2 recessive alleles—recessive trait is seen
 1 dominant and 1 recessive allele—you see BOTH the dominant and
recessive phenotype
 Ex.: If R=red and r=white, Rr would be a red flower with white spots
 Incomplete Dominance
 2 dominant alleles—dominant trait is seen
 2 recessive alleles—recessive trait is seen
 1 dominant and 1 recessive allele—you see a combination of the dominant
and recessive
 Ex: If R=red and r=white, Rr would have a blend of the two, a pink flower
 Genotype
 The genetic make-up of an organism, what genes (letter) combination the
organism has.
 Represented by 2 letter pairs
 Ex: HH, Hh, hh
 How are genotypes related to phenotypes?
 GENOTYPE DETERMINES PHENOTYPE
 The genes you have determine the traits you express.
 Homozygous
 An organism that has 2 of the same alleles for a trait.
Homozygous dominant: 2 capital letters
Homozygous recessive: 2 lower case letters
Prefix “homo” means same
 AKA—pure, or purebred
 Ex: HH, aa, GG, bb
 Heterozygous
 An organism that has 1 dominant and 1 recessive allele for a trait
 Prefix “hetero” means different
 AKA—hybrid
 Ex: Aa, Hh, Gg, Bb
 Examples
 GG=homozygous dominant
Same, and 2 dominant
gg=homozygous recessive
Same, and 2 recessive
Gg= heterozygous
 Practice Questions
 1. Aa _______________________________
 2. cc _______________________________
 3. RR ______________________________
 4. Bb ______________________________
 Practice Questions
 1. Aa ___Heterozygous________
 2. cc _Homozygous recessive_________
 3. RR __Homozygous dominant________
 4. Bb ___Heterozygous_________
 Who was Gregor Mendal?
 http://youtu.be/GTiOETaZg4w
 During this short video consider the following questions:
What observation (remember the scientific method!) prompted Mendal to begin
studying genetics
What do YOU think Mendal’s greatest discovery was?
 Some Important Terms
 Heredity-The passing of traits from parents to offspring.
 Genetics- the scientific study of heredity
 Trait- A characteristic that an organism can pass on to its offspring through
its genes.
 Purebreds - offspring that are the result of mating between genetically
similar kinds of parents
 Hybrids- offspring that are the result of mating between two genetically
different kinds of parent
 Mendal’s Hypothesis
 1. Alternative versions of genes account for variations in inherited characters
 2. For each character trait (ie: height, color, texture etc.) an organism inherits
two genes, one from each parent.
 3. If the two alleles differ, then one, the dominant allele, is fully expressed in
the organism's appearance; the other, the recessive allele, has no noticeable
effect on the organism's appearance
 4. The two genes for each character segregate during gamete production
 Why Study Peas?
 Can be grown easily in large numbers and their reproduction can be
manipulated.
 Pea plants have both male and female reproductive organs. As a result, they
can either self-pollinate themselves or cross-pollinate with another plant.
 Self pollination- Transfer of pollen from the anther(male part) to the stigma
(female part) or the same flower
 Cross pollination-The transfer of pollen from an anther of the flower of one
plant to a stigma of the flower of another plant.
 Pea Traits Studied
 1. Flower color: purple or white
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Flower position: axial or terminal
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Stem length: long or short
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4.
Seed shape: round or wrinkled
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Seed color: yellow or green
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Pod shape: inflated or constricted
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Pod color: green or yellow
What Did Mendal Do?
In order to conduct his experiments correctly, Mendal had to prevent the pea
plants from self pollinating and cross pollinated the plants himself
Color Example
In cross-pollinating plants that either produce yellow or green pea seeds
exclusively, Mendel found that the first offspring generation (f1) always has
yellow seeds. However, the following generation (f2) consistently has a 3:1
ratio of yellow to green.
Mendel found that this same ratio occurred in later generations
Height Example:
The F1 Offspring
In one experiment, Mendel crossed purebred tall plants with purebred short
plants.
Scientists today call these parent plants the parental generation, or P
generation.
The offspring from this cross are the first filial (fil ee ul) generation, or the F1
generation.
**You do not need to write every word, but you do need to know what
the P and F1 generations are**
The F2 Offspring
Once the F1 offspring were full grown, Mendal allowed them to self pollinate
and the offspring produce were a mix of both tall and short!
About three fourths of the plants were tall, while one fourth were short.
Experiments With Other Traits
Mendel also crossed pea plants with other contrasting traits.
In all of Mendel’s crosses, only one form of the trait appeared in the F1
generation. However, in the F2 generation, the “lost” form of the trait always
reappeared in about one fourth of the plants.
Results
Mendal’s Conclusions
1.
that the inheritance of each trait is determined by "units" or "factors"
that are passed on to descendants unchanged
2.
that an individual inherits one such unit from each parent for each
trait
3.
that a trait may not show up in an individual but can still be passed on
to the next generation.
Things to Consider
It is important to realize that, in this experiment, the starting parent plants
were homozygous for pea seed color while the plants in the f1 generation
were all heterozygous .
Homozygous- has two identical alleles of the gene for this trait (2 yellows or
2 greens.)
 Allele- the different forms of a gene
 Heterozygous- two different alleles (one from each parent plant.)
 It becomes clearer when we look at the actual genetic makeup, or genotype ,
of the pea plants instead of only the phenotype , or observable physical
characteristics.
 Genotype- An organism’s genetic make-up or allele combinations.
 Phenotype- An organism’s physical appearance or visible traits.
 Example: Someone with brown eyes can have a genotype of either BB
(homozygous) or Bb (heterozygous) but, both will have a phenotype of
brown eyes
 Gene- The set of information that controls a trait; a segment of DNA on a
chromosome that codes for a specific trait.
 Alleles- The different forms of a gene.
 An organism’s traits are controlled by the alleles it inherits from its parents.
Some alleles are dominant, while other alleles are recessive.
 Dominant allele- An allele whose trait always shows up in the organism
when the allele is present.
 Recessive allele- An allele that is masked when a dominant allele is present.
 Probability and Heredity
 What Are the Odds?
 Suppose you were to toss a coin 20 times. Predict how many times the coin
would land with heads up and how many times it would land with tails up.
 Test Your Predictions
 Test your prediction by tossing a coin 20 times. Record the number of times
the coin lands with heads up and the number of times it lands with tails up.
 Combine the data from the entire class. Record the total number of tosses,
the number of heads, and the number of tails.
Think It Over:
 Predicting: How did your results in Step 2 compare to your prediction? How
can you account for any differences between your results and the class
results?
 Probability
 Probability- A number that describes how likely it is that an event will
occur.
 The laws of probability predict what is likely to occur, not necessarily what
will occur.
 Percentage
 One way you can express a probability is as a percentage. A percentage (%) is
a number compared to 100. For example, 50% means 50 out of 100.
 Suppose that 3 out of 5 tossed coins landed with heads up. Here’s how you
can calculate what percent of the coins landed with heads up.
Write the comparison as a fraction then, multiply the fraction by 100% to
express it as a percentage.
 Practice Problem Suppose 3 out of 12 coins landed with tails up. How can
you express this as a percent?
 Probability and Genetics
 So how is probability related to genetics?
What do you think?
 Additional PP on Website!!
 Punnett Squares
 A tool that can help you understand how the laws of probability apply to
genetics is called a Punnett square
 Punnett Square- A chart that shows all the possible combinations of alleles
that can result from a genetic cross.
 How to Make a Punnett Square
 Coin Crosses