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WHAT ARE ALLELES? FORM oAre ONE FORM of a gene (there can be more than one form) one oSex cells have one form of a gene on their chromosomes two oBody cells have two forms or ALLELES for a single gene (you got one from Mom and one from Dad) dominant oOne may be dominant over another. If this happens, the dominant gene is the one expressed. If not, the recessive trait is expressed.
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• HeredityHeredity : the passing of traits from parent to parent to offspringoffspring
Traits are controlled by genesgenes, SO what is GENETICS?
Genetics: The study of how traits are inheritedinherited.
GREGOR MENDELGREGOR MENDELo First known geneticist and “father father of genetics”
o Was an Austrian monk and was born in 18221822
o Did most of his genetic studies on peapea plants
WHAT ARE ALLELES?WHAT ARE ALLELES?o Are ONE FORM FORM of a gene (there can be more than one form)
o Sex cells have one one form of a gene on their chromosomes
o Body cells have two two forms or ALLELES for a single gene (you got one from Mom and one from Dad)
o One may be dominantdominant over another. If this happens, the dominant gene is the one expressed. If not, the recessive trait is expressed.
DOMINANT AND RECESSIVEDOMINANT AND RECESSIVE
o A Dominant trait: will always be expressed and will “maskmask” a recessive trait
o A recessive trait can only be expressed if there
are no dominant dominant alleles present.
ExampleExample: Eyecolor—Brown color is dominantdominant and blue is recessive.
A person can have a brown allele and a blue allele but still have brownbrown eyes because the brown allele is dominant and “hideshides” the blue allele.
Example:RR= dominant rr = recessive
• Generally, dominant alleles are represented with a capitalcapital letter, and recessive alleles are represented with a lower caselower case letter.
Each organism
is represented by TWOTWO letters, one for each
allele.
o “Purebred” species have two alleles of the same same traito Represented by two of the same letters. This is called homozygoushomozygous. For For instance: BB or bb.instance: BB or bb.
o Species with two different alleles or two different forms of the gene would be “hybrid”o Represented by two different “lettersletters” and by called “heterozygous”. For For instance: Bbinstance: Bb
o The alleles present in the organism are referred to as its genotypegenotype. For instance, BB, Bb, or bb.BB, Bb, or bb.
o The PHYSICALPHYSICAL trait that shows, regardless of genotype is called a PHENOTYPEPHENOTYPE.
o For instance, BlueBlue or BrownBrown Eyes.
PROBABILITYPROBABILITYo Helps predict the chance chance that something will happen
o ExampleExample: the probability of throwing heads or tails on a coin is 50% 50% (1/2 chances)
o Your predictions become more accurateaccurate with the more trials you run!
Using a Punnett Square…Using a Punnett Square…
o Used to help predict Mendelian genetics
Steps for using the Punnett square:
1) One parent’s alleles (genotype) (genotype) go along the top
2) The other parent’s alleles go down the side.
3) You fill in the squares like doing the communicative property of multiplication.
B bB
b
BB
bbBb
Bb
Let’s try some practice Let’s try some practice problems…problems…
Practice Problem #1Practice Problem #1
• Predict the fur color of the offspring of a brown heterozygous hamsters and a white homozygous hamster. Brown is dominant. White is recessive.
• Use any letter you like.
Practice Problem #1Practice Problem #1
Bb bbBb bb
B bb
b
Practice Problem #2Practice Problem #2
• Predict the offspring of 2 white homozygous cows. Black is dominant over white.
• Use any letter you like.
Practice Problem #2Practice Problem #2
bb bbbb bb
b bb
b
Practice Problem #3Practice Problem #3
• Predict the offspring of 2 Grey Heterozygous rats. Gray is dominant over white, which is recessive.
• Use any letter you like.
Practice Problem #3Practice Problem #3
GG GgGg gg
G gG
g
Practice Problem #4Practice Problem #4
• Predict the pea shape of the offspring of one Heterozygous Round Pea plant and one homozygous wrinkled pea plant. Round is dominant over wrinkled.
• Use any letter you like.
Practice Problem #4Practice Problem #4
Rr rrRr rr
R rr
r
Practice Problem #5Practice Problem #5you don’t have to write this one down…you don’t have to write this one down…
• What are the chances of having a boy or a girl?
• How would you solve this one?
Practice Problem #5Practice Problem #5
XX XYXX XY
X YX
X
