Mendel’s Genetics B

Hannah, Ting Wei, Beau, Anthony

Punnett Squares• Punnett squares can be used to predict and compare the

genetic variations that will result from a cross.• The gene combinations that might result from a genetic

cross c an be determined by drawing a diagram known as a punnett square.

• Also known as monohybrid crosses.

Dominant/Recessive Traits• Dominant traits are represented by a capital letter.• Recessive traits are represented by a lowercase letter.• For an organism to inherit a recessive trait, it would need

homozygous recessive.• If both a dominant and recessive trait are present in a

genotype, only the dominant trait is shown.

Homozygous/Heterozygous• Organisms that have two identical alleles for a particular

trait are homozygous.• Organisms that have two different alleles of the same trait

are heterozygous.• Homozygous organisms are purebred.• Heterozygous organisms are hybrids.

Genotypes/Phenotypes• The phenotypes are the physical characteristics of an

organism.• The genotypes are the genetic makeup of an organism.• Genotypes are represented by letter codes.• Phenotypes are represented by detailed descriptions.

Probability• Probability is the likelihood that an

event will occur.• The principles of probability can be

used to predict the outcome of genetic crosses.

Dihybrid• Dihybrid crosses involve two separate traits.• Each genotype are composed of four alleles.

Independent Assortment• The principle of independent assortment states that genes

for different traits.• Independent assortment is the separation of alleles for traits

that are controlled by more than one allele

Independent Assortment Continued

• When the alleles separate, the first letter in the first set of alleles is combined with the first letter of the second set of alleles then it is combined with the second letter of the second set of alleles. Then the process is repeated for the second letter of the first allele.

Incomplete Dominance• Incomplete dominance is when neither of the possible

phenotypes are completely dominate.• When an animals genotype is heterozygous for a trait, both

of the possible phenotypes are mixed together.

RR RW WW

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Codominance• Codominance is when neither of the two phenotypes are

dominate. • When an animals genotype for a codominate trait is

heterozygous, both phenotypes are shown. This may happen in the form of spots, or two different colors or feathers or furs.

RR

RW

WW

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1. If you flip a coin twice, what is the probability of getting heads on both coins?•a) 0%•b) 25%•c) 100%•d) 1,000%

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2. What are the letters in the blank part of the punnett square below.

A a

A AA

a aa

a) aab) Aac) AAd) none of the above

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3. Punnett squares can be used to predict the probability of…•a) one being exposed to a contagious disease.•b) having an inherited disease or a genetically determined physical trait.•c) a person’s physical traits like eye color and hair color.•d) both b and c

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4. If two parents are homozygous for a genetically inherited recessive trait, what is the probability that they will have a child who does not have this trait in his or her phenotype?•a) 0%•b) 25%•c) 50%•d) 100%

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5. For a species of birds that either have blue (dominate) or red (recessive) eyes, and Green (dominate) or black (recessive) feathers. What are the possible gametes for a specific bird with the genotype BbGG•a) BG, bG•b) BB, bG, bG, bb•c) GG, Bb, Gg, gg•d) Not enough information given

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6. What is the probability that 2 parents who are heterozygous for a trait will have a child with the dominate phenotype:•a) π%•b) 25%•c) 50%•d) 75%

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(for questions 6-8 use the following)•Once upon a time, in a galaxy far far away, there was a species of animals known as the group 2’s. This species was characteristically extremely good looking and stupendously smart. Every member of this species either had blonde or dark hair. (Dark dominate, blonde recessive) and freckles or no freckles (Freckles are dominate, and no freckles are recessive. Two members in particular of this species fell madly in love one day. There names were π and ∆. π was Homozygous for dark hair, and had freckles. ∆ on the other hand was heterozygous for dark hair, and heterozygous for not having freckles. π and ∆ are intending to have a child in the first few years of their long and happy life together.

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7. What are the possible gametes for π?•a) ff, DF, dF•b) DD, dd, ff, FF•c) Df•d) 15.3

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8. What are the possible gametes for ∆?•a) Mrs. Lawless is amazing•b) Df•c) DD, ff•d) DF, Df, dF, df

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9. For two parents who have the genotypes rryy and RRYY for a trait, what is the probabillity that their child will have a genotype of RrYy•a) 16/16•b) 6/16•c) 9/16•d) shoe/kitten

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10. What is the genotypic ratio of for a child who’s parents are each heterozygous for both of the traits?•a) 8:4:4•b) 9:3:3:1•c) 8:8•d) 1:1:1:1:1:1:1:1:1:1:1:1:1:1:1:1

ANSWERS!!!

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