GeneticsReview Biology Class

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Vocabulary Review

• trait -A physical characteristic.• heredity -The passing of traits from parents to offspring.• genetics - The scientific study of heredity.

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Question

Which of the following is an example of a trait?

A. Bb

B. Talking loud

C. Brown eyes

D. Bleach blonde hair

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Alleles

• Genes are the factors that control Traits.

• Alleles are the different forms of Genes.

• Individual Alleles control the inheritance of Traits.

• An offspring receives one allele from each parent.

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Question

What is the term for factors that control traits?

A. Genes

B. Purebreds

C. Recessives

D. Parents

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Question

Which term refers to physical characteristics that are studied in genetics?

A. Traits

B. Offspring

C. Generations

D. Hybrids

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DOMINANT and recessive Alleles

• A dominant allele is one whose trait always shows up in an organism when the allele is present.

- capital letter (AA, Aa)• A recessive allele is covered up

when the dominant allele is present.

- lower case letter (aa)

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Practice

• R is the dominant allele for a one eyed monster.

• r is the recessive allele for a monster with two eyes.

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Monster Genetics

• Rr

• How many eyes will our monster have?????

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Monster Genetics

• RR

• How many eyes will our monster have??

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Monster Genetics

• rr

• How many eyes will our monster have??

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Question

What does the notation TT mean to geneticists?

A. Two dominant alleles

B. Two recessive alleles

C. No dominant alleles

D. One dominant and on recessive allele

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Codominance

• Some alleles are neither dominant or recessive.

• Codominance is when alleles are neither dominant or recessive, both alleles are expressed in the offspring.

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What will Happen?

• You have two flowers, a white and a red, that are crossed.

• The flowers are codominant.

• What color will their offspring be.

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Phenotype

• Phenotype is an organisms physical appearance or its visible traits.

• Example: a pea plant stem height can be short or tall.

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Genotype

• Genotype is an organisms genetic makeup, or allele combination.

• Example: TT, Tt, tt

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Describing genotypes

• Homozygous (or Purebred) is used to describe an organism that has two identical alleles for a trait.

• Example: TT and tt

• Heterozygous (or Hybrid) is used to describe an organism with two different alleles.

-Example: Tt

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Question

Pick the answer that best describes “Aa”.

A. Homozygous

B. heterozygous

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Punnett Squares

• A punnett square is a chart that shows all possible combinations of alleles that can result from a genetic cross.

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Punnett Example

• Yellow is dominant over Green.

• What is the probability that the offspring will be yellow?

100%

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Punnett Problems

• In purple people eaters, one-horn is dominant and no horns is recessive.

• Draw a Punnet Square showing the cross of a purple people eater that is hybrid for horns, with a purple people eater that does not have horns.

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Answer

• Hybrids have two different alleles for one trait.

• Hh is the hybrid in the example.

• No horns would have to be hh because it is a recessive allele.

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Punnett Problems

• In Bears the dominant allele for brown fur is R, black fur is recessive.

• The female bear is Rr and the male bear is rr.

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Question

• What are the four possible phenotypes for the cubs?

A. RR, Rr

B. Rr, rr

C. 2 brown, 2 black

D. 3 brown, 1 black

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Question

• What is the probability that the cub will have black fur?

A. 50%

B. 25%

C. 75%

D. 100%

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Question

What do you call one set of instructions for an inherited trait?

a. alleles

b. phenotype

c. albinism

d. genes

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Question

Two forms of a gene, one from each parent, are called

a. alleles.

b. phenotypes.

c. albinism.

d. genes.

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Question

What is a plant that has two dominant genes or two recessive genes called?

a. organism

b. genotype

c. homozygous

d. heterozygous

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Question

The allele for freckles, F, is dominant among humans. If a woman with freckles (FF) and a man without freckles (ff) have children, what are the possible genotypes of the children?

A. Ff

B. FF, Ff, ff

C. Ff, ff

D. ff

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QuestionPart of a mouse’s tail is cut off as the mouse

escapes from a cat. The mouse later reproduces. Which explanation best describes why the mouse’s offspring have long tails?A. Long tails are a dominant trait.B. Short tails do not appear in the first

generation or the second generation.C. Cutting the tail of the mouse changed its genes.D. Cutting the tail of the mouse did not

change its genes.

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Question

What is the genotype of the offspring represented in the upper left-hand box of the Punnett square?

A RRB RrC rrD rrr

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Question

What is the genotype of the offspring represented in the upper left-hand box of the Punnett square?

A RRB RrC rrD rrr

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Question

What is the ratio of Rr (purple-flowered plants) to rr (white-flowered plants) in the offspring?

A 1:3B 2:2C 3:1D 4:0

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QuestionGreen seed color (G) is dominant to

yellow seed color (g). If two heterozygous parents are crossed, what will be the resulting genotypes of the offspring?

A. GG, Gg, gg

B. Gg, gg

C. GG, Gg

D. gg, GG