Genotypes and Phenotypes – Practice



Name _________________________________________ Class ________ Date ____________

Biology 9

ANSWERS!

Mendelian Genetics Review Packet

Part I: Genotypes & Phenotypes

1. Trait: Pinky shape

Alleles: Bent pinky is dominant (B)

Straight pinky is recessive (b)

Fill in the chart with the correct genotype or phenotype.

|Genotype |Phenotype |

|BB |bent pinky |

|Bb |BENT PINKY |

|bb |STRAIGHT PINKY |

|bb |straight pinky |

|BB or Bb |bent pinky |

2. Trait: Ear lobes

Alleles: Free earlobes (un-attached) is dominant (A)

Attached earlobes is recessive (a)

Fill in the chart with the correct genotype or phenotype.

|Genotype |Phenotype |

|AA |FREE |

|aa |ATTACHED |

|Aa |FREE |

|AA or Aa |free earlobes |

|aa |attached earlobes |

3. Fill in the blanks with DOMINANT or RECESSIVE.

If a person has two copies of the dominant gene, they show the DOMINANT phenotype.

If a person has one copy of the dominant gene and one copy of the recessive gene, they show the DOMINANT phenotype.

If a person has two copies of the recessive gene, they show the RECESSIVE phenotype.

4. If a person shows the recessive phenotype for a trait, their genotype could be… (circle one or more)

AA Aa aa

If a person shows the dominant phenotype for a trait, their genotype could be… (circle one or more)

AA Aa aa

5. If a person is homozygous dominant, their genotype is AA

6. If a person is homozygous recessive, their genotype is aa

7. If a person is heterozygous, their genotype is Aa and they show the DOMINANT phenotype.

Check your answers before moving on to Part II!

Part II: Genetics Vocabulary Review

Match the definitions with the words.

dominant recessive homozygous brown hair alleles

phenotype Aa heterozygous genotype gene

|Word |Definition |

|GENOTYPE |The genetic make-up, or combination of alleles, that an organism has |

|PHENOTYPE |An organism’s physical characteristics and exhibited traits |

|Aa |An example of a genotype |

|HETEROZYGOUS |A genotype that has two different alleles |

|HOMOZYGOUS |A genotype that has two of the same alleles |

|BROWN HAIR |An example of a phenotype |

|DOMINANT |An allele that always shows up (is expressed as a trait) if it is present |

|RECESSIVE |An allele that only shows up if no dominant alleles are present (it can be hidden by a dominant allele) |

|GENE |A section of genetic material (DNA) that holds instructions for one protein or trait |

|ALLELE |Different versions of a gene (example: brown eyes vs. blue eyes) |

More Words, More Practice:

zygote gamete meiosis fertilization homologous chromosomes 46 23

mitosis Mendel’s Law of Segregation Mendel’s Law of Independent Assortment

|Word |Definition |

|GAMETE |An egg cell or a sperm cell |

|FERTILIZATION |The process in which an egg and sperm join together |

|ZYGOTE |A fertilized egg cell that will grow and develop into an offspring |

|MITOSIS |The process of cell division that creates two new cells identical to the original one; used for growth|

| |and repair of tissues |

|MEIOSIS |The process of cell division that creates 4 gametes with half the number of chromosomes as the |

| |original cell |

|46 |The number of chromosomes in all human cells except eggs and sperm |

|23 |The number of chromosomes in human egg and sperm cells |

|LAW OF SEGREGATION |Every organism has two alleles for each gene. During meiosis, these alleles separate into gametes, so|

| |every gamete has one allele for each gene. |

|LAW OF INDEP. ASSORTMENT |During meiosis, alleles for different genes are put into gametes in every possible combination (Ex: |

| |from AaBb, gametes could be AB, Ab, aB, or ab) |

|HOMOLOGOUS CHROMOSOMES |A pair of chromosomes that are the same size and shape, and carry the same genes but not necessarily |

| |the same alleles. |

Check your answers before moving on to Part III!

Part III: Monohybrid Crosses

(if you are up for a challenge, then skip right to Question 2)

1. In aliens, a certain gene controls the size of the eyes. The allele for bulging eyes (B) is dominant over the allele for small eyes (b).

Larry is an alien who is heterozygous for the eye gene.

Larry’s genotype is Bb

Larry’s phenotype is bulging eyes

Mary is an alien who is homozygous recessive for the eye gene.

Mary’s genotype is bb

Mary’s phenotype is small eyes

If Larry and Mary have an alien-baby…

Draw a Punnett Square: B b

b Bb bb

b Bb bb

What is the probability that their baby will have bulging eyes? ½ or 50%

2. Challenge Question: In guinea pigs, rough coat (R) is dominant over smooth coat (r). A homozygous dominant guinea pig is mated with a smooth guinea pig.

a) What is the probability that an offspring will have a rough coat? Show your work below:

homozygous dominant = RR

smooth guinea pig = rr

R R

r Rr Rr

r Rr Rr

b) If two of the offspring mate together to produce a second (F2) generation of offspring, what is the probability that an F2 offspring would have… (show work below)

A rough coat? ¾ or 75% Rr x Rr

A smooth coat? ¼ or 25%

R r

R RR Rr

r Rr rr

Check your answers before moving on to Part IV!

Part IV: Dihybrid Crosses

(if you are up for a challenge, then skip to Question 4)

3. In aliens, a certain gene controls antennae – having antennae (A) is dominant over no antennae (a). Recall from the previous worksheet that there is also an alien gene for eye size: the allele for bulging eyes (B) is dominant over the allele for small eyes (b).

a) Consider this cross: AaBb x AaBb

List the gametes that each alien could make: AB, Ab, aB, ab

Draw a Punnett Square:

AB Ab aB ab

AB AABB AABb AaBB AaBb

Ab AABb AAbb AaBb Aabb

aB AaBB AaBb aaBB aaBb

ab AaBb Aabb aaBb aabb

What is the probability of having a baby with the genotype AaBb? 4/16 = ¼ or 25%

What is the probability of having a baby with no antennae and bulging eyes?

Genotype will be aaBB or aaBb = 3/16

4. Challenge Question: Larry the alien is heterozygous for both antennae and eye size.

Mary the alien is heterozygous for antennae and homozygous recessive for eye size.

What is the probability that they will have a baby with no antennae and small eyes? Show your work…

Larry = AaBb

Larry’s gametes = AB, Ab, aB, ab

Mary = Aabb

Mary’s gametes = Ab, ab

AB Ab aB ab

Ab AABb AAbb AaBb Aabb

ab AaBb Aabb aaBb aabb

Baby with no antennae and small eyes = aabb = 1/8

Check your answers… if you feel 100% confident about everything in this packet,

get a set of Extention Problems!

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