Download Unit 7 Study Guide

Name: __________________________________________
Unit 7 Study Guide: Genetics
Date: ______________
Period: ______
3.3.E.a Explain how genotypes (heterozygous and homozygous) contribute to phenotypic variation within a species
- Genotype refers to the alleles that an organism received from their parents
- Dominant trait is represented by a capital letter (T), recessive trait is represented by lower case letter (t)
- 3 possible genotypes: homozygous dominant (TT), homozygous recessive (tt) or heterozygous (Tt)
- Phenotype refers to how the genotype is expressed in an organism (Ex: tall or short)
- An organism with the heterozygous genotype will display the dominant phenotype (Ex: Tt = tall)
Practice:
Trait
Dominant Trait
Recessive Trait
Fur Color
Brown (B)
White
Ear Size
Long (L)
Short
Tail Size
Short (S)
Long
Eye Color
Red (R)
blue
1. Using the information from the table above, write the phenotype of each individual:
RR ______________
ss _______________
Ll ______________
LL ___________
Ss _______________
bb ______________
Bb _____________
rr ___________
2. Using the information from the table above, write the genotype for each individual (Some may have 2 answers!)
Short tail _________
Blue eyes ________
Long ears _______
White fur ______
Brown fur ________
Long tail _________
Red eyes _______
Short ears ______
3. Determine the following genotypes for fur color:
Homozygous Dominant _________
Homozygous Recessive _________
4. Determine the following genotypes for tail size:
Heterozygous ___________
Homozygous Recessive _____________
Heterozygous _____________
Homozygous Dominant ________
3.3.E.b Predict the probability of the occurrence of specific traits, including sex-linked traits, in an offspring by using a
monohybrid cross
- To predict the probability of traits in offspring, a Punnett Square is used
- One parent’s genotype goes on the top and the other goes on the left side, the 4 boxes are filled in
- Since there are 4 boxes, each box represents a 25% chance of the trait occurring
- Genotypic Ratio= TT: Tt: tt Phenotypic Ratio= Tall : short (Only write the # of each genotype or phenotype!)
Practice:
5. Create a Punnett Square to show the cross of a heterozygous brown rabbit and a white rabbit:
Parent 1 Genotype: ______
Parent 2 Genotype: ______
Genotypic Ratio: ______________
Phenotypic Ratio: _____________
Percent brown offspring: _______
6. Create a Punnett Square to show the cross of a homozygous red-eyed rabbit and a blue-eyed rabbit:
Parent 1 Genotype: ______
Parent 2 Genotype: ______
Genotypic Ratio: ______________
Phenotypic Ratio: _____________
Percent red-eyed offspring: _______
3.3.D.c Recognize that new heritable characteristics can only result from new combinations of existing genes or from
mutations of genes in an organism’s sex cells
- Sometimes one allele will not be completely dominant over another allele
- In the case of codominance or incomplete dominance, two capital letters are used to represent the traits
- In codominance, both traits are expressed, Ex: RR = red flower, WW = white flower, RW = red and white flower
- In incomplete dominance, both traits are mixed, Ex: RR = red flower, WW = white flower, RW = pink flower
Practice:
7. In dogs, fur color is a codominant trait. Dogs can have black fur, white fur or black and white spotted fur.
What is the genotype of a black dog? ___________
What is the genotype of a white dog? ___________
What is the genotype of a spotted dog? __________
8. Create a Punnett Square to show the cross of a black dog and a spotted dog:
Parent 1 Genotype: ______
Parent 2 Genotype: ______
Percent spotted offspring: _______
Percent black offspring: _________
9. Create a Punnett Square to show the cross of a white dog and a spotted dog:
Parent 1 Genotype: ______
Parent 2 Genotype: ______
Percent spotted offspring: _______
Percent white offspring: _________
10. In fish, scale color is controlled by incomplete dominance. Fish can be blue, red or purple.
What is the genotype for blue? ________
What is the genotype of red? ___________
What is the genotype for purple? _________
11. Create a Punnett Square to show the cross of a two purple fish:
Parent 1 Genotype: ______
Parent 2 Genotype: ______
Percent red offspring: _______
Percent blue offspring: ______
Percent purple offspring: _____
12. Your teacher loves the color purple so she wants all purple fish. Draw a Punnett Square showing the cross that
would create the most purple offspring:
3.3.E.c Explain how sex-linked traits may or may not result in the expression of a genetic disorder (e.g., hemophilia,
muscular dystrophy, color blindness) depending on gender
- Remember, females = XX, males = XY
-Y chromosome is smaller so it contains fewer genes
- Sex-linked traits are located on the X chromosome so females have 2 alleles, males only have one
- Females can be homozygous dominant (XTXT), homozygous recessive (XtXt) or heterozygous (XTXt)
- Males can only be dominant (XTY) or recessive (XtY)
- If a recessive genetic disorder is sex-linked, females can be carriers (heterozygous) but males cannot
Practice:
13. All sex-linked traits are located on the ______ chromosome.
14. Only ______________ can be heterozygous for sex-linked traits.
15. A carrier does NOT have the disorder, but they _________________________________________.
Graphing Review:
16. What should the title of your graph always start with?
17. If I did an experiment and my IV was medicine and my DV was length of illness, what would be the title of my
graph?
18. If you make a line graph, what always goes on the X axis?
19. In any graph, what goes on the Y axis?
*REMEMBER TO READ THE INFORMATION UNDER EACH CLE. THIS IS IMPORTANT!!!! IF YOU KNOW THAT
INFORMATION BY HEART, YOU WILL DO GREAT ON YOUR TEST!*
STUDY HARD!