Transcript Document
Genetics B
Patrick McClanahan
Jill Farinsky
Jesse Chen
Matt Kang
Definitions
• Monohybrid: off springof parents that
differ in only one genetic characteristic.
Usually imples heterzygosity at a single
locus under study.
• Dihybrid: a cross between two
individuals that are hetrozygos at two
loci for example, AaBb/AaBb
Pictures of monohybrid
QuickTime™ and a
decompressor
are needed to see this picture.
QuickTime™ and a
decompressor
are needed to see t his picture.
Pictures of dyhibrid
QuickTime™ and a
decompressor
are needed to see this picture.
Vocabulary
•
•
•
•
•
•
•
•
Punnett Square: the gene combinations that might result from a genetic
cross can be determined by drawing a diagram.
Homozygous: organisms that have two identical alleles for a particaular
trait.
Heterozygous: organisms that have two different alleles for the same
trait.
Phenotype: physical characteristics.
Genotype: genetic make up.
Independent assortment: alleles for seed shape segregate
independently of those for seed color.
Incomplete dominance:cases in which one allele is not completely
dominant over another.
Co-dominance: in which both alleles contribute to the phenotype.
How to do a monohybrid cross
• To do it you draw a square and devide it
in to four parts.
• Then you write the parents traits one
above each box on the top and on the
side.
• Then you combine the letters in to all
four box’s to see what your children will
look like.
How to do a dihybrid cross
• Foial the four letters and then make a
16 square box instead of a 4 square
box.
• Then you write the four letters above
and on the top and the side
• Then you combine the letters in all of
the 16 boxes.
Why you use monohybrid
croses
• You use monohybrid crosses so you
can predict the phenotype and the
genotype for your offspring.
Why do you use a dyhibrid
crosses
• You use dyhibrid crosses for the same
reason you would use monohybrid
crosses except with dyhibrid you are
trying to determine 2 different traits.
Intersting facts about
monohybrid and dihybrid
crosses
• Monohybrid and dihybrid crosses can
be used to determine traits for any
organism.
• Each square in a monohybrid cross is
25% total.
• Different combinations of alleles can be
considered multiple alleles
Interesting facts cont.
• Capital letters represent dominant traits,
and lowercase letters represant
ressessive traits.
• Some alleles are nither dominant or
ressive.
• Many traits are controlled by multiple
alleles or multiple genes.
Questions
• 1. Monohybrid crosses use a punnet square with how many sections
A:2 B:4 C:6 D:8
• 2.Dihybrid crosses involve how many traits?
A:1 B:2 C:3 D:4
• 3.Do monohybrids and dyhybrid crosses show genotypes or phenotypes?
A: Genotype B: Phenotype C:both
D:nither
• 4. True of False: dihybrid crosses are more common then monohybrid crosses?
• 5. How many squares are used in a punnet square when it’s a dihybrid cross?
A:16 B:20 C:4 D:18
• 6. True or false: before you write out the letters across the top or side of the
punnet square for a dihybrid cross you foial the four letters for each organism.
•
•
7. True or false: every trait is represented by two letters.
8. True or false: if the parents both have all recessive, what is the chance that the off sprong
will have a dominant trait
A:0% B:25% C:50% D:75%
•
9. What is monohybrid
•
10. What is dihybrid
•
11. A phenotype ratio of 9:3:3:1 in the offspring of a mating of two organisms heterozygous
for two traits is expected when:A. the genes reside on the same chromosomeB. each gene
contains two mutationsC. the gene pairs assort independently during meiosis <- AnswerD.
only recessive traits are scoredE. none of the above
•
12. Which of the following genetic crosses would be predicted to give a phenotypic ratio of
9:3:3:1?A. SSYY x ssyyB. SsYY x SSYyC. SsYy x SsYy <- AnswerD. SSyy x ssYYE. ssYY
x ssyy
•
•
•
13. The gametes of a plant of genotype SsYy should have the
genotypes:A. Ss and YyB. SY and syC. SY, Sy, sY, and sy <- AnswerD.
Ss, Yy, SY and syE. SS, ss, YY, and yy
14. Which of the following genotypes would you not expect to find
among the offspring of a SsYy x ssyy test cross:A. ssyyB. SsYyC.
SsyyD. ssYyE. SsYY <- Answer
15. The expected phenotypic ratio of the progeny of a SsYy x ssyy test
cross is:A. 9:3:3:1B. 3:1C. 1:1:1:1 <- AnswerD. 1:2:1E. 3:1:1:3
16. A phenotypic ratio of 3:1 in the offspring of a mating of
two organisms heterozygous for a single trait is expected when:
•A. the alleles segregate during meiosis. <- Answer
•B. each allele contains two mutations.
•C. the alleles are identical.
•D. the alleles are incompletely dominant.
•E. only recessive traits are scored.
17. A genetic cross between two F1-hybrid pea plants having yellow seeds will yield what percent green-seeded plants inthe F2 generation? Yellow seeds are
dominant to green.
A. 0%
B. 25% <- Answer
C. 50%
D. 75%
E. 100%
18. When true-breeding tall stem pea plants are crossed with true-breeding short stem pea plants, all of the _________ plants, and 3/4 of the
__________ plants had tall stems. Therefore, tall stems are dominant.
A. F1, F2. <- Answer
B. G1, G2.
C. parental, F2.
D. F2, parental.
E. P1, P2
19. To identify the genotype of yellow-seeded pea plants aseither homozygous dominant (YY) or heterozygous (Yy), you could do a test
cross with plants of genotype _______.
A. y
B. Y
C. yy <- Answer
D. YY
E. Yy
20. What are the possible blood types of the offspring of a cross between individuals that are type AB and type O? (Hint: blood type O is recessive)
A. AB or O
B. A, B, or O
C. A o r B <- Answer
D. A, B, AB , or O
E. A, B, or AB