AP Biology Discussion Notes

Monday 3/30/2015

Goals for the day

• Be able to define and perform dihybrid crosses and use multiple strategies to predict the outcomes

• Be able to predict the outcomes of crosses with intermediate inheritance.

• Be able to predict the probability of an event (getting particular offspring or getting a particular gamete)

Question of the day 3/30• If I did the following cross:

•RrYytt x RRYyTt

What is the probability of having an offspring who is Round, green, and short?

• R- Round• r – wrinkled• Y – Yellow• y – green• T – Tall• t -short

Genetics Problem Set #2

1. In guinea pigs, black coat color (B) is dominant to white (b) and rough hair (R) is dominant to smooth hair (r). A homozygous black, smooth guinea pig is crossed with a white, homozygous rough guinea pig. Their offspring are crossed to give an F2 generation. For the F2 generation, give the expected ratios for the resulting phenotypes.

• Parents:

• Gametes:

• F1 Generation:

• F2 Generation:

2. In garden peas, tall (T) is dominant to dwarf (t), and round seeds (R) are dominant to wrinkled (r). What would be the genotype(s) and phenotype(s) of the F1 and F2 generations if a homozygous tall, homozygous round seeded plant was crossed with a dwarf, wrinkled seeded plant?

• Parents:

• Gametes:

• F1 Generation:

• F2 Generation:

2. In garden peas, tall (T) is dominant to dwarf (t), and round seeds (R) are dominant to wrinkled (r). What would be the genotype(s) and phenotype(s) of the F1 and F2 generations if a homozygous tall, homozygous round seeded plant was crossed with a dwarf, wrinkled seeded plant?

• Parents:

• Gametes:

• F1 Generation:

• F2 Generation:

Dihybrid Cross – F.O.I.L

F1 generation: RrYy

F – first

O – Outside

I – Inside

L - Last

 Possible Gametes from RrYy:

______ , ______ , ______ , _______

RrYy 

Dihybrid Cross – F.O.I.L

F1 generation: RrTt

F – first

O – Outside

I – Inside

L - Last

 Possible Gametes from RrTt:

______ , ______ , ______ , _______

RrTt 

 RY Ry rY ry

RY RRYY  RRYy  RrYY  RrYy

Ry RRYy  RRyy  RrYy  Rryy

rY RrYY  RrYy  rrYY  rrYy

ry RrYy  Rryy  rrYy  rryy

R=Round r =wrinkledY= Yellow y= green RrYy

 

 RT Rt rT rt

RT RRTT  RRTt  RrTT  RrTt

Rt RRTt  RRtt  RrTt  Rrtt

rT RrTT  RrTt  rrTT  rrTt

rt RrTt  Rrtt  rrTt  rrtt

R=Round r =wrinkledT= Tall t= short/dwarf RrTt

 

Phenotype (Phenotypic Ratio)

Round & Tall: ___/16

 

Round & dwarf: ___/16

 

Wrinkled & Tall: ___/16

 

Wrinkled & Dwarf: ___/16

 

Genotype (Genotypic Ratio)

RRTT: ___/16

RRTt: ___/16

RrTT: ___/16

RrTt: ___/16

RRtt: ___/16

Rrtt: ___/16

rrTT: ___/16

rrTt: ___/16

rrtt: _ __/16

 

1

2

2

4

1

2

1

2

1

 

9

3

3

1

 

3. A red-flowered pea, when crossed with a white-flowered pea produced all red-flowered plants. When the F1 plants were crossed among themselves, they produced 32 red and 11 white plants. What is the genotype of all parents and offspring?

Legend

 

 

 

Parents Cross it Genotypic Ratio

Phenotypic Ratio

R = Red

r = white

RR

rr

R R

r

r

RrRr

RrRr

RR:Rr:rr 0 : 4 : 0

Red: 4 White:0

3. A red-flowered pea, when crossed with a white-flowered pea produced all red-flowered plants. When the F1 plants were crossed among themselves, they produced 32 red and 11 white plants. What is the genotype of all parents and offspring?

Legend

 

 

 

Parents Cross it Genotypic Ratio

Phenotypic Ratio

R = Red

r = white

Rr

Rr

R r

R

r

RRRr

Rrrr

RR:Rr:rr 1 : 2 : 1

Red: 3 White:1

4. How could you tell which of the red flowered plants of the F2 generation of problem 3 were homozygous and which were heterozygous?

• What would you want to breed your unknown flower with to find out whether yours was homozygous or heterozygous?

• Test Cross – breed an individual with unknown genotype, but dominant phenotype with an individual who is homozygous recessive to “test” whether the unknown individual is homozygous dominant or heterozygous.

Legend

 

 

 

Possible Cross 1

Possible Cross2

Cross it

Cross it

Genotypic Ratio 1

Genotypic Ratio 2

Phenotypic Ratio 1

Phenotypic Ratio 2

R = Red

r = white

Rr X rr

RR X rr

R

R R

Rr Rr

Rr Rr

Rr

Rr

rr

rr

r

r

r

r

r

RR:Rr:rr 0 : 2 : 2

Red: 2 White:2

RR:Rr:rr 0 : 4 : 0

Red: 4 White:0

5. Suppose you have only one heterozygous red-flowered pea plant, and no other pea plants whatsoever. You want to sell seed that will only grow into plants that produce white flowers. Explain the process you would go through to produce this seed.

Legend

 

 

 

Parents Cross it Genotypic Ratio

Phenotypic Ratio

R = Red

r = white

Rr

Rr

R r

R

r

RRRr

Rrrr

RR:Rr:rr 1 : 2 : 1

Red: 3 White:1

5. Suppose you have only one heterozygous red-flowered pea plant, and no other pea plants whatsoever. You want to sell seed that will only grow into plants that produce white flowers. Explain the process you would go through to produce this seed.

Legend

 

 

 

Parents Cross it Genotypic Ratio

Phenotypic Ratio

R = Red

r = white

rr

rr

r r

r

r

rr rr

rrrr

RR:Rr:rr 0 : 0 : 4

Red: 0 White:4

6. In cattle, we find in a cross between a red bull (RR) and a white cow (rr) that all offspring of the F1 generation are an intermediate color called “roan”. What will be the genotype of the offspring? What do we learn of the inheritance of color in cattle from this mating?

7. If the offspring (roan) from problem 6 was crossed with an individual of similar color, what would be the expected resulting phenotypic ratio in the F2 generation.

• Note: this is one option of how to write these

Legend

 

 

 

Parents Cross it Genotypic Ratio

Phenotypic Ratio

CRCR = Red

CWCW = white

CRCW = roan

CRCW

XCRCW

CR CW

CR

CW

CRCR

CRCW

CRCW

CWCW

Red:White:Roan

8. In problem 6, what would the resulting offspring in the F1 and F2 generations look like if the bull also had the dominant genes for short horns (SS) and the cow was homozygous recessive for long horns (ss). There are never any cattle with “medium” length horns.

• Parents:

• Gametes:

• F1 Generation:

• F2 Generation:

8. In problem 6, what would the resulting offspring in the F1 and F2 generations look like if the bull also had the dominant genes for short horns (SS) and the cow was homozygous recessive for long horns (ss). There are never any cattle with “medium” length horns.

• Parents:

• Gametes:

• F1 Generation:

• F2 Generation:

 CRS CRs CWS CWs

CRS CRCRSS  CRCRSs  CRCWSS  CRCWSs

CRs CRCRSs  CRCRss  CRCWSs  CRCWss

CWS CRCWSS CRCWSs CWCWSS  CWCWSs

CWs CRCWSs  CRCWss  CWCWSs  CWCWss

CRCWSs 

Phenotype (Phenotypic Ratio)

Red & short: ___/16

Red & Long: ___/16

Roan & Short : ___/16

Roan & Long: ___/16

White & Short : ___/16

White & Long: ___/16

3

1

6

2

3

1

9

3

3

1

9. In the honeybee, unfertilized eggs may develop into offspring via the process of “parthenogenesis”. (Remember those crazy all female lizards we talked about? It’s kind of like that.) When this happens, all offspring are males—also called “drones”. The fertilized eggs produce females—workers or queens. In spermatogenesis in bees, there is no reduction division. If the females contain 32 chromosomes in their body cells and if oogenesis is the same as in other species (like humans), how many chromosomes would you expect to find in the body cells of the males? • Male BODY cells -

10. A queen bee that is heterozygous for a dominant trait mates with a drone that shows the same trait. What forms of that trait would you expect to see in the male and female offspring?

• Queen (Heterozygous) X Drone male (Dominant ONLY)

• Female offspring = • Male offspring = • 50% Dominant

• 50% Recessive

• 100% Dominant trait

11. What fraction of the offspring of parents, both with the genotype KkLlMm, will be kkllmm?

12. What fraction of the offspring of parents of the cross KKLlMm x KKLLMm will be KKLlmm?

13. In a plant that is heterozygous for two pairs of genes (AaBb), state the probability that a pollen grain it produces will carry: a. an A allele

b. an a allele and a b allele

c. and a allele and a B allele

d. a B allele or a b allele

14. If the plant in #13 (AaBb) self-pollinates, figure the probability that a seed will contain: a. two a alleles

b. an A allele and an a allele

c. two a alleles and two b alleles

d. all four alleles (AaBb)

15. Show your work (AS ALWAYS) and explain the questions below. If a couple has three daughters, and no sons…..

A. What is the probability that their 4th child will be another daughter? B. What is the probability of having 4 daughters in a row?

16. What questions do I still have and what do I still need more practice with?

Upcoming events…

• Species of the day DUE TOMORROW

• March birds/geese sheet due Wednesday we get back from break (April 8th)