Genetics Worksheet Answers

Briefly define Mendel's law of segregation and law of independent assortment.

Mendel's law of segregation states that an organism contains two discrete genes for each trait and these genes segregate (separate) during gamete formation so that each gamete contains only one gene. Mendel's law of independent assortment states that members of each pair of genes segregate independently of all other pairs if the genes are on different chromosomes.

T = taster
Father = Tt

t = non-taster
Mother = tt

Tt	tt
Tt	tt

50% Tt = tasters

50% tt = non-tasters

I^A

I^B

I^A

I^B

I^A

I^AI^A	i
I^Ai	ii

Yes, possible

I^A

I^AI^A	I^AI^B
I^Ai	I^Bi

I^A

I^AI^A	I^AI^B
I^AI^A	I^AI^B

Not Possible

I^A

I^B

I^BI^B	I^BI^B
I^BI^B	I^BI^B

Not Possible

I^A

I^AI^B	I^Ai
I^BI^B	I^Bi

Yes, possible

I^B

ii	ii
ii	ii

Not Possible

Test Cross

R = red

r = black

Rr	Rr
Rr	Rr

Rr	rr
Rr	rr

T = tall t = short

F₁

F₂

Tt	Tt
Tt	Tt

TT	Tt
Tt	tt

Phenotypic ratio: 100% tall plants

3:1 (tall : short)

Genotypic ratio: 100% Tt

1:2:1 (TT : Tt: tt)

R'R' = Red

RR = white

F₁

R'R	R'R
R'R	R'R

100% pink flowers

AaBb	AaBb	AaBb	AaBb
AaBb	AaBb	AaBb	AaBb
AaBb	AaBb	AaBb	AaBb
AaBb	AaBb	AaBb	AaBb

AaBb	AaBb	aaBb	aaBb
AaBb	AaBb	aaBb	aaBb
AaBb	AaBb	aaBb	aaBb
AaBb	AaBb	aaBb	aaBb

Phenotypic ratio: 100% green, tall plants

Phenotypic ratio: 1:1 green, tall: blue, tall plants

Genotypic ratio: 100% AaBb

Genotypic ratio: 1:1 AaBb:aaBb

AABB	AABb	AaBB	AaBb
AABb	AAbb	AaBb	Aabb
AaBB	AaBb	aaBB	aaBb
AaBb	Aabb	aaBb	aabb

AaBb	Aabb	aaBb	aabb
AaBb	Aabb	aaBb	aabb
AaBb	Aabb	aaBb	aabb
AaBb	Aabb	aaBb	aabb

Phenotypic ratio: 9:3:3:1

Phenotypic ratio: 1:1:1:1

Genotypic ratio: 1:2:1:2:4:2:1:2:1

Genotypic ratio: 1:1:1:1

B = brown b = white

parent's genotypes: BB = brown, bb = white

dominance

F₁

Bb	Bb
Bb	Bb

F₂

BB	Bb
Bb	bb

75% brown
25% white

Test Cross

Bb	Bb
Bb	Bb

Bb	bb
Bb	bb

10.

X⁺ = red eyes X = white eyes

X⁺

X⁺X	X⁺X
XY	XY

100% of the females have red eyes

11.

R = red r = purple L = large s = small

Rrll x RrLl

RRLl	RRLl	RrLl	RrLl
RRll	RRll	Rrll	Rrll
RrLl	RrLl	rrLl	rrLl
Rrll	Rrll	rrll	rrll

Phenotypic ratio:

Genotypic ratio:

12.

R = red eyes r = white eyes

F₁

Rr	Rr
Rr	Rr

F₂

RR	Rr
Rr	rr

Genotype ratio: 1:2:1

Phenotype ratio: 3:1

13.

Incomplete dominance C^BC^B = blue C^WC^W = white

F₁

C^B

C^W

C^BC^W	C^BC^W
C^BC^W	C^BC^W

C^W

F₂

C^B

C^W

C^B

C^BC^B	C^BC^W
C^BC^W	C^WC^W

C^W

100% pale blue

Genotype ratio: 1:2:1

Phenotype ratio: 1:2:1

14.

X^C = color blind X = normal

X^C

X^CX^C	X^CX^C
X^CY	X^CY

X^C

XX	XX^C
XY	X^CY

Yes

X^C

XX	XX^C
XY	X^CY

15.

Woman's father is Cc
father's parents:

Cc	Cc
Cc	Cc

Cc	cc
Cc	cc

the only genotype coding for Cyclops is Cc in both scenarios

16.

woman = AB I^AI^B

child = A I^AI^A or I^Ai

I^A

I^B

I^A

I^AI^A	I^AI^B
I^AI^A	I^AI^B

I^A

I^B

I^AI^B	I^BI^B
I^Ai	I^Bi

possible

I^A

I^B

I^Ai	I^Bi
I^Ai	I^Bi

I^A

I^B

I^A

I^AI^A	I^AI^B
I^AI^A	I^AI^B

I^A

possible

17.

~~Aas~~ ArS Ars ~~arS~~ ~~aRs~~ ~~Arr~~ AS ~~AarrSs~~

18.

BB or Bb b. bb only

B locus is inconsequential

EE or Ee EE or Ee

ee is epistatic

100% BbEe bbee X BBEE

100% black labs

19.

You should first cross a mouse with brown fur with a mouse with white fur. If the alleles
demonstrate incomplete dominance, you will see an intermediate phenotype such as tan
fur color. If this does not occur, you may rule out incomplete dominance.

To determine if fur color is an example of complete dominance, cross the white fur colored
mouse with the brown fur colored mouse. You should be able to draw some conclusions
from this cross.

Example 1

If white is dominant

W = white w = brown

Ww	Ww
Ww	Ww

Ww	ww
Ww	ww

100% white mice

50% brown 50% white

Example 2
If brown is dominant
B = brown b = white

Bb	Bb
Bb	Bb

Bb	bb
Bb	bb

100% brown

50% brown 50% white

If you get the second result (50%/50%), then perform another cross to
determine which allele is dominant.

20.

Name the nucleotides found in the following nucleic acids:

a)	DNA	b)	RNA

	_adenine__		_adenine__

	_guanine__		_guanine__

	_cytosine__		_cytosine__

	_thymine__		_uracil___

21.

Name the purines and pyrimidines.

The purine nitrogenous bases are adenine (A) and guanine (G).
The pyrimidine bases are cytosine (C), thymine (T), and uracil (U).

22.

List the enzymes involved in replication and their functions.

DNA helicase- unwinds the DNA double helix
DNA topoisomerase- prevents supercoiling of DNA as it unwinds
DNA polymerase- adds nucleotides to an elongating DNA strand in a 5' ? 3' direction; also proofreads and performs mismatch repair
DNA primase- creates a primer sequence to initiate DNA replication
DNA ligase- ligates (joins) discontinuous strands of DNA created by the lagging strand

23.

Given the following nucleotide sequence of this template DNA strand, transcribe and translate the sequence into a protein.

mRNA

Protein Sequence

__methionine___ _leucine___ __arginine____ __alanine___ _glutamine__ __aspartate__ __stop___

24.

Name the 3 types of RNA, giving the function of each.

mRNA

carries information specifying the sequence of amino acids of a protein from DNA to the ribosomes
DNA's genetic code is transcribed into mRNA codons

tRNA

translates mRNA codons into amino acids
transfers amino acids in the cytoplasm to the ribosome

rRNA

comprises the majority of ribosomes' structure

25.

Where do the following take place or exist in the cell?

a) transcription- nucleus
b) translation- cytoplasm, on ribosomes
c) DNA replication- nucleus
d) tRNA synthesis- nucleus