Download Which best describes an allele? (A) a physical trait

Heredity Test 1-5 Notes
*Lots of questions on blood type. MULTIPLE answers for multiple choice.
Which best describes an allele?
(A) a physical trait
(B) a section of a gene
(C) a variation of a given gene
(D) all of the above
Solution
From Biology B.1.1.2: Alleles
(C) is the correct answer. An allele is a variation on a gene, which codes for a
specific physical trait. It is not the physical trait itself (A). For example, the gene
codes for eye color, and the allele specifies blue or green eyes. (B) may have
been tempting, but it is too general to say it is a section.
In a BB x bb cross, how many of the offspring are predicted to have a
homozygous genotype,
out of 20 offspring? Write your answer as a whole number.
0
Solution
From Biology B.1.2.6: Monohybrid Cross Practice
0. None of the offspring are homozygous. They are all heterozygous.
The law of segregation states that during meiosis,
(A) a diploid cell divides into four haploid gametes
(B) homologous chromosomes will separate
(C) two alleles coding for the same trait will separate
(D) all of the above
From Biology B.1.2.4: Law of Segregation
(C) is the correct answer. Two alleles coding for the same trait will separate
during gamete formation (or meiosis). (A) and (B) accurately describe processes
that occur during meiosis, but the law of segregation is specifically about allele
separation.
If there is a 75% chance event A will happen, and a 30% chance event B will
happen, what is the probability that both event A and B will happen? Write your
answer as a percentage. Round to the nearest tenth.
Solution
From Biology B.1.1.1: Probability
Use the multiplication rule!
We know P(event A) = 75% and P(event B) = 30%
That means, P(event A+B) = 75% x 30% = 0.75 x 0.30 = 0.225 = 22.5%
So there is a 22.5% chance that both event A and B will occur.
A basketball player has a free throw shooting average of 60%. What’s the
probability that he makes three baskets in a row? Write your answer as a
percentage. Round to the nearest tenth.
We know that P(making one basket) = 60%
That means, P(making three baskets in a row) = 60% x 60% x 60% =
0.60 x 0.60 x 0.60 = 0.216 = 21.6%
You could also write (0.60)^3 = 0.216 = 21.6%
There is a 21.6% chance that the basketball player will make three baskets in a
row.
The law of independent assortment states that
(A) genes for different traits are inherited separately
(B) alleles for the same trait are inherited separately
(C) homologous chromosomes are inherited separately
(D) traits of the same organism are inherited separately
Solution
From Biology B.1.2.7: Law of Independent Assortment
(A) is the correct answer. The law of independent assortment states that genes
for one trait are not inherited together with the genes for another trait. (B)
basically describes the law of segregation, which states that alleles for the same
trait are separated into different gametes. Homologous chromosomes are
separated into different gametes during meiosis, a slight variation on (C). (D) is
just wrong.
You find a stray dog with black fur. You want to perform a cross to determine
whether he has homozygous dominant or heterozygous fur. What is the best way
to do so?
(A) cross him with another heterozygous dog
(B) cross him with a homozygous dominant dog
(C) cross him with a homozygous recessive dog
Solution
From Biology B.1.3.1: Backcross or Test Cross
(C) is the correct answer. If the dog has heterozygous black fur, crossing him
with a homozygous recessive dog will give you a 50% chance for homozygous
recessive offspring. This is better than (A) crossing him with another
heterozygous dog in a monohybrid cross, because there’s only have a 25% of
producing homozygous offspring. That means if the offspring all have black fur,
you can say the dog is homozygous dominant with more certainty in a cross with
a homozygous recessive dog. A cross with a homozygous dominant dog is
pointless (B). All the offspring will have black fur by the law of dominance.