Biology Question! :]?

Question

i think its simple enough, but im not quite sure.

If two parents with dominant phenotypes produce an offspring with a recessive phenotype, then
(a) both parents are heterozygous
(b) one parent is heterozygous
(c) both parents are homozygous
(d) one parent is homozygous

im guessing its either A or B, along with answering the question, umm can anyone give me detail on wat they mean by both parents with dominant phenotype? may i have an example?

Answer 1

I believe the answer is A.

Dominant phenotype means like a trait that will mask the recessive trait. Usually, caps is used to show dominant traits while small case letters are used to show recessive.

For example, you cross 2 kinds of pure-bred peas. One with a smooth coat and one with a wrinkled coat. Let's say that the smooth coat allele (trait) dominates over the wrinkled coat allele.
This means:
Smooth coat = SS (pick any letter)
Wrinkled coat = ss

Now, if you make a punnet squre,
____s_____s___
S_I_Ss_I__Ss_I_
S_I_Ss_I__Ss_I_

When you have the same kind of something like SS or ss, it's called being homozygous for that trait. On the other hand, when you have an Ss, it's called being heterozygous for that trait.

Answer 2

I am assuming you have been using those square diagrams. If so, then dominant = capital letter, recessive = lower case letter.
If not, dominant means that if you have one gene for blue eyes and one gene for brown eyes, you will have brown eyes because the brown gene is dominant, and will overpower the blue gene.
In your question, the answer is A. In order for the child to show a recessive trait, it has to have two recessive genes (if there was one dominant, one recessive, the dominant phenotype would show). In order for the child to receive two recessive traits, both parents have to have at least one recessive gene. However, since both the parents have dominant phenotypes and their child has a recessive phenotype, the parents have to be heterozygous (meaning one of each type - dominant and recessive).

Answer 3

Both a) and b) are correct. If both parents are heterozygous, then one parent technically is heterozygous (so is the other one).
But that is not what they mean. The answer is a) - both must be carrying the recessive gene, as well as the dominant. T
he phenotype is the presenting feature; dominant features, such as brown hair, will show if the dominant genotype is present. The recessive trait (phenotype) will only be apparent if the dominant genotype is absent.

Answer 4

Dominant trait refers to a genetic feature that hides the recessive trait in the phenotype of an individual. A dominant trait causes the phenotype that is seen in a heterozygous (Aa) genotype. Many traits are determined by pairs of complementary genes, each inherited from a single parent. Often when these are paired and compared, one allele (the dominant) will be found to effectively shut out the instructions from the other, recessive allele. For example, if a person has one allele for blood type A and one for blood type O, that person will always have blood type A because it is the dominant allele. For a person to have blood type O, both their alleles must be O (recessive). When a person has two dominant alleles, they are referred to as homozygous dominant. If they have one dominant allele and one recessive allele, they are referred to as heterozygous.

A dominant trait when written in a genotype is always written before the recessive gene in a heterozygous pair. A heterozygous genotype is written Aa, not aA.

Answer 5

The answer is A.
Phenotype is the physical appearance of a gene. If you have blond hair it means that you have the gene for the blond hair and your physical appearance indicates that. The fact that you have the gene for blond hair is your genotype and your physical appearance is phenotype. You can think of phenotype as your physical picture and of genotype as the picture of DNA.
For recessive traits such as blond hair to appear in the phenotype of a kid, the kid must have inherit 2 similar alleles of the gene (one from each parent). For dominant traits such as black hair only dominant allele is sufficient. This means that a person with dominant phenotype may have 2 dominant alleles or 1 dominant and 1 recessive alleles. Therefore if both parents have dominant phenotype but their child has a recessive phenotype, both parents must have one recessive gene.
When an individual has one recessive allele and one dominant allele of the same gene it is said that he or she is heterozygous.

Answer 6

The answer is a).

Parents are Aa and Aa

the recessive phenotype will only appear if it is aa.

Do a Punnett Square to prove it.

An example would be having two plants who have the dominant gene for being tall (T) but also carry the recessive gene for being short (t). These plants are both Tt. When they cross polllinate, they will have a 25% chance of producing an offspring who is short tt. The other combinations would have a 0% chanceof producing an offspring who is short (tt)

Answer 7

The answer is B

A dominant phenotype is where there are genes for two different forms but only one is actually happening. Take eyes. If you have a blue eye gene and a brown eye gene then you have a dominant phenotype of brown eyes - your eyes will be brown.

If two people both have one blue eye gene and one brown eye gene, they will both have brown eyes (brown eyes is the dominant phenotype, which means that brown-eye genes over-rule blue-eye genes). But if they have children, they could each pass on a blue eye gene which means that the child will have blue eyes (the recessive phenotype).

Answer 8

it's a.

a domiant phenotype can be expressed even if you are a carrier for the reccessive trait. let's use eye color. if brown in domiant (BB or Bb) and blue is recessive (bb). if you make the punnet square, you will see that it takes two parents of Bb to produce a bb offspring.

** B *** b
B BB Bb

b Bb bb

there is a 1/4 chance for the recessive bb, blue eyed, offspring, and 3/4 chance for the dominant BB/Bb, brown eyed offspring

Answer 9

It must be A. if both are dominant and produce a recessive than both must have the recessive trait or are Aa.

Aa +Aa - AA +2Aa + aa. The offspring has to be the aa.