Mendelian Genetics Questions- Please Help!?

Question

I am taking a take home quiz for biology, and the teacher said we could use any resources. I can't find the answers online, so please help!!!

1. A gene located only on the female (X) chromosome having no allelic partner on the Y chromosome would be:
a. incompletely dominant
b. codominant
c. sex-linked
d. heterozygous

2. An organism that is heterozygous for a trait is
a. haploid
b. homozygous
c. diploid
d. all of the above

3. An example of a trait controlled by multiple alleles is
a. baldness in males
b. color blindness
c.the ABO blood groups
d. blue Andalusian chickens

4. A nucleus containing only one of the two homologues is
a. sex-linked
b. an improbable event
c. diploid
d. haploid

thank you so much for your help!!! My teacher is a really funny guy, you can tell he is really passionate about biology, but i just dont think he gets the concept of teaching! People in my class complain abou not learning anything all year, so your help is really appreciated!

Answer 1

1. The phenotypic expression / inheritance of a gene present on X but not on Y would follow a sex-linked pattern (not an incompletely dominant or co-dominant pattern; the question doesn't even specify whether there is a dominant allele or not)
2. to be heterozygous you need two *different* forms (alleles) of a gene. therefore two copies of the gene are present, therefore two homologous chromosomes with the gene are present, therefore two sets of chromosomes are present (that's the meaning of diploid = having 2 sets)
3. A,B, and O are three alleles of one gene (multiple means more than 2). You'll need to remember this example and understand how blood type is inherited for your exams, I bet. When they say "multiple alleles" think blood groups.
4. one homologue just means one chromosome of its kind. If only one of a pair is present, only one set of chromosomes is present; that's the meaning of haploid.

It should help you to remember ~ homologous refers to whole chromosomes only. Homozygosity refers to diploid genotypes.

Homology is the relationship between the set of 23 c'somes you got from Mom, and the 23 you got from Dad. C1(Mom) is the homolog of C1 (Dad). C17(Mom) is the homolog of C17(Dad).

Homologous chromosomes have the same genes on them. They may have different alleles (forms) of those genes. Haploid means having only Mom's set [c'somes 1-22+X from the egg], or only Dad's set [1-22+X or Y from the sperm] ... sperm and eggs are haploid. A diploid cell (all animal cells except sperm and eggs) has both sets.

Homozygous refers to a gene. Homozygous for a gene = diploid cell where both homologs have the same allele of that gene. Heterozygous means the gene allele on the homolog from Mom is different from the one from Dad (have to be diploid for that to make sense).

Answer 2

I appreciate your honesty about doing a take home quiz, but I hope no one just outright gives you the answers. However, here are a few explanations that might help.

Homologous chromosomes are the pairs of chromosomes that have genes for the same trait. Each person has one of the pair from Mom and the other chromosome of the pair from Dad.

Haploid cells have one of every kind of chromosome.
Diploid cells have two of every kind of chromosome.

Incomplete dominance causes a heterozygous individual to have an intermediate, or "in-between", form of the trait.
Codominance causes a heterozygous individual to exhibit both forms of a trait at once.
Multiple alleles means that there are more than two possible alleles for a trait, even though the individual still only gets two alleles.

Sex-linked traits have their genes on the sex chromosomes.

Homozygous means that the alleles match: RR or rr.
Heterozygous means that the alleles don't match: Rr.