14.1
A colorblind girl's father must be colorblind.
.
In humans, the inheritance of Rhesus (Rh) factor follows a pattern of simple dominance. This means that a heterozygous person has the same phenotype as a person who has two dominant alleles.
.
How many chromosomes are shown in a normal human karyotype?
46
A man who is not colorblind and a woman who is a carrier of the disorder have a son. What is the probability that their son will be colorblind?
50%
What percentage of human sperm cells carry an X chromosome?
50%
Compare and contrast the information you can learn from looking at a pedigree with the information you can learn from a karyotype.
A karyotype gives information about a person's chromosomes—how many they have and which sex chromosomes they have inherited. A pedigree gives you a person's phenotype for a specific trait, along with the phenotypes of their relatives.
What is a pedigree chart?
A pedigree chart is a drawing that shows the genetic relationships within a family.
If human gametes have just 23 chromosomes, why does a human karyotype show 46?
A sperm that has 23 chromosomes fertilizes an egg that has 23 chromosomes resulting in a 23 pairs of chromosomes (46 total) in the autosomal cells of the individual.
If a man with blood type A and a woman with blood type B produce an offspring, what might be the offspring's blood type?
A, B, AB, or O
Explain why the father of a girl who is colorblind must also be colorblind.
Because the allele for colorblindness is recessive and X-linked, the girl must have inherited the alleles for colorblindness on the X chromosomes from both her mother and father. Since the father has a single X chromosome, it must carry the allele for colorblindness, and he must be colorblind.
1. How might karyotypes be useful to doctors?
Doctors can use karyotypes to determine the sex of an individual. They can also use karyotypes to determine whether an individual has an abnormal number of chromosomes or noticeable chromosomal mutations, such as large deletions, additions, or translocations.
Why are Barr bodies not found in male cells?
Males have just one X chromosome.
Why are all X-linked alleles expressed in males, even if they are recessive?
Males have just one X chromosome.
In humans, there are three different alleles for blood type and two of these alleles are codominant, so there are ____________ possible phenotypes.
four
If a cat has both orange and black spots, it is __________ for the alleles on the X chromosome that code for spot color.
heterozygous
what term is used to describe the pair of chromosomes in each
homologous chromosomes.
If the allele for having a white forelock is dominant, family members WITHOUT a white forelock are
homozygous recessive.
A cat that has spots of more than one color
is probably female.
Colorblindness is more common in males than in females because the allele for colorblindness
is recessive and located on the X chromosome.
A boy who is colorblind inherited the disorder from his ____________________.
mother
Human females produce egg cells that have
one X chromosome.
what form(s) a Barr body?
one of the X chromosomes in a female cell
The formation of a Barr body inactivates
one whole X chromosome in a female cell.
A human female inherits
two copies of every gene located on the X chromosome.
how are the chromosomes that make up each numbered pair
The chromosomes in each pair are similar in shape and size. They also contain the same genes, though not necessarily the same alleles of those genes.
The only people with Rh negative blood are people who have inherited two recessive alleles for this trait. But some people who are colorblind have inherited only one recessive allele for this trait. Explain why these traits are different in terms of how many recessive alleles are needed to produce the recessive phenotype.
The inheritance of Rh blood groups follows a pattern of simple dominance, but the colorblindness is sex- linked. Men who are colorblind receive only one recessive allele, but have no corresponding dominant allele, so they have the recessive phenotype.
What type of abnormality is this, and how might it have occurred?
The karyotype shows a chromosomal abnormality. Position 23 has 3 chromosomes instead of the usual two. This abnormality was caused by nondisjunction of sex chromosomes during meiosis while a sperm or egg cell was developing in a parent.
What can you conclude if you observe a male cat that has both black and orange spots? Explain your answer.
The male cat inherited an extra X chromosome. One of the X chromosomes carries the allele for black spots, while the other carries the allele for orange spots. The two X chromosomes are randomly inactivated in the cat's cells, producing the orange and black spots.
Why are the sex chromosomes considered homologous, even though they vary in size and appearance?
The sex chromosomes are homologous because one sex chromosome is inherited from one parent, and the other is inherited from the other parent.
Study the human karyotype in Figure 14-11. Explain whether the person will be male or female, and describe the abnormality that this person has.
This person will be male, due to the presence of a Y chromosome. This person has Klinefelter's syndrome and is likely to be infertile.
A Barr body is an inactivated ____________________ chromosome.
X
