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Chapter 86: Linked Genes
The genes are called linked genes.
Thousands of genes are linked because there are many more genes than chromosomes.
Every cell has 46 chromosomes.
Humans have 46 linkage groups.
Unless they are separated by a crossover event during meiosis and gamete formation, linked genes tend to be inherited together.
Sex-linked traits can be found on the X chromosomes.
Sex chromosomes X and Y are found on 44 of the 46 human chromosomes.
There are few genes on the Y.
There are two copies of the sex-linked genes in females.
A female will only express her sex-linked trait if she carries two different genes.
She will be a carrier if she only carries one X-linked gene.
If a sex-linked trait is due to a dominant mutation, a female will only express the phenotype with a single variant of the X-X gene.
Males only have one X-linked gene.
The male will express the X-Y gene if he inherit it.
Sex-linked conditions are more common in males than in females.
Sex-linked traits are not the only ones where expression depends on the sex of the individual.
Human males can't produce milk because of their mammary glands.
There are some important facts about sex.
Some examples of sex-linked diseases are color blindness, and Duchenne muscular dystrophy.
The daughters of affected fathers are carriers.
The son cannot inherit a sex-linked trait from his father.
A boy has a 50 percent chance of inheriting a sex-linked trait from his mother.
There is no carrier state for X-linked traits in males.
The male will express the genes if he has them.
It is rare for a female to have a sex-linked condition.
She needs to inherit a gene from both of her parents in order to be affected.
The farther apart the two genes are, the more likely they will be separated during meiosis.
A physical bridge built around the point of exchange can be seen at the site of a crossover and recombination.
A cross-over is a recombination.
Heterogeneity is a major source of variation in sexually reproducing organisms.
A function of the distance between genes is the probability that genes on the same chromosomes will separate.
The resulting four gametes would contain the following genes.
There are two different types of gametes.
Four gametes contain the following genes: Ab, aB, and Ab.
There are different types of gametes.
Recombination occurs 1 percent of the time if the map unit distance on a chromosomes is one.
The order of the linked genes on the chromosomes is shown by the rate of crossover.
This is an example.
Three genes are linked.
The frequencies for B and D are 5 percent, for B and A are 30 percent, and for D and A is 25 percent.
The data can be used to create a linkage map.
The results of the experiment do not match the predictions.
The genes for wing size and body color are on the same chromosomes.
The existence of small numbers of nonparental phenotypes can only be explained by occasional breaks in the linkage.
It's important to remember that crossing-over accounts for the recombination of genes.
This is how to determine the recombination Frequency.
You can use the results from the cross.
The Gg and Nn genes are linked.
A family tree is a representation of a trait being studied for every member of the family.
Genetics use the pedigree to determine how a trait is passed down.
Females are represented by a circle and males by a square.
Sometimes the carrier state is not shown.
Sometimes it is represented by a half-shaded-in shape.
A shape is shaded if a person has that trait.
Determine the pattern of inheritance.
Eliminate all possibilities first.
In order for a child to have dominance, she or he would have had to receive a single mutant gene from one afflicted parent, and that's not the case.
In order for F 3 generation daughter #1 to have the condition, she would have had to inherit two genes from each parent.
Her father does not have the condition.
The trait must be related to the person.
One of the X chromosomes in the embryo of a female mammal is inactivated.
This happens randomly.
Some cells have one X inactivated, some cells have the other X inactivated in an embryo that is a genetic mosaic.
The cells of female mammals are not the same.
The nucleus of the female's cells can be seen at the outer edge of a dark spot on the inactivated chromosomes.
The Barr body is a dark spot.
Female body cells have one Barr body.
Normal male cells do not have any.
In the genetics of the female calico cat, the alleles for black and yellow fur are carried on the X chromosomes.
Male cats can be either yellow or black with only one X chromosomes.
There are patches of both yellow and black on the coats of cats.
The fur was developed from cells with different X chromosomes.
Some fur- producing cells have the X B active chromosomes.
Yellow fur can be produced by cells with the X Y active chromosome.
A cat with yellow and black fur is characteristic of the breed.
In humans, there is an example of X chromosome inactivation.
The development of sweat glands is prevented by a certain X-linked genetic variation.
A woman with this trait is more than just a carrier.
She has patches of normal skin and patches of skin that don't have sweat glands.
There are any changes to the genome.
They can occur in the body's cells and be responsible for the development of cancer, or they can occur during gametogenesis and affect future offspring.
Radiation and certain chemicals cause changes in the environment, but it's not random.
There are two types of genes.
There is a change in the DNA sequence.
Some human genetic disorders are caused by genes.
In the next chapter, the nature of genes at the DNA level is discussed.
Human genetic diseases can be caused by a single gene or a chromosomal abnormality.
Under a microscope, genes can't be seen.
A karyotype is a technique that shows the size, number, and shape of the chromosomes.
Karyotypes can be used to look for chromosomal abnormality.
Alterations in the number of chromosomes can result in human limitations.
There are three conditions that result from nondisjunction in the formation of the ovum or the sperm.
Sometimes during meiosis, the chromosomes fail to separate as they should, and this is called nondisjunction.
One gamete gets two of the same type of chromosomes and the other doesn't.
The rest of the chromosomes may be normal.
The result of fertilization will have an abnormal number of chromosomes if either gamete is abnormal.
Aneuploidy is an abnormal number of chromosomes.
The condition is known as trisomy if a chromosomes is present in triplicate.
There are people with Down syndrome.
The condition is called trisomy 21.
Extra chromosomes are almost always present in cancer cells grown in culture.
The triploid is an organisms in which the cells have an extra set of chromosomes.
The 4 n chromosomes number is known as the tetraploid number.
There are strawberries.
Polyploid is an organisms with extra sets of chromosomes.
Plants that were polyploidy were studied by Hugo de Vries.
Plants that are large in size are caused by polyploidy.
It can be responsible for the evolution of new species.
Today, the word is used to refer to any genetic or chromosomal abnormality.
The discussion was furthered in this chapter.
Punnett squares and the rules of probability can be used to determine how specific traits are passed down.
It is possible to analyze and interpret information about the inheritance of a particular trait.
Laws of Dominance, Segregation, and Independent Assortment can be accounted for by single genes.
Segregation and independent assortment of genes only apply to genes on different chromosomes and result in genetic variation in offspring.
It is not possible to predict the inheritance pattern of many traits.
Some examples include incomplete dominance, codominance, multiple alleles, and genes in mitochondria, which are inherited from the mother.
Polygenic inheritance is a trait that spans a range of characteristics along a continuum like height, hair color, and skin color in humans.
There are random changes in the genome.
Human diseases caused by genes include PKU, cystic fibrosis, Tay-Sachs disease, Huntington's disease, and sickle cell disease.
Errors during meiosis and gamete formation are to blame.
Down syndrome, Turner syndrome, and Klinefelter syndrome are examples.
The number and placement of chromosomes are not the only factors that determine a karyotype.
A backcross or testcross is an actual mating carried out between an animal of unknown genetics that shows the dominant trait and one that shows the recessive trait.
The purpose is to determine the dominant trait of the animal.
If they are close together, linked genes are often passed on.
If two genes are far apart, there is a chance that they will separate during meiosis.
The increase in genetic diversity is necessary for evolution.
Data of recombination frequencies can be used to create linkage maps.
Sex-linked genes are located on the X chromosomes.
Duchenne muscular dystrophy is one of the examples.
Females can carry things.
They need two X chromosomes to express the condition.
The condition is expressed by males if they inherit only one X-Y.
A father can't pass an X-linked condition to his sons because they have their Y chromosomes from him.
His daughters will inherit his X chromosomes and be carriers.
Men who express an X-linked condition inherit it from their mothers.
One of the X chromosomes is usually inactivated during the development of the female.
In males and females, the X chromosomes are equal in dosage.
The Barr body is a dark spot on the X chromosomes.
The environment affects the expression of genes.
IQ in humans has a genetic component that is enhanced or diminished by stimulation, or lack of it, from the environment.
Two genes are on different chromosomes.
The probability of A segregating into a gamete is 12 while the probability of B segregating into a gamete is 14.
A round watermelon is crossed with a long watermelon and all the offspring are oval.
The trait for tall is dominant and the trait for short is not.
The yellow and green seeds have the same trait.
A child has blood type O.
A person crossed two flowers.
The tall flower had a smooth seed coat, while the short flower had a wrinkled seed coat.
There was a distribution of traits in the offspring.
Two genes control the eye color of a mammal.
A dominant allele of the genes controls the color of the pigments in the eye and results in pink eyes and yellow eye color.
A sex-linked gene controls the expression of the colored pigments and also has two alleles, one of which does not allow for the expression of the colored pigments.
White eyes are not a problem for people with no C allele, even if they have other eye-color genes.
An illustration of a human female's karotype.
A couple has 6 children.
Two genes, A and B, are not related.
The genes for short and long hair are different in guinea pigs.
The genes for black hair color and white hair color are related.
A cross between two guinea pigs produces a litter of black and white pigs.
In one strain of mice, fur color varies from white to dark brown with every shade of brown in between.
The genes that cause Huntington's disease are related.
Consider a couple where the wife and mother have the same disease.
The husband doesn't.
The children are considering taking a blood test to see if they have the genes for Huntington's disease.
Many people have decided not to take the test.
A and B are linked, but they are not usually passed down.
A cross was made between two fruit flies.
One hundred F 1 offspring were produced.
All the males and females were wild.
The F 2 flies were observed when these F 1 flies were allowed to mate.
There is a family that carries the genes for Huntington's disease.
The shaded individuals are those who express a trait.
A family's blood types are shown in this figure.
There is a male and female black and white guinea pig.
A different male black guinea pig #3 is crossed with the same male black guinea pig #2 in a second mating.
This time, there are 8 black and 6 Albino pigs produced.
Round, oval, and long are the names of the animals.
The inheritance is an example of incomplete dominance.
This is the way to solve the problem.
The traits should be considered separately at first.
The height ratio in the offspring is 3:1.
The parents have to be Tt and Tt.
There is a 3:1 ratio of yellow to green in the offspring.
The parents must be Yy and Yy.
Put the two genotypes together.
The parents have to be TtYy and TtYy.
A person with blood type O must have two genes from each parent.
I A i or I B i could be the parents.
They do not have to be type O.
The parents had to have been hybrid and ttss recessive, regardless of which trait was dominant and which was not.
They are a result of two genes exchanging.
It is necessary for genes to be located far apart on a single chromosomes.
Choice B can't be correct because the traits located close together wouldn't undergo crossover.
Choice C cannot be correct because the ratios of the offspring would have been 9:3:3:1.
Choice D doesn't account for the odd results of the 8 and 9 offspring.
For the sex-linked gene, C, which allows for colored pigments, is dominant and C, which prevents colored pigments regardless of the presence of P or p, is the only one.
The female lacks the sex-linked gene for the deposition of pigment in choice A.
She has white eyes.
The male has a dominant C. He has pink eyes because he has at least one dominant P. What is asked in the question is satisfied by that.
There are 44 autosomes and two sex chromosomes for an adult female.
It is true that the sex of the child is determined by the sex of the sperm, but that is irrelevant to the question here.
To find the probability of two independent events, you have to take the chance of one and the chance of the other.
The parents could not produce offspring with the same coat color as choice B.
You can eliminate choice C because it will produce offspring in a 9:3:3:1 ratio, which is not a choice.
choice D is the best choice to produce offspring.
The parents could also be the same.
The mother has the disease and the genes are dominant.
HD is caused by H. Since he does not have the condition, the husband's genotype is pure.
The HD genes are not sex-linked.
All the female offspring are carriers and all the male offspring have white eyes.
The second cross is here.
A male has a 50 percent chance of being white-eyed and a 50 percent chance of being red-eyed.
A female has a 50 percent chance of being white-eyed and a 50 percent chance of being red-eyed.
The sex-linked trait is shown in X-.
The father gives the condition to his daughters.
The daughters do not have the condition because they have a normal X to provide the enzymes that are missing from the impaired X-.
The daughters are not carriers.
Huntington's disease is an inheritable disease.
The F 2 daughter who doesn't have the condition must have one of the healthy genes from her parents.
It can be either I A or I A i.
Since his father has type O blood, person 14 must haveherited the A from his mother and the i from his father.
His genetics are I A i.
There are backcrosses or testcrosses between the guinea pigs.
The black people's genetics are revealed through the matings.
It is most likely that black guinea pig #1 is the dominant one.
If it had been a hybrid, there would have been at least one white child.
The fact that there are several white offspring from the second mating indicates that the second black male, #3, is a hybrid.
You cross the organisms that show the same trait.
If white fur is a recessive trait, and an organism has white fur, you know the organism's genotype by looking at it.
There will never be offspring that show the trait in a testcross if the parent is dominant.
50% of the time, the offspring of a hybrid parent will have white fur.
This is a male.
There is an extra chromosome at the 21st position.
This is a test for Down syndrome.
The normal 23 chromosomes were donated by one gamete.
The extra chromosomes were caused by an error called nondisjunction, in which one pair of chromosomes failed to separate.
A normal meiotic division would produce normal gametes, normal offspring, and a normal karyotype.
Choice B is incorrect because the error occurred during meiosis and the formation of gametes.
Choice D is not correct because the question involved an entire chromosomes.
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