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Chapter 85 -- Part 1: Genes and the Environment
The environment can change the expression of genes.
The temperature of the environment can affect the expression of the vestigial wings in fruit flies.
When raised in a hot environment, fruit flies can grow wings almost as long as normal wild-type wings.
Many human diseases are multifactorial.
There is an underlying genetic component.
Some examples are heart disease, diabetes, cancer, alcoholism, and schizophrenia.
Intelligence is the result of an interaction of genetic predisposition and the environment.
The expression of the geno in an organisms is influenced by environmental factors.
Penetrance is the proportion or percentage of individuals in a group with the same genetics.
Many people who inherit a genetic variation of the breast cancer risk factor develop the disease in their lifetimes.
Some people with the allele don't get breast cancer.
Maybe this is caused by a factor from the environment.
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.
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