The mature egg has 23 chromosomes, but the sperm and egg nuclei have 46.
The diploid number of chromosomes is restored by fertilization.
The production of haploid gametes and fusion of those gametes into a diploid zygote completes a human life cycle.
Take the number of gametes produced during oogenesis and spermatogenesis.
The normal separation of chromosomes during meiosis is dependent on crossing-over.
The maintenance of normal chromosomes in living organisms is dependent on the proper separation of chromosomes during meiosis I and II.
Extra or missing parts of chromosomes can be caused by errors in crossing-over.
Euploidy is the correct number of chromosomes in a species.
Plants and animals have aneuploidy.
There are two aneuploid states.
The result of nondisjunction is monosomy and trisomy.
fertilization with normal sperm and nondisjunction of chromosomes duringoogenesis During meiosis I, abnormal eggs that have one more or one less than the normal number of chromosomes can occur.
If the sister chromatids separate, the resulting daughter chromosomes go into the same daughter cell.
The egg will have more or less chromosomes than usual.
The abnormal eggs are fertilized with normal sperm and the abnormal chromosomes are removed.
There are two normal gametes and two aneuploid gametes when there is a secondary nondisjunction.
Normal gametes are not produced when primary nondisjunction occurs.
The effects of primary nondisjunction tend to be more harmful than those of secondary nondisjunction.
Trisomic individuals are more likely to survive than monosomic ones in animals.
There are trisomy 13, 18, and 21 that are viable beyond birth.
Sex chromosomes aneuploids have a better chance of producing survivors than sex chromosomes.
The most common trisomy is Down syndrome.
Short stature; an eyelid fold; a flat face; stubby fingers; a wide gap between the first and second toes; a large, fissured tongue; a round head; and some degree of intellectual disability are some of the characteristics of this syndrome.
Individuals with Down syndrome have a shortened life expectancy due to their increased risk of leukemia.
These individuals have a higher chance of developing Alzheimer's disease later in life.
The chance of a woman having a child with Down syndrome increases with age.
In women ages 20 to 30 the incidence of trisomy 21 is about 1 in 1,400 births, while in women 30 to 35 it is about 1 in 750 births.
It is thought that the longer the oocytes are in the female, the greater the chance of nondisjunction.
Even though an older woman is more likely to have a Down syndrome child, most babies with Down syndrome are born to women younger than 40.
In 23% of the cases studied, the sperm contributed the extra chromosomes.
A karyotype, a visual display of the chromosomes arranged by size, shape, and banding pattern, can be used to identify babies with Down syndrome and other aneuploid conditions.
There is an extra chromosome 21 in people with Down syndrome.
The individual has three copies instead of two.
Several genes that may account for various conditions seen in people with Down syndrome have been discovered.
They have found the genes most likely to cause leukemia, cataracts, and an accelerated rate of aging.
A sex chromosomes number is caused by too many or too few X or Y chromosomes.
Gametes with an abnormal number of sex chromosomes can be a result of nondisjunction during oogenesis or spermatogenesis.
Extra copies of the sex chromosomes are more easy to tolerate in humans than extra copies of autosomes.
A person with Turner syndrome is a female, and a person with Klinefelter syndrome is a male.
A hormone called testis-determining factor is important for the development of male genitals in individuals with Swyer syndrome.
A person becomes a female in its absence.
Because females have two X chromosomes and males have only one, we might expect females to produce more genes than males, but both males and females produce the same amount.
Both males and females only have one functioning X chromosomes.
Females and males with extra X chromosomes have an inactive mass named after Murray Barr, the person who discovered it.
Extra sex chromosomes are easier to tolerate than extra autosomes because of the natural method for gene dosage compensation of the sex chromosomes.
An X and O are the sex chromosomes of an individual with Turner syndrome.
The nucleus does not have a Barr body.
It is estimated to be 1 in 10,000 females.
Sex chromosomes are better than autosomes.
There is only one X chromosomes in Turner syndrome.
There are two X and Y chromosomes.
The individuals have a low neck webbing.
The uterus is small and underdeveloped.
Turner females don't go through puberty or menstruate, and their breasts don't develop.
Some have given birth using donor eggs.
If they receive hormone supplements, they can lead normal lives.
A male with Klinefelter syndrome has two or more X chromosomes.
The extra X chromosomes are called Barr bodies.
There is an incidence of 1 in 500 to 1000 males.
Lack of facial hair and underdeveloped testes are common in Klinefelter males.
Some breast development is possible.
Affected individuals have long arms and legs.
Unless they have more than two X chromosomes, they don't have an intellectual disability.
No matter how many X chromosomes there are, an individual with a Y is a male.
testosterone therapy can help increase muscle strength, sex drive, and concentration ability in men with Klinefelter syndrome.
Testosterone treatment doesn't reverse the sterility associated with Klinefelter syndrome due to incomplete testicle development.
A female with more than two X chromosomes and Barr bodies in the nucleus is called a poly-X female.
Females with three X chromosomes have a tendency to be tall and thin.
Most poly-X females do not have an intellectual disability because of their delayed motor and language development.
Many menstruate regularly and are fertile, even though they may have menstrual difficulties.
Children have a normal karyotype.
Poly-X females have an incidence of about 1 in 1,500.
Rarely do females have more than three X chromosomes.
XXXX females are usually taller and have a more severe intellectual disability than XXX females.
There are physical anomalies that may menstruate.
Jacobs syndrome can only be caused by nondisjunction during spermatogenesis.
One in 1,000 live male births have the XYY karyotype.
Affected males are usually taller than average and have speech and reading problems, but they are fertile and may have children.
There is no difference in behavior between XYY and XY males.
There are changes in the chromosomes.
There are some changes in the chromosomes that can be detected.
Various agents in the environment can cause chromosomes to break.
When breaks occur in chromosomes, the two broken ends unite to give the same sequence of genes.
Alterations in the structure of the chromosomes include deletions, duplications, and translocations.
A occurs when an end of a chromosomes breaks or when two simultaneous breaks lead to the loss of an internal segment.
A deletion can cause problems even if only one member of a pair of chromosomes is affected.
The loss of a piece of a chromosomes is called deletion.
The same piece is repeated in the same place.
Inversion occurs when a piece of chromosome breaks loose and rejoins in a different direction.
The exchange of chromosomes is called translocation.
There is a chromosomal segment more than once in the same chromosome.
Depending on the size of the duplicated region, there may or may not be visible abnormality.
A segment of a chromosomes has been turned around 180 degrees.
The reversed sequence of genes can result in duplications or deletions being passed on to their children if they have inversions.
A is the movement of a nonhomologous chromosomes.
If the individual has children, they will receive one normal copy of the chromosomes from the normal parent and one of the abnormal ones.
The individuals who are born with unbalanced translocations often have severe symptoms.
Some Down syndrome cases are caused by an unbalanced Page 181 translocation.
The individual has three copies of the genes that bring about Down syndrome when they are present in triplet copy.
Down syndrome is passed on normally, as is any other genetic trait, in these cases.
Many syndromes are being discovered because of changes in chromosome structure in humans.
Alterations in the chromosomes can be detected by doing a karyotype.
They can be discovered by studying the inheritance pattern of a disorder.
Children with this syndrome have turned-up noses, wide mouths, a small chin, and large ears.
They have good verbal and musical abilities despite their poor academic skills.
The health of the cardiovascular system can be affected by the missing gene that governs the production of the elastin.
Such individuals are friendly but need an ordered life because of the loss of a gene that is normally active in the brain.
Williams syndrome is caused by the loss of an end piece.
The children have the same appearance, health, and behavioral problems.
When the end piece is missing, there is a syndrome called cri du chat.
The individual has a small head, intellectual disability, and facial abnormality.
The infant's cry resembles that of a cat because of abnormal development of the glottis and larynx.
A person who has both of the chromosomes involved in a translocation has the normal amount of genetic material and is healthy.
The person who only has one of the translocated chromosomes has only one copy of certain alleles.
A genetic counselor is starting to suspect that a translocation has occurred when family members suffer from various syndromes.
A technician can use a technique to determine if a translocation has occurred.
Some forms of cancer are linked to certain genes.
Chronic myeloid leukemia is an example.
In the 70s, new staining techniques revealed a portion of chromosomes 22 to 9.
The Philadelphia chromosome is a translocated one.
Individuals with CML have a rapid growth of white blood cells, which prevents the body from forming red blood cells and reduces the effectiveness of the immune system.
The pink cells are dividing quickly.
A variety of disorders can be caused by translocations.
There is a large tumor in the region of the jaw when a cancer is common in children in Africa.
This disorder involves a change from one part of the chromosomes to another.
Alagille syndrome is caused by a translocation between chromosomes 2 and 20.
There is a deletion on chromosome 20.
The eyes and internal organs may be affected by the syndrome.
Some people may not be aware that they have Alagille syndrome.
Sex chromosomes aneuploidy is more common than autosome aneuploidy.
The process ensures that the number of chromosomes in offspring stays constant.
There are two cell divisions and four daughter cells required for meiosis.
Before meiosis begins, the Replication of DNA takes place.
The chromosomes are aligned at the metaphase plate.
The daughter cells have one pair of chromosomes.
During meiosis II, the sister chromatids separate and become daughter chromosomes that move to opposite poles.
The four daughter cells have a haploid number of chromosomes.
The ability of a species to survive is increased by the fact that the offspring have a different genetic makeup than the parents.
The chromatids that separate during meiosis II have different combinations of genes.
The maternal or the paternal chromosomes can be facing either pole when the chromosomes align at the metaphase plate.
There are all possible combinations of chromosomes in the gametes.
Bivalents form and crossing-over occurs as the nuclear envelope fragments as Meiosis I is divided into four phases.
Bivalents are aligned at the metaphase plate.
Heterologous chromosomes move to poles.
Telophase I--nuclei becomes haploid after receiving one duplicated chromosome from each pair.
The nuclear envelope fragments are part of Prophase II.
The haploid number of duplicated chromosomes is aligned at the metaphase plate.
Sister chromatids separate and become daughter chromosomes that move to the poles.
Four haploid daughter cells are different from the parent cell.
Meiosis produces a multicellular haploid adult that produces gametes.
In single-celled protists and fungi, the zygote undergoes meiosis and becomes a haploid adult that gives rise to gametes.
The polar bodies are not active.
During the life cycle of all animals, matosis is involved in growth and repair.
Down syndrome is caused by an extra copy of chromosome 21.
Aneuploidy of the sex chromosomes is easier to tolerate than aneuploidy of the autosomes.
Sex chromosomes aneuploidy are examples of Turner syndrome.
Williams syndrome, cri du chat syndrome, and Alagille syndrome are all syndromes caused by changes in chromosomes.
Pick the best answer for the question.
Each of the daughter cells following meiosis will have a parent cell's 16 chromosomes.
There is a bivalent.
There are chromosomes at the metaphase plate.
There are chromosomes at the metaphase plate.
Match the statements that follow the items in the key.
More than one answer may be used.
A parent cell with five duplicated chromosomes will produce daughter cells with one chromatid each.
Nondisjunction can cause abnormal gametes to form.
During the spermatogenesis process, polar bodies are formed.
Eggs that have a normal number of chromosomes will result from meiosis.
Some men with Klinefelter syndrome are able to father children.
It was found that most fertile individuals with Klinefelter syndrome exhibit mosaicism, in which some cells are normal but others have an extra chromosomes.
A man has two copies of the same sex.
In a karyotype, larger chromosomes are given smaller numbers.
The smaller the chromosomes, the more viable trisomy 21 is.