Quiz 3

Genes

A set of instructions for a specific trait. A gene is a portion of a DNA molecule on a chromosome. Humans have approximately 20,000 genes arranged on their chromosomes. Genes code for proteins to build things like eye pigments and freckles. Some genes are small (300 letters long) and some are well over a million. The length and sequence of a gene determine the size and shape of the protein it builds. The size and shape of the protein determine the function that protein will have inside the body.

Explain the chromosomal basis of human chromosomal disorders d. XYY

ANEUPOLIDY OF THE Y CHROMOSOME. IN MOST CASES, MUST OCCUR DURING PATERNAL MEIOSIS II AFTER A NORMAL MEIOSIS I. Trisomy of sex chromosomes. Jacob's syndrome. 47 chromosomes total. An extra copy of the Y chromosome is in each of the male's cells. Does not appear to make an individual have a more aggressive personality. XYY males are known to have great height and sometimes learning problems. About 1 in 1,000 males is an XYY individual. Many males with this condition are taller than average, but the chromosomal change sometimes causes no unusual physical features. Most males with 47 XYY syndrome have normal production of the male sex hormone testosterone and normal sexual development, and they are usually able to father children. It is associated with an increased risk of learning disaiblities and delayed development of speech and language skills. Affected boys can have delayed development of motor skills (such as sitting and walking) or weak muscle tone (hypotonia). Other signs and symptoms of this condition include hand tremors, or other involuntary movements (motor tics), seizures, and asthma. Have an increased risk of behavioral, social, and emotional difficulties compared with their unaffected peers. ADHD, depression, anxiety, autism, etc. Physical features can include increased belly fat, a large head, unusually large teeth, flat feet, fifth fingers that curve inward, widely spaced eyes, and abnormal side to side curvature of the spine.

Nonsister chromatids

Are on different chromosomes. Homologous chromosomes, one maternal and one paternal. one chromatid is on the maternal chromosome and the other chromatid is on the paternal chromosome, so they are non-sister chromatids. Nonsister chromatids are on different chromosomes, one chromatid being from the maternal chromosome and the other chromatid being from the paternal chromosome. Nonsister chromatids belong to different members of a homologous pair. Nonsister chromatids are chromosomes of corresponding homologous members that have the same length, staining pattern, centromere position, and the same gene coding for a particular characteristic (ex: eye color) at a particular loci (but these genes have different alleles, like blue eyes on one or brown eyes on the other). Homologous pairs of chromosomes have the same genes at a specific location, but the alleles might be different. Crossing over occurs between segments of non-sister chromatids during the production of gametes.

Explain the chromosomal basis of human chromosomal disorders g. down syndrome

Down syndrome, also called trisomy 21, is a condition in which an individual has three copies of chromosome 21. In most instances, the egg contained two copies of this chromosome instead of one. However, in around 20% of cases, the sperm contributed the extra chromosome 21. Down syndrome is recognized by the following characteristics: short stature; an eyelid fold; stubby fingers; a wide gap between the first and second toes; a large, fissured tongue; a round head; a palm crease; and, at times, mental disabilities, which can sometimes be severe. The chance of a woman having a Down syndrome child increases rapidly with age, starting at about age 40. The frequency of Down syndrome is 1 in 800 births for mothers under 40 years of age and 1 in 80 for mothers over 40. However, since women under 40 have more children as a group, most Down syndrome babies are born to them than to women over 40.

Describe what causes an abnormal sex chromosome number a. barr body

Females have a small, darkly staining mass of condensed chromatin adhering to the inner edge of the nuclear envelope. This structure is an inactive X chromosome. It is regarded as a diagnostic of genetic femaleness. i. When you look into the nucleus of a cell, in every cell of every female, one of the X chromosomes will be active, but the other one will be inactive. ii. Men with Klinefelter syndrome (47, XXY) have Barr bodies in their nuclei. If they are an XXXY male, then they have two Barr bodies. iii. i. Women with Triple X syndrome have two barr bodies.

Differentiate between gametic and somatic cells and their chromosome numbers

Gametes- Sex cells to create offspring. Sperm and egg cells. Haploid, n. Only one set of chromosomes. 23 chromosomes total. Have half the number of chromosomes than the somatic cells. When two haploid cells fuse during fertilization, they each contribute one set of chromosomes to make a single diploid zygote. Somatic cells- Diploid, 2n. Have two sets of chromosomes. Humans have 46 total chromosomes in each diploid cell, or 23 pairs. Somatic cells make up the majority of the body's cells and account for any regular type of cell that does not perform a function in the sexual reproductive cycle.

Interphase

Happens before meiosis and mitosis when DNA replicates itself

Paternal chromosome

In diploid organisms, the genome is composed of homologous chromosomes. One chromosome of each homologous pair comes from the father, called a paternal chromosome. We inherit one of each chromosome from each parent. Homologous chromosomes are a set of one paternal and one maternal chromosome, either unreplicated or replicated: ) ( ) ( ) (

Maternal chromosome

In diploid organisms, the genome is composed of homologous chromosomes. One chromosome of each homologous pair comes from the mother, called a maternal chromosome. We inherit one of each chromosome from each parent. Homologous chromosomes are a set of one paternal and one maternal chromosome, either unreplicated or replicated: Homologous chromosomes example 1: ) ( Homologous chromosomes example 2: ) ( ) (

Oogenesis

In females, meiosis is part of oogenesis, which occurs in the ovaries and produces eggs. Ova can only contribute an X chromosome to the offspring. Oogenesis begins prior to birth, so a baby girl is born with all the primary oocytes she will ever have. The process is paused at prophase I of meiosis until the beginning of puberty (where the primary oocyte divides until the secondary oocyte). Meiosis 2 doesn't begin until fertilization.

Spermatogenesis

In males, meiosis is a part of spermatogenesis, which occurs in the testes and produces sperm. Approximately one-half of spermatozoa contain either an X or Y chromosome. About 200-300 million sperms are produced daily in the testes. The immature sperm undergo maturation in the epididymis to form mature sperms. Begins at puberty and continues into old age.

Explain how meiosis is a process of chromosome reduction number and why this is important in living organisms

Meiosis is important because, if it did not halve the chromosome number, the gametes would contain the same number of chromosomes as the body cells and the number of chromosomes would double with each new generation. Within a few generations, the cells of sexually reproducing organisms would be nothing but chromosomes! But meiosis, followed by fertilization, keeps the chromosome number constant in each generation. · Meiosis 1 begins with a diploid parent (2n = 4) cell and ends with two haploid (n = 2) cells. · Meiosis 2 begins with two haploid parent cells and ends with four haploid daughter cells. · The number of chromosomes is reduced by half at the end of meiosis.

State the general purpose of meiosis

Meiosis provides gamete variation and keeps the chromosome number constant generation after generation. Meiosis serves two major functions: 1) reducing the chromosome number and 2) shuffling the chromosomes and genes to produce genetically different gametes called sperm (males) and eggs (females). In animals, meiosis begins the process that produces cells called gametes, which play an important role in sexual reproduction. Meiosis reduces the chromosome number in such a way that the gametes (sperm and egg) have one chromosome derived from each homologous pair of chromosomes. Because of a process called meiosis, two individuals can create offspring that are genetically different from themselves and from each other. This process creates an enormous amount of diversity; in humans, more than 70 trillion different genetic combinations are possible from the mating of just two individuals! In other words, meiosis ensures that you are unique; statistically it is unlikely that anyone will ever be the same genetically as you.

Gametes

Meiosis provides variation that is important in the production of gametes. In humans, sperm are the male gametes and eggs are the female gametes. The processes by which they are formed are called spermatogenesis and oogenesis. Males and females differ in the ways that they form gametes. While meiosis in the two sexes is very similar, there are some important differences in how spermatogenesis and oogenesis occur. One major difference pertains to the age at which the process begins and ends. In males, sperm production does not begin until puberty but then continues throughout a male's lifetime. In females, the process of producing eggs has started before the female is even born and ends around the age of 50, a time called menopause. Another difference concerns the number of gametes that can be produced. In males, sperm production is unlimited, whereas females typically produce only one egg a month. Many more eggs start the process than ever finish it.

Differentiate between haploid and diploid as it pertains to the organization of chromosomes

N refers to the number of chromosomes 46 chromosomes altogether is diploid (2n) number of chromosomes in humans. Half this number is haploid (n) number of chromosomes. Diploid has paired sets of chromosomes, one from each parent. In a diploid cell, a parent gets one set from their mom and one set from their dad. Haploid has just a single copy of each chromosome. In a haploid cell, a person gets only one set that is a combination of chromosomes form their mom and dad. Haploid- gametes (sperm and eggs) sperm and egg each have 23 chromosomes. Diploid- Somatic cells have 46 chromosomes. 2n = 46. We have 23 chromosomes, but we have 2 copies of each chromosome.

Explain the chromosomal basis of human chromosomal disorders c. XY

NORMAL MALE. Total of 46 chromosomes or 23 pairs of chromosomes

Explain the chromosomal basis of human chromosomal disorders m. OY

Nonviable zygotes. Fails to develop further. Humans cannot survive when they lack the genes on the X chromosome.

Explain the chromosomal basis of human chromosomal disorders e. XX

Normal female. Total of 46 chromosomes or 23 pairs of chromosomes.

Chromosome

One chain of DNA in a well defined structure. Long chains of DNA wrapped tightly around each other. We get one chromosome from mom and one from dad. DNA packs together tightly before it replicates and before a cell can divide. ) This is called a chromosome [unreplicated] )( This is called a chromosome [replicated]

Explain how the chromosomes line up in the middle of the cell in meiosis I can contribute to genetic diversity

Pg 53-54 During metaphase 1, the tetrads attach to the spindle and align at the spindle equator, with each homologue facing an opposite spindle pole. It does not matter which homologous chromosome faces which pole; therefore, all possible combinations of chromosomes will occur in the gametes. In effect, metaphase of meiosis I shuffles the chromosomes into new combinations. The orientation of each pair on the spindle axis is random: either the maternal or paternal homologue may orient toward a given pole. The number of possible chromosome orientations equals 2 raised to the power of the number of chromosome pairs.

Identify what occurs at each phase in meiosis a. Meiosis I

Prophase I- Chromosomes condense, and the nuclear membrane fragments. Centrosomes, which duplicate at the beginning of meiosis, begin moving apart, and the spindle fibers begin forming. Homologous pairs of sister chromatids lie side-by-side in a process called synapsis, forming a tetrad or bivalent. A bivalent is composed of four sister chromatids. Crossing over is an exchange between chromosome segments of nonsister chromatids, which increases genetic diversity. After crossing over, the sister chromatids of one chromosome are no longer identical to one another. Prometaphase I- The spindle apparatus is fully formed, and the centrosomes are in place. The sister chromatids attach to the spindle fibers by their kinetochores. Homologous chromosomes remain aligned, so that a pair of sister chromatids is attached to only one pole by the kinetochore microtubules. One pair of sister chromatids is connected via kinetochore microtubules to one pole while the homologous pair of sister chromatids is connected to the opposite pole. The complete assembly of the spindle apparatus occurs during prometaphase I. Metaphase I- The nuclear membrane is gone. Microtubules have formed a spindle. Centrosomes attach at the kinetochores to the chromosomes. Bivalents are aligned along the metaphase plate (homologous chromosomes line up along the equator of the cell), and this alignment is random due to independent assortment and adds to genetic diversity. Once the chromosomes are lined up, the ends of the spindle fibers attach to each centromere. Spindle fibers attach to only one side of each centromere and the two homologous chromosomes attach to microtubules orienting from opposite poles. Either homologue can face either pole. Bivalents are aligned along the metaphase plate rather than individual pairs of sister chromatids, as in mitosis. The centrosomes attach at the kinetochores to the chromosomes. Anaphase I- Homologous chromosomes separate and move toward opposite poles. The centrosomes are splitting the homologous pairs along the microtubules, taking both sister chromatids with them. The kinetochore microtubules shorten. Each new cell will have only one member of the homologous pair and will be haploid. When the conjoined sister chromatids reach the poles of the cell, they detatch from the spindle apparatus, and the nuclear membrane begins to reform. Telophase I- Chromosomes decondense, the sister chromatids detach from the spindle, nuclear membrane may reform. A cleavage furrow forms, and cell divides (cytokinesis) to form two haploid daughter cells, each with a haploid number of two chromosomes each, with each chromosome consisting of a pair of sister chromatids. Microtubules are also dissolving. After cytokinesis is complete, and after a period of interkinesis, meiosis II starts.

Sister chromatids

Replicated chromosome attached at the centromere. Refers to the identical copies (chromatids) formed by the DNA replication of a chromosome, with both copies joined together by a common centromere. In other words, a sister chromatid may also be said to be "one-half" of the duplicated chromosome. A pair of sister chromatids is called a dyad. Sister chromatids code for the exact same DNA and are identical. Sister chromatids have the same genetic information. Sister chromatids are on the same chromosome. During the s phase of interphase, a full set of sister chromatids are produced when the entire cell's DNA is duplicated. "Chromatids" are terms used in the process of meiosis and mitosis. Sister chromatids separate and move towards opposite poles of the cell in Meiosis II anaphase II. Sister chromatids also separate during mitosis (anaphase).

Identify similarities and differences between meiosis I and II, especially how the chromosomes separate differently in MI and MII.

Similarities between meiosis I and II: · Can only occur in eukaryotes, · means of sexual reproduction in plants, animals, and fungi, · four phases occur: prophase, metaphase, anaphase, telophase. differences: 1) Meiosis 1 starts as diploid and ends as haploid. Meiosis 2 starts as haploid and ends as haploid. 2) Meiosis 1 Reductive division (the chromosome number is reduced from diploid to haploid); Meiosis 2 equational division because it does not reduce chromosome numbers. 3) Meiosis 1 homologous chromosomes separate; meiosis 2 sister chromatids separate 4) Meiosis 1 crossing over happens, meiosis 2 crossing over does not happen 5) Meiosis 1 ends with 2 daughter cells, meiosis 2 ends with 4 daughter cells 6) Meiosis 1 Metaphase I bivalents are aligned along the metaphase plate; Meiosis 2 metaphase II individual pairs of sister chromatids aligned along the metaphase plate 7) Meiosis 1 anaphase 1 homologous chromosomes separate. Meiosis 2 Anaphase II sister chromatids separate. 8) Meiosis 1 metaphase I- independent assortment occurs when either homologue can face either pole; Meiosis 2 metaphase II- independent assortment does not occur

Differentiate between synapsis and a tetrad

Tetrad- a set of four sister chromatids Synapsis- During meiosis 1, the homologous chromosomes of each pair come together and line up side-by-side in an event called synapsis

Which pair of chromosomes don't always cross over or go through recombnation?

The 23rd pair, the sex chromosomes. If you're female, you have two XX that can cross over since they're the same. If you're male, you have one X and one Y. The X and the Y want nothing to do with each other because they are not homologous and don't match up, so the XY pairs will be split into single chromatids, and half the resulting sperm will be X, leading to female offspring, and half will be Y, leading to male offspring

Centromere

The centromere holds together two chromatids in a chromosome. The centromere is a region of specialized chromatin found within each constricted chromosome that provides the foundation for kinetochore assembly and serves as a site for sister chromatid attachment. Errors in centromere or kinetochore function are catastrophic for cells. Such errors can lead to aberrant division and chromosomal instability, both of which are often observed in cancerous cells. The centromere is the most constricted region of a condensed mitotic chromosome. Centromeres are not only found at the very middle; centromeres are located at a variety of positions that are characteristic for each particular chromosome. The position of the centromere provides a useful landmark for dividing chromosomes into karyotype groups and for establishing a standardized nomenclature for mapping the positions of genes on chromosomes. The centromere ensures accurate segregation during mitosis. Each centromere is a region of highly specialized chromatin.

Define nondisjunction and briefly explain how nondisjunction may bring about an abnormal chromosome number

The normal number of chromosomes in human cells is 46 (2n = 46), but occasionally humans are born with an abnormal number of chromosomes because the chromosomes fail to separate correctly, called nondisjunction, during meiosis. If nondisjunction occurs during meiosis I, both members of a homologous pair go into the same daughter cell. If it occurs during meiosis II, the sister chromatids will fail to separate and both daughter chromosomes will go into the same gamete. If an egg that ends up with 24 chromosomes instead of 23 is fertilized with a normal sperm, the result is a trisomy, so called because one type of chromosome is present in three copies. If an egg that has 22 chromosomes instead of 23 is fertilized by a normal sperm, the result is a monosomy, so called because one type of chromosome is present in a single copy. Down syndrome, also called trisomy 21, is a condition in which an individual has three copies of chromosome 21. In most instances, the egg contained two copies of this chromosome instead of one. However, in around 20% of cases, the sperm contributed to the extra chromosome 21.

Explain the chromosomal basis of human chromosomal disorders f. nondisjunction

The normal number of chromosomes in human cells is 46, (2n = 46), but occasionally humans are born with an abnormal number of chromosomes because the chromosomes fail to separate correctly, called nondisjunction, during meiosis. If nondisjunction occurs during meiosis I, both members of a homologous pair go into the same daughter cell. If it occurs during meiosis II, the sister chromatids will fail to separate and both daughter chromosomes will go into the same gamete.

What are the raw materials for meiosis?

They're in your ovaries or your testes, called either primary oocytes or primary spermatocytes. Male germ line cell (Diploid, 2n) Female germ-line cell (Haploid, n)

Describe what causes an abnormal sex chromosome number c. Klinefelter syndrome

Trisomy of sex chromosomes. Aneuploidy. May occur due to nondisjunction of X chromosomes during prophase of meiosis I in females. One egg receives both X chromosomes, and the other receives no X chromosomes. A person with Klinefelter syndrome (47, XXY) is a male. A Klinefelter male has two or more X chromosomes in addition to a Y chromosome. The extra X chromosomes become Barr bodies. In males with Klinefelter syndrome, the testes and prostate gland are underdeveloped. There is no facial hair, but some breast development may occur. Affected individuals generally have large hands and feet and very long arms and legs. They are usually slow to learn but are not mentally handicapped unless they inherit more than two X chromosomes. As with Turner syndrome, it is best for parents to know as soon as possible that their child has Klinefelter syndrome because much can be done to help the child lead a normal life.

Explain the chromosomal basis of human chromosomal disorders l. XXY

Trisomy of sex chromosomes. Aneuploidy. May occur due to nondisjunction of X chromosomes during prophase of meiosis I in females. One egg receives both X chromosomes, and the other receives no X chromosomes. A person with Klinefelter syndrome (47, XXY) is a male. A Klinefelter male has two or more X chromosomes in addition to a Y chromosome. The extra X chromosomes become Barr bodies. In males with Klinefelter syndrome, the testes and prostate gland are underdeveloped. There is no facial hair, but some breast development may occur. Affected individuals generally have large hands and feet and very long arms and legs. They are usually slow to learn but are not mentally handicapped unless they inherit more than two X chromosomes. As with Turner syndrome, it is best for parents to know as soon as possible that their child has Klinefelter syndrome because much can be done to help the child lead a normal life.

Explain the chromosomal basis of human chromosomal disorders j. translocation

When part of a chromosome is transferred to another chromosome. In another type of translocation, two chromosomes trade pieces with each other. Reciprocal translocation - Two chromosomes swap a piece of chromosomal material. (A piece of chromosome 1 swaps onto chromosome 2 and a piece of chromosome 2 swaps onto chromosome 1). Balanced chromosomal translocation. Can occur between any two chromosomes. Most people with balanced reciprocal translocations are healthy. Can cause infertility, miscarriage, child with birth defects or learning difficulties. An unbalanced version can happen with a baby having too much of one chromosome than another. The larger the imbalance- more likely a miscarriage. Smaller imbalance- more likely a baby can be born with birth defects or learning difficutlies. Robertsonian translocation- Where someone has 45 chromosomes instead of 46. Only occur between acrocentric chromosomes which are chromosomes 13, 14, 15, 21, and 22. Two acrocentric chromosomes get stuck together, making one large chromosome together. Chromosomes 13 and 14 are likely to get stuck together, as are chromosomes 14 and 21. Other possible translocations occur much less frequently. A robertsonian translocation carrier is healthy. However, problems can arise if the Robertsonian carrier wishes to have children. For example, Carl has translocation chromosome 13 and 14 stuck together. He also has another normal standalone chromosome 13 and 14. If he hands on the normal chromosomes 13 and 14, the child will be healthy and have normal chromosomes. If he hands on the translocated chromosome on its own, his child willb e a healthy translocation carrier like himself. However, if he hands on the translocated chromosome alongside one of the stand alone chromosomes 13 or 14, the baby will have a whole extra chromosome 13 or 14, which causes trisomy chromosome 13 or 14 (the baby will have 3 copies of either 13 or 14). Babies with trisomy 14 will miscarry. Babies with trisomy 13 (Patau syndrome) miscarry, but some may survive till birth, but baby is not compatible with life. If Carl carried a translocation involving chromosome 14 and 21,he would have a risk of trisomy 14 or trisomy 21 (down syndrome). Risk of having a Down syndrome child is higher if Carl's sister carries the translocation. Transloaction families can have a history of infertility. Rare disorders can occur with specific translocations.

Describe what causes an abnormal sex chromosome number b. Turner syndrome

a. Occurs when part or all of an X chromosome is missing from most or all of the cells in a girl's body. Aneuploidy. Occurs when an egg or sperm cell is forming. A person with Turner syndrome (45, XO) is a female. The number 45 indicates the total number of chromosomes the individual has, and the O signifies the absence of a second sex chromosome. Turner syndrome females are short, with a broad chest and webbed neck. The ovaries, uterine tubes, and uterus are very small and underdeveloped. Turner females do not undergo puberty or menstruate, and their breasts do not develop. However, some have given birth following in vitro fertilization using donor eggs. These women usually have normal intelligence and can lead fairly normal lives if they receive hormone supplements.

Describe how crossing over occurs and why it is important a. nonsister chromatids

a. nonsister chromatids- Crossing over is the exchange of genetic material during sexual reproduction between two homologous chromosomes' non-sister chromatids. Crossing over is important because it accounts for genetic variation since the sister chromatids are no longer identical. The sister chromatids will have a different combination of alleles, and the resulting gametes will be genetically different. Thus, even though two of the gametes will have the same chromosomes, these chromosomes may not have the same combination of alleles as before because of crossing-over. Crossing over is only between two individual chromatids, so the possible haploid cells after meiosis have four different genetic combinations. Two will come from the chromatids that did not participate in crossing over and thus will still have the parental combination of alleles, either A and B or a and b. The other two will be recombinant, either A and b or a and B alleles. Thus, crossing over allows for the reassortment of linked genes.

Differentiate between a tetrad and a dyad

A tetrad is four chromatids. A tetrad is also called a bivalent. A dyad is two sister chromatids.

Alleles

Alleles are alternate versions of a gene for a particular trait. The location of the alleles of a gene on homologous chromosomes is the same, but the information within the alleles may be slightly different. (Ex: your mother's allele is for freckles, your father's allele is for no freckles).

Explain the chromosomal basis of human chromosomal disorders a. Aneuploidy

Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example, a human cell having 45 or 47 chromosomes instead of the usual 46.

Cytokinesis can begin as early as what in mitosis

Can begin as early as anaphase in mitosis

Explain the chromosomal basis of human chromosomal disorders k. monosomics

If an egg that has 22 chromosomes instead of 23 is fertilized by a normal sperm, the result is a monosomy, so called because one type of chromosome is present in a single copy. Examples of monosome are turner syndrome (with one X chromosome and the other is missing), cri du chat syndrome (where the end of the short p arm of chromosome 5 is missing) and 1p36 deletion syndrome (where the end of the short p arm of chromosome 1 is missing)

Identify what occurs at each phase in meiosis a. Meiosis II

Prophase II- Starts with two cells each with two chromosomes. The chromosomes condense. The nuclear membrane fragments. Spindle fibers start to form at the poles of the cell. Centrioles duplicate and move to opposite ends of each cell. Prometaphase II- The spindle apparatus forms, and the sister chromatids become attached to kinetochore microtubules. A pair of sister chromatids is attached to both poles, not one pole as in prometaphase I. Metaphase II- Spindle fibers bind to both sides of the centromeres. The sister chromatids are aligned along the metaphase plate (or equator), with each chromatid being attached to one pole. This is different from metaphase I where bivalents were aligned along the metaphase plate rather than individual pairs of sister chromatids. Anaphase II- The sister chromatids separate (or disjoin) and begin moving to the poles of the cells along the spindle fiber as the spindle fiber contracts. Telophase II- The nuclear membrane reforms around the sets of daughter chromosomes and chromosomes decondense. In animal cells, a cleavage furrow is formed that causes cytokinesis, or cellular division. Four genetically different haploid cells are formed as cytokinesis is completed.

Describe the purpose of meiosis and why genetic diversity is important for many species

Purpose of meiosis: The production of gametes that have a reduced chromosome number and are genetically different from each other and from the parent cell. Genetic diversity is important for many species because it serves as a way for populations to adapt to changing environments. With more variation, it is more likely that some individuals in a population will posses variations of alleles that are suited for the environment. Those individuals are more likely to survive to produce offspring bearing that allele.

The end of meiosis II makes how many sperm and egg?

Sperm: Half of the four resulting cells will be for making girls and half will be for making boys Eggs: The result is one egg that took up most of the cell goodness (cytoplasm and organelles) during telophase I and II. The other three cells are polar bodies and are useless in people but helpful in plants. In plants, these polar bodies get fertilized too, and become the endosperm [the nutrient that feeds the plant embryo, the seed].

Homologous chromosomes

The members of a chromosome pair are called homologous chromosomes, or homologues, because they have the same size, shape, and location of the centromere. When chromosomes are stained and viewed under a microscope, homologous chromosomes have the same characteristic banding pattern. One homologue of each pair was contributed by each parent. Homologous chromosomes contain the same types of genes arranged in the same order. The location of the alleles of a gene on homologous chromosomes is the same, but the information within the alleles may be slightly different. (Ex: your mother's allele is for freckles, your father's allele is for no freckles). ) ( homologous pair of chromosomes unreplicated [one from mom, one from dad] ) ( ) ( also homologous pair of chromosomes but replicated [ one from mom, one from dad. each chromosome has two sister chromatids. ) one ( two. ) one ( two. ]

Explain the chromosomal basis of human chromosomal disorders i. XO

Turner's syndrome, monosomy, X, baby only born with one X chromosome rather than the usual pair.

Diploid

Two sets of chromosomes

Chromatid

When looking at a replicated chromosome, which looks like this )(, one of the legs is called a chromatid. The chromatids of the same chromosome have the same genetic information. )( this chromosome has two chromatids. In mitosis and meiosis, when the chromatids separate, they are now individually become chromosomes and are no longer connected by the centromere. Now you have two separate chromosomes, each made up of one chromatid. ) is one chromosome. ( is one chromosome.

Crossover

When one chromatid from each X gets tangled up with the other X

Recombination

When the non-sister chromatids are all tangled up and trade sections of DNA. The sections that they are trading are from the same location on each chromosome, so one is giving up its genetic code for hair color or body odor, and in return, its getting the other chromosome's genes for that trait. This is important because they are creating new gene combinations on a single chromosome. It's the whole point of reproducing this way. All four chromatids are now different from each other.

Crossing over and linked genes

-Crossing over alters the linkage between genes on the same chromosome -For example, one parental chromosome has alleles A and B, and the other parental chromosome has the alleles a and b. Without crossing over, each haploid cell will inherit a chromosome with the same combination of alleles that was on one of the parental chromosomes. Thus, the arrangement of linked genes is not altered in this case. -Since crossing over in only between two individual chromatids, the possible haploid cells after meiosis have four different genetic combinations. Two will come from the chromatids that did not participate in crossing over and thus will still have the parental combination of alleles, either A and B or a and b. The other two will be recombinant, with either A and b or a and B alleles. Thus, crossing over allows for the reassortment of linked genes.

Random Orientation of Chromosomes During Meiosis

-During metaphase I of meiosis, each joined pair of homologues lines up on the metaphase plate. The orientation of each pair on the spindle axis is random: either the maternal or paternal homologue may orient toward a given pole. -The number of possible chromosome orientations equals 2 raised to the power of the number of chromosome pairs. In this hypothetical cell with three chromosome pairs, 2^3 possible orientations exist. -Each orientation produces gametes with different combinations of paternal chromosomes.

Explain the chromosomal basis of human chromosomal disorders h. XXX

Trisomy X, 47, XXX, affects 1 in 1,000 females. Trisomy of sex chromosomes. Mild symptoms, or more apparent symptoms like developmental delays and learning disabilities. Seizures and kidney abnormalities occur in a small number of girls and women with triple X syndrome.

Chromatin

1) DNA wrapped around structural proteins that gives DNA its shape 2) big mess of DNA and proteins in the nucleus; a whole mess of DNA from multiple chromosomes. Not well defined. Messy. DNA is easier for transcription when it is not all bundled up. For most of the cell's life, DNA isn't all bundled up. That would make replication and transcription hard! Normally, DNA is completely separated around the cell and looks like a mess of proteins and DNA in the nculeus. The proteins in the chromatin are called histones.

Differences between meiosis and mitosis

1) Meiosis has three unique features: synapsis (homologous pair all along their length), homologus recombination (exchange process between paired chromosomes), and reduction division (at the end of meiosis, each cell contains only half the original complement of chromosomes). -Meiosis requires two consecutive nuclear divisions, but mitosis requires only one. -Meiosis produces four haploid daughter cells, but mitosis results in two daughter cells that have the same number of chromosomes as the parent cell -Following meiosis, the daughter cells are genetically different from each other and from the parent cell. Following mitosis, the daughter cells are genetically identical to each other and to the parent cell)

Explain the chromosomal basis of human chromosomal disorders b. Trisomics

If an egg that ends up with 24 chromosomes instead of 23 is fertilized with a normal sperm, the result is a trisomy, so called because one type of chromosome is present in three copies.

Identify where cells in the human body reproduce meiotically

Meiosis only occurs in reproductive cells, as the goal is to create haploid gametes that will be used in fertilization. Meiosis occurs only in the testes and the ovaries, where it is involved in the production of gametes.

Haploid

One set of chromosomes

Describe the human life cycle a. Fertilization b. zygote (diploid) c. sperm (haploid) d. egg (haploid)

The human life cycle in sexually reproducing organisms refers to all the reproductive events that occur from one generation to the next. The human life cycle involves two types of nuclear division: mitosis and meiosis. Male (2n, diploid) Female (2n, diploid) à Meiosis à Egg (n, haploid) Sperm (n, haploid) à fertilization (egg and sperm join) à Zygote (2n, diploid) à Zygote undergoes mitosis until it eventually develops into an unborn child à Mitosis continues throughout life during growth and repair (mitosis repairs tissues at any time. As a result of mitosis, each somatic cell has the diploid number of chromosomes). Fertilization- The process of combining the male gamete, or sperm, with the female gamete, or ovum. After the sperm and the egg join during fertilization, the resulting cell, called the zygote, again has a diploid number of homologous chromosomes. Zygote- A diploid cell resulting from the fusion of two haploid gametes; a fertilized ovum Sperm (haploid)- In males, meiosis is a part of spermatogenesis, which occurs in the testes and produces sperm. Sperm is the male reproductive cell, or gamete. Sperm production does not begin until puberty but continues throughout a male's lifetime. Egg (haploid)- In females, meiosis is a part of oogenesis, which occurs in the ovaries and produces eggs. An egg is the female sex cell, or gamete. The female starts producing eggs before she is even born and egg production ends around the age of 50, a time called menopause.

Distinguish between autosomes and sex chromosomes in a karyotype

· Geneticists and genetic counselors can visualize chromosomes by looking at a picture of the chromosomes called a karyotype. · 22 of the 23 pairs of chromosomes are called autosomes, and are the same in both males and females. · The remaining pair are called sex chromosomes because they contain the genes that determine gender. · The larger sex chromosome is the X chromosome, and the smaller is the Y chromosome. Females have two X chromosomes; males have a single X and Y. · In a karyotype, the pairs are numbered. · In autosomes the centromere position is identical but in sex chromosomes the centromere position is non-identical. · Normal karyotypes for females contain two X chromosomes and are denoted 46, XX; males have both an X and a Y chromosome denoted 46, XY.