Bio exam 3 mastering bio

Eukaryotic cells

, however, can be either haploid (e.g. gametes) or diploid (e.g. your body cells). Therefore, the terms homologous chromosomes and sister chromatids ONLY apply to eukaryotic cells, and ONLY diploid eukaryot

medium length Hair

A cat that is heterozygous for the fur length gene will have

must be autosomal recessive The disease described must be an autosomal recessive disease, and both parents must be carriers. Both children (son and daughter) must have inherited one disease allele from each parent. Since neither of the parents are affected, the disease cannot be an autosomal dominant disease (one of the parents would have been affected if it was an autosomal dominant disease). Females that have X-linked recessive diseases must have TWO copies of the disease allele to be affected - one inherited from their father and one from their mother. Since the father in this scenario was NOT affected, he could not have had a disease allele to pass on to his daughter. Sons inherit a Y chromosome from their father, so sons cannot inherit any X-linked alleles from their father.

A couple has a son and a daughter that are both affected by the same genetic disease. Neither of the parents is affected. From this information, the disease

eight, eight Diploid cells have two sets of chromosome - one set inherited from the egg and the other set inherited from the sperm that fertilized the egg. Therefore, a diploid cell with 16 total chromosomes has eight homologous pairs (eight pairs of chromosomes with the same genes). Although the total amount of DNA in a cell doubles when DNA replication occurs, the number of homologous pairs does not change. Each chromosome is now a pair of sister chromatids (two identical copies of a chromosome generated by DNA replication that stick together following replication).

A diploid cell has 16 total chromosomes (pieces of DNA). Therefore, the cell has _____ pairs of homologous chromosomes prior to DNA replication, and after the cell has replicated its DNA, there will be _____ pairs of homologous chromosomes.

tweleve In DNA replication, all DNA in a cell is replicated. If a cell has six pairs of homologous chromosomes, it has twelve total pieces of DNA (two each of the six different chromosomes).

A diploid cell has six pairs of homologous chromosomes. How many individual chromosomes (pieces of DNA) will be copied during DNA replication?

Diploid organisms

A diploid organism has two alleles for every gene that can be the same or different. For example, an individual spider could have two brown bristle alleles, or they could have a brown bristle allele and a black bristle allele.

both are Aa Bb Agouti mice can either be AA or Aa; black mice can be either BB or Bb. To get offspring with all four possible offspring phenotypes, the parents must both have been heterozygous for both genes so that all possible allele combinations could be generated.

A litter of mice from the mating of two agouti black parents includes offspring with the following fur colors listed below. What are the genotypes of the parents in this mating? Offspring Phenotypes:solid blacksolid brownagouti blackagouti brown HINT - Determine the possible genotypes for each of the offspring phenotypes. Then use them to help you determine the parents' genotypes. Remember that if a particular allele appears in the offspring, at least one of the parents must have that allele.

EGQ, EGq, EgQ, and Egq

A male that is EEGgQq mates with a female that is EeggQq. The three genes are on different chromosomes. What are the possible gamete genotypes for the male?

A, B, AB, or O The genotype of the man with type B blood could be IB IB or IB i, so his gametes could be IB or i. The genotype of the woman with type A blood could be IA IA or IA i, so her gametes could be IA or i. Therefore, their offspring could be IA IB, IA i, IB i, or ii .

A man who is type B and a woman who is type A could have children with which of the following phenotypes? Hint - First determine ALL possible genotypes for the male parent and for the female parent. Then figure out the possible gamete genotypes for all the possible parent genotypes you identified. Finally, match up the possible male gamete genotypes with the possible female gamete genotypes to identify all possible offspring genotypes and phenotypes (use Punnett squares if it helps).

could be FF ll or Ff ll ; must be ff Ll Because light fur is recessive compared to dark fur, a cat with light fur must have the genotype ff. Medium-length fur (between short and long) can only result from the presence of both a long (L) allele and a short (l) allele. Therefore, the first cat with medium-length fur must be ff Ll. The cat with dark fur could be either FF or Ff, and short hair can only result from the presence of two short alleles. Therefore, the second cat could be FF ll or Ff ll.

A short-haired cat with dark fur _________, and a cat with light colored, medium-length fur _________.

type O and type AB Each person only has TWO alleles. If a person is type AB, then they must have both the IA and IB alleles. Type O individuals can only have i alleles (two of them). The other phenotypes, type A and type B, can be produced by two different allele combinations. For example, a person that is type A could be IAIA or IAIi.

ABO blood type in humans is determined by a single gene that has three alleles. Presence of the IA allele results in red blood cells with "A" carbohydrates attached to their surfaces. Presence of the IB allele results in red blood cells with "B" carbohydrates on their surfaces. Individuals that are IA IB have both "A" and "B" carbohydrates and are type AB. The i allele has no effect on the carbohydrates attached to red blood cell surfaces and is recessive compared to the other two alleles. When two copies of the i allele are present, the individual has an O phenotype. What ABO blood type phenotype(s), if any, result from only ONE possible genotype (i.e. individuals with that blood type can only have one particular genotype)?

haploid

All prokaryotic cells are______ because they only have one chromosome

none Gametes are haploid, meaning that they only have one set of chromosomes (i.e. there are no homologous pairs), and therefore can only have one allele for each gene. Alleles of the same gene separate during meiosis when homologous chromosomes are separated. The possible gametes for an organism that is AaBb are therefore AB, Ab, aB, and ab. Each gamete genotype is equally likely (the probability is 1/4 for each).

An organism has the genotype AaBb. What proportion of its gametes, if any, would be Bb?

Mitosis vs. Meiosis

DNA is replicated once prior to mitosis, and is also replicated once prior to meiosis. Therefore, both processes begin with cells that have replicated chromosomes (pairs of sister chromatids). Sister chromatids are distributed to opposite sides of a dividing cell during mitosis AND meiosis (specifically meiosis II). Mitosis involves one cell division, producing two genetically identical daughter cells. Therefore division of a diploid cell by mitosis produces two dipolid cells. Meiosis, which must start with a dipolid parent cell, involves two cell divisions and results in four genetically unique haploid cells.

The protein produced by expression of the CNCR gene promotes cell division.

Expression of the human gene human gene CNCR produces a protein that's important for controlling cell division. A mutation in the CNCR gene that has been linked to various types of cancer increases the activity of the CNCR protein. Based on this information, which of the following is a reasonable prediction?

has TWO alleles for the FUZY gene.

FUZY is a gene involved in determining bristle ("fur") color in a certain species of spider, which is a diploid organism. Therefore, an individual spider

EEGgcc Mendelian traits are examples of complete dominance. Individuals with one or two alleles that correspond to a dominant trait have the same phenotypes, so EE and Ee have the same phenotype, as do GG and Gg. The recessive trait is only observed when two alleles that correspond to the recessive trait are present (i.e. are homozygous for the recessive allele). Therefore, only cc (or gg) individuals show the recessive trait associated with that gene.

For Mendelian traits, an individual that has the genotype EeGGcc will have the same phenotype as an individual with the genotype _________. (Reminder - By convention, capital letters represent alleles that correspond to dominant traits, and lower-case letters represent alleles that correspond to recessive traits.)

more than two different alleles In a species, it is possible for more than two different alleles for a particular gene exist. For example, in a spider population, one spider could have a brown bristle and a black bristle allele, and another spider could have a black bristle allele and an orange bristle allele. The presence of more than two different alleles for a particular gene within a species is common.

How many alleles for the FUZY gene could there be in a population of spiders?

Meiosis involves two cell divisions. In meiosis I, homologous chromosomes pair up and are then separated into the two daughter cells. Therefore, although the parent cell is diploid (has sets of chromosomes), the two daughter cells produced by meiosis I are haploid (have only one set of chromosomes each). The chromosomes present in the cells generated by meiosis I are still replicated (pairs of sister chromatids). -In meiosis II, the sister chromatids are separated. The four daughter cells that result are therefore haploid with unreplicated DNA.

Identify the steps of meiosis based on what you know about the behavior of chromosomes during the process.

25%

If the couple has a child, what's the probability the child will be a son with a widow's peak?

dark fur

In a certain breed of cat, fur color is an autosomal trait determined by one gene. The dark fur allele (F) is completely dominant to the light fur allele (f). Fur length is determined by an autosomal gene on a different chromosome, and the long hair allele (L) and short hair allele (l) show incomplete dominance. A cat that is heterozygous for the fur color gene will have

1/4 black eyes, green skin ; 1/4 black eyes, white skin ; 1/4 orange eyes, green skin ; 1/4 orange eyes, white skin Sam's genotype must be BbGg. Sam has a parent that shows both recessive traits (orange eyes and white skin). Therefore, one of Sam's parents was homozygous recessive (two alleles that correspond to the recessive trait) for both the eye color gene and the skin color gene. This means that Sam inherited the orange eye allele and white skin allele from that parent. Since Sam shows both dominant traits (black eyes and green skin), he must have inherited the black eye color and green skin color alleles from his other parent. Carole's genotype must be bbgg because she shows the recessive trait for both skin color and eye color. Sam can produce BG, Bg, bG, or bg gametes. Carole's gametes can only be bg. You can set up a Punnett square to see that there are four possible offspring genotypes if Sam and Carole mate, and each genotype is equally likely to occur. Each of the genotypes also relates to a unique phenotype, so there are four different offspring phenotypes that are equally likely to occur.

In a diploid species of alien (MendAliens) that reproduces sexually, eye color and skin color are Mendelian traits. Black eyes are completely dominant to orange eyes, and green skin is completely dominant to white skin. B = black eyes allele; b = orange eyes alleleG = green skin allele; g = white skin alleleSam, a MendAlien with black eyes and green skin, has a parent with orange eyes and white skin. Carole is a MendAlien with orange eyes and white skin. If Sam and Carole were to mate, what are the possible offspring phenotypes and their probabilities? HINT - Figure out Sam's and Carol's genotypes based on the information given about their phenotypes and, for Sam, his parent. Use their genotypes to determine their possible gamete genotypes, then set up a Punnett square.

both daughter cells will have one mutated and one non-mutated copy of the gene

In a human lung cell, a substitution mutation occurs in a gene on one chromosome, but not in the homologous chromosome. Therefore the lung cell has one mutated copy of the gene, and one non-mutated copy of the gene. What will be found in the daughter cells when this cell divides by mitosis? Hint - Think about the chromosomes present in a diploid cell and what you know about the process and products of mitosis.

independent orientation Independent orientation mixes the alleles an individual inherited from each parent that are on different chromosomes when gametes are produced by meiosis. The image below illustrates this. Because the genes for body color and wing shape are on different chromosomes, crossing over does not apply.

In a species of fly, the genes for body color and wing shape are on different chromosomes. A fly has the black body allele and the gray body allele for the body color gene, and the pointy wing allele and the rounded wing allele for the wing shape gene. Some of the gametes produced by the fly have the black body allele and the rounded wing allele, while other gametes have the black body allele and the pointy wing allele. What mechanism of genetic variation explains this?

DD Rr Because the female parent is Dd Rr, she can produce DR, Dr, dR, or dr eggs. None of the offspring have plain shells, so none of them can be dd. Based on this, you know that the male parent must have been homozygous for the D allele (DD). If the male parent had one or more copies of the d allele, dd offspring would be possible. Because ~25% (1/4) of the offspring have green shells, ~25% must be rr. For rr offspring to be produced, the male parent must have one r allele (i.e. be Rr). If he had two r alleles, then half of the offspring would have a green shell (and so would he!), and if he was RR, all offspring would have red shells. Therefore, the male parent must be DD Rr. The Punnett square for the cross between Dd Rr and DD Rr parents is shown below.

In an insect species, shell spots and shell color are Mendelian traits. A spotted shell is completely dominant to a plain shell (no spots), and red shells are completely dominant to green shells. For the questions below, use D for the spotted shell allele, d for the plain shell allele, R for the red shell allele, and r for the green shell allele. In the following cross the genotype of the female parent is Dd Rr. What is the genotype of the male parent?

0% All of the mice will inherit the B color allele from one parent and the b color allele from the other parent (they'll be heterozygous). Black is the dominant allele, so the pigment produced in all the mice will be black. Therefore it is not possible to have an offspring with brown fur. The offspring could either be agouti black (50% chance Aa Bb) or solid black (50% chance aa Bb).

In mice, fur color is determined by multiple genes, each of which has two or more different alleles. The genes are all on different chromosomes. Agouti fur is a dominant trait resulting in individual hairs having a light band of pigment on an otherwise dark hair shaft. A mouse with agouti fur is shown below, along with a mouse with solid color fur, which is the recessive phenotype (A = agouti; a = solid color). A separate gene contains the information to make either a dominant black pigment or a recessive brown pigment (B = black; b = brown). A mouse that is Aa bb is crossed with a mouse that is aa BB. What is the probability that an offspring mouse will be agouti brown? Hint - Set up a Punnett square (and remember that you need to figure out the possible gamete genotypes for the mice that were crossed to set up your Punnett square!).

have more than one nucleus and more total chromosomes than the parent cell. Cytokinesis is the last step of mitosis (and is sometimes classified as a separate event that follows mitosis). In cytokinesis, fibers form a ring and pinch a dividing cell in half to form two daughter cells. Cytokinesis occurs after sister chromatids have been distributed to opposite sides of a cell and new nuclear membranes have formed around the chromosomes at each end. Therefore, cells that undergo the other steps of mitosis normally, but not cytokinesis, will have more than one nucleus. Remember that all DNA is replicated prior to mitosis, so if a cell is not split into two cells, there's going to be twice as much DNA in the cell. Each of the two nuclei will contain the same number of chromosomes present in the nucleus of the parent cell, so there will be double the number of total chromosomes compared to the parent cell.

In some organisms (e.g. certain fungi and algae), all steps of mitosis occur normally except cells do not undergo the last step, cytokinesis. The daughter cells produced when this happens

all the offspring have long fins. -The long-finned fish are either homozygous for the long-fin allele or heterozygous. The short-finned fish must be homozygous for the short-fins allele (otherwise they would not have short fins!). All of the offspring obtained by crossing an individual that is homozygous for the allele that corresponds to the dominant trait (long fins) with an individual that is homozygous for the allele that corresponds to the recessive trait (short fins) are heterozygous for the gene and show the dominant trait (have long fins). -If the long-finned parent was heterozygous, then one-half of the offspring from a cross with a short-finned fish would be predicted to have short fins, and the other half long fins. -It is not possible to end up with a group of offspring that all have short fins; that would only be possible if both parent fish had short fins. A group of offspring where 75% of the offspring have long fins and 25% of the offspring have short fins could only be obtained from crossing two heterozygotes, both of whom would have long fins.

In zebrafish, long fins are completely dominant to short fins. A scientist has a group of fish with long fins, and wants to identify the fish that are homozygous for the long fin allele. The scientist crosses each of the long-finned fish to a short-finned fish, and observes the fin length of the offspring. To identify the long-finned parent fish that are homozygous for the long fin allele, she should pick ones where

Cross a true-breeding round leaf tomato plant with a true-breeding pointed leaf tomato plant. All of their offspring will have the dominant trait for leaf shape. A true-breeding tomato plant is homozygous for the leaf shape gene. Therefore, the offspring of a cross between a true-breeding round leaf tomato plant and a true-breeding pointed leaf tomato plant will all be heterozygous for the leaf shape gene. For Mendelian traits, the dominant trait is the trait observed when two different alleles are present. Dominant traits are not necessarily more beneficial for an organism compared to recessive traits, nor are they necessarily more prevalent in the population.

Leaf shape is a Mendelian trait in certain species of tomato. How could you determine which leaf shape, rounded or pointed, is dominant and which is recessive?

-DNA replicated prior to the process -daughter cells have replicated chromosomes -homologous chromosomes are separated -produces two daughter cells

Meiosis I

Ww XNY; ww XnXn

Red-green color blindness is due to an X-linked recessive allele in humans. A widow's peak (a hairline that comes to a peak in the middle of the forehead) is due to an autosomal dominant allele. A man with normal color vision and a widow's peak marries a color blind woman with a straight hairline. The man's father had a straight hairline, as did both of the woman's parents. Use "W" and "w" for the hairline alleles (widow's peak and straight), and the "XN" and "Xn" for the color vision alleles (normal color vision and red-green color blindness).Use this information to answer the questions below. The genotype of the man with a widow's peak and normal color vision is _________. The genotype of the color-blind woman with a straight hair line is _______.

EEggqq EeGgQq EeggQQ

Select ALL genotypes below that could be observed for offspring of this male and female. HINT - Use the correct gamete genotypes from the questions above to set up a Punnett Square.

-The two copies of a chromosome generated by DNA replication are distributed to opposite ends of a dividing cell. -Produces two genetically identical daughter cells. -DNA is replicated once prior to division. All of a cell's DNA must be copied once (and only once) prior to any type of cell division. In both binary fission and mitosis, the two copies of a chromosome (the one chromosome in a prokaryotic cell; each of the multiple chromosomes in a eukaryotic cell) must be distributed to opposite sides of a dividing cell so that each daughter cell produced has a complete set of genetic information. -Both binary fission and mitosis result in two daughter cells that are genetically identical. -Prokaryotic cells cannot be diploid; they only have one chromosome (one piece of DNA). Prokaryotic cells lack organelles, so they do not have nuclei.

Select ALL statements that correctly describe BOTH prokaryotic division (binary fission) and mitosis.

-Two diploid cells are produced when a dipoid cell divides by mitosis; division of a diploid cell by meiosis produces four haploid cells -In mitosis, the daughter cells are genetically identical, but in meiosis the daughter cells are genetically different.

Select ALL statements that correctly describe mitosis and meiosis.

pleiotropy; polygenic inheritance Pleiotropy refers to situations where a particular gene affects multiple characters. In polygenic inheritance, one specific character is influenced by multiple genes

Shell color in beetles is determined by one gene that also affects their ability to eat toxic plants. Feather color in birds is determined by four different genes that only affect feather color. Shell color in beetles is an example of __________, and feather color in birds is an example of __________.

mitosis and meiosis II. Sister chromatids are separated in both mitosis and meiosis II. Homologous chromosomes are separated in meiosis I and are not separated in mitosis.

Sister chromatids are separated in

100%

The couple has a daughter with normal vision and a widow's peak. What is the chance that she is heterozygous for both genes?

haploid, haploid Homologous chromosomes are separated in meoisis I, therefore the daughter cells are haploid with replicated chromosomes. Meiosis II separates sister chromatids generating haploid daughter cells with unreplicated chromosomes.

The daughter cells produced by meiosis I are _________. The daughter cells produced by meiosis II are ________.

50% Female offspring will be either XrXr or XRXr, and therefore half of the female offspring will have abnormally shaped wings and half will have slightly misshapen wings.

The gene that controls wing formation in fruit flies is located on the X chromosome. The R allele allows normal wing formation, while the r allele causes the wings to be abnormallyshaped. The alleles show incomplete dominance. Heterozygotes have only slightly misshapen wings. A cross is performed between two fruit flies where the male is Xr Y and the female is XR Xr. What percentage of the female offspring are predicted to have abnormally shapedwings?

A and C A and D B and C B and D For a pair of homologous chromosomes, any two chromatids that are not sisters (i.e. not replicated copies of a chromosome) represents a pair of non-sister chromatids.

The image below shows a pair of homologous chromosomes following DNA replication. Letters indicate individual pieces of DNA. Which of the letter pairs below represent non-sister chromatids?

The two genes are on the same chromosome and no crossing over occurred between the genes during meiosis. Alleles will always be inherited together if they are on the same chromosome and no crossing over occurs between the genes. The offspring inherited the A and B alleles from one parent and the a and b alleles from the other parent. If these genes are on the same chromosome and no crossing over occurs between them, then the A and Balleles will stay packaged together, and the a and b alleles will also stay packaged together because they are physically part of the same piece of DNA.

The offspring generated by the mating described above are all heterozygous for both genes (AaBb). If ALL the gametes produced in the offspring are AB or ab (there are no Ab or aBgametes), what must be true of the two genes?

EgQ, egQ, Egq, and egq

What are the possible gamete genotypes for the female?

It is not possible to get a male offspring with slightly misshapen wings because males only inherit ONE X chromosome and therefore only have one allele for the wing shape gene. A male will have either abnormally shaped wings (Xr Y) or normal wings (XR Y). none

What cross, if any, has the potential to generate male offspring with slightly misshapen wings?

Homologous chromosomes are separated in meiosis I. In meiosis I, homologous chromosomes are separated, which means that the cells produced by meiosis I are haploid. Haploid cells have ONE allele for each gene because every chromosome has a different set of genes (there are no homologous pairs).

What event in meiosis explains why gametes are haploid?

25%

What is the probability of the couple having a color blind child (son or daughter) with a straight hairline?

0%

What is the probability of the couple having a color blind daughter with a widow's peak?

Homologous chromosomes can exchange pieces of DNA (crossing over).

What process during meiosis explains why the combination of alleles carried on the same chromosome can be different in the gametes produced by meiosis than in the parent cell that divides?

meiosis I only In meiosis I, homologous chromosomes form pairs. This is important because it allows each chromosome of a homologous pair to be distributed to a different daughter cell, resulting in haploid cells (one set of chromosomes). Homologous chromosomes do not pair up in mitosis. And homologous chromosomes cannot pair up during meiosis II because the homologous chromosomes have already been separated in meiosis I.

When do homologous chromosomes pair up?

Stuff to know

When replicated homologous chromosomes pair up in meiosis I, non-sister chromatids can exchange pieces of DNA that have the same genes. If (and only if) the homologous chromosomes have different alleles, this can generate new allele combinations. For example, imagine that one homologous chromosome has a purple flower allele and a green pod allele, for the flower color and pod color genes, respectively. The other homologous chromosome has a yellow flower allele and a yellow pod allele. If the non-sister chromatids swap the piece of DNA with the flower color gene, you'll end up with a chromatid that has a purple flower allele and a yellow pod allele, and a chromatid that has a yellow flower allele and green pod allele. When sister chromatids are separated in meiosis II, the four cells will have chromosomes with the allele combinations listed below. Draw out this example (or a different one with your choice of genes) to help you visualize the effects of crossing over on gamete genotypes. Possible Gamete Allele Combinations:-yellow flower; yellow pod-yellow flower; green pod-purple flower; green pod-purple flower; yellow pod

-. ic cells have homologous chromosomes. -Prokaryotic cells (e.g. bacteria) divide by binary fission, and NOT my mitosis (or meiosis!). -Haploid eukaryotic cells can divide by mitosis; diploid eukaryotic cells can divide by mitosis or meiosis. -Division of a prokaryotic cell IS asexual reproduction - all prokaryotic organisms are unicellular (one cell), and the daughter cells produced are genetically identical (and identical to the parent cell). Some eukaryotes reproduce sexually, while others (e.g. single-celled eukaryotes like yeast; some multi-cellular eukaryotes) reproduce asexually.

Which of the following statements, if any, correctly describes a difference between prokaryotic and eukaryotic cells/organisms?

-Homologous chromosomes can have the same or different alleles for each gene; -Sister chromatids always have the same alleles for each gene.

Which of the following, if any, correctly compares homologous chromosomes and sister chromatids?

eight The diagram below shows the eight possible gamete genotypes using the letters "R," "E," and "Q." Each genotype would be equally likely.

You are assessing three genes that are on different chromosomes. Determine the number of possible gamete genotypes (for those genes) for an individual that is heterozygous for all THREE genes. HINT - Draw a forked-line diagram to help you keep track of the alleles; use whatever letters you prefer for the three genes.

All off the offspring will be heterozygous for both genes Both of the parent flies are homozygous for both traits. This means the parent that's homozygous for straight bristles and short antennas (AABB) can only produce gametes with a straight bristle allele and a short antenna allele. And the parent that's homozygous for curly bristles and long antennas (aabb ) can only produce gametes that have a curly bristle allele and a short antenna allele. Therefore, the offspring will all be heterozygous for both genes.

You are studying two Mendelian traits in flies, bristle shape and antenna length. Bristles are either straight or curly and antennas are either short or long. You cross a fly that is homozygous for both straight bristles (A) and short antennas (B) with a fly that is homozygous for both curly bristles (a) and long antennas (b) and obtain offspring. What do you know about the genotypes of the offspring?

Homologous chromosomes, diploid cells

________ are pairs of chromosomes with the same genes, and therefore are only present in________. One of the homologous chromosomes in a pair was inherited from the egg and the other one from the sperm during fertilization. Although homologous chromosomes always have the same genes, they can have different alleles (versions of a gene) for one or more of the genes. -Sister chromatids are the two copies of a chromosome generated by DNA replication. Therefore, sister chromatids always have the same genes AND alleles. Unless errors occurred during DNA replication, the sequences of sister chromatids are identical.

-produces four daughter cells -daughter cells have unreplicated chromosomes -sister chromatids are separated

meiosis II

Mutations that increase the activity

or expression of proteins that promote cell division can cause cells to divide uncontrollably, leading to cancer.