Bio Exam 3 Follow-up Questions

Explain why it's necessary for eukaryotic chromosomes to condense prior to mitosis. Explain why condensing of chromosomes prior to division is NOT necessary in prokaryotic cells.

- allows chromosomes to be distributed (otherwise they'd get tangled up!) - the duplicate copies of a chromosome (sister chromatids) stay attached - allows each sister chromatid to be distributed to a different daughter cell

Describe the steps of mitosis. Draw and label pictures to illustrate your description Keep it simple and stick to a diploid cell with two sets of chromosomes. You could also try drawing it out for a haploid cell!

1) chromosomes condense and spindles form 2) nuclear membrane breaks down 3) spindles line up chromosomes in center 4) sister chromatids are pulled to opposite sides of cell 5) new nuclear envelope forms around chromosomes 6) cytokinesis- cell pinches in middle

A gene important for determining fur color in rabbits has four different alleles. How many different alleles could an individual rabbit have for the fur color gene?

2

How many different offspring genotypes are possible when a female that is FFBbTT mates with a male that is ffBbTT? (Answer posted at the end of the slides).

3, FfBBTT, FfBbTT, FfbbTT

A diploid cell has 15 different chromosomes. How many individual chromosomes (pieces of DNA) are in the nucleus? What about a haploid cell with eight different chromosomes?

30 pieces of DNA in haploid 8 pieces of DNA in diploid

Focusing on one gene, use the steps we followed for predicting genotypes to determine the possible offspring genotypes and how likely each one is for a mating between male that is homozygous for the gene, and a female that is heterozygous for the gene. (Use any letter you want for the gene).

50% chance heterozygous dominant 50% chance homozygous dominant

A woman with an autosomal recessive disease has a child with a man who is a carrier of the disease. What is the probability that the child will be affected? A carrier? Homozygous for the non-disease allele? If their first child is affected by the disease, what is the probability that a second child will be affected?

50% chance that the child will have the disease because we cross Aa (carrier) with aa (has disease). 50% chance that the child will be a carrier. Same probability that first and second child will be affected.

A disease is determined by a single gene (i.e. the combination of alleles you have for that one gene determines whether or not you have the disease). If you are BB or Bb you have the disease, and if you are bb you do not. A male that is heterozygous for the disease gene and a female that does not have the disease mate. What is the probability that their offspring will have the disease? If their first offspring has the disease, does that tell you anything about the probability a second offspring will have the disease? Explain your answer.

50% probability the offspring will have the disease Bb, Bb, bb, bb No, the chances for the outcome of an offspring is the same every time

A human character is determined by three different genes and there are four different alleles for each gene. For each individual gene, how many alleles does a human body cell have? A human gamete?

A human body cell would only have 2 alleles for each gene because we are diploid individuals. A human gamete would only have 1 allele for each gene because gametes are haploid.

Fruit files have three pairs of autosomes (chromosomes with autosomal genes). For an autosomal gene, what's the maximum number of different alleles an individual fruit fly can have? The minimum number? What about a gamete produced by the fruit fly? Are these numbers different for humans that have 22 pairs of autosomes? Why or why not?

An individual fruit fly can have 2 alleles for an autosomal gene. This is because fruit flies are diploid, and so they can only inherit 2 alleles (one from each parent). Gametes of a fruit fly will have one allele for a gene. no they are not different because concerning autosomal genes, anything will always have two alleles for a specific gene and when it comes to gametes, they will always have one allele for a gene because the homologous chromosomes have been split up.

Describe the process of prokaryotic cell division (aka binary fission).

DNA is replicated DNA is pulled to opposite ends of the cell cell pinches in the middle cell physically splits two genetically identical offspring are produced

Explain why two individuals with the exact same genotypes can have different phenotypes. Will these phenotypic differences show particular patterns of inheritance? Why or why not?

Environmental factors can also affect the phenotype of an organism, but they have nothing to do with inheritance because they are obtained from outside conditions and not genes that can be passed down.

Explain why the gametes of diploid organisms that reproduce sexually must be haploid, and not diploid.

Gametes must be haploid because they will be combining with another gamete.

Can the term carrier be applied to autosomal dominant diseases? To males for X- linked recessive diseases? Explain your answers.

No because if one dominant allele is present, the person will have it (so autosomal dominant cannot have a carrier). Males with x-linked recessive disease can also not be carriers because they only have one x chromosome and could not carry the disease on another.

What are the possible offspring genotypes for parents that are RrQq and Rrqq? (Solution to this lecture follow-up question is posted at the end of the slides.)

RRQq RrQq RRqq Rrqq rrQq rrqq

You are studying the inheritance of two genes that each have two alleles (D or d, and Q or q). You notice that the gametes produced by an individual that is DdQq are virtually all DQ or dq; the presence of Dq and dQ gametes is very rare. Propose a hypothesis to explain this result.

That during meiosis 1, the homologous chromosomes lined up n a way that the chromosomes with D and P

Do the two cells produced in meiosis I have replicated or unreplicated chromosomes? Are they haploid or diploid? Explain why.

The cells produced in meiosis 1 are diploid because they further divide into 4 haploid cells in meiosis 2.

A couple has a son and a daughter that are both affected by the same genetic disease. Both of the parents are unaffected. From this information can you tell whether the disease is autosomal dominant, autosomal recessive, or X-linked recessive? If so, which one is it? If not, why not? What, if anything, can you say anything about the genotypes of the parents?

The disease is autosomal recessive and both of the parents are heterozygous for the disease.

The seed coats of some lentil seeds have spots that can be different sizes. Seed coat spot size is determined by one gene. Design an experiment to test whether seed coat spot size is an example of complete dominance, incomplete dominance, or codominance. Include a description of the results you'd expect to obtain for each inheritance pattern.

We could cross homozygous recessive plants and homozygous dominant plants in order to determine how the heterozygote plants behave.

Describe the relationships between the terms homologous chromosomes, gene, allele, trait, and character. Use sketches to illustrate the relationships if that helps.

a sister chromatid is a duplicated chromosome homologous chromosomes are not sister chromatids when homologous chromosomes are replicated, there are pairs of sister chromosomes that are homologous to each other Characters are like genes and traits are like alleles (Note that most characters are influenced by multiple genes)

Explain the difference between autosomal genes and sex-linked genes.

autosomal genes effect males and females the same way as they do not appear on the sex chromosomes because when you are combining male and female gametes, the male will only carry half of the genes that the female does because a male only has one X chromosome whereas a female has two, this eventually means that the concept of dominant vs recessive does not apply to genes on the male sex chromosomes because the chromosomes do not carry the same genetic information and therefor cannot have two versions of the same allele.

Thinking about the differences between mitosis and meiosis, why does it make sense that diploid cells can divide by meiosis, but haploid cells can't?

because a haploid cell would not be able to generate 4 cells (not enough DNA)

Explain why cancer that occurs due to mutations in the genes of body cells cannot be passed on to an individual's offspring.

because body cells are not used to form offspring, sex cells are.

Why does cancer development require mutations in multiple genes?

because many mechanisms work together to prevent uncontrolled growth, so the mutation of one gene could be stopped by the body

Compare complete dominance, incomplete dominance, and codominance. What observation(s) would allow you to distinguish between each particular pattern of inheritance? Use examples if it helps you answer the questions.

complete dominance- one allele has full dominance over the recessive allele and will always show up when it is present. incomplete dominance- both alleles contribute to phenotype, causing heterozygotes to have a phenotype that is in the middle (a mixture) of the two alleles (ex. dark purple and white combine to form light purple). codominance- heterozygotes have both traits (ex. roan cows show both allele colors).

***Describe the sources of genetic variation in sexually reproducing organisms. Explain which of these sources also occur in asexually reproducing organisms and why the other sources do not.

crossing over: can generate different allele combinations for genes on the same chromosome independent orientation: generates different allele combinations for genes on different chromosomes what are sources of genetic variation in asexual reproduction?

Humans have twenty-three pairs of chromosomes. During division of a human skin cell, the two sister chromatids of one replicated chromosome fail to separate. How many individual chromosomes will each of the daughter cells have?

each daughter cell will have one less chromosome

Explain why genotype predictions for complete dominance, incomplete dominance, and codominance are all the same.

genotype predictions for these are all the same because each trait still has its own allele and the phenotype is the only thing that changes depending on how the alleles combine.

Curly hair is primarily determined by a single autosomal gene in humans. There are two alleles for the gene, "curly" and "straight," and the alleles show incomplete dominance. What are the genotype and phenotype probabilities for children of a curly haired mom and a dad with straight hair?

genotypes- Cc or cc Phenotypes- wavy or straight

ABO blood type in humans is determined by a single autosomal gene; three alleles different alleles exist for the gene. 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. The i allele has no effect on the carbohydrates attached to red blood cell surfaces and is recessive compared to each of the other two alleles. The IA and IB blood type alleles show codominance. What are the possible offspring genotypes and phenotypes of parents that are IAIB and IBi?

genotypes- IBIA, IBIB, IAi, IBi phenotypes- AB, B, A

Explain why haploid cells cannot divide by meiosis.

haploid cells cannot divide by meiosis because there is not enough DNA to generate 4 genetically different daughter cells.

Review the terms haploid and diploid. Use these terms to describe the process of meiosis.

haploid egg and haploid sperm (one set of chromosomes) combine to form a diploid zygote. then further divides into 4 haploid daughter cells.

What does it mean if an individual is heterozygous for a gene? Homozygous for a gene?

homo- same alleles for gene (RR or rr) hetero- different alleles for genes (Rr)

If two chromosomes are homologous, what does that mean? Do two homologous chromosomes always have the same genes? The same alleles for each gene?

homologous chromosomes are pairs of chromosomes with the same sets of genes. They all have the same genes, but they can have different alleles for the same genes.

Explain why homologous chromosomes, which have the same genes at the same positions (loci), can have different DNA sequences.

homologous chromosomes can have different DNA sequences because while homologous chromosomes have the same set of DNA, they may carry different alleles for particular genes.

In pea plants, purple flower color is dominant to white flowers (no color). You are given a plant with purple flowers, but do not know whether it is heterozygous or homozygous for the flower color gene. If you crossed the purple plant with a true- breeding white flowered plant, would you be able to determine the genotype of the purple-flowered plant from the F1 offspring's phenotype(s)? If so, what are the expected offspring phenotype probabilities if the purple flowered plant was heterozygous for the flower color gene? Homozygous?

if the purple flower is homozygous and crossed with a true-breeding white plant, the only possible phenotype is purple flowers (Pp). If the purple plant is heterozygous, the offspring phenotype possibilities are 50% purple and 50% white.

Why is it important to look at lots of offspring (a large sample) when assessing patterns of inheritance?

larger sample size is more similar to the actual population

Explain why the gametes produced in males that have X chromosomes always have the same alleles for all X-linked genes. Explain why gametes produced in females can have different alleles.

males only have one x chromosome while females have 2

***Genes A and B are both on the same chromosome. An individual has different alleles for Gene A. Does this tell you anything about whether or not they have the same or different alleles for Gene B?

no

Can you apply the terms homozygous and heterozygous to prokaryotic cells? To gametes produced by a diploid organism? Explain your answers.

no because those terms only apply to diploid organisms which prokaryotes are never

Can a male be heterozygous for an X-linked gene? Why or why not?

no, because only one x chromosome

Compare pleiotropy and polygenic inheritance. Explain why characters that demonstrate polygenic inheritance often have a wide variation in phenotypes.

pleiotropy- one gene affects more than one character (ex. VgVg= normal wings and vgvg= short wings and bristles are moved to different part of back) polygenic inheritance- a character is determined by more than 1 gene (ex. AABB= disc shape, aabb= long, AaBb= disc shape

Compare the purposes of cell division in prokaryotes and eukaryotes.

pro- asexual reproduction eu- growth and repair

Describe the differences between prokaryotic and eukaryotic cells/genomes that contribute to differences in the purposes and processes of cell division.

pro- one chromosome to be copied eu- multiple chromosomes to be copied

A mutation in the gene PTEN has been linked to cancer. The mutation increases the activity of the protein produced by expression of PTEN. Based only on this information, do you predict that this protein promotes or inhibits cell division? Explain your reasoning.

promotes cell division because cancer is caused by rapidly dividing cells.

List at least three characteristics important in organisms that are used to study inheritance.

short lifespans visual phenotypes reproduce quickly inexpensive and easy to grow produce many offspring mating can be controlled

Explain why sister chromatids always have the same alleles for each gene. Explain why non-sister chromatids can have the same OR different alleles for each gene.

sister chromatids have the same alleles for each gene bc they are exact duplicates of the chromosomes. non-sister chromatids can have the same or different bc they contain one from each replicated chromosome.

Sketch and label a picture to describe the relationships between the terms sister chromatids, non-sister chromatids, replicated chromosomes, and homologous chromosomes. Use your sketch to explain the relationships to someone that's not in the class.

sister chromatids- duplicate copies of an individual chromosome generated by DNA replication non-sister chromatids- chromatids of a homologous chromosome pair that are not sisters (one from each of the replicated chromosomes) replicated chromosomes- contains two identical double strand -DNA- molecules, the chromatids, that are joined at their centromere. homologous chromosomes- pair of chromosomes w same sets of genes (can have different alleles)

In fruit flies, red eyes is dominant and white eyes is recessive. A red-eyed female fruit fly mates with a white-eyed male. If some of their male offspring have white eyes, what (if anything) do you know about the genotype of the female fly?

the female is heterozygous for eye color

Explain why the genotype of an organism plays a primary role in determining its phenotype, and why the genotype of an organism is NOT the only thing that determines its phenotype.

the genotype is the combination of alleles that an organism has while the phenotype of the combination of physical traits. The genetics of an organism determines the phenotype, but physical traits can also be altered without genes (for example, we can dye our hair).

An error occurs during meiosis of a human cell, and the pair of chromosome 11's (homologous chromosomes) fail to separate in meiosis I. At the end of meiosis II, two of the gametes each have an extra chromosome 11 (two rather than just one). Will the other two gametes have zero, one, or two chromosome 11's? Explain your answer. Hint - Draw pictures to help you visualize what happened; don't worry about drawing all the other chromosomes.

they will have no chromosomes because when the homologous chromosomes failed to separate in meiosis 1, they would both give extra to 2/4 cells

Explain why you know a plant that's true-breeding for a particular trait is homozygous for the gene associated with that trait.

true breeding- all offspring of self-fertilization always have same trait of parent (applies to a particular trait, NOT to all traits) you know they are homo bc if they were hetero, their offspring would have the chance of getting the other allele

Round peas are dominant to wrinkled peas and yellow pea color is dominant to green pea color in a species of pea plant. Using R as the allele for round peas, r as the allele for wrinkled peas, Y as the allele for yellow peas, and y as the allele for green peas, figure out the possible offspring phenotypes and their probabilities from a cross between plants that are RrYy and Rryy.

wrinkled yellow- 1/8 wrinkles green- 1/8 round yellow- 3/8 round green- 3/8

X-linked recessive diseases are due to a recessive allele for a particular X chromosome gene in humans. Explain why X-linked recessive diseases affect more males than females.

x-linked recessive genes affect males more because they only have one allele for x-linked genes, so it is not possible for males to have a recessive and dominant gene (cant be heterozygous)

If a pair of homologous chromosomes have the same sets of alleles, can crossing over occur? If so, can it result in new genetic variation?

yes crossing over can occur but it will not cause genetic variation.

Are both chromosomes of a homologous chromosome pair copied during DNA replication?

yes, EVERY chromosomes of a homologous chromosomes pair gets copied BEFORE division.

Elephants are diploid organisms. Can more than two alleles for a particular gene exist in an elephant population? Can an individual elephant have more than two alleles for a particular gene? Can an individual elephant have only one allele for a particular gene? Explain your answers.

yes, more than 2 alleles for the same gene can exist in a population no, because they are diploid no, because they are diploid