Genetics Unit Review Flashcards
How many autosomes does a human somatic cell contain? How many autosomes does a human gamete contain?
44 (diploid + excludes sex chromosomes)
22
How many pairs of homologous chromosomes does a human somatic cell contain? How many chromosomes does a human somatic cell contain?
23
46
The diploid number of chromosomes for shrimp is 254. How many more chromosomes does a shrimp somatic cell have than a human somatic cell?
208 (254-46)
What did X-ray crystallography reveal to
Rosalind Franklin about the structure of
DNA?
uses X-rays to determine the geometry or arrangement of atoms in a molecule
-Franklin determined that DNA had the form of a
spiral, or helix
Use a diagram to illustrate James Watson and
Francis Crick’s model of a DNA molecule
regular DNA packaging diagram (4.5 pg 98)
What is meant by “base pairing” when referring
to a DNA double helix?
The two helical strands are connected through interactions between pairs of nucleotides, also called base pairs.
Two types of base pairing occur: nucleotide A pairs with T, and nucleotide C pairs with G
What is the cell cycle?
A cell cycle is a series of events that takes place in a cell as it grows and divides.
Meiosis I vs. meiosis II
Genetic reassortment occurs during meiosis I. The first meiotic stage is also an example of reductional division, wherein a change in ploidy takes place as a diploid parent cell forms haploid daughter cells. Meiosis II, being an equational division, does not feature a change in ploidy; it instead produces haploid daughter cells from haploid parent cells. Meiosis I, also produces cells in which the chromosomes are still whole and are composed of two chromatids; on the other hand, the separation of sister chromatids occurs in meiosis II.
Meiosis II is generally regarded as being very similar to mitosis, except for the presence of two parent cells, instead of only one. In both meiosis I and II, cytokinesis occurs, and there are two daughter cells per parent cell.
Which type of chromosomal damage might
affect more than one chromosome? Explain.
In a translocation, a segment from one chromosome is transferred to a nonhomologous chromosome or to a new site on the same chromosome.
Translocations place genes in new linkage relationships and generate chromosomes without normal pairing partners
What is the term for an allele that is not
expressed in the phenotype of a heterozygous
individual?
recessive allele
How is the concept of probability applied when examining genetic crosses?
One probability rule that’s very useful in genetics is the product rule, which states that the probability of two (or more) independent events occurring together can be calculated by multiplying the individual probabilities of the events
The principles of probability can be used to predict the outcomes of genetic crosses. The gene combinations that might result from a genetic cross can be determined by drawing a diagram known as a Punnett square
What is a hybrid (in the context of genetics)?
Give an example
Hybrids are offspring that result from crossing two true breeding varieties of the same species
E.g. Mendel produced hybrids by crossing tall-stemmed pea plants with short-stemmed pea plants
What is the term for a trait determined by
more than one gene?
Polygenic trait
-characteristic, such as height or skin colour, that is influenced by two or more genes.
-because multiple genes are involved, polygenic traits do not follow the patterns of Mendelian inheritance
List and briefly explain the four main points
in Mendel’s model of genetic inheritance
1) Genes have alternative versions (alleles)
2) For each gene, organism inherits 2 alleles from parents (both same=homoz.) (both diff=heteroz.)
3) Allele may be expressed as a trait or hidden in a heterozygous individual (dominant vs recessive)
4) Each gamete carries only 1 allele for each hereditary trait due to the separation of allele pairs when gametes form
Differentiate between the law of independent
assortment and the law of segregation.
law of segregation states that every individual possesses two alleles and only one allele is passed on to the offspring
law of independent assortment states that the inheritance of one pair of genes is independent of inheritance of another pair (doesn’t affect other genes)
What does a gene map show?
shows the locations of and distances of genes on a chromosome
Do human ABO blood type alleles show
incomplete dominance or codominance?
Explain.
The human ABO blood group system exhibits codominance. The system consists of three alleles A, B, and O. Both A and B are dominant in relation to O, and therefore blood group A can have the genotype AA or AO. Blood group B can have the genotype BB or BO.
-both alleles expressed at same time… no intermediate phenotype
Why are there more men than women with
red-green colour blindness?
- x-linked recessive disorder
- males are hemizygous(X Y)= more likely to get it
(needs 1 recessive allele) - females = very rare (need 2 recessive alleles)
What is the name for the initiative to determine
the nucleotide sequence of all human
chromosomes?
Human Genome Project
What are some ways to identify genes in DNA
sequences?
- Automated DNA sequencing machines (a computer
is given instructions for finding genes in the sequence
and is then left to find them) - Fluorescent dyes (nucleotides labelled with diff.
colours)
How has the ability to label nucleotides with
fluorescent dyes benefited genetic research?
can be used to rapidly and accurately sequence a DNA template in a DNA polymerase reaction
What are some features of plasmids that make
them useful in genetic engineering?
amplify, or produce many copies of certain genes
What is a DNA chip?
small glass wafer or slide spotted with an array of single-stranded DNA fragments
-some spots (for example) could contain DNA with mutations known to cause cystic fibrosis
Give one application for a transgenic plant
and one for a transgenic animal.
GM plants are used in biotechnology for the production of pharmaceuticals, industrial products, or biofuels (renewable fuels from plant matter or other
organic materials). For example, genetic engineers have developed lines of safflower plants that produce a wide variety of products. One of these products is insulin, for the treatment of diabetes. Transgenic
safflower can efficiently produce authentic molecules of human insulin
goal is to make a transgenic animal that produces a large amount of a rare biological substance for medical use. Using transgenic animals to produce pharmaceuticals is sometimes called “pharming.” Most cases involve adding a gene for a desired human protein, such as a hormone, to the genome of a farm mammal
Give two reasons for determining the nucleotide sequence of a gene
-tells scientists the kind of genetic information that is carried in a particular DNA segment
-blueprint that contains the instructions for building an organism, and no understanding of genetic function or evolution could be complete without obtaining it
Was Dolly the sheep a transgenic organism?
Explain
She was cloned with a genetically modified cell using somatic cell nuclear transfer (SCNT).
This was the method used to produce Dolly the Sheep, although she was not genetically modified as she was created using an unmodified cell. (nuclear transplantation)
transgenic: acquired 1 or more genes from a different type of organism
List two difficulties with using somatic cells
to clone animals
many embryos do not survive, and the clones
can have serious health problems
What is the main difference between taking
a pharmaceutical, such as an antibiotic, and
undergoing gene therapy?
Antibiotics are medications that destroy or slow down the growth of bacteria. They include a range of powerful drugs used to treat diseases caused by bacteria.
Gene therapy replaces a faulty gene or adds a new gene in an attempt to cure disease or improve your body’s ability to fight disease. Gene therapy holds promise for treating a wide range of diseases, such as cancer, cystic fibrosis, heart disease, diabetes, hemophilia and AIDS
What is the term for a line of mice with a
gene that has been altered so that it no
longer functions?
Knock-out mice
-transgenic mice used in medical research
-genome is altered in knockout mice so that a gene no longer functions (the gene is “knocked out”).
Why is it important for cells to have a control
system that regulates cell division? Describe a
possible consequence of a malfunction in cell
cycle control
Disruption of normal regulation of the cell cycle can lead to diseases such as cancer. When the cell cycle proceeds without control, cells can divide without order and accumulate genetic errors that can lead to a cancerous tumor
Why would undergoing meiosis be a problem
for an organism that reproduces asexually?
it would make the cells haploid instead of diploid and daughter cells would have half the number of chromosomes/DNA as parent cells
In which phase of the cell cycle would most of
your somatic cells be at any particular time?
Explain your reasoning
Interphase - 90% of time
A cell spends most of its time in what is called interphase, and during this time it grows, replicates its chromosomes, and prepares for cell division.
Predict what would happen if spindle fibres
were disrupted during anaphase of mitosis.
One daughter cell would be missing their DNA and the other daughter cell would have double the amount of DNA in their cell
the chromosomes would also fail to segregate naturally. The spindle fibers are involved in the movement and positioning of chromosomes during cell division.
=non-disjunction in mitosis
Describe how crossing over during meiosis
recombines the genetic material of an
individual organism’s two parents
During meiosis, homologous chromosomes (1 from each parent) pair along their lengths. The chromosomes cross over at points called chiasma. At each chiasma, the chromosomes break and rejoin, trading some of their genes. This recombination results in genetic variation
Explain how the assortment of chromosomes
during meiosis contributes to variation in
the gametes
When cells divide during meiosis, homologous chromosomes are randomly distributed to daughter cells, and different chromosomes segregate independently of each other. This called is called independent assortment. It results in gametes that have unique combinations of chromosomes
Use diagrams to illustrate the four main types
of large-scale mutations in chromosomes
Deletions, Translocations, Duplications and Inversions
Is it possible for a mutation to be beneficial to
an organism? Explain
Beneficial mutations are essential for evolution to occur. They increase an organism’s chances of surviving or reproducing, so they are likely to become more common over time. There are several well-known examples of beneficial mutations. Here are just two:
Mutations in many bacteria that allow them to survive in the presence of antibiotic drugs. The mutations lead to antibiotic-resistant strains of bacteria.
A unique mutation is found in people in a small town in Italy. The mutation protects them from developing atherosclerosis, which is the dangerous buildup of fatty materials in blood vessels.
If DNA damage occurs in G1 phase, what
might happen to the damaged region during
S phase?
-it won’t replicate or the damaged DNA will replicate
Contrast the possible impacts of a chromosomal
mutation that occurs in meiosis to one that
occurs in mitosis in a somatic cell
meiosis:
-result in changes in the number of chromosomes in a cell or changes in the structure of a chromosome
-chromosome mutations change and impact the entire chromosome
-examples of conditions that result from abnormal chromosome numbers are Down syndrome and Turner syndrome.
mitosis:
-not passed on to children
-can (but do not always) cause cancer or other diseases
-production of daughter cells with too many or too few chromosomes, a feature known as aneuploidy.
-nearly all aneuploidies that arise due to mistakes in meiosis are lethal
-can be any genomic variation: repeats, deletions, insertions, multiplication, loss of copy number, and others
-chromosomal somatic mutations occur when somatic cells divide
How might a biologist use a karyotype to
identify a species?
Karyotypes can be used to identify a species because different species have different numbers of chromosomes. Humans have 46 chromosomes, while mallards have 80 and fruit flies have only eight. This applies to the species of any type of organism.
In a human, how many pairs of chromosomes would there actually be at the start of meiosis I?
23
Give three reasons that fruit flies are useful
model organisms for genetic research
75% of the genes that cause disease in humans are also found in the fruit fly.
Drosophila have a short, simple reproduction cycle. It is normally about 8-14 days, depending on the environmental temperature. This means that several generations can be observed in a matter of months
It is relatively straightforward to mutate (disrupt or alter) fruit fly genes.
What evidence from Gregor Mendel’s
experiments showed that alleles assort
randomly in meiosis?
When an organism makes gametes, each gamete receives just one gene copy, which is selected randomly. This is known as the law of segregation
pea plants with two different traits produced offspring that all expressed the dominant trait, but the following generation expressed the dominant and recessive traits in a 3:1 ratio.
Sexually reproducing organisms use mitosis
and meiosis, while asexual organisms use only
mitosis. Which type of reproduction, asexual
or sexual, results in offspring with a greater
variation? Explain
Sexual reproduction provides genetic diversity because the sperm and egg that are produced contain different combinations of genes than the parent organisms.
Asexual reproduction, on the other hand, does not need sperm and eggs since one organism splits into two organisms that have the same combination of genes(genetically identical)
Some genes for animal coat colour or feather colour are expressed differently depending on body temperature or season. How might this phenomenon benefit an animal in the wild?
Camouflage, also called cryptic coloration, is a defense or tactic that organisms use to disguise their appearance, usually to blend in with their surroundings. Organisms use camouflage to mask their location, identity, and movement. This allows prey to avoid predators, and for predators to sneak up on prey
Why would it be important for an animal
breeder to know the genotype of an animal
and not only its phenotype?
Bc genotype is the set of genes that determine a phenotypic trait within an animal
