Unit 5 Exam Study Guide Flashcards
Homologous chromosomes are…
pairs of chromosomes that have the same genes in the same locations.
When a cat produces sperm, how many chromosomes does the sperm have?
19 chromosomes
Chromosomes contain ______.
genes
Chromosomes are large molecules of ____ that contain _____ of genes.
DNA, 100/1000s
What are genes?
Genes are segments of DNA that affect traits. A gene comprises a specific DNA sequence located in a particular region of a specific
chromosome.
What do genes provide?
Most genes provide instructions for proteins that the cells make.
______ organisms have ______ of most genes.
Diploid, two copies
Where do diploid cells get their gene copies/where are they located?
Each copy comes from a biological parent. They are located on homologous chromosomes.
What is an allele?
An allele is a particular version or variant of a gene.
What do mutations do to alleles?
Mutations create alleles (“variants”) that differ in their DNA sequences.
Different alleles ___ produce different traits.
may
Individuals may have two alleles that are ________ or two that are ___________.
the same, different
We all have different combinations of _______.
alleles
What is our genome?
Our complete sequence of DNA is called our genome.
What is our genotype?
The collection of alleles is called our genotype.
What is our phenotype?
The collection of expressed traits is called our phenotype.
Hair length is determined by a _______.
single gene
A trait determined by a single gene is
monogenic.
A trait determined by several genes are
polygenic
What is homozygous?
When two alleles are the same (LL or ll) they are homozygous.
What is heterozygous?
When two alleles are different (Ll) they are heterozygous.
What is a dominant allele? Give an example.
Dominant alleles are typically represented by capital letters. Ex. In cats, the short hair allele (L) is dominant. As long as one copy of the L allele is present the cat has short hair.
What is a recessive allele? Give an example.
The recessive allele is always masked when the dominant allele is present. Recessive alleles are typically represented by lower-case letters. Ex. in cats, the allele for long hair (l) is recessive.
The dominant allele is _____ necessarily the most common.
not
What is the wild-type allele?
In genetics, the most common allele in populations is called wild type allele.
What are autosome chromosomes?
Any chromosome other than the X and Y chromosomes.
What are allosome chromosomes?
The X and Y chromosomes.
What is complete dominance? Give an example.
It’s when one allele is completely dominant over the other. Ex. The hair length gene is an example of complete dominance.
_____________ and ___________ individuals have the same phenotype.
Homozygous dominant (LL), heterozygous (Ll)
In cats, fur color is ________.
polygenic
True or false: There can be multiple alleles for one gene.
True
An individual has two alleles for each ________. But there can be ____ possible alleles in a population.
autosomal gene, many
In cats, what is an example of many possible alleles in a population?
The B gene that codes for black (B) or brown (b) fur actually has another possible allele (b^1). b^1 codes for cinnamon color fur. Both B and b are completely dominant over b^1.
What are X-linked genes? Give an example.
Genes on the X chromosome are called X-linked genes. Ex. the orange color gene ( O gene) is on the X chromosomes.
In cats, orange color is ______________.
X-linked dominant
What does the X-linked dominant gene code for and block for in cats?
The dominant O allele codes for red-orange pigment and blocks the formation of black pigment.
Female cats who are _____ and male cats who are ____ are _____ regardless of what the alleles for the _____ are.
OO, O, orange, B genes
The _________ allows the ________ pigment in cats to be made.
recessive o allele, black-brown
Females cats that are __ and male cats that are _ will have other colors.
oo,o
Female cats that are __ will have patches of _____. This phenotype is called ________.
Oo, orange, tortoiseshell
Heterozygous (Oo) female cats are a mix of fur color because…
one X is inactivated.
During embryonic development in mammals, heterozygous (Oo) female cats have…
one X chromosome inactivates and condenses into a barr body.
Some genes in cats affect ____________.
pigment density
What gene in cats affects pigment density?
The Dilution gene (D gene) impacts how much pigment is deposited in the fur.
What type of trait is diluted color?
Diluted color is a recessive trait (d). Individuals who are dd have a diluted phenotype.
What creates the phenotype of blue for the dilution gene?
If a Black cat (BB or Bb) is dd for the diluted gene, its phenotype is blue.
What creates the phenotype of lilac for the dilution gene?
If a brown cat (bb or bb^1) is dd for the dilution gene, its phenotype is lilac.
What creates the phenotype of cinnamon for the dilution gene?
If a cinnamon cat (b^1b^1) is dd for the dilution gene, its phenotype is sable.
What creates the phenotype of cream for the dilution gene?
If an orange cat (OO or O) is dd for the dilution gene, its phenotype is cream.
What is the white spotting allele in cats?
The S allele of the spotting gene produces white spotting that masks the cat’s true color.
For white spotting, a cat that is SS…
will have a lot of white-almost all white.
For white spotting, a cat that is Ss…
will have a medium amount of white.
For white spotting, a cat that is ss…
is the recessive allele that produces no white fur at all.
The white spotting gene is an example of __________.
incomplete dominance
What is incomplete dominance?
One allele doesn’t completely mask the other. That means that the heterozygous individuals have an intermediate phenotype.
Genes can have multiple possible _______, but for ________ organisms, an individual only carries ____________.
alleles, diploid, two alleles
What are five possible types of alleles?
- Dominant
- Recessive
- Incompletely dominant
- Autosomal
- Sex-linked
The combination of ________ (________) determines the ________ (__________).
alleles (genotypes, traits (phenotype)
What is “true breeding”?
When true-breeding green pea plants self-fertilize, they always produce green-seeded peas. This pattern is also seen with yellow pea plants.
What is a Punnett Square?
In a Punnett Square, all possible genotypes of the gametes are listed
along the top (for one parent) and side (for the other parent) of a grid. The combinations of gametes are then made in the boxes in the table based on which alleles are combined. Each box then represents the diploid genotype of the offspring.
What is codominance?
It’s when both alleles for the same
characteristic are simultaneously expressed when present.
What’s an example of codominance?
An example of codominance occurs in the ABO blood groups of humans. The A and B alleles are expressed as A or B molecules
present on the surface of red blood cells. Homozygotes (IAIA and IBIB) express either the A or the B phenotype, and heterozygotes (IAIB) express both phenotypes equally.
What’s an example of incomplete dominance?
The allele for red flowers is incompletely dominant
over the allele for white flowers. The pigment produced by the red allele (anthocyanin) is diluted in the
heterozygote and appears pink because of the white background of the flower petals.
What is the wild type?
When many alleles exist for the same gene, the most common phenotype or genotype in the natural population as the wild type.
What is the variant of the wild type?
All other phenotypes or genotypes are considered variants (mutants) of this typical form, meaning
they deviate from the wild type. The variant may be recessive or dominant to the wild-type
allele
What is the term used to describe the situation when many alleles exist for the same gene at the population level?
Multiple alleles
What is the purpose of a Punnett square?
to predict the outcome of a genetic cross
When a female parent is
homozygous for an X-linked trait, how will this be passed down to the male offspring?
The female parent will pass the trait on to 100 percent of the male offspring because the males will receive the Y chromosome from the male parent.
What are examples of X-linked disorders?
- Color blindness
- Hemophilia
- Muscular dystrophy
What happens when a female offspring is heterozygous for an X-linked trait? How will they pass these traits to their offspring?
They are carriers and may not exhibit any phenotypic effects. These females will pass the
disease to half of their male offspring and will pass carrier status to half of their female
offspring.
True or false: X-linked traits appear more frequently in males than females.
True
What is epistasis?
Genes may also oppose each other, with one gene “erasing” the expression of another. One gene masks or interferes with the expression of another.
Does the outcome of a Punnett Square change depending on whether it is the first kitten that’s born or the second or third?
No
Two brown-eyed parents can have a child with blue eyes because…
Multiple genes are involved with eye color (polygenic) that determine eye color.
What are antigens?
Blood cells have sugars attached to the cell membrane. These sugars are called antigens.
One gene with _________________ determines the blood antigens.
three possible alleles
What are three possible allele blood types?
- Allele A (I^A)=A antigen
- Allele B (I^B)=B antigen
- Allele O (i)= no antigen
Why do we care about blood type?
If someone with type B blood is given type A blood, their body will recognize the A antigens as foreign antigens and attack the blood cells.
Why is Type O considered a universal donor blood type?
Type O blood does not have any A or B antigens, so it can safely be given to any ABO blood group.
Most traits are the results of _______ and the __________ interacting.
many alleles, environment
What are rare genetic diseases?
Some rare genetic diseases can be caused by changes in single genes.
Sickle cell disease is a disease that affects _______________.
red blood cells
What is hemoglobin in red blood cells?
These cells contain a protein called hemoglobin, which carries oxygen to other cells.
How do red blood cells travel throughout the body?
Red blood cells travel throughout the body via a large network of blood vessels- narrow tubes like veins, arteries, and capillaries that transport blood.
Sickle cell is an _____________.
inherited genetic disease
What are genetic diseases?
Genetic diseases are caused by mutations in genes that interfere with resulting proteins.
How must mutations be inherited?
Mutations must be present in gametes to be inherited (passed down through genes from one generation to the next).
Like all genetic diseases, sickle cell disease is _____.
rare
Some rare genetic conditions, like __________, are determined primarily by ________.
sickle cell disease, a single gene
What causes sickle cell disease?
Sickle cell disease is caused by a variation in a gene that codes for part of the hemoglobin protein (HBB).
When the HBB gene mutates, how does this cause sickle cell disease?
A mutation in the HBB gene creates a mutated hemoglobin, which creates the formation of a sickled cell.
Sickle cell disease is a ________ condition.
recessive
To have sickle cell disease, what cell allele must they have?
To have sickle cell disease, an individual must be homozygous recessive for the sickle cell allele.
What does a heterozygous allele express for sickle cell disease?
Heterozygotes express some abnormal hemoglobin, but under most conditions, they don’t have any symptoms. (They’re said to have sickle cell trait).
People who are heterozygotes (carriers) for sickle cell disease can have symptoms…
in low oxygen environments
What are pedigree charts?
Pedigrees trace the inheritance of a trait or health condition in several biologically related individuals spanning more than one generation.
What is autosomal recessive inheritance?
Autosomal means the gene is on one of the autosomes (1-22). Recessive means that two recessive alleles for that condition are required for an individual to show the trait.
What are three characteristics of autosomal recessive inheritance pedigrees?
- Typically skips generations
- Two parents who don’t have the condition can have children who have it.
- Number of affected males is usually similar to affected females.
What is an example of an autosomal recessive disease?
Fanconi anemia is an autosomal recessive disease caused by a mutation in a single gene.
What is fanconi anemia?
It’s a disease of the bone marrow. It results in decreased production of all types of blood cells.
Diseases caused by __________ are rare and _____ to be inherited.
dominant alleles, less likely
For dominant allele conditions…
people with the disease allele have the disease and may be less likely to reproduce.
For recessive allele conditions…
carriers don’t have symptoms and are more likely to pass on the disease-causing allele.
Many dominant alleles are caused by ___________.
new mutations
What causes rare dominant allele mutations?
In most cases, the rare mutation happens by chance during meiosis. It’s in the gametes and can be passed on. Ex. The allele that causes progeria is rarely passed down in families.
Dominant alleles that are inherited usually…
cause diseases later in life. By that time, individuals with the mutation have reproduced and passed on their mutated allele.
What is an example of a dominant allele condition?
Huntington’s disease. It’s a rare inherited disease that causes brain degeneration, disability, and death.
What causes Huntington’s disease?
The disease is caused by a dominant mutant allele (if you have the allele you have the disease).
Most people for rare, deadly dominant diseases are __________.
heterozygous
What is autosomal dominant inheritance?
Autosomal means that hte gene is on one of the autosomes (1-22). Dominant means that one dominant allele for that condition is enough for an individual to show the characteristics.
What are four characteristics of autosomal dominant inheritance?
- Typically doesn’t skip generations.
- At least one of the biological parents of someone with the condition also has the condition.
- Number of affected males is usually similar to affected females.
- Usually people with a dominant disease are heterozygous.
What is an example of X-linked inheritance?
Duchenne Muscular Dystrophy. It’s caused by a mutation in the dystrophin gene which is located on the X-chromosome.
What is dystrophin needed for?
Dystrophin is a protein that is needed for normal muscle function.
What happens to the muscle in a patient with Duchenne Muscular Dystrophy?
The cells of patients don’t make any dystrophin or they make a nonfunctional dystrophin.
What does X-linked Recessive Inheritance mean?
- X-linked means that the gene is carried on the X chromosome.
- Recessive means that XX individuals require two mutant alleles to be affected and XY individuals only need one mutant allele to be affected.
What are the characteristics of X-linked recessive inheritance?
- Usually more boys are affected.
What are nucleotides?
A DNA molecule consists of two strands of nucleotides (C and G to T and A) paired together to make a “double helix.”
What are the three parts that make up a nucleotide?
Phosphate group, a sugar, a nitrogenous bases (C and G to T and A)
Mutations are changes in ___.
DNA
______ can occur in ____ that codes for ________ or the __ that controls ______, then they can affect traits.
Mutations, DNA, proteins, DNA, genes
In sickle cell disease, a _______ in the ___ gene causes _____________ to ____________
mutation, HBB, hemoglobin molecules, stick together
What is a polypeptide?
It’s a string of amino acids that folds into a particular 3-D shape.
How many polypeptide subunits are proteins made of?
Proteins can be made of one polypeptide subunit or many polypeptide subunits.
What determines a protein’s function?
The shape of the protein is important to how it functions in the cell.
Where are the instructions for making proteins?
In the DNA (nucleus)
Where are proteins made?
At the ribosomes in the cytoplasm.
What is gene expression?
Gene expression is the process of decoding the information in a gene to make a protein.
What are the two steps of gene expression?
Transcription and Translation
What is transcription? Where does it occur?
Transcription (in the nucleus) is when a DNA message gets copied onto an RNA molecule. The “messenger” RNA (or mRNA) molecule leaves the nucleus and travels to the ribosome.
What is translation? Where does it occur?
Translation (at ribosome) is when DNA instructions are “read” and a protein is assembled.
What is the simple sequence of how DNA gets copied?
DNA —–> RNA ——> Protein
What are four similarities/differences between DNA and RNA?
- Both are made of nucleotides.
- Both are involved in making proteins.
- RNA is single-stranded. DNA is double-stranded.
- RNA has uracil instead of thymine.
DNA carries the ________ for making ______. It stays in the ______. RNA is involved in different aspects of ____________.
instructions, proteins, nucleus, gene expression
What is mRNA?
It’s the “messenger” RNA and carries the DNA instructions from the nucleus to the ribosome in the cytoplasm.
What is tRNA?
It’s the transfer RNA and carries the appropriate amino acids to the ribosome to be assembled into a polypeptide.
What is a codon?
The nucleotide bases on a DNA molecule are triplets of bases. (Ex. AAACCGGCAAAA) These triplets form codons on the corresponding mRNA molecule. (Ex. UUUGGCCGUUUU)
What do these codons on a mRNA molecule specify for?
The codons specify the amino acid sequence of the polypeptide.
What are the four nucleotide bases in RNA?
Uracil (U) to adenine (A) and Cytosine (C) to Guanine (G)
What is the universal genetic code?
It’s a key for mRNA codon and amino acid correspondence.
What are the components of the universal genetic code?
- Code is redundant because amino acids are coded by more than one codon. (Ex. ala is coded by four different codons GCU, GCC, GCA, and GCG).
- Code is also unambiguous because each codon codes for only ONE amino acid and no other.
What is the universal start codon at the start of each polypeptide?
AUG (met)
What are the three universal stop codons in each polypeptide?
UAA, UAG, UGA
What is transcription (deeper)?
In the nucleus, RNA polymerase enzyme binds to DNA and assembles mRNA using complementary base pairing rules.
C in DNA pairs with G in RNA
G in DNA pairs with C in RNA
T in DNA pairs with A in RNA
A in DNA pairs with U in RNA
What is translation (deeper)?
At ribosome in cytoplasm, ribosome reads mRNA and assembles protein. tRNA assists by bringing amino acids to the appropriate codon.
What is a point mutation?
A mutation that happens at one particular location. (Ex. When you loose a base, gain an extra base)
What are four types of point mutations?
- Missense
- Nonsense
- Silent
- No mutation
What is the missense mutation?
It’s when a mutation codes for an amino acid, but not the correct amino acid.
What is a nonsense mutation?
It’s a mutation of an amino acid codon into a sudden stop codon. (Ex. Causes a nonfunctional protein)
What is a silent mutation?
It’s a mutation in the a nucleotide codon sequence that still codes for the same amino acid and doesn’t affect the function of the protein. (Ex. AAA and AAG both code for Lys)
What are three reasons why carriers of sickle cell disease don’t have symptoms?
- Their blood cells are round under most conditions.
- One copy of the healthy HBB gene produces a sufficient amount of “normal” protein that does not cause proteins to form stiff rods under most conditions.
- Sickle cell is a recessive disease.
Why is Ceniya less affected by sickle cell disease compared to Ingrid?
Ceniya has a second mutation that keeps the gene for fetal hemoglobin turned on. The fetal hemoglobin provides enough healthy hemoglobin for her red blood cells.
What are regulatory regions?
Genes have regulatory regions (or switches). Regulatory regions control whether a gene is expressed by turning on/off transcription.
What’s two examples of regulatory regions?
- Lactose tolerance most people turn off the lactase gene as adults.
- Most people turn off the fetal hemoglobin gene after birth.
Why do the cells in our body look different even though they all have the same DNA?
They turn on different genes
How do the cells in our body express themselves?
Each cell expresses, or turns on, only a fraction of its genes. The rest of the genes are turned off (not making proteins).
Why are different genes turned on/off in different cells?
Different genes are turned on and off in different cells depending on their functions. Genes are turned on and off at different times during development.
Turning certain genes on/off, allows for __________ and ____________.
normal development, specialization
What are three main takeaways about mutations?
Mutations can:
1. Change a protein
2. Change whether a protein is produced or not produced
3. Or don’t do anything (This is the majority of small changes in DNA)
What’s the difference between traditional vs. genetic medicines?
- Most medicines treat the symptoms (pain medications/blood transfusions).
- Genetic medicines treat the root cause (the mutations)
Gene editing changes the DNA in a cell to (3 ideas)…
- Turn off a gene (gene silencing) to prevent it from making a harmful protein.
- Turn on a gene or instruct a cell to make more of a needed protein.
- Correct a mutated gene
How does gene therapy add a new gene to a cell?
The new gene may be a normal version of the mutated gene or a different gene that improves the way the cell works. Usually delivered using a virus.
The sickle cell disease treatment is an example of ______________. Federal funds cannot be used for research on _______________.
somatic gene editing, germline gene editing
