Genetics and inheritance Flashcards
What causes differences in the characteristics of individuals of the same species?
Differences may be due to genetic causes, environmental causes, or a combination of both.
Genetic causes refer to the genes inherited, while environmental causes involve the conditions of development.
Where is genetic material stored in a cell?
In the nucleus, in the form of chromosomes.
Chromosomes are long strands of DNA.
What is a gene?
A section of DNA that codes for the production of a particular protein.
Genes are fundamental units of heredity.
What does diploid mean in relation to human body cells?
Diploid means having two copies of each chromosome.
The human cell nucleus contains 46 chromosomes arranged in pairs.
Who discovered the structure of DNA?
James Watson and Francis Crick in 1953, with contributions from Rosalind Franklin.
Their discovery was pivotal in understanding genetics.
What is the structure of a DNA molecule?
A DNA molecule consists of two strands called nucleotides coiled to form a double helix.
The strands are linked by paired bases and have a phosphate and sugar backbone.
What are the four bases of DNA?
Adenine (A), Cytosine (C), Guanine (G), and Thymine (T).
These bases are crucial for genetic coding.
What is complementary base pairing?
A only pairs with T, and C only pairs with G.
This pairing is essential for DNA replication.
What is a nucleotide?
The small building block of a DNA molecule.
Nucleotides consist of a phosphate group, a sugar (deoxyribose), and a base.
Fill in the blank: The human cell nucleus contains _____ chromosomes.
46
What is DNA replication?
The process when DNA copies itself exactly.
Why is DNA replication important?
It ensures all cells contain the same amount and type of DNA.
When does DNA replication occur?
Whenever new cells are made in mitosis or meiosis - to make gametes.
What happens during DNA replication?
The polynucleotide strands of DNA separate and each strand acts as a template for a new strand.
What role does DNA polymerase play in DNA replication?
It assembles nucleotides into new strands based on complementary base pairing.
What is a gene?
A section of DNA containing a different sequence of bases used for making a particular protein.
How does the order of bases in a gene affect protein synthesis?
It decides the order of amino acids in the protein.
What is a codon?
A triplet of three bases that codes for one amino acid.
How many possible codons are there for 20 amino acids?
64 possible codons.
What is the function of messenger RNA (mRNA)?
To transport the genetic code from the nucleus to the ribosomes.
What is the function of transfer RNA (tRNA)?
To match anticodons to codons of the mRNA, coding for specific amino acids.
What are the main differences between DNA and RNA?
DNA is a double helix with 2 strands; RNA is a single strand. DNA has deoxyribose; RNA has ribose. DNA contains Thymine (T); RNA has Uracil (U). DNA is larger than RNA.
What is the first step in protein synthesis?
DNA unwinds and is transcribed in the nucleus.
What does the mRNA molecule produced during transcription contain?
A specific sequence of codons, with U instead of T.
What happens to the mRNA molecule after transcription?
It moves out of the nucleus and joins with a ribosome in the cytoplasm.
How do tRNA molecules interact with mRNA during protein synthesis?
They line up against mRNA, matching their anticodons to the mRNA codons.
What is formed when amino acids bond together?
A polypeptide chain or protein.
Where does transcription occur?
In the nucleus
What happens to the DNA helix during transcription?
Part of the DNA helix unzips and RNA nucleotides line up along the template strand according to complementary base pairing
What is formed at the end of transcription?
An mRNA molecule
What is the role of mRNA after transcription?
It can leave the nucleus
Where does translation occur?
At the ribosome in the cytoplasm
What does translation convert?
mRNA into protein
What lines up on the ribosome during translation?
Each codon on the mRNA
What matches the codon on the mRNA during translation?
A tRNA molecule with a complementary anticodon
What does the tRNA molecule hold at one end?
A specific amino acid
What determines the amino acid brought by tRNA?
The anticodon
What happens when tRNA brings an amino acid to the ribosome?
A bond is formed between the two amino acids
Define a mutation
A rare, random change in the genetic material / DNA base sequence of an organism
Can mutations be inherited?
Yes, sometimes
What can happen if the sequence of bases in DNA changes?
The amino acid sequence in a protein may be altered
What can increase the rate of mutations?
Agents called mutagens
Give examples of mutagens
- Ionising radiation (UV light, X-rays, gamma rays) * Chemicals (mustard gas, carcinogens, nitrous oxide, tar)
What is the effect of most mutations on phenotype?
Most mutations have little effect
What can some mutations increase?
Variation
What happens when a nucleotide is inserted twice?
The entire base sequence is altered, coding a different protein
What is the effect of missing out a nucleotide?
The entire base sequence is altered, coding a different protein
What can a different nucleotide potentially code for?
A different amino acid
What may happen if the sequence of bases is reversed in one codon?
It may or may not result in different amino acids and an altered protein structure
What is the effect of mutations on DNA?
Change in DNA base sequence results in a different triplet code.
This can lead to changes in the amino acids that make up a protein.
What happens to the mRNA codon when a mutation occurs?
The mRNA codon is changed, leading to a different tRNA molecule with a different anticodon binding a different amino acid to the polypeptide chain at the ribosome.
This alteration can affect the protein’s function.
What is the consequence of a mutation on the polypeptide chain?
The sequence of amino acids in the polypeptide chain is altered, potentially changing the protein’s shape and function.
The active site of an enzyme may change shape, affecting its ability to bind substrates.
What occurs during cell division?
Each chromosome condenses to become visible under a microscope and is then replicated to produce two identical chromatids joined at the centromere.
This process is crucial for cell division and genetic consistency.
What is mitosis?
Mitosis occurs during the growth and repair of tissues by cloning, as well as during asexual reproduction.
It results in two identical diploid cells.
In mature animals, what is the primary purpose of mitosis?
Repair tissues.
Mature animals typically do not grow significantly, so mitosis is mainly for tissue repair.
What are some examples of organisms that reproduce asexually through mitosis?
- Plants
- Some organisms
Asexual reproduction results in offspring with identical genes to the parent, leading to no variation.
What happens when a diploid cell divides by mitosis?
You get two identical diploid cells.
This process maintains the chromosome number across generations.
List the stages of mitosis.
- Prophase
- Metaphase
- Anaphase
- Telophase
Each stage plays a critical role in the orderly division of the cell.
How does mitosis work?
A diploid cell containing a full set of chromosomes undergoes DNA replication, forming x-shaped chromosomes, which line up at the center of the cell and are pulled apart by cell fibers. The nuclear envelope breaks down and the two sides of each chromosome are separated and go to opposite ends of the cell where membranes form around them. These are the new nuclei and the cell then splits in two.
This ensures each daughter cell receives an identical set of chromosomes.
What is the purpose of meiosis in humans?
To produce haploid gametes with 23 chromosomes each
This ensures that the zygote formed during fertilization has a diploid number of chromosomes (46 in humans)
What type of cell division occurs after the zygote is formed?
Mitosis
Meiosis only occurs for the production of gametes
What is the chromosome composition of gametes in humans?
Haploid - 23 chromosomes
This is necessary for fertilization to create a diploid zygote
During which phase do homologous chromosomes line up in pairs?
Before the cell divides
This occurs during interphase
What happens to the homologous pairs during the first division of meiosis?
They are pulled apart into two new cells
Each new cell receives one copy of each chromosome
What is produced after the second division of meiosis?
Four haploid gametes
Each gamete has a single set of chromosomes and is genetically different
How does meiosis contribute to genetic variation?
By shuffling genetic material
This leads to gametes that are slightly different genetically
What increases the number of possible genetic combinations in offspring?
Random fusion of gametes during fertilization
This process enhances genetic diversity
True or False: Meiosis produces identical gametes.
False
Meiosis results in genetically different gametes
Fill in the blank: Meiosis produced variation in a population because all gametes are _______.
slightly different genetically
This diversity is crucial for evolution
When does mitosis occur?
Occurs in all cells where there is growth and repair of tissues and in asexual reproduction.
What is the chromosome composition of daughter cells produced by mitosis in humans?
Diploid with a full set of chromosomes - 46 in humans.
When does meiosis occur?
Occurs when gametes are being produced for sexual reproduction.
What is the genetic composition of daughter cells produced by meiosis in humans?
Haploid - one of each of the homologous pair of chromosomes - 23 in humans.
What type of daughter cells are produced by mitosis?
2 genetically identical daughter cells (clones).
What type of daughter cells are produced by meiosis?
4 genetically different daughter cells, giving variation.
What is a karyotype?
A lab produced image of all the pairs of chromosomes of a person.
What are homologous chromosomes?
The 46 chromosomes in humans arranged into 23 pairs, one from each parent.
What are alleles?
Different versions of the same gene.
What is discontinuous variation?
When characteristics fall into discrete categories controlled only by genes.
What is continuous variation?
When characteristics are controlled by a combination of environment and genes.
Fill in the blank: During meiosis, when homologous chromosomes separate, there are different combinations of _______ that could end up in the gametes.
alleles
True or False: Genetic variation between individuals is only due to environmental factors.
False
How many copies of each gene are present in daughter cells after meiosis?
1 copy of each gene.
What results from the random combination of egg and sperm?
Different combinations of alleles brought together.
What is the genome?
The entire DNA of an organism
The genome contains all genetic information necessary for the growth, development, and functioning of an organism.
Define genotype.
The combination of alleles held by an organism for each gene
The genotype determines the potential traits that an organism can express.
What is phenotype?
The expression of the genotype (e.g. physical characteristics)
Phenotype can be influenced by environmental factors as well as genetic factors.
What does homozygous mean?
The organism has two identical alleles for a particular gene
Homozygous can be either dominant (e.g., AA) or recessive (e.g., aa).
What does heterozygous mean?
The organism has two different alleles for a particular gene
Heterozygous individuals may express the dominant allele in their phenotype.
Define dominant allele.
The allele is expressed in the phenotype if 1 or 2 copies are present
Dominant alleles mask the effects of recessive alleles in heterozygous conditions.
What is a recessive allele?
The allele is only expressed in the phenotype if a dominant allele isn’t present
This means the organism must have two copies of the recessive allele for it to be expressed.
What does codominant mean?
Neither allele is dominant over the other, so both alleles are expressed in the phenotype
An example is red and white alleles expressing as a pink phenotype in petal colors.
What is a monohybrid cross?
A genetic cross between parents that involves one trait
It predicts the possible genotypes of the offspring from known gametes.
Fill in the blank: Each individual must have ______ copies of each gene.
two
In a monohybrid cross, what are the possible gametes of two heterozygous parents (Ww)?
W and w
The gametes produced by each parent can be either the dominant or recessive allele.
True or False: A homozygous recessive organism will express a dominant phenotype.
False
A homozygous recessive organism will only express the recessive phenotype.
What is a Punnett square?
A way to show genetic diagrams, displaying parents’ genotype, gametes on the edges, and possible offspring genotypes.
Used to predict the genetic outcomes of a cross between two organisms.
What are the genotypes of females and males in humans?
Females have XX and males have XY.
This is related to sex determination based on the X and Y chromosomes.
What is the probability of being male or female based on a Punnett square?
50% chance of being male and 50% chance of being female.
This is derived from the combination of parents’ genotypes.
What is codominance?
When two alleles are expressed in the phenotype because neither is recessive or dominant.
An example is blood type expression.
What are the three blood type alleles in humans?
A, B, and O.
A and B are codominant and both are dominant over O.
Which blood types can result from the alleles A, B, and O?
Blood type A, B, AB, or O.
This results from the combinations of alleles inherited from parents.
What is selective breeding?
The process of breeding organisms for particular genetic traits.
It is a simple form of genetic engineering.
What is the main goal of selective breeding?
To allow individuals with desired characteristics to breed, leading to the prevalence of those traits in future generations.
Why are animals selectively bred?
- Increase yield of meat
- Higher milk yields
- Greater numbers of eggs
- Adaptable to changing conditions
- Coping with extreme conditions
- More wool production
- Docility in pets
- Aesthetic traits
- Good hunting capabilities.
What are some problems associated with selectively bred animals?
- Breathing difficulties in flat-faced breeds
- Infected ears and eyes
- Legs unable to support accelerated growth.
Why are plants selectively bred?
- Increase crop quality and yield
- Increase tolerance to environmental pressures
- Resistance to viruses, fungi, and bacteria
- Tolerance to insect pests
- Tolerance to herbicides.
Fill in the blank: Selective breeding is a simple form of _______.
genetic engineering.
True or False: Selective breeding can lead to a decrease in certain genetic traits over generations.
False.
