B13 - Reproduction Flashcards
What are alleles?
Different forms of the same gene, sometimes referred to as variants
What is asexual reproduction?
involves only 1 individual and the offspring is identical to the parent. There is no fusion of gametes or mixing of genetic information
What are bases (DNA)?
Nitrogenous compounds that make up part of the structure of DNA and RNA. They are represented by the letters A, T, C, and G
What are carriers?
Individuals who are heterozygous for a recessive allele linked to a genetic disorder. Carriers have one healthy allele so are not affected themselves, but can pass on the affected allele to their offspring
What is cystic fibrosis?
An inherited disorder that affects lungs, digestive, and reproductive system and is inherited through a recessive allele
What is a dominant allele?
The phenotype will be apparent in the offspring even if only one of the alleles is inherited
What is genetic engineering?
The process by which scientists can manipulate and change the genotype of an organism
What is a genotype?
The genetic makeup of an individual for a particular characteristic, for example hair or eye colour
What is a heterozygote?
Individual with different alleles for a characteristic
What is a homozygote?
Individual with different alleles for a characteristic
What is meiosis?
2 stage process of cell division that reduces the chromosome number of daughter cells. It is involved in making gametes for sexual reproduction
What is a mutation?
A change in the genetic material of an organism
What is natural selection?
The process by which evolution takes place. Organisms produce more offspring than the environment can support. Only those that are most suited to their environment will survive to breed and pass on their useful characteristics to their offspring
What is a nucleotide?
A molecule made up of a sugar, a phosphate group, and one of 4 different bases. They are key units in the structure of DNA and RNA
What is a phenotype?
The physical appearance of an individual for a particular characteristic
What is polydactyly?
A dominant inherited disorder that results in babies born with extra fingers and/or toes
What is a Punnet square diagram?
A way of modelling a genetic cross and predicting the outcome using probability
What is a recessive allele?
A phenotype that will only show up in the offspring if both of the alleles coding for that characteristic are inherited
What are sex chromosones?
Carry the information that determines the sex of an individual
What is sexual reproduction?
Involves the fusion of male and female gametes producing genetic variation in the offspring
What is reproduction?
The process by which genetic information is passed on from parents to their offspring
What are advantages of a asexual reproduction?
- Partner not required
- Genetically identical offspring (known as clones) meaning there is no genetic variation and therefore desirable characteristic are passed on. This also is an advantage in favourable conditions.
- It is faster and more rapid than sexual reproduction
What are the disadvantages of asexual reproduction?
- Genetically identical offspring (known as clones) meaning there is no genetic variation and therefore undesirable characteristics may be passed on
- Large groups may be susceptible to the same disease, meaning none of the population are immune, causing the entire population to fall ill to the disease. If one organism cannot survive, none can.
What are gametes?
an organism’s reproductive cells, they contain 1 set of chromosomes so can carry only 1 of the 2 alleles that the parent have in their own cells
What are the advantages of sexual reproduction?
*There is genetic variation, therefore if the environment changes, variation gives a survival advantages to the population as some offspring will be able to survive and reproduce. This is known as natural selection
What are the disadvantages of sexual reproduction?
- 2 gametes (from 2 parents) are required. This is less time and energy efficient than asexual reproduction as it takes time and energy to find a mate and spread gametes
How many chromosomes does a human have?
46 (23 pairs)
How many chromosomes does a human gamete have?
23
What is a gene?
a small section of DNA on a chromosome that codes for a particular sequence of amino acids, to make a specific protein
Describe where to find a gene if you begin outside the cell
Inside the cell there is a membrane bound organelle called the nucleus. Inside the nucleus there are chromosomes. These Chromosomes are thin strands of DNA. Small sections of the DNA are known as genes.
What does the base A pair with?
T
What does the base T pair with?
A
What does the base G pair with?
C
What does the base C pair with?
G
How do the 4 bases in DNA combine?
Complementary base pairing
How many bases code for a particular amino acid?
A sequence of 3 bases in the gene code for a particular amino acid
What do the order of the bases in DNA control?
The order of the bases controls the order in which amino acids are joined together to form a certain protein
What do the sections of DNA that do not code for proteins do?
The non-coding parts of DNA switch genes on and off, they control whether or not a gene is expressed (used to make a protein)
What is a mutation?
A change in the order of the bases that causes the wrong protein to be made
What is the structure of DNA?
The long strands of DNA are made of alternating sugar and phosphate sections. One of 4 basses - A, C, G, T - is attached to each sugar. Each unit containing a sugar, a phosphate, and a base is called a nucleotide. The 2 strands of DNA run in opposite directions and interwind to form a double helix structure
What is protein synthesis controlled by?
The DNA in the nucleus
What are the 2 steps of Proteins Synthesis?
Transcription
Translation
Describe the process of protein synthesis:
The DNA is too large to leave the nucleus (protein synthesis occurs in ribosomes outside of the nucleus), so a template of the gene for the protein is created. This template is known as mRNA and reflects the sequence of bases in the DNA, but it is small enough to leave the nucleus through the pores in the nuclear membrane as it is only a single strand and a single gene. The mRNA then leaves the nucleus through a pore in the nuclear membrane and binds to a ribosome in the cytoplasm
The cytoplasm contains carrier molecules (tRNA), that each carry a specific amino acid. The carrier molecules also contain 3 bases that are complementary to a specific triplet of bases of the mRNA. The corresponding carrier molecule attaches itself to the template. Further Carrier molecules attach themselves to the template in the order given by the DNA. The amino acids they carry join together to form a specific protein chain. Carrier molecules keep bringing specific amino acids to add to the growing protein chain in the correct order until the template is completed. The protein chain detaches from the carrier molecules and the carrier molecules detach from the template and return to the cytoplasm to pick up more amino acids
Once the protein chain is complete, the molecule folds up to form a unique shape that will enable it to carry out its functions in the cell
What are 3 examples of proteins?
- Enzymes - the protein folds to produce a specific active site
- Structural proteins - form fibrous structures
- Hormones
How is mRNA created?
The enzyme RNA polymerase moves along a DNA strand in the gene, reading the bases 1 by 1 and creating an mRNA strand that is complementary to the DNA strand
What does mRNA stand for?
Messenger RNA
What is a genome of an organism?
The entire genetic material of the organism. That includes all the chromosomes, and the genetic material found in the mitochondria
Where do you inherit your mitochondrial DNA from and why?
You always inherit your mitochondrial DNA from your mother as it comes from the mitochondria in the egg
What is offspring?
The generation resulting from reproduction
What type of cell division does asexual reproduction involve?
Mitosis
Why do your cells reproduce asexually all the time?
For growth and repair
Describe the process of asexual reproduction
The cells divide by mitosis to form 2 identical daughter cells. It only involves parent and there is no fusion of gametes. Their genetic material is identical to their parent and other clones, there is little variation as all genetic information comes from 1 parent.
Describe the process of sexual reproduction
The 2 gametes from the parents fuse together to form a zygote, which goes onto develop into a new individual.
How are gametes formed?
Meiosis
Why does meiosis involve halving the number of original chromosomes?
When the gametes fuse, the new cell will have the correct number of chromosomes as it is receiving half the correct number from both gametes
What are the gametes in plants?
egg cells and pollen
What are the gametes in animals?
egg cells and sperm
Why are the offspring of sexual reproduction not identical to either parent?
The offspring has a combination of 2 different sets of genes, therefore there is variation
Where are the female gametes produced?
The ovaries
Where are the male gametes produced?
The testes
Describe how gametes are formed by meiosis
During meiosis the genetic information inside the nucleus of a cell is copied so there are 4 sets of each chromosome instead of the normal 2 sets. The cell then divides, and the new cells immediately divide again. This happens in quick succession to form 4 gametes, each with a single set of chromones
How does variation occur during meiosis?
Each gamete produced is genetically different from the other gametes as it contains a random mixture of the original chromosomes
How does variation occur during fertilisation
Each sex cell has a single set of chromosomes, when 2 gametes fuse together during fertilisation, the new cell has a full set of chromosomes. The combination of genes in the new pair of chromosomes will contain different forms of the same genes (alleles) from each parent. This also helps to produce variation in the characteristics of the offspring as it is unique from both parents.
Name 3 organisms that reproduce both sexually and asexually
- Fungi
- Plants
- Malaria Parasite
Describe reproduction in Fungi
Fungi most commonly reproduce asexually. Fungi are made up of a mass of thin threads called hyphae that together form the structures we can see. In asexual reproduction, the fungal spores are reproduced by mitosis and they are genetically identical to the parent. These spores can go onto germinate and form a new fungus
Fungi can also reproduce sexually in adverse conditions, such as when it is dry. 2 hyphae from different fungi join and the nuclei fuse so the new hyphae has 2 sets of chromosomes. It then undergoes meiosis to make haploid spores, each with only 1 set of chromosomes which are different from the original hyphae. Some of the spores may produce fungi better adapted to survive the adverse conditions
Describe reproduction in plants
In plants, the flowers contain the organs of sexual reproduction. The gametes, the pollen and egg cells, are produced using meiosis. The pollen from one flower must reach the female parts of another flower in a process called pollination. Flowers are either adapted to attract animal pollinators or make it easy for their pollen to be carried by the wind and caught by another flower. Once the pollen has fused with the egg cell, seeds are formed. Sexual reproduction introduces variation and enables plants to survive as condition change through natural selection.
Some plants can also reproduce asexually. A new plant grows as a result of specially directed mitosis. Asexual reproduction means that new plants are formed even if flowers are destroyed by frost, eaten, or fail to be pollinated
What is an example of asexual reproduction in plants?
Specialised stems called runners grow new plants, plants such as strawberries grow like this
Describe reproduction in malaria paraistes
The parasites that cause malaria reproduce differently in different stages of their life cycle. Both asexual and sexual reproduction are part of the life cycle - asexual reproduction is not an alternative for adverse conditions
Malarial parasites reproduce asexually in human liver and blood cells.
When the mosquito takes her blood meal, the drop in temperature between the human body and mosquito triggers sexual reproduction in some of the parasites inside the red blood cells. There is a 20 minute window when sexual forms develop, burst out of the blood cells, and meet to form zygotes with 2 sets of chromosomes. These zygotes then undergo meiosis to produce new asexual parasites that will infect a new human host. The parasites show a lot of variation
What does DNA stand for
Deoxyribonucleic Acid
What is the monomer of DNA?
Nucleoids
How does sequencing the human genome help humans?
Knowing the human genome can help scientists and doctors:
- Understand inherited disorders
- Discover genes linked to certain types of disease
- Trace human migratory patterns and evolution
How does sequencing the human genome allow doctors and scientists to understand inherited disorders?
Understanding the human genome helps us to understand inherited disorders such as cystic fibrosis and sickle cell disease. The more we can understand these diseases, the more chance we have of overcoming them either through medicine or by repairing the faulty genes
How does sequencing the human genome allow doctors and scientists to search for genes linked to different types of disease?
There are genes that are links to an increased risk of developing many diseases, from heart disease to type 2 diabetes. Understanding the human genome allows us to discover which genes cause this increased risk. This can help predict the risk for each individual, so they can make lifestyle choices to help reduce the risk. It can also help doctors become better at choosing the best treatment method.
How does sequencing the human genome allow doctors and scientists to trace human migratory patterns and evolution?
Understanding the human genome allows us to understand human evolution and history. People all across the world can be linked by patterns in their DNA, allowing scientists to trace human migration patterns from our ancient history. We can also be linked to early members of the family tree.
What forms the backbone of DNA?
Alternating sugar and phosphate sections
What is the structure of a nucleotide?
A unit containing a sugar, a phosphate, and a base
What are nucleotides grouped into?
groups of 3
What would variations in the non-coding part of the DNA result in?
Variations in the way our genes are expressed
What does it mean if a gene is expressed?
The gene codes for a protein that is synthesised in the cell
How can the human body synthesise so many different proteins with so few genes?
Gene expression can cause each gene to control the synthesis of many proteins as it may depend on how much of the gene is expressed or not expressed, or whether other genes are expressed at the same time or not
How can mutations occur?
Spontaneously when a chromosome is replicated incorrectly or due to ionising radiation
What are the 3 types of mutation?
- Insertions - this is when a new base is inserted into the DNA sequence when it should not be, this changes the way the groups of 3 bases are “read” which can change the amino acid they code for. This can change more than 1 amino acid as they may have knock on effects
- Deletions - This is when a random base is deleted from the DNA sequence, this changes the way the groups of 3 bases are “read” which can change the amino acid they code for. This can change more than 1 amino acid as they may have knock on effects
- Substitutions - This is when a random base in the DNA sequence is changed to a different base
What can mutations cause?
- Most of the time mutations do not alter the protein form or alter it so slightly that its appearance and function is not changed.
- However, numerous mutations can result in an altered protein that folds to give a different shape. For example, the active site of an enzyme could be changed
- Mutations in non-coding regions of DNA can alter how genes are expressed
- Some mutations may be beneficial (a changed enzyme could be more efficient)
How can mutations in the non-coding part of the DNA indirectly cause a change in the phenotype of the organism?
Mutations in the non-coding part of the DNA does not directly affect the phenotype. However, it can affect which genes are expressed, and by doing so affect the phenotype of the organism
What sex chromosomes do females have?
XX
What sex chromosomes do males have?
XY
What percent of sperm contains the X chromosome and what percent of sperm contains the Y chromosome?
50% X
50% Y
How does inheritance work?
The chromosomes you inherit carry your genetic information in the form of genes. Many of these genes have alleles. Each allele codes for a different protein. The combination of alleles you inherit will determine your characteristics
What are 2 examples of genetic disorders?
- Polydactyly
* Cystic Fibrosis
What is Polydactyly?
Polydactyly is a genetic condition where a baby is born with extra fingers or toes. It is caused by a dominant allele.
What is the chance that you will pass on polydactyly if you have polydactyly and are heterozygous?
50%
What is cystic fibrosis?
Cystic fibrosis is a genetic condition caused by a recessive allele. It affects cell membrane and causes the production of thick, sticky mucus. The mucus can affect several organs, including the lungs and pancreas, digestive system and reproductive system.
What problems are caused by cystic fibrosis?
Cystic fibrosis causes mucus to clog up organs, especially the lungs, and prevent them from working properly. The pancreas cannot make and excrete enzymes properly because the tubes through which the enzymes are released into the small intestine are blocked with mucus. The reproductive system is also affected, so many people with cystic fibrosis are infertile.
What are the treatments for Cystic fibrosis?
- Physiotherapy and antibiotics can be used to help keep the lung clear of mucus and infections
- Enzymes can be used to replace the ones the pancreas cannot produce and to thin the mucus
There is no cure
How can genetic disorders be cured?
Currently there is no way of curing genetic disorders, however scientists hope that genetic engineering will allow them to replace the faulty alleles with healthy ones
What does genetic screening allow?
It allows people to know whether they carry a faulty allele, it can also be performed on embryos and foetuses during pregnancy to to discover whether they will have a genetic disorder or not
Describe how genetic screening of embryos is carried out
To screen an embryo or foetus you must first collect a sample of cells from the developing individual. Once the cells have been collected (either before implantation or by techniques such as amniocentesis or chorionic villus sampling) they need to be screened. The DNA is isolated from the embryo cells and tested for specific disorders
What are the methods for collecting cells for embryo screening?
- Pre-implantation
- Amniocentesis
- Chorionic Villus Sampling
Describe how collecting cells for screening embryos is done pre-implantation
Some couples with an inherited disorder in the family may decide for their embryo to be produced via IVF to be tested before they are implanted in the mother, so only babies without that disorder are born.
Describe how collecting cells for screening embryos is done via Amniocentesis
Amniocentesis is carried out at around 15-16 weeks of pregnancy. It involves taking some of the fluid from around the developing fetus. This fluid contains fetal cells, which can then be used for genetic screening.
Describe how collecting cells for screening embryos is done via Chroionic villus sampling
Chorionic villus sampling of embryonic cells is done at between 10 and 12 weeks of pregnancy by taking a small sample of tissue from the developing placenta. This provides fetal cells to scan
What are the risks of collecting embryo cells during pregnancy?
Both amniocentesis and chorionic villus sampling have an associated risk of cauing a miscarriage
What are social concerns about embryo screening?
- The processes used to collect cells from a developing fetus increase the risk of miscarriage. So, in come cases, a healthy fetus will be miscarried as a result of a test to see whether it has a genetic abnormality, which is very distressing for the parents
- The screening processes may give false positives or false negatives. This may lead to the termination of a healthy pregnancy or the unexpected birth of a child with a genetic disorder
What are ethical concerns about embryo screening?
- Embryo screening means that people may have to make a decision about whether or not to terminate a pregnancy. This can be a very difficult and stressful decision due to their emotions, ethical framework, and religious beliefs
- Some people are concerned that genetic screening could give rise to a demand for “designer babies”. This would occur if parents used genetic screening to choose children with “desirable” characteristics such as a particular sex, good looks, or intelligence
What are economical concerns about embryo screening?
- Screening for embryos is expensive, it is usually only offered to people with family histories of genetic disorders and older parents who are more at risk of having a child with genetic problems
- However, if a couple have a child affected by a genetic disorder it can be very costly for society to provide health care and support the family
Which allele has a capital letter in genetic crosses?
Dominant
earlobes are either attached or detached, attached earlobes are recessive. Determine the chances of the offspring of a female with attached earlobes and a heterozygous male having attached earlobes
.
A rabbit breeder has a stock of rabbits which is a mixture of homozygous and heterozygous and white and brown. Describe how a breeder could breed his existing stock of rabbits in order to find out which of the white rabbits were homozygous. (White fur is dominant)
1) Select 1 white rabbit and 1 brown rabbit at random and allow them to breed
2) Make sure there is a minimum of 4 offspring from the 2 rabbits
3) If all offspring are white then the rabbit is homozygous, if there are any brown offspring, then the white rabbit is heterozygous
A rabbit breeder has a stock of rabbits which is a mixture of homozygous and heterozygous and white and brown. Describe how a breeder could breed his existing stock of rabbits in order to find out which of the white rabbits were homozygous. (White fur is dominant)
1) Select 1 white rabbit and 1 brown rabbit at random and allow them to breed
2) Make sure there is a minimum of 4 offspring from the 2 rabbits
3) If all offspring are white then the rabbit is homozygous, if there are any brown offspring, then the white rabbit is heterozygous
