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B13 Reproduction Flashcards

1
Q

What creates genetic variation in a species?

A

Spontaneous mutations
Sexual reproduction

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2
Q

What is a mutation?

A

A random change to the base sequence in DNA which results in genetic variants. They occur continuously.

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3
Q

What are the 3 types of mutation?

A
  1. Insertions:
    A new base is randomly inserted into the DNA sequence
    An insertion mutation changes the amino acid that would have been coded for by
    the group of three bases in which the mutation occurs
    Remember – every group of three bases in a DNA sequence codes for an amino
    acid
    An insertion mutation also has a knock-on effect by changing the groups of three
    bases further on in the DNA sequence
  2. Deletions
    A base is randomly deleted from the DNA sequence
    Like an insertion mutation, a deletion mutation changes the amino acid that
    would have been coded for by the group of three bases in which the mutation occurs.
    Like an insertion mutation, a deletion mutation also has a knock-on effect by
    changing the groups of three bases further on in the DNA sequence
  3. Substitutions
    A base in the DNA sequence is randomly swapped for a different base
    Unlike an insertion or deletion mutation, a substitution mutation will only change
    the amino acid for the group of three bases in which the mutation occurs; it will
    not have a knock-on effect
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4
Q

How may a gene mutation affect an organism’s phenotype?

A
  • Neutral mutation does not change the sequence of amino acids. Protein structure and function same. No effect on phenotype
  • Mutation may cause a minor change in an organism’s phenotype e.g. change in eye colour.
  • Mutation may completely change the sequence of amino acids. This may result in a non-functional protein. Severe changes to phenotype.
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5
Q

Do all mutations alter proteins?

A

Most do not alter the protein or alter it only slightly so the function is not affected. A few mutations code for a protein with a different shape, which affects the function. This might cause an advantage or a disadvantage.

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6
Q

What happens when mutations take place in non coding DNA?

A

These mutations do not directly affect the phenotype. But the can affect which genes are switched on/ off. By changing the genes that are expressed there might be a big impact on the phenotype.

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7
Q

What is meant by gene expression?

A

Gene expression is when a gene codes for a protein that is synthetized in a cell

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8
Q

What is the role of non coding parts of the DNA?

A

They switch genes on and off so variations in these parts of DNA may vary how genes are expressed.
If a mutation occurs in a section of non-coding DNA that controls gene expression, the expression of these genes may be altered or in some cases, the mutation may cause them not to be expressed at all

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9
Q

How can humans synthetize so many proteins with so few genes?

A

Because non coding parts of DNA can switch genes on and off

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10
Q

What is sexual reproduction?

A
  • Involves the production of gametes (sex cells) by meiosis.
  • A gamete from each parent fuses to form a zygote.
  • Genetic information from each gamete is mixed so the resulting zygote is unique.
  • Offspring inherit some characteristics from both parents.
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11
Q

What are gametes?

A

Sex cells (sperm cells and egg cells in animals, pollen and egg cells in flowering plants).

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12
Q

What is meiosis?

A
  • Form of cell division involved in the formation of
    gametes (non-identical haploid cells) in reproductive organs.
  • Chromosome number is halved.
  • Involves two divisions.
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13
Q

Describe the process of meiosis?

A
  • Each chromosome is duplicated, forming X-shaped chromosomes
  • First division: the chromosome pairs line up along the centre of the cell and are then pulled apart so that each new cell only has one copy of each chromosome
  • Second division: the chromosomes line up along the centre of the cell and the arms of the chromosomes are pulled apart
  • A total of four haploid daughter cells will be produced
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14
Q

What does it mean that gametes are haploid?

A

We describe gametes as being haploid – having half the normal number of chromosomes

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15
Q

Why is meiosis important?

A
  • Produces gametes eg. sperm cells and egg cells in animals, pollen grains and ovum cells in plants
  • Increases genetic variation of offspring
  • Meiosis produces variation by forming new combinations of maternal and paternal chromosomes every time a gamete is made, meaning that when gametes fuse randomly at fertilisation, each offspring will be different from any others
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16
Q

What happens during fertilisation?

A
  • Gametes join at fertilisation to restore the normal number of chromosomes
  • When the male and female gametes fuse, they become a zygote (fertilised egg cell)
  • This contains the full number of chromosomes, half of which came from the male gamete and half from the female gamete
  • The zygote divides by mitosis to form two new cells, which then continue to divide and after a few days form an embryo
  • Cell division continues and eventually many of the new cells produced become specialised (the cells differentiate) to perform particular functions and form all the body tissues of the offspring
  • The process of cells becoming specialised is known as cell differentiation
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17
Q

What is asexual reproduction?

A
  • Asexual reproduction does not involve sex cells or fertilisation
  • Only one parent is required so there is no fusion of gametes and no mixing of genetic information
  • As a result, the offspring are genetically identical to the parent and to each other (clones)
  • Asexual reproduction is defined as a process resulting in genetically identical offspring from one parent
  • Only mitosis is involved in asexual reproduction
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18
Q

What are the pros and cons of sexual reproduction?

A

+ Increases genetic variation
The species can adapt to new environments thanks to mutations. This gives them a survival advantage
Disease is less likely to affect a population due to mutations
An additional advantage of sexual reproduction is our ability to use it and control it for our own needs:
- Natural selection can be speeded up by humans in selective breeding to increase food production
We have controlled sexual reproduction in cows and selectively bred them to produce offspring that produce more milk and more meat than they would have under natural conditions

  • Time and energy to find a partner
    Hard for isolated member of a species to reproduce
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19
Q

Advantages and disadvantages of asexual reproduction

A

+
- Population can increase rapidly when conditions are right
- more time and energy efficient
- much faster
Cons
- offspring identical to parents
- population is vulnerable to change in conditions and might be suited for only one habitat
- disease is likely to affect the whole population

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20
Q

What are examples of organisms that reproduce both sexually and asexually?

A

Malarial parasites
- Malaria is caused by parasites that are carried by mosquitoes
- The parasites are transferred to a human when the mosquito feeds on the human’s blood
- These malarial parasites reproduce asexually in the human host, but sexually in the mosquito
Fungi
- Many fungi reproduce both asexually and sexually
- These species of fungi release spores, which develop into new fungi
- These spores can be produced via asexual or sexual reproduction
- Spores that are produced via sexual reproduction show variation (they are genetically different from each other)
Plants
- Many plants produce seeds via sexual reproduction but are also able to reproduce asexually
- They reproduce asexually in different ways:
Some plants (eg. strawberry plants) produce ‘runners’ (stems that grow horizontally away from the parent plant, at the end of which new identical offspring plants form)
Some plants (eg. daffodils) reproduce via bulb division (new bulbs form from the main bulb underground and then grow into new identical offspring plants)

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21
Q

What is meant by genome?

A

The entire set of the genetic material of an organism is known as its genome

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22
Q

What is The Human Genome Project

A

The Human Genome Project (completed in 2003) was the name of the international, collaborative research effort to determine the DNA sequence of the entire human genome and record every gene in human beings
This was a very important breakthrough for several reasons:
From a medical perspective, as it has already and will continue to improve our understanding of the genes linked with different types of disease and inherited genetic disorders, as well as the help us in finding treatments
The human genome has also made it possible to study human migration patterns from the past, as different populations of humans living in different parts of the world have developed very small differences in their genomes

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23
Q

What is DNA

A

-The genetic material in the nucleus of a cell is composed of a chemical called DNA. DNA, or deoxyribonucleic acid, is the molecule that contains the instructions for growth and development of all organisms.
DNA is a polymer made up of two strands forming a double helix
DNA is contained in structures called chromosomes
Chromosomes are located in the nucleus of cells

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24
Q

What are genes?

A

A gene is a short length of DNA found on a chromosome. Each gene codes for a particular sequence of amino acids. These sequences of amino acids form different types of proteins.
There are many different types of proteins but some example of these could be:
structural proteins such as collagen found in skin cells
enzymes
hormones
Genes control our characteristics as they code for proteins that play important roles in what our cells do

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25
What is a polymer?
A molecule made from many repeating subunits
26
What are nucleotides?
The individual subunits of which DNA is made of are called nucleotides
27
What are nucleotides made of?
Each nucleotide consists of a common sugar and phosphate group with one of four different bases attached to the sugar
28
How many types of nucleotides exist? And in what do they differ?
- There are four different nucleotides. - These four nucleotides contain the same phosphate and deoxyribose sugar, but differ from each other in the base attached - There are four different bases: Adenine (A), Cytosine (C), Thymine (T) and Guanine (G)
29
How many bases do exist?
- There are four different bases: Adenine (A), Cytosine (C), Thymine (T) and Guanine (G) Exam Tip You do not need to learn the names of the bases, just their letters. Make sure you know which base bonds with which (the complementary base pairs), as this is the most commonly asked question about this topic.
30
What is meant by complementary base pairing?
The bases always pair up in the same way: Adenine always pairs with Thymine (A-T) Cytosine always pairs with Guanine (C-G) This is known as ‘complementary base pairing’
31
What causes the two strands of DNA to be in a double helix?
The bases on each strand pair up with each other, holding the two strands of DNA in the double helix
32
How are amino acids coded for?
A sequence of three bases is the code for a particular amino acid The order of bases controls the order and different types of amino acids that are joined together These amino acid sequences then form a particular type of protein In this way, it is the order of bases in the DNA which eventually determines which proteins are produced
33
What determines which proteins are produced?
It is the order of bases in the DNA which eventually determines which proteins are produced
34
Explain in detail the double helix shape of DNA (eg. What are the ‘backbone’ of the DNA strand made of? What constitute the rungs of the ladder?)
The phosphate and sugar section of the nucleotides form the ‘backbone’ of the DNA strand (like the sides of a ladder) and the base pairs of each strand connect to form the rungs of the ladder. It is this sequence of bases that holds the code for the formation of proteins The DNA helix is made from two strands of DNA held together by hydrogen bonds
35
What holds together the two strands of DNA?
The DNA helix is made from two strands of DNA held together by hydrogen bonds
36
How does protein synthesis work?
Proteins are made in the cell cytoplasm on structures called ribosomes. Ribosomes use the sequence of bases contained within DNA to make proteins. DNA cannot travel out of the nucleus to the ribosomes (it is far too big to pass through a nuclear pore) so a template is made. Then the template leaves the nucleus and binds to the surface of a ribosome. The ribosome ‘reads’ the code on the template in groups of three Each triplet of bases codes for a specific amino acid Carrier molecules bring specific amino acids and attach themselves to the template in the order given by the DNA. This is done until the template is completed. In this way, the ribosome translates the sequence of bases into a sequence of amino acids that make up a protein Once the amino acid chain has been assembled, it is released from the ribosome so it can fold and form the final structure of the protein. The carrier molecules go back to the cytoplasm to pick up more amino acids.
37
How do changes to proteins happen and what might they cause?
A change in DNA structure may result in a change in the protein synthesised by a gene. If there is a change in the order of the bases in a section of DNA (eg. in a gene), then a different protein may be produced. This protein may not function in the same way as the original protein would have (before the change occurred in the DNA)
38
What does a protein unique shape allow it to do?
When the protein chain is complete it folds up to form a unique shape. This unique shape enables the proteins to fulfil a specific function.
39
Talk about three types of proteins: enzymes, hormones and structural proteins. What is their function and examples
Enzymes – proteins that act as biological catalysts to speed up chemical reactions occurring in the body (eg. maltase is an enzyme that breaks down maltose into glucose) Hormones – proteins that carry messages around the body (eg. testosterone is a hormone that plays an important role in the development of the male reproductive system and development of male secondary sexual characteristics, such as increased muscle mass and growth of body hair) Structural proteins – proteins that provide structure and are physically strong (eg. collagen is a structural protein that strengthens connective tissues such as ligaments and cartilage)
40
What are alleles?
They are different versions of a particular gene. Each allele codes for a different protein. The combination of alleles you inherit determines your characteristics
41
What is a dominant allele?
It is one that is always expressed even if only one copy is present. A dominant allele only needs to be inherited from one parent in order for the characteristic to show up in the phenotype
42
What does homozygous mean?
An individual with two identical alleles for a characteristics
43
What does Heterozygous mean?
An individual with two different alleles for a characteristics
44
What is meant by genotype
This describes the alleles present or genetic make up of an individual regarding a specific characteristics eg Bb or bb
45
What is meant by phenotype
It is the physical appearance of an individual eg brown hair
46
What are recessive alleles?
It is an allele expressed only if two are present. A recessive allele needs to be inherited from both parents in order for the characteristic to show up in the phenotype.
47
What is meant by polygenic characteristics?
Characteristics that are controlled by more than one gene are described as being polygenic. An example of polygenic inheritance is eye colour – while it is true that brown eyes are dominant to blue eyes, it is not as simple as this as eye colour is controlled by several genes This means that there are several different phenotypes beyond brown and blue; green and hazel being two examples
48
How can inheritance controlled by a single gene be predicted?
This can be determined using a genetic diagram known as a Punnett square A Punnett square diagram shows the possible combinations of alleles that could be produced in the offspring
49
What is a family tree?
Family tree diagrams are usually used to trace the pattern of inheritance of a specific characteristic (usually a disease) through generations of a family. This can be used to work out the probability that someone in the family will inherit the genetic disorder
50
How is a family tree constructed?
Males are indicated by the square shape and females are represented by circles Affected individuals are red and unaffected are blue Horizontal lines between males and females show that they have produced children (which are shown underneath each couple). Exam Tip You should always write the dominant allele first, followed by the recessive allele.If you are asked to use your own letters to represent the alleles in a Punnett square, try to choose a letter that is obviously different as a capital than the lower case so the examiner is not left in any doubt as to which is dominant and which is recessive. For example, C and c are not very different from each other, whereas A and a are!
51
What is Cystic fibrosis?
Cystic fibrosis is a genetic disorder of cell membranes. It results in the body producing large amounts of thick, sticky mucus in the air passages. Over time, this may damage the lungs and stop them from working properly.
52
What is Cystic fibrosis caused from?
Cystic fibrosis is caused by a recessive allele (f) This means: People who are heterozygous (only carry one copy of the recessive allele) wonʼt be affected by the disorder but are ‘carriers’. People must be homozygous recessive (carry two copies of the recessive allele) in order to have the disorder If both parents are carriers, the chance of them producing a child with cystic fibrosis is 1 in 4, or 25% If only one of the parents is a carrier (with the other parent being homozygous dominant), there is no chance of producing a child with cystic fibrosis
53
What is Polydactyly?
Polydactyly is a genetic disorder that causes someone to be born with extra fingers or toes
54
What causes Polydactyly?
Polydactyly is caused by a dominant allele (D) This means: Even if only one parent is a carrier, the disorder can be inherited by offspring
55
What is In vitro fertilisation (IVF)?
In vitro fertilisation (IVF) is the process by which embryos are fertilised in a laboratory and then implanted into the motherʼs womb.
56
How can screening for genetic disorders be carried out?
In case of IVF a cell can be taken from the embryo before being implanted and its genes can be analysed. It is also possible to get DNA from the cell of an embryo that’s already in the womb and analyse its genes in the same way Genetic disorders (eg. cystic fibrosis) can be detected during this analysis
57
What are the concerns linked to genetic screening?
This has led to many economic, social and ethical concerns: An IVF embryo (ie. a potential life) might be destroyed if alleles causing a genetic disorder are found in its genes Pregnancy might be prematurely terminated if an embryo already in the womb (also a potential life) is found to have alleles causing a genetic disorder within its genes
58
What are arguments for & against embryo screening
For: Avoid suffering by preventing children with genetic disorders being born Treatment for genetic disorders is expensive and cost money to tax payers Law in place to prevent abuse eg choosing certain characteristics Against: Embryo screening is very expensive and not available to all It might be abused and parents choose characteristics Might give false negative/ positives
59
What is Gene therapy?
Gene therapy is the process by which normal alleles are inserted into the chromosomes of an individual who carries defective alleles (eg. those that cause a genetic disorder). It is a developing technology and is not always successful. The process raises similar economic, social and ethical concerns to embryo screening: Many people believe that gene alteration is unnatural Many believe it is a good idea as it can help to alleviate suffering in people with genetic disorders
60
How are sex chromosomes in males and females?
In females, the sex chromosomes are the same (XX) In males, the sex chromosomes are different (XY)
61
How is inheritance of sex shown?
Using a Punnett square. Mother is XX, Father XY so each pregnancy carries a 50% chance of male and 50% of female
62

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