Genetics Flashcards
What is it called when organisms reproduce without a sex cell?
Asexual reproduction
What does asexual reproduction produce?
Clones - offspring that are genetically identical to the parent
In animals asexual reproduction is very rare but are much more common In what?
Invertebrates (such as insects)
During the summer female aphids produce offspring from cells formed by what? (Asexual)
Mitosis
For some plants in asexual reproduction what are runners?
Special stems that grow out from the adult plant
How do some plants reproduce new plants?
From bits of leaves or roots, this helps them spread quickly in areas near the parent plant
In plants what do the runners do?
They supply water and nutrients to the daughter plant until it’s leaves and roots are well developed
Using a runner in plants, where does the daughter plant grow?
Where a node (joint) in a runner touches the ground. New plants grow leaves then roots
Sexual reproduction combines characteristics from both parents, and so produces offspring that are different from each other. How is this an advantage?
If the offspring move to an area with different environmental conditions, also if the environment changes, for example if the temperature changes or a new pest or disease comes to the area
What does variation mean?
That there is a greater chance that some offspring will be better suited to new conditions and so will be more likely to survive and reproduce
How is asexual reproduction faster than sexual reproduction and how is this an advantage?
There is no need to find a mate and this is an advantage when they are lots of resources such as food
Aphids feed off sap in the summer, plant growth is most rapid in the summer, so what does asexual reproduction help help aphids to do?
Make the most of all the food in the summer
Humans start life as a single fertilised egg called a zygote, when is this formed and what happens next?
When two gametes fuse during fertilisation, the zygote then forms a ball of cells using a type of cell division called mitosis
What is mitosis?
DNA cell replication. There are 6 stages they are interphase, prophase, metaphase, anaphase, telophase and cytokinesis
Almost all human cells carry exactly the same instructions. What do these instructions control?
Each individual cell, shape, and shape and coordinate our bodies
How big is the nuclear in a zygote?
0.006mm in diameter
What is a genome?
All of the DNA in an organism, each body cell contains a copy of this genome
Why are the instructions for an organism found?
As code in a molecule called DNA
Where is the DNA of an organism?
In its genome, and most cells contain a complete copy of an organisms genome
Where is the human genome found?
On 46 very long molecules of DNA, and each molecule is inside a chromosome. Along the length of a DNA molecule are sections that each contain a code for making a protein. These DNA sections are genes. Proteins are polymers, made by linking different amino acids together in a chain. The order of amino acids is controlled by a gene. Humans have about 20 000 genes
There are 23 different chromosomes in humans and most nuclei contain two of each type. So a body cell contains two sets of 23 chromosomes, making 46 in all. A cell like this is called diploid, the shorthand for diploid is 2n. What happens if 2 diploid cells fuse together?
If two diploid cells joined in fertilisation, the zygote would have 4 sets of chromosomes, so gametes would only need one set of chromosomes, they have to be haploid. The shorthand for haploid is 1n
What is the process meiosis used to do?
Produce gametes
What cells do mitosis produce?
Diploid cells
Explain the process of meiosis
Each chromosome replicates - makes a copy of itself. The two copies remain attached, making each chromosome look like an X. The two sets of chromosomes ‘pair up’ forming 23 pairs, and the pairs them separate into two new cells. Next, the two copies of a chromosome in each X-shape split into two more cells. Meiosis therefore produces four haploid daughter cells, which is how gametes are produced
Why are gametes all different?
Because they are genetically different chromosomes, this is why brothers and sisters often look similar but not identical
Each chromosome in a pair contains different versions of the same what?
Gene
How many sets of chromosomes does the gamete making cell have?
Two sets they are diploid
Go to page 53
And look at the diagram
What do The nuclei of your cells contain?
Very long molecules of DNA. Each molecule is tightly coiled and packaged up with proteins to form chromosomes
What shape is DNA?
A double helix
What does a molecule of contain?
Two strands which form a helix, the two stands are joined together by pairs of substances called bases, to form a double helix w
What are the four bases in DNA?
Adenine, thymine, cytosine and guanine (A, T, C and G)
What are the complementary base pairs? (Matching bases)
A and T
C and G
Go to page 54
And look at the diagram
What is each base attached to?
A sugar, and each sugar is attached to a phosphate group, this grouping is called a nucleotide. The sugars and phosphate groups form the backbone of the DNA strands. DNA is therefore made of many similar units joined In a chain, and so it is a polymer
What is a hydrogen bond?
Parts of DNA bases have very slight electrical charges. A slightly negatively charged part of one base attracts a slightly positively charged part of another base. This forms a weak force of attraction called a hydrogen bond
Adenine and thymine form two hydrogen bonds, cytosine and guanine form three, what does this help explain?
Why C Paris with G and A pairs with T
The DNA code?
The order of bases in a gene contains the coded instructions for a protein. However, we all have slight different orders of bases in our DNA. In fact, everyone except identical twins has different DNA. This allows scientists to match DNA from cells to specific people. And, since DNA has passed down through families, analysing DNA allows scientists to find out how people are related
Go to page 55 and 56
And looks at the experiment on DNA extraction
how do most animals and plants reproduce?
By sexual reproduction (involving fertilisation of a female sex cell by a male sex cell)
Who won the race to work out the structure of DNA?
James Watson and Francis crick in 1953, they used evidence from other scientists
Who did chromatography experiments that showed that the amounts of A and T in an organisms DNA were the same, as were the amounts of G and C
Erwin Chargaff
Who took an X-Ray photograph suggesting that DNA was a helix
Rosalind Franklin
Who showed them how DNA bases could form hydrogen bonds?
Jerry Donahue
Go to page 58
And look at the diagram
Who worked out the genetic code?
Watson, crick, Chargaff and 21 other international scientists
What is the genetic code?
How the order of bases caused amino acids to be joined in a certain order in a protein,
What is the first stage of the genetic code and what is it?
Transcription and its when the DNA bases are used to make a strand of RNA (ribonucleic acid)
What does the enzyme called RNA polymerase attach itself to?
The DNA in front of a gene in a non-coding region (so called because it does not contain code for a protein) the enzyme separates the two strands. The enzyme then moves along one DNA strand (the template strand) adding complimentary RNA nucleotides. These contain the same bases as DNA except that uracil (u) instead of thymine (t). The nucleotides link to form a strand of messenger RNA (mRNA)
What happens in translation? The second part of the genetic code
The mRNA strands travel out of the nucleus through small holes in its membrane, called nuclear pores. In the cytoplasm the mRNA strands attach to ribosomes. A ribosome then moves along an mRNA strand three bases at a time. Each triplet of bases is called a codon. At each mRNA codon, a molecule of transfer RNA (tRNA) with complimentary bass lines up. Each tRNA molecule carries a specific amino acid. As the ribosome moves along, it joined the amino acids from the tRNA molecules together, forming a polypeptide. This process is called translation
Go to page 59
And look at the diagram
Who cracked the genetic code?
Har gobind
Go to page 60
And look at the diagram
What can a change in the bases of a gene create, and how can a change in the bases be caused?
A mutation or genetic variant, it can be caused when DNA is not properly copied in cell division. Environmental factors can also cause mutations. Some mutations change an organism phenotype
What’s a phenotype?
Observable characteristics
What’s the reason that genes exist in different forms called alleles?
Mutations, one gene can have many alleles caused by mutations, your characteristics are shaped by the alleles you inherit
Explain what happens with mutations in non-coding DNA?
RNA polymerase attaches to DNA bases in front of a gene. A mutation in this non-coding region may result in RNA polymerase not binding well, reducing transcription
What is transcription?
The process by which the genetic code in one strand of DNA molecules is used to make mRNA
What is translation?
The process which the genetic code in a molecule of mRNA is used to make a polypeptide
What is a polypeptide?
A chain of amino acids
What does RNA mean?
Ribonucleic acid
What ideas did a monk called Gregor Mendel (1822-1884) start to develop?
Modern ideas about genes, which we now know control inherited characteristics
What did Mendel do to develop his ideas about how this are inherited?
He bred pea plants together using a paintbrush to move pollen (containing male gametes) from one plant to the flower of another plant. A bag was then placed over the flower on the plant and sealed. Mendel planned the seeds that formed and observed the characteristics of the offspring, the first generation contained only tall plants, but when he crossed two of these he got some short plants again. After lots of experiments, he concluded that inherited factors control the variation of characteristics. Theses factors exist in different versions (now called alleles) that don’t change. A plant has two factors for each characteristic, which are either the same version or two different versions. Plants with two factors of the same version were true breeding. This meant that, if the plant was self pollinated, the offspring all had the same variation as the parent
What was Mendelssohn 3 laws of inheritance?
Each gamete receives only one factor for one characteristic
The version of a factor that a gamete receives is random and does not depend on he other factors in a gamete
Some versions of a factor are more powerful than others and always have an effect in the offspring
Why was Mendelssohn work largely ignored?
Partly because scientists did not see how factors could explain the many variations in characteristics such as human eye colour, but one chromosomes were discovered, scientists could see how it would work
Genes for the same characteristic can contain slightly different instructions that create variations, what are they called?
Alleles (different forms if the same gene)
Because there are two copies of every chromosome in a body cell nucleus, a body cell contains two copies of every gene, what may each copy of a gene be?
A different allele,mothers are many alleles for most of the 20 000 human genes, and the different combinations of alleles in each person gives each of us slightly different characteristics (genetic variation)
What does homozygous mean?
If both alleles in an organism for one gene are the same
What does heterozygous mean?
In an organism if the alleles are different
In alleles, if the allele has an effect what is it called?
Dominant
In alleles, if an allele has no effect, what is it called?
Recessive
Turn to page 64
And look at the diagram
When is a recessive characteristic only seen?
If both alleles are recessive
How are dominant and recessive alleles portrayed?
D -capital letters
R - lower case
What are the alleles in an organism?
It’s genotype
What is what an organism looks like?
It’s phenotype
What’s a genotype?
The alleles for a certain characteristic that are found in an organism
Two of your chromosome determine what sex you are, what letters represent this?
X and Y, females have two X sex chromosomes and males have one X and one Y, a woman gametes all contain an X sex chromosome, but male sperm cells contain either an X or a Y
Go to page 65
And look how to do the diagram thing
What is a punnet square?
Another way to demonstrate inheritance
What are punnet put squares used to do?
Show the probability of an offspring inheriting a certain genotype
Got to page 66 and 67
And look at punnet squares
What different blood types are there?
A, B, AB, O
Go to page 68
And read blood groups
Go to page 68 and 69
And read genetic disorders
What is variation in eye colour caused by?
OCA2 gene, it controls the amount of melanin produced
What is melanin?
A protein that makes hair, eyes and skin darker in colour
Why is it thought that early humans had brown eyes?
Our ancestors moved north from Africa p, changes in alleles for melanin production in some people resulted in blue eyes and fair skin
What does a change in a gene create?
It creates a new allele called a mutation, mutations often occur during cell division
When do mutations happen?
When there is a mistake in coping DNA during cell division, eg one base in a DNA sequence. Might be replaced with another, rather like typing the wrong letter in a word. This can happen naturally, but is more likely to happen if there is damage to the DNA caused by radiation or certain substances
What does a mutation sometimes produce?
An allele that causes a big change in the protein that is produced. This will affect how the body works. However mutations can occur in different parts of s gene and so may only have a small effect on the protein that is produced. Many other mutations will not change the protein at all and so have no effect on the phenotype
What was the human genome project?
In 2003 lots of different scientists from different countries produced a map of 3.3 billion complementary base pairs in one set of 46 chromosomes. Further work has found many sections of DNA that are genes. This has shown that there are variations between people, but that over 99% of the DNA bases in different people are the same
What can mapping a person genome indicate?
It can indicate their risk of developing diseases that are caused by different alleles of genes. It can also help identify which medicines might be best to treat a persons illness, because the alleles we have can affect how medicines work in the body
How is genetic variation caused?
By the different alleles inherited during sexual reproduction
How do many characteristics show environmental variation?
Because they are affected by their surroundings
What are acquired characteristics?
Characteristics that are changed by the environment during the life of the individual
What two groups can variation be put into?
Discontinuous variation and continuos variation
What is discontinuous variation?
Where the data can only take a limited set of values
What is continuos variation?
Where data can be any value in range
Go to page 73 and look at the charts
F
What is normal distribution?
Continuos data for variation that often forms a bell-shaped curve, it is called this because it is what is expected for a large amount of data for a characteristic where the most common value is the middle value in the whole range and the further a value is from the median, the fewer individuals have that range
