Human Structure and Function C11
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| Allele | An alternative form of a gene
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| Autosomal | Autosomal
A chromosome that is not a sex chromosome
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| Chromatid | Chromatid
One half of a chromosome
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| Chromosome | Chromosome
Cellular structure which contains the primary genetic information of the cell
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| Cytokinesis | Cytokinesis
Cytoplasmic division during mitosis
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| Deoxyribonucleic acid (DNA) | Deoxyribonucleic acid (DNA)
The genetic information of a cell
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| Gene | Gene
Functional unit of heredity
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| Gametes | Gametes
A cell (ovum or sperm) that is specialized
for sexual reproduction
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| Homologous | The maternal and paternal pair of chromosomes
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| Meiosis | The act of germ cell division
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| Mitosis | The series of events that lead to the production of two cells by division of a mother cell into two daughter cells
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| Nitrogenous base | A nitrogen containing molecule that has the same chemical properties as a base and bonds nucleic acids together
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| Ribonucleic acid (RNA) | An nucleic acid containing ribose as the sugar component which helps direct protein synthesis
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| Ribosome | A cytoplasmic organelle which is the site of protein synthesis
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| Somatic | The cells of the body except the reproductive cells
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| You should now be aware that proteins carry out a range of functions in the cell and body: Structural proteins: | o Microtubules and microfilaments, which are part of the cell cytoskeleton and are involved in maintenance of cell shape
o Collagen fibres in connective tissue
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| You should now be aware that proteins carry out a range of functions in the cell and body: Enzymes: | o Those that catalyse the breakdown of macronutrients in the digestive system
o Those that catalyse the breakdown of glucose in cellular respiration
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| You should now be aware that proteins carry out a range of functions in the cell and body: Transport: | o Oxygen transport by haemoglobin in red blood cells
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| 1. What happens to DNA before the cell can divide? Why is this so important? | It must replicate so that when cells divide, each new cell has the full amount of DNA
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| How and why does the cell package its DNA ready for division? | DNA condenses to form chromatin, which then winds up to form chromosomes.
Packaging the DNA in this way means it is protected during cell division and is easier to divide in half
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| What do the terms diploid and haploid mean? Give an example of a diploid cell and a haploid cell. | Diploid means a cell has the full amount of DNA e.g. all cells of the body except gametes
Haploid means a cell has half the amount of DNA e.g. gametes (sperm and egg)
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| Why do gametes only have a haploid amount of DNA? | Sperm and eggs only have half the amount of DNA (haploid) so that when a sperm fertilizes an egg the resulting embryo has the full correct amount of DNA (diploid).
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| Number of chromosomes in human cells? | 46
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| Number of pairs of chromosomes? | 23
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| Number of pairs of autosomal chromosomes? | 22
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| Sex chromosomes in men are: | X and Y
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| Sex chromosomes in women are: | X and X
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| What is a gene and what does it do? | A gene is a segment of DNA that codes for a particular protein
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| What is an allele? | A version of a gene.
You inherit one allele from your mum and one from your dad for every gene.
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| What is the name of the process by which DNA is converted into mRNA and where does this event take place within the cell? | Transcription, which takes place in the cell’s nucleus.
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| What is the name of the process by which RNA is converted into protein and where does this event take place within the cell? | Translation, which takes place in the cytoplasm.
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| There are four characteristic functions of a cell: | 1. Cell metabolism and energy use
2. Synthesis of molecules
3. Reproduction and inheritance
4. Communication
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| During digestion proteins are broken down into ___ that are absorbed through the wall of the ___. These ___ can then be used as the fundamental building blocks for the proteins we make inside our cells. | During digestion proteins are broken down into amino acids that are absorbed through the wall of the small intestine. These amino acids can then be used as the fundamental building blocks for the proteins we make inside our cells.
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| In your groups make a list of the roles of proteins in the body i.e. what do proteins do? | Enzymes, hormones, structural proteins e.g. collagen, receptors on the cell surface, transport e.g. cell membrane transport, transport of oxygen
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| Proteins are all made from chains of amino acids. The sequence of amino acids is called the primary ___. | Proteins are all made from chains of amino acids. The sequence of amino acids is called the primary structure of a protein.
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| Amino acids all have different shapes, charges and side chains. This means proteins have different ___ - they are not just long straight chains of amino acids. | amino acids all have different shapes, charges and side chains. This means proteins have different shapes - they are not just long straight chains of amino acids
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| Proteins fold up in different shapes to form specific ___ and ___ structures. If the mature protein involves more than one polypeptide chain twisted together, the protein is said to have ___ structure | Proteins fold up in different shapes to form specific secondary and tertiary structures. If the mature protein involves more than one polypeptide chain twisted together, the protein is said to have quaternary structure
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| For example, a collagen fibril (found in connective tissue) is made up of three ___ chains twisted around each other and is called a ___ protein | For example, a collagen fibril (found in connective tissue) is made up of three polypeptide chains twisted around each other and is called a fibrous protein
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| A haemoglobin molecule consists of four ____ chains that twist around to form a ___ protein | A haemoglobin molecule consists of four polypeptide chains that twist around to form a globular protein
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| What is the difference between a protein and a peptide? | A peptide is a short chain of amino acids.
The distinction between peptide vs. polypeptide vs. protein is flexible
Generally peptides are 2 or more amino acids, polypeptides are 10 - 50 amino acids long, and proteins are > 50 amino acids long.
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| What is the relationship of DNA to proteins? | DNA carries the code for the specific sequence of amino acids that form a particular protein.
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| How does the cell make proteins? | Amino acids are the building blocks of proteins, with each type of protein within the body consisting of a specific sequence of amino acids. The sequence of amino acids determines the shape of the proteins (structure), structure determines its function.
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| How do cells know which amino acids need to be linked together to form a specific protein? | The amino acid sequence for each protein is located on deoxyribonucleic acid (DNA).
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| How do cells know which amino acids need to be linked together to form a specific protein? Simplified | Simplified, DNA carries the recipe for each protein. A gene is a segment of DNA that carries the instructions that specify the structure of a specific protein. The production of a protein, using the information stored in DNA, is called gene expression.
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| Gene expression can be divided into two parts: | 1. Transcription
2. Translation
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| The structure of DNA and RNA DNA is a ___. ___ are large molecules composed of carbon, hydrogen, oxygen, nitrogen and phosphorus. DNA is a long, ___ molecule that comprises much of the genetic material in the cell, and directs the structure of proteins | DNA is a nucleic acid. Nucleic acids are large molecules composed of carbon, hydrogen, oxygen, nitrogen and phosphorus. DNA is a long, double stranded molecule that comprises much of the genetic material in the cell, and directs the structure of proteins
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| The structure of DNA and RNA Ribonucleic acids (RNA) are ___ and structurally related to DNA. There are 3 types of RNA that all play a role in protein synthesis (___, ___ and ___). | Ribonucleic acids (RNA) are shorter and structurally related to DNA. There are 3 types of RNA that all play a role in protein synthesis (mRNA, rRNA and tRNA).
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| The structure of DNA and RNA Both DNA and RNA consist of the basic building blocks called___ | Nucleotides
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| The structure of DNA and RNA Each nucleotide is composed of a ___ molecule (monosaccharide) to which a ___ and ___ are attached | Each nucleotide is composed of a sugar molecule (monosaccharide) to which a phosphate and nitrogenous base are attached
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| DNA The sugar molecule is ___ and the nitrogenous bases are: guanine, cytosine, thymine, adenine. The nucleotides of each strand join together to form a long twisted ladder-like structure called a ___. | DNA
The sugar molecule is deoxyribose and the nitrogenous bases are: guanine,
cytosine, thymine, adenine. The nucleotides of each strand join together to form a long twisted
ladder-like structure called a double helix.
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| DNA adenine always pairs with ____ cytosine always pairs with ____ | DNA
adenine always pairs with thymine
cytosine always pairs with guanine
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| RNA The sugar molecule is ___ and nitrogenous bases are: guanine, cytosine, ___, adenine. That is, thymine in DNA is replaced by ___ in RNA. | RNA
The sugar molecule is ribose and nitrogenous bases are: guanine, cytosine, uracil, adenine. That is, thymine in DNA is replaced by uracil in RNA.
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| Feature DNA Number of strands and shape of molecule Type of sugar Names of bases Relative length of molecule | Number of strands and shape of molecule - 2 Double helix
Type of sugar - deoxyribose
Names of bases - adenine, guanine, cytosine, thymine
Relative length of molecule - very long
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| Feature RNA Number of strands and shape of molecule Type of sugar Names of bases Relative length of molecule | Number of strands and shape of molecule - 1, may be folded
Type of sugar - ribose
Names of bases - adenine, guanine, cytosine, uracil
Relative length of molecule - shorter
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| State where mRNA is made and whether this is called transcription or translation? | mRNA is made in the nucleus, and this is called transcription
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| How many nucleic acid bases code for one amino acid? | 3, this group of 3 is called a CODON
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| State the major role that each type of RNA plays during protein synthesis Messenger RNA (mRNA) | Messenger RNA (mRNA)
takes the information from the genes (DNA) in the nucleus out to the ribosomes
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| State the major role that each type of RNA plays during protein synthesis Transfer RNA (tRNA) Ribosomal RNA (rRNA) | Transfer RNA (tRNA)
transfers amino acids from the cytoplasm to the ribosome and lines them up opposite their mRNA codon
Ribosomal RNA (rRNA)
major structural component of the ribosome
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| When we talk about transcription we must remember that DNA is a double-stranded molecule and consists of two stands – the ___ strand and the ___ strand | When we talk about transcription we must remember that DNA is a double-stranded molecule and consists of two stands – the coding strand and the template strand
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| Which amino acid has the same codon as the start codon? What does this tell you about all proteins? | Methionine has the same codon as the start codon.
All proteins originally start with this amino acid. However, short peptides are usually formed
by cutting up longer ones, so after processing, they don’t necessarily start with methionine
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| Cells differ from other cells because they “turn on” different genes, only genes that are turned on that are available for transcription and translation into proteins. When a gene is “turned off” it means the cell will not make that particular protein. | Cells differ from other cells because they “turn on” different genes, only genes that are turned on that are available for transcription and translation into proteins.
When a gene is “turned off” it means the cell will not make that particular protein.
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| Each time another gene is switched __, the cells functional abilities become more restricted, and the cell specialises (___). This means the proteins made by muscle cells is very different from those made by a liver cell, they have very different ___. | Off
Differentiates
Functions
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| Human beings go from a single cell at fertilisation to roughly 75 trillion cells at maturity. This increase in size and complexity occurs because most cells are able to divide and produce replicas of themselves, called ___. | Human beings go from a single cell at fertilisation to roughly 75 trillion cells at maturity. This increase in size and complexity occurs because most cells are able to divide and produce replicas of themselves, called daughter cells.
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| Even once a person is fully developed, cell division must still occur as cells have a __. Some cells may survive for only a few hours whilst others can last for decades | Even once a person is fully developed, cell division must still occur as cells have a limited lifespan. Some cells may survive for only a few hours whilst others can last for decades
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| The life span of many cells is already programmed and ceases by activation of certain “suicide” genes leading to their death. This is called ___. | The life span of many cells is already programmed and ceases by activation of certain “suicide” genes leading to their death. This is called apoptosis.
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| Cells only spend a small part of their time actively engaged in cell division (___) | Cells only spend a small part of their time actively engaged in cell division (mitosis)
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| The majority of their time is spent in a state known as ___. ___ includes the time when the cell is performing normal cell functions or preparing for cell division. | The majority of their time is spent in a state known as interphase. Interphase includes the time when the cell is performing normal cell functions or preparing for cell division.
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| When a somatic cell is ready to divide it enters ___. At the end of ___ one cell has divided to produce two genetically identical ___. | When a somatic cell is ready to divide it enters mitosis. At the end of mitosis one cell has divided to produce two genetically identical daughter cells.
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| Mitosis occurs in all cells of the bodies except ___ (ova and sperm), which replicate using ___. | Mitosis occurs in all cells of the bodies except gametes (ova and sperm), which replicate using meiosis.
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| Some terminology that may help…. Chromosome | Consists of DNA and associated proteins (DNA is coiled around proteins to protect it from
damage).
Humans have 22 pairs of autosomal chromosomes (1 - 22) and 1 pair of sex
chromosomes, XX in females and XY in males.
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| Some terminology that may help…. Chromatid | When a chromosome replicates ready for cell division, the two bits of the chromosome are
called chromatids.
Each of these chromatids is called a chromosome again when they separate and move into
the daughter cells.
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| Some terminology that may help…. Homologous pair | Chromosome pairs are called homologous pairs, each member of the pair is called a homologue.
One homologue is derived from mother and one from father.
Each chromosome in pair codes for same genes, you have 2 versions of every gene (alleles).
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| Some terminology that may help…. A pair of unduplicated homologous chromosomes | When they duplicate the two strand are
called chromatids
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| Interphase 1 | 90% of a cell life is spent in interphase.
Cell undergoes normal growth and normal metabolic processes and prepares to divide.
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| Interphase 2 | Interphase is split into 3 separate parts
o G1 – normal metabolic activities
o S – DNA replicates producing 2 identical copies of each chromosome (new DNA is synthesised)
o G2 – Cell prepares for division – organelles replicate
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| Mitosis PMATC | Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
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| Mitosis | 2 identical daughter cells produced.
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| Prophase 1 | Chromatin condenses into chromosomes; Each chromosome = two chromatids joined by centromere
Centrioles divide, move to each end of cell
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| Prophase 2 | Nuclear envelope disappears
Microtubules form near the centrioles, project in different directions, some project to equator of cell.
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| Metaphase | Duplicated chromosomes (two chromatids) align along centre of the cell (equator)
Microtubules (spindle fibres) attach to centromere of each chromosome (or to each sister chromatid)
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| Anaphase 1 | The two chromatids of each chromosomes begin to separate
The centromere holding the chromatids together divides.
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| Anaphase2 | The chromosomes assisted by the microtubules migrate towards the centrioles
Anaphase ends when the chromosomes reach the end of each cell.
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| Telophase | The chromosomes unravel to become less obvious chromatin strands
The nuclear envelop reforms and the microtubules disappea
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| Cytokinesis | The division of cell organelles and cytoplasm.
Results in two identical daughter cells.
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| Meiosis is a highly specialised kind of cell division used only to produce the ___, ___ and ___. It involves cell division like mitosis but includes an additional process that halves the genetic material in the daughter cells. | Meiosis is a highly specialised kind of cell division used only to produce the gametes, ova and sperm. It involves cell division like mitosis but includes an additional process that halves the genetic material in the daughter cells.
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| Why is the genetic material halved? | So that the union of sperm and ovum at fertilisation produces a cell that has the full amount of genetic material again. Without this reduction, a fertilised ovum would have a double the amount of genetic material.
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| First division: 1. Like mitosis: | a cell in the ovary or testicle goes through the process of doubling its DNA and condensing the material down into visible chromosomes, each with two chromatids (so far just like mitosis)
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| First division 2. Unlike mitosis: | 2.the members of all homologous chromosome pairs move together in the centre of the cell (matching chromosomes find each other). At this stage they can swap bits of their chromatids (crossing over).
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| First division 3. Unlike mitosis: | 3. the cell divides and pulls one of each pair of homologous chromosomes into each daughter cell (each chromosome still has two chromatids).
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| Second division 4. | After this, the rest is relatively easy. Like mitosis, each of daughter cells goes through cell division (similar to mitosis) two chromatids of each chromosome are pulled apart.
The end result is 4 cells, each with half of the original set of genes
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| What is the purpose of the first meiotic division? | Meiosis I separates homologous chromosomes, producing two haploid cells (23 chromosomes) which is half the amount of DNA in a “normal” cell.
Thus, meiosis I is referred to as a reductional division
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| What do you think is the purpose of allowing some ‘swapping’ of bits of chromatid between members of homologous pairs during meiosis I? | It increases variety in humans
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| After the second meiotic division is completed, are the four haploid cells (i.e. cells with half the number of chromosomes) genetically identical? | Close – but no, the key is in the swapping or crossing over of chromatids
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| How many alleles for a given gene does a gamete (sex cell) have? | One, because each gamete only has one copy of each chromosome, not two like a somatic (body) cell
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