Page 4 - Science Fundamentals 2

Genetics & DNA (continued)
Genes & Chromosones

Essential Knowledge: chromosomes. – Males have one X and one Y • determine which traits a person will have.
• Every cell contains chromosomes – Each set contains 23 matching chromosome (XY). • appear through mutations.
that contain DNA, the special homologous pairs. – Sex cells are an exception. • Gregor Mendel: during the 19 century,
th
code for the genes that – Each set carries the code for o Female egg cells contain only Mendel experimented with pea plants and
determine nearly everything 30,000–40,000 genes. one X chromosome. discovered that traits
about our bodies. – Genes occur in the same order o Male sperm cells contain were dominant or Fun Facts:
• Through reproduction, each along both chromosomes of a either one X or one Y recessive: • All humans have
parent’s DNA gets passed on to pair. chromosome. – recessive traits only 99.9 percent
children. – Therefore, genes also occur in • Y chromosome has the genetic manifest when a identical genes.
• Specific features are passed on, pairs. code to develop male offspring. person has two • The 0.1 percent
but generations are not identical. • Sex is determined by one set of recessive alleles. difference creates
• Chromosomes are packed inside 46 chromosomes. ALLELES: • the actual appear- all existing variety &
the cell nucleus. – Sex chromosomes are classified • are different versions of a gene. ance of an organism
diversity.
• Humans have the same 46 as either X or Y, based on their • provide code for the same char- is its phenotype. • A cytologist studies
chromosomes in each nucleus. appearance. acteristic. • the genes that influ-
• Most cells are diploid, meaning – Females have two X • produce the variations that make ence this appearance cells and a geneticist
they contain two sets of chromosomes (XX). individuals unique. are the genotype. studies genes & DNA.
Mitosis & Meiosis
Essential Knowledge: • Mitosis ends with cytokinesis, when the cyto- Stage: Activity:
• Cells divide and reproduce one of two ways. plasm divides and two identical cells are created.
• Mitosis is when the nucleus divides and the number of • In meiosis: prophase I • chromosomes replicate to
chromosomes stays the same. – cells divide to form sex cells (gametes) form chromatids
• Meiosis is when the nucleus divides and the number of with only 23 chromosomes (haploid cell). • chromosomes pair with
chromosomes is halved. – male sperm cells form in testes. homologues
• In mitosis: – female egg cells form in ovaries. • crossing over between
– chromosomes copy themselves. – the original cell produces four daughter cells. matching pairs may occur
– chromosomes form two linked strands (chromatids) joined – these daughter cells each have only half (chromosomes share
the number of chromosomes.
at a centromere. – there are two general phases: meiosis I pieces and create new
chromosomes with unique
– chromatids line up and separate as the cell divides. and meiosis II. genetic pattern)
– the two new cells are identical (genetically) to the old cell.
– there are four general stages. Fun Facts: metaphase I • chromosome pairs line up
• When a fertilized egg splits, identical twins in center of cell
Stage: Activity:
develop. anaphase I • homologous pairs separate
prophase • chromosomes replicate and form chromatids • When two eggs are fertilized by two sperm, and move apart
joined by centromere fraternal twins develop.
• Each sex cell contains one of 8,388,608 telophase I • chromatids collect at
metaphase • nuclear membrane breaks down and opposite sides of cell
chromatids line up in center of cell possible genetic combinations from the • new nuclear membrane
original cell. forms around each group
anaphase • centromeres split and chromatids move apart • The fertilized egg (zygote) contains a • two daughter cells formed
telophase • chromatids collect at opposite sides of cell complete set of 46 chromosomes—23 prophase II– • resembles ordinary
• new nuclear membrane forms around each group from father (inside sperm cell) and 23 telophase II mitosis
• two daughter cells formed from mother (inside egg cell).
DNA & RNA
Essential Knowledge: • Proteins form part of nearly everything in the body. – Transfer RNA (tRNA) carries amino acids to ribosome
• Most DNA (deoxyribonucleic acid) is located – They are made of 20 different types of amino and mRNA.
inside the nucleus of a cell. acids. o tRNA contains bases to match codons on mRNA.
• Mitochondrial DNA (mtDNA) is found inside the – Each protein is composed of a specific order o Bases join and amino acids are joined together with
mitochondria. of amino acids. enzymes.
• DNA is composed of millions of nucleotides. – This order is determined by genes in DNA. o Amino acids form a chain and produce a new protein.
– Nucleotides are composed of a sugar, a – Proteins are made in the cytoplasm of a cell. – Proteins then direct the development of all types of
phosphate, and a chemical base. – DNA is too big to permeate the nuclear cells and cellular activities.
• DNA resembles a twisted ladder with four membrane.
chemical bases as rungs. • RNA (ribonucleic acid) assists in protein Fun Facts:
– Its shape is called a double helix. synthesis and translating the genetic code. • The 46 chromosomes in each cell contain six feet of
– The four bases are: adenine (A), cytosine (C), – DNA unzips to form single-strand RNA. DNA.
guanine (G), and thymine (T). – Free nucleotides pair with the unzipped bases. • If the total DNA in one person were laid in a straight
o Adenine and thymine always combine. – In RNA, the chemical base thymine is replaced line, it would stretch to the sun and back more than
o Cytosine and guanine always combine. with uracil. 30 times.
• DNA can self-replicate. o Uracil acts the same way as thymine. • Evolution is the naturally occurring change in
– It “unzips” to form two separate strands, with o Adenine and uracil always combine. inherited traits over generations. It progresses as
a result of natural selection and mutation.
one-half of each base pair. – Messenger RNA (mRNA) carries the genetic • Charles Darwin suggested that species changed
– Free nucleotides attach to unzipped bases and code for a protein. to adapt to surroundings. He coined the term
form two new complete strands. o mRNA travels through nuclear membrane to “Survival of the Fittest.”
• Groups of three bases are known as a codon. cytoplasm. • In 1944, Oswald Avery proved that DNA carried
– Codons are analogous to a genetic “word” o mRNA attaches to ribosome, which decodes genetic instructions.
(ex. ACG, TCA). message. • In 1953, James Watson and Francis Crick
– There are 64 different codons that compose o Ribosome translates mRNA code and builds discovered the double-helix construction.
the genetic code. protein with amino acids.

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