how is inheritance explained? Flashcards
chapter 6, unit 2 AOS 1, + year 10 DNA recap
DNA – Deoxyribonucleic Acid
DNA is the same in all organisms – it consists of the same 4 bases (A, G, T, C)
The information encoded by DNA directs how cells, tissues, and whole organisms are to be built and how they will function
DNA Structure
Double Helix –Twisted ladder made of a sugar-phosphate backbone (sides of the ladder) and nitrogenous bases (rungs of the ladder)
nucleotides
the basic building block of DNA, made up of a
five-carbon sugar, a phosphate group and a nitrogenous base
-A nitrogenous base (A, G, T, C)
Nitrogen bases
Make up the rungs of the twisted ladder
4 types, Adenine, Guanine, Thymine, Cytosine
Genes
Genes are a sections of coding DNA that code for a specific protein in the body, Only about 1% of all DNA is actually coding DNA
Alleles
different versions of genes, eg. eye colour, freckles or no freckles
Genome
-sum of all an organism’s DNA
-measured by the number of base pairs contained in a sex cell (sperm or egg cell)
Heredity
the study of inheritance; the genetic transmission
of characteristics from one generation to another
histone
a protein around which DNA winds in eukaryotic
cells
chromosome
is comprised of DNA molecules that physically carry genes from one generation to the next
genomics
the study of the genome – how genes interact with each other and the environment, and the resultant proteins produced; it requires a knowledge of an organism’s entire DNA sequence, so studies rely on powerful sequencing technologies and bioinformatics
Proteomics
the study of the entire protein content produced by a cell, tissue or organism
why does DNA Replicate?
So that all newly created cells have a copy of the instructions they need to create proteins
how does DNA replicate
Enzymes! Enzymes unzip the two strands of DNA and add complementary bases to create 2 new double-stranded molecules of DNA
DNA helicase
unzips double stranded DNA as it moves along the DNA.
DNA polymerase
adds complementary nucleotides to unzipped DNA strands
DNA ligase
joins Okazaki fragments of the lagging strand together
Topoisomerase
rewinds DNA strands back up and prevents them from becoming tangled
Getting started with DNA replication
Replication starts at the origin of replication , Helicase unzips DNA forming a replication fork.
Unzipping the Double helix
Helicase unwinds DNA by breaking the hydrogen bonds between the nitrogenous base pairs
Creating the new strands
-An RNA primer binds to DNA, providing a place for DNA polymerase to bind.
-DNA polymerase starts adding complementary nucleotides to the each of the unwound strands.
5’ and 3’
-“five prime” and “three prime”, indicates the carbon numbers in the DNA’s sugar backbone.
-The carbons are numbered from 1-5 in a clockwise direction after the oxygen
ribosome
a small structure in all cells that builds amino acids
into complex proteins
protein
A molecule made up of amino acids. Proteins are needed for the body to function properly. They are the basis of body structures, such as skin and hair, and of other substances such as enzymes, cytokines, and antibodies
RNA – ribonucleic acid
RNA nucleotides contain a ribose sugar NOT a deoxyribose sugar like DNA, when transcribing DNA to RNA, U is replaced by T
mRNA (messenger RNA)
carries the genetic information from DNA to the ribosomes
tRNA (transfer RNA)
brings the amino acids to the ribosomes according to the codons on mRNA.
rRNA (ribosomal RNA)
forms the core of the ribosomes and catalyzes the formation of peptide bonds between amino acids.
transcription
The process of converting a DNA strand into an mRNA strand.
Unlike DNA, mRNA contains only a single strand.
transcription process
copying a gene’s DNA sequence to make an RNA molecule. RNA polymerase binds to DNA, separates the strands, then uses one strand as a template to assemble MRNA. Transcription has three stages: initiation, elongation, and termination.
translation
translation is the production of a polypeptide (protein) using the information that is coded on the mRNA molecule.
translation process
- Ribosomes attach at 5’ end of mRNA and read mRNA in groups of 3 bases, called “codons”
- tRNA (transfer RNA) – have complementary anticodons for the mRNA codon (opposite nucleotides) and carry an associated amino acid
- Peptide bonds form between amino acids as ribosome moves along
- When stop codon is reached the polypeptide is released
why is transcription necessary?
Transcription makes messenger RNA (MRNA) to carry the code for proteins out of the nucleus to the ribosomes in the cytoplasm.
why is translation necessary?
Translation assures that the right amino acids are joined together by peptides to form the correct protein.
aneuploidy
a genome that has an additional or loss of a chromosome from a cell, include monosomy or trisomy
autosome
a chromosome that is the same in both males and females that match together to make the 22 homologous pairs
chiasmata
contact points between
chromatids of homologous chromosomes that may become sites for crossing over and recombination during meiosis
diploid
having two haploid sets of chromosomes in each
cell, represented by 2n, human somatic cells have a diploid number of chromosomes (46)
haploid
the condition of gametes having a single set of
chromosomes, represented by n
human gamete cells have a haploid number of chromosomes (23)
homologous chromosomes
a matched pair of chromosomes with the same banding pattern and centromere position
hydrogen bond
weak molecular chemical bond
karyotype
an image of all the chromosomes in a somatic cellobserved at late
prophase and metaphase
non-disjunction
-homologous chromosomes (sister chromatids) fail to separate.
-In these cases, one gamete receives two of the same chromosome and the other gamete receives no copy.
-causes anueploidy
sex chromosomes
the pair of chromosomes that determines the sex of an individual, female is XX and male is XY
sex inked
describes genes that are found on the sex
chromosomes
trisomy
the condition in which somatic cells contain three copies of a particular chromosome
zygote
the diploid cell that results from the fusion of two
haploid gametes
locus or loci
The location of a gene on a chromosome. In homologous chromosomes, the allele for each gene is found at exactly the same locus on each chromosome, This gives homologous chromosomes the same banding patterns
gamete
sex cell (sperm or egg cell)
monosomy
loss of a chromosome, con only occur with the x sex chromosome
trisomy
an extra chromosome
non-coding DNA
A DNA that does not code for a protein but may have other functions in chromosome structure or regulating production of proteins from genes
recombination
n breaking and rejoining of pieces of chromosome during crossing over leading to a new
combination of alleles in any resulting offspring
zygote
the diploid cell that results from the fusion of two
haploid gametes
meiosis
Meiosis is a process of cell division that occurs in the germ cells to create gametes (sperm and egg).
a germ cell divides twice to produce four gametes containing half the original amount of genetic information
meiosis 1
the first division of meiosis is called a ‘reduction’ division because it reduces (halves) the number of chromosomes in the nucleus
I.e. One chromosome from each homologous pair is donated to each intermediate cell
stages of meiosis
interphase
-g1
-s phase
-g2 phase
prophase 1
metaphase 1
anaphase 1
telophase 1
prophase 2
metaphase 2
anaphase 2
telophase 2
meiosis 2
The second division of meiosis is called a ‘mitotic’ division because it is similar to mitosis, as the chromosomes split into chromatids - except the resulting cells are haploid
interphase: G1 phase
growth so that cells are big enough to divide
interphase: S phase
synthesis- DNA doubles (46 to 92 chromosomes)
Prophase 1
-chromosomes shortens and thicken
-Homologous chromosomes pair up
-crossing over and recombination occurs between homollogous chromosomes
-spindle forms
metaphase 1
-homologous pairs align at the eqautor of the cell
-nuclear membrane disapears
Anaphase 1
-the spindle fibres retract towards the poles pulling the homologous pairs to separate
telophase 1
-nuclear membrane begins to reform
-cytokinesis occurs (cell divides)
-new nuclei have one member of each homologous pair but each chromosome consists of two chromatids
prophase 2
-nuclear membrane breaks down
-spindle fibres reform and reconnect to the chromosomes
metaphase 2
-the sister chromatids move to the equator of the spindle, and spindle fibres attach to the centromere of each chromosome
Anaphase 2
-centromeres divide and chromatids separate
-sister chromatids spit apart and move to opposite poles
telophase 2
-spindle breaks down
-nuclear membrane begins to reform
-cytokinesis occurs (cell divides into 2)
law of segregation
half the gametes formed during meiosis contain one member of each gene pair and half contain the other member
linked genes
Genes located close together on a chromosome, so they are inherited together
Arnt affected by crossing over, they don’t recombine because they are linked together
law of independent assortment
genes on different homologous chromosomes separate independently into gametes during meiosis; the combination of genes (and alleles) that occurs in each gamete is therefore the result of chance
Genetic Diversity
-The biological significance of meiosis is that it produces genetic variability among the offspring
-Recombination produces variation
-gametes carry unique genetic combinations because of:
Crossing over between homologous (matching) chromosomes.
Independent disjoining (separation) of non-matching chromosomes during meiosis.
chromatid
is one of the two identical halves of a chromosome that has been replicated in preparation for cell division, two sister chromatids are joined together at the centromere to make a chromosome
