Unit 2: Chapter 13,14,15,16 Flashcards
DNA building blocks
Nucleotides
Phosphate backbone - deoxyribose sugar and phosphate head
Nitrogenous bases - ATCG
Nitrogenous bases ATCG
Adenine
Guanine
Cytosine
Thymine
5 prime end
Head to tail - the phosphate head then the deoxyribose sugar
3 prime end
Tail to head - the deoxyribose sugar then the phosphate head
Genome
Sum total of the genes present in a cell or an organism. Each genome is the sum total of an organism’s DNA and is expressed as the base sequence of the haploid set of chromosomes.
Human Genome project
International project directed at the identification of the sequence of the more than three billion bases in the human genome.
Benefits of HGP
DIagnosis Treatment Prevention Human biology Human evolution
What does HGP tell us?
The differences between the genomes of different people are single-base differences in the DNA sequences of their genomes
Comparative genomics
Comparing the genomes of various species will elucidate how various features have evolved and how the genomes of closely related species differ
Chargaff’s rule
The relative proportions of A and T are equal and, similarly, the proportion of C is equal to that of G
Features of DNA
Consists of two nucleotide chains.
The chains run in opposite directions -‘anti-parallel’.
The sugar–phosphate backbones of the two chains are on the outside of the DNA double helix
There are weak hydrogen holding the bases together
Dissociation
separation of a double-stranded DNA molecule into its single strands, which occurs when the hydrogen bonds stabilising the two strands are broken, such as by heating.
Reassociation
Pairing again of single strands of DNA during cooling after the two strands of a DNA double helix have been dissociated by heating
Hybridisation
Pairing between single-stranded complementary DNA segments from organisms from the same or even different species.
How is DNA packed into a chromosome
Base pairs> double helix > DNA > Histone > Nucleosomes > Chromatid > Chromosome
Monohybrid crosses
A cross in which alleles of only one gene are involved.
Dihybrid crosses
Refers to a cross in which alleles of two different genes are involved.
Dominant
refers to a trait that is expressed in the heterozygous condition; also refers to a trait that requires only a single copy of the responsible allele for its phenotypic expression.
Recessive
Refers to a trait that is not expressed but remains hidden in a heterozygous organism.
Gene
Inherited instruction carried on a chromosome; specific segment of DNA carrying an instruction encoded in its base sequence for a specific protein product.
Function of genes
Controls a general function and its alleles produce specific expressions of that function
Alleles
The different forms of a particular gene.
Karyotype
Specific complement of chromosomes present in a cell or an individual arranged in an organised manner according to an agreed convention.
Karyotype organisation
Size
Centromere position
Banding
Sex chromosomes
The pair of chromosomes that differ in males and females of a species.
Autosomes
Any one of a pair of homologous chromosomes that are identical in appearance in males and females of a species.
Homologous
Refers to members of a matching pair of chromosomes.
Non - homologous
Nonmatching chromosomes.
Kinetochore
A special attachment site of a chromatid by which it links to a spindle fibre
Down syndrome
chromosomal disorder due to the presence of an additional number 21 chromosome, either as a separate chromosome (trisomy- or triplo-DS) or attached to another chromosome (translocation DS)
Trisomy
describes a cell or organism with three copies of a particular chromosome that is normally present as an homologous pair.
Monosomy
Condition in which a cell or organism has only one copy of a particular chromosome that is normally present as a homologous pair.
Turner syndrome
Missing sex chromosome XO
Klinefelter syndrome
Extra sex chromosome XXY
Duplication
Type of chromosome change in which part of a chromosome is repeated.
Deletion
type of chromosome change in which part of a chromosome is lost.
Translocation
the location of a chromosome segment is altered so that it becomes relocated to a new region within the karyotype
Nondisjunction
failure of normal separation of homologous chromosomes during meiosis or failure of normal separation of the two strands of a double-stranded chromosome during meiosis or mitosis.
Phenotype
Expression of an organism’s genotype in its structural, biochemical and physiological characteristics.
Genotype
refers to both the double set of genetic instructions present in a diploid organism and to the genetic make-up of an organism at one particular gene locus.
Homozygous
refers to a diploid cell or organism whose genotype for a particular gene comprises two identical alleles. This state may be denoted, for example, as AA or aa..
Heterozygous
refers to a diploid cell or organism whose genotype for a particular gene comprises two different alleles. This state may be denoted, for example, as Aa..
X linked
gene with its locus on the X chromosome; also refers to a trait that is controlled by such a gene.
Y linked
gene with its locus on the Y chromosome; also refers to a trait that is controlled by such a gene.
Hemizygous
in a male mammal, describes the genotype with respect to any gene carried on either the X or the Y chromosome, which comprises just a single allele for each gene.
Autosomal genes
have two copies of each gene located on an autosome.
Carrier
Refers to a heterozygote that has the allele for a recessive trait but does not show the trait
Co-dominance
relationship between two alleles of a gene such that a heterozygous organism shows the expression of both alleles in its phenotype; sometimes termed partial dominance or incomplete dominance.
Environment and genotype
genotype+environment→phenotype
PKU
Kids with this condition have pp and cannot produce phe hydroxolase which helps with the breakdown of proteins, if they do not eat protein then they can stop mental retardation
Monogenetic traits
refers to traits that are under the control of single genes.
Discontinuous variation
type of variation in which members of a population can be grouped into a few non-overlapping classes with regard to expression of a trait.
Polygenetic traits
traits controlled by the action of two or more polygenes.
Polygenes
genes that have a small, but cumulative effect on the phenotype and control polygenic traits.
Continuos variation
type of variation in which members of a population vary across a range.
Working out the number of variations from polygenes
2n + 1
Test cross
cross of an organism (uncertain genotype A–) with a homozygous recessive organism (genotype aa) to determine whether that organism is homozygous (AA) or heterozygous (Aa); cross of a double heterozygote (AaBb) with a homozygous recessive (aabb) to determine whether or not the two genes concerned are linked, and, if they are linked, to obtain an estimate of the distance between the two loci.
Pedigrees
graphic representation using standard symbols showing the pattern of occurrence of an inherited trait in a family.
Pedigree - autosomal dominant
Both males and females can be affected.
All affected individuals have at least one affected parent
Pedigree - autosomal recessive
Both males and females can be affected.
Two unaffected parents can have an affected child
The trait may disappear from a branch of the pedigree, but reappear in later generations; that is, it can ‘skip a generation’.
Over a large number of pedigrees there are approximately equal numbers of affected females and males.
Pedigree - Xlinked dominant
A male with the trait passes it on to all his daughters and none of his sons.
A female with the trait may pass it on to both her daughters and her sons
Pedigree - X linked recessive
All the sons of a female with the trait are affected.
All the daughters of a male with the trait are carriers of the trait and do not show the trait; the trait can appear in their sons.
Pedigree - Y linked
Only males can show the trait.
An affected male with the trait will pass the allele to all his sons, who, in turn, will pass it to all their sons, and so on across generations.
