story of us - part 1 Flashcards
name the bases
- adenine
- thymine
- cytosine
- guanine
what is a gene
a short section of DNA that codes for a particular protein
what is a genome
the entire DNA of an organism
where is genetic information found
nucleus
describe the structure of DNA
- 2 strands (double stranded)
- complimentary base pairing
- made of nucleotides (polynucleotide)
- double helix
- sugar-phosphate backbone
how many chromosomes are there in all human body cells (except gametes), and how are they arranged
46, arranged in 23 pairs
how many chromosomes are there in human gametes
23
in humans, of the 23 pairs, what are 22 of the pairs called
autosomes
what are the 23rd pair of chromosomes called
sex chromosomes
what are pairs of matching chromosomes called
homologous pairs
what is an allele
an alternate form of a gene
what is a chromosome
made of DNA, genes located on, found in the nucleus
diploid definition
number of chromosomes found in body cells
haploid definition
number of chromosomes found in gametes
dominant definition
different forms of the same gene
recessive definition
allele that is not expressed in phenotype when dominant allele is present
codominance definition
both alleles are expressed in the phenotype
what does adenine always pair with
thymine
what does cytosine always pair with
guanine
variation definition
differences between individuals of the same species
what are the 3 causes of variation in humans
environmental, genetic, a combination of both
phenotypic variation definition
variability in the phenotype that exists in a population because of genetic variation and environmental factors
discontinuous variation:
- usually caused by genetic variation alone
- where there are distinct differences for characteristics
- for example, blood group or eye colour
- display data using bar chart
continuous variation:
- often vary because of a combination of genetic and environmental causes
- when there are very small degrees of difference for a characteristic
- for example, height, mass, intelligence
- display data using a histogram with a normal distribution curve - usually gives a smooth bell curve because of the small degrees of differences
what are phenotypic features
observable + measurable characteristics of an individual that can be affectedly environmental factors + genetics
homozygous definition and example
same alleles
e.g. bb
heterozygous definition and example
different alleles
e.g. Bb
polygenic inheritance definition
many characteristics controlled by two or more genes working together
what does a pedigree diagram show
the family history of a genetic condition
what is the role of the nucleus
to control the activities of the cell, using genes
where is genetic information ‘stored’
on chromosomes
what do chromosomes consist of
a long section of DNA held in place by structural proteins (called histones)
what is DNA composed of
small sections called genes
what are the male chromosomes
XY
what are the female chromosomes
XX
what are pairs of matching chromosomes called
homologous pairs
what do homologous pairs carry
genes of the same features
these genes are arranged in the same positions and sequence along the chromosome
what are cells with chromosomes arranged in homologous pairs called
diploid cells
what does the genetic code in the DNA determine
which proteins are built by the cell
how does DNA replicate
mitosis
what do genes do
instruct cells to produce a particular protein which leads to the development of features
what do individual nucleotides join together to form
a polynucleotide
in complementary base pairing how are the amounts of each A / T / C / G distributed
the amounts of A and T are always equal
the amounts of C and G are always equal
what causes phenotypic variation
genetic - controlled entirely by genes
environmental - caused entirely by the environment in which the organism lives
genetic variation:
- meiosis creates genetic variation between the gametes produced by an individual
- this means each gamete carries substantially different alleles
- during fertilisation, any male gamete can fuse with any female gamete to form a zygote
- this random fusion of gametes at fertilisation creates genetic variation between zygotes as each will have a unique combination of alleles
examples of genetic variation in humans
- presence of earlobes
- blood group
- ability to roll tongue
- eye colour gender
environmental variation
- characteristics of all species can be affected by environmental factors
- ‘environmental’ simply means ‘outside of the organism’ so can include factors like climate, diet, culture, lifestyle and accidents during lifetime
examples of environmental variation
- accidents (leads to scarring)
- eating too much + not exercising will cause weight gain
properties of continuous variation
describes characteristics that can change over a range of values
properties of discontinuous variation
either you have this characteristic or you don’t
examples of continuous variation
height, mass, intelligence
examples of discontinuous variation
blood group, eye colour
continuous variation graph
smooth bell shaped curve
discontinuous variation graph
bar chart, steep
what is continuous variation caused by
both genetic and environmental factors
what is discontinuous variation controlled by
genetic factors only
what are phenotypic features
observable and measurable characteristics of an individual that can be affected by environmental factors and genetics
what is polygenic inheritance
characteristics that are controlled by more than one gene
what do chromosomes in a homozygous pair contain
the same type of genes that code for the same characteristics, such as eye colour
each chromosome in the pair, however, may have a different version of the gene
example of polygenic inheritance
skin colour
-> the amount of melanin in the skin is controlled by many genes
-> each gene has alleles that promote melanin production and alleles which do not
-> this produces a wide range of phenotypes
