human bio extended response 2

gene pool

the sum of all alleles by the members of a population

population

a group of organisms of the same species living together in a particular place at a particular time

gene pool vs pop

gene pool represents genetic makeup of the pop + individuals who can reproduce whereas pop is the group of organisms that share that genetic makeup

mutation

a permanent change in a gene or chromosome leading to new characteristics in an organism

induced mutation

mutations caused by mutagens

mutagen

environmental agent that increase the rate of mutations e,g mustard gas, UV rays, sulfur dioxide

spontaneous mutation

mutations that occur due to an error in a natural, biological process such as cell division

gene mutation

changes in a single gene so that the traits normally produced by that gene are changed or destroyed

chromosomal mutation

a change to the structure and/or number of chromosomes in an organism

gene mutation vs chromosomal mutation

• gene only affects a single gene, so will not have a large impact on the organism as only 1 trait coded for is impacted

• chromosomal affects MANY genes so will have a large affect on the organism as many traits coded for are impacted

point mutation

a change in a single nucleotide in a DNA molecule

inserted

a new nucleotide is added to the DNA strand

substituted

an existing nucleotide is replaced with another nucleotide with a diff base

deleted

a nucleotide is removed from the DNA strand

frameshift mutation

A mutation involving an insertion or a deletion that results in a change in the way that the sequence is read

duplication

a section of a chromosome occurs twice

deletion

a piece of DNA is removed

inversion

breaks occur in a chromosome and the broken pieces join back in, but the wrong way around

translocation

part of a chromosome breaks off and is rejoined to the wrong chromosome

non disjunction

during meiosis, a chromosome pair does not separate and so 1 daughter cell has an extra chromosome and 1 daughter cell has one less than the normal number

aneuploidy

a change in the chromosome no.

down syndrome/trisomy 21

a genetic disorder resulting from an extra copy of chromosome 21

symptoms of down syndrome

• intellectual disability, weak muscles + characteristic facial expression

• may suffer from heart defects or digestive abnormalities

patau syndrome

a genetic disorder resulting from an extra copy of chromosome 13

symptoms of Patau syndrome

intellectual disability, microcephaly, an extra finger on each hand, a cleft palate, and/or cleft lip

where does the extra chromosome come from in Patau syndrome

either from mother’s egg cell or father’s sperm

how often does Patau syndrome occur

• 1 in every 5000 live births

• 80% of children with syndrome die within a month of birth

Klinefelter syndrome

a genetic disorder resulting from inheritance of two X chromosomes and 1 Y chromosome

characteristics of Klinefelter

small testes that cannot produce sperm, breasts are enlarged, body hair is sparse and occasionally intellectual disability

Cri-du-chat syndrome

a rare genetic disorder caused by a missing part of chromosome 5

characteristics of cri-du-chat syndrome

when infants are born with the disease, they sound just like a meowing kitten due to problems with the larynx + nervous system

turner syndrome

a genetic disorder resulting from inheritance of 1 X chromosome and no other sex chromosome

characteristics of turner syndrome

short in stature, lack secondary sexual characteristics + infertile

advantageous mutation (A.M)

a mutation that produces a trait that increases an organisms chance of survival + reproduction

how do A.M change in allele frequency in a gene pool over time

• found in very high allele frequencies as the advantageous mutation is passed onto offspring as the trait is selected FOR

• over many, many gens may become fixed

disadvantageous mutation (D.M)

a mutation that produces a trait that decreases an organisms chance of survival + reproduction

how do D.M change in allele frequency in a gene pool over time

• found in very low allele frequencies in the gene pool as the mutation is not passed onto offspring as it is selected AGAINST

• over many, many generations may become extinct

germline mutation (G.M)

a change in the hereditary material in the gametes that become incorporated into the DNA of every cell in the body of the offspring

somatic mutation (S.M)

a change occurring in a gene in a somatic cell

how is a G.M diff to a S.M

• G.M usually does not affect individual that carries the mutation whereas somatic only affects the individual that carries the mutation

• G.M can be passed onto offspring but S.M cannot

how is sickle cell anaemia caused

• due to a substitution point mutation in the HBB gene

• instead of glutamic acid being coded for in A.A seq, the A.A valine is coded for instead

• this leads to a diff protein being produced, thus altering the shape of haemoglobin, which leads to the distorted sickle cell shape

what does HBB usually code for

one of the beta globulin proteins that make up haemoglobin

original DNA seq at point of mutation

CTC

GAG

mutated DNA seq at point of mutation

CAC

GTG

how must sickle cell be inherited

from both parents as it is recessive, meaning both parents would have to pass on the recessive allele

symptoms of sickle cell

• jaundice

• clogged blood vessels

• rheumatisms

• anaemia as sickled blood cells often die early

• blocked blood flow and lack of oxygen into cells as sickled red blood cells are inflexible and become caught in blood vessels

how does sickle cell anaemia affect heterozygotes

they will have mild sickling and will only displays symptoms if they have a short supply of oxygen

is sickle cell anaemia more prevalent in some populations, if so which ones

yes, pops that have the highest risk of malaria have the highest conc of sickle cell alleles

what locations is sickle cell anaemia prevalent in

Sub-Saharan Africa, India, Middle East, Caribbean + Mediterranean

does sickle cell anaemia provide any advantage to people that carry or have the disease

yes, individuals with the disease have a lower chance of contracting malaria than those without the disease

how does sickle cell anaemia provide resistance to malaria

malaria parasites require red blood cells as a host, so having the sickle shape makes it hard for the parasite to multiply in the r.b.c and spread the disease

who tested this advantage of sickle cell

Anthony Allison

how did Anthony Allison test the advantage of sickle cell

• he inoculated sicklers + non sicklers with malaria and treated those in which malaria developed

• was found that recessive homozygotes were less susceptible to infection from malaria than normal individuals

has sickle cell change allele frequency in gene pools of pops

• yes, in pops where malaria is prevalent, the gene pool will have a higher frequency of sickle cell alleles than regular pops as it offers a survival advantage

• is it still not found in LARGE concs as homozygotes will die before they could pass on both recessive alleles but still larger conc than regular pops

how does sickle cell offer a survival advantage

if you were heterozygous, you had the survival advantage of not being able to contract malaria, meaning that the trait was selected FOR, which increased its allele frequency as heterozygotes could pass on both the alleles

how was homozygous dominant a disadvantage

it did not offer the survival advantage of malaria resistance, meaning their alleles were selected AGAINST and they would not pass them on as frequently as heterozygotes would

how frequent is the sickle cell allele in normal pops

not very frequent as the disease does not offer a survival advantage against malaria, meaning heterozygotes won’t be as likely to pass on their alleles + homozygotes will die before they can pass on alleles