Biology S2 T4

Genetics

Genetics

study of inherited characteristics called traits

alleles (2)

variation of genes

occupy the same position on homologous chromosomes

pure breeding

where all individuals have the same genetic material

homozygous

individual carries two of the same alleles (rr and RR)

genotype

actual genetic information carried by an individual

phenotype

the observable characteristics or traits of the individuals

sex determination

if a sperm containing an x chromosome fertilises an egg, the offspring will be female. If a sperm carrying a Y chromosome fertilises an egg, then the offspring will be male

sex linked genes (3)

genes that are found on the sex chromosomes

present on one of the chromosomes that are also responsible for the determination of sex

x chromie is longer and carries more genes

pedigree

a diagram used to show patterns of inheritance over generations

chromosomal abnormality

if the chromatids fail to seperate during meiosis, the child will be born with an extra chromosome or part of a chromosome.

Aneuploidy and how leads to trisomy (3)

addition or loss of a single chromosome

via nondisjunction: failure of separation of chromosomes/chromatids. produces gamete missing chromosome and gamete with two copies.

fertilisation of a gamete with 2 chromosomes can produce a zygote with three copies of the chromosomes (trisomy)

different trisomys (6)

down syndrome: 21

edwards syndrome: 18

patau syndrom: 13

may also affect sex chromosomes

klinefelter: XXY

turner syndrome: XO

syndrome

when a disease causes multiple effects. virtually all chromosomal abnormalities are in this category.

mutations (2)

permanent change in DNA

mutagens and carcinogens, what can a mutation cause, kinds of mutagens/carcinogens

agents that cause mutations

carcinogen: agent that causes a mutation to lead to cancer

cause breaks in DNA to replace normal base
form abnormal bonds between bases
activate genes that cause cell to grow out of control

types of mutations

spontaneous → sudden, by chance

induced → by environmental factors such as

• chemical mutagens (Nitrous acid, formaldehyde)

• radiation (UV rays, X rays, Cosmic rays)

genetically modified organism

the genetic information is changed by inserting new genes

(new genes are copied to daughter cells when the parent cell divides by meiosis. these modified cells will mature into a completely new strain of plant)

examples of genetically modified organisms

canola: GM it to be resistant to herbicides

Rice: GM it to have high levels of vitamin A

gene mutations

changes in a single gene

point mutations

frameshift mutations

insertions

deletions

point mutation

change in a single nucleotide in the DNA sequence (silent, missense, nonsense)

frameshift mutations

can be caused by insertions or deletions

deletions

nucleotides are removed from the DNA sequence

chromosomal mutations

involving larger changes in the strucutre or number of chromosomes

deletion

duplications

inversions

translocations

aneuploidy

deletion

portion of the chromosome is lost

duplication

segment of chromosome is duplicated

inversions

chromosome breaks off, flips around and reattaches

translocations

a segment of one chromosome breaks off and attaches to another chromosome

aneuploidy

change in the number of chromosomes (trisomy, monosomy)

recombinant DNA technology

the technology of combining different segments of DNA

human genome project + what is a genome

project to identify all of the genes in the human genome

to determine sequence of the 3 billion base pairs that make up one set of human chromosomes

a genome is a complete set of DNA including all the genes of a cell, individual or species

took 13 years, published in 2003. more refined in 2006

why was the human genome project important?

provided fundamental information about the human blueprint, which has since accelerated the study of human biology and improved the practice of medicine.

gene testing

once the DNA testing for a gene is known, scientists are able to test for the gene.

• help avoid diseases that are controlled by lifestyle as well as genetics

• tell people if they are carrying specific disease causing genes that could be passed on to their children (e.g cystic fibrosis and huntington disease)

• detect a problem gene, but cannot predict how severely they will. be affected.

single nucleotide polymorphins

genes that are different by one nucleotide from one person to another

natural selection

a process by which an environmental factor acts on a population and results in some organisms having a greater chance of survival and producing more offspring than others

what are the environmental factors called? what types?

selective agent

• biotic selective agent → another living thing such as a bacterial infection, competitor or predator

• abiotic selective agent → physical factor such as temperature, water, soil nutrients or fire

effect of the selective agent on the population is called

selective pressure.

• usually act by killing, but not always. such as sexual selection

an outcome of natural selection

species gradually becomes better adapted to its environment

what did darwin conclude in terms of natural selection

darwin concluded that natural selection could only act if there is variation within population, which is caused by difference in genes hence, variation is inherited.

natural selection in modern terms

change of a particular genotype of a species over many generations due to environmental selection of phenotype

darwin’s finches

• darwin observed finches on galapogos isalnds

natural selection pressures

variation: different beak shapes based on available food sources (larger beaks for cracking seeds, smaller beaks for insects)

selective pressure: food scarcity or changes in environment favoured birds wirth beaks better suited to available food

adaptation: finches with favourable traits survided and reproduced

peppered moths

variation: moths came in light and dark

selective pressure: pollution darkened tree bark during industrial revolution, light moths were made easier prey

adaptionL dark moths were more likely to surivive and reproduce

snails

thicker shells/colours provided camoflauge to surivve and produced

icefish

developed antifreeze proteins to prevent freezing

lack haemoglobin, as oxygen dissolves more easily in cold temperature

superbugs

strains of baceteria that have become resistant to antibiotics due to natural selection

variation: genetic mutations make them resistant to antibiotics

selective pressure: antibiotics kills off non-resistant bacteria, leaving resistant ones

adaptations: resistant bacteria reproduce, spreading resistant genes. superbugs have become more common and harder to treat.

speciation

process by which one species splits into two or more species

responsible for the formation of any new specieis that appear in the fossil record

biodiversity

number and range of different species that exist

speciation has resulted in high level of biodiversity on earth

steps of speciation

1. variation

2. isolation

3. selection

variation in terms of speciation

must be variation or speciation cannot occur

natural selection can only act on variation that is already present

isolation, what does it do? how does it occur?

different groups of the population are prevented in some way from interbreeding

prevents gene flow, stopping difference in one population from reaching the other population

geographical barrier: oceans, rivers, mountain ranges, gorges

climatic barriers: rainfall, temperature, salinity, ocean currents

selection

once isolated, natural selection affects the genotype of each group

changes in genotype prevent groups from breeding even if they meet

courtship: develop different breeding songs, displays, rituals

breeding seasons: breeding at different times of the year

sterility: may breed but offspring are sterile

chemical barriers: sperm from males killed off by the chemistry of the females in the other group

hybrids

offspring of different species

artificial selection and dogs

process by whcih we choose to breed particular organisms with desirable features

domestic dogs/cats are one species, but the different breeds in these two species come from artificial selection

selective breeding methods

cross breeding → crossing one individual with desirable features and onother individual with desirable features

inbreeding/linebreeding → related individuals mate. not often used tdue to health issues (deformities, sterlity and genetic diseases)

sources of evidence of evolution (5)

fossil record

comparative anatomy

genetics and biochemistry

geographic distribution of species

embryology

comparative anatomy

science of comparing physical structures of a species with others

homologous structures

features that have the same basic structure due to a shared evolutionary history. (e.g cat and lion parts)

do not always need to share the same function

analogous structures

characteristics that look similar but do not share a common ancestry (e.g

geographical distribution

all the places on the earth where a particular species is found

what did darwin and wallace find? why?

isolated places → unique species, many species are found only in particular places separated from others by geographical barriers

have unique species because they are limited to reproducing with species with those on the isand. barrier to gene flow

embryology

study of the development, structure and function of embryos

dominant

the allele that gets expressed even in heterozygous conditions

genetic engineering

manipulation of genetic information using modern technology and human intervention

genotype

combination of alleles per trait

incomplete dominance

not completely dominant or recessive; expresses as a gradient phenotype

karyotype

chromosomes arranged according to size and band patterns

monohybrid cross

cross between two individuals with homozygous genotypes which result in the opposite genotype for a certain genetic trait

mutation

permanent change in the genetic information

pedigree

a diagrammatic representation of lineage and individual descent

phenotype

physical representation of the allelic combination

recessive

the allele that can be expressed only when homozygous

sex linkage

genes present on the sex chromosome, hence, inheritance pattern linked with them.

silent mutations

are changes with no change and occurs when a base on the DNA strand is changed

missense mutations

changes that do not stop the gene from making protein, however the protein is different and may not function correctly and cause disease

nonsense mutations

cause cells to stop reading information on the gene before it ends, meaning the protein is incomplete and cannot function

recombinant dna technology

procedures used to produce DNA that has been modified by inserting DNA into a cell from a different organism

evolution

change in the characteristics of a species over many generations

fossil

evidence of, or remains of, an organism that lived long time ago

fossil record

a list showing the classification of all the species on Earth that have been found as fossils

species

a group of similar individuals that can interbreed in natural conditions to produce fertile offspring

biochemistry + evidence to evolution

study of molecules and chemical reactions found in living organisms

e.g 96% of genes in chimps are identical to those of humans.

embryology how it contributes to evidence of evolution

all have a tail

fish, lizards and humans all have branchial arches, that are homologous features. These features provide evidence that the species are related through evolution