GCSE Biology- B6 Inheritance, Variation and Evolution

Cell

smallest unit of life that makes up all living things

nucleus

contains genetic information in the form of chromosomes, controls the activities of the cell

DNA

complex chemical molecules carrying the different codes needed for different proteins to be made

chromosomes

coiled DNA strands that are found in the nucleus

gene

section of DNA that codes for a specific protein or charecteristic

genetic materials inside the nucleus (Large to small)

cell, nucleus, chromosomes, DNA, Gene

sexual reproduction

2 parents, shared traits, variation to offspring, meiosis and mitosis both used

asexual reproduction

1 parent, genetically identical to parents (clones)

binary fission

method of reproduction in bacteria

mitosis process

cell growth, DNA and organelles duplicate, 1 from each pair of organelles and chromosomes pulled to each end, 2 identical daughter cells produced

Haploid

1 set of chromosome

Diploid

2 sets of chromosomes

Meiosis

type of cell division that happens in the reproductive organs to halve the number of chromosomes, making gametes, without meiosis sexual repro cannot happen

Meiosis process

cell organelles and chromosomes duplicate, then divide to form a clone of the original, then another division, isolating the chromosomes into 4 genetically unique gametes

DNA

Deoxyribonucleic acid

RNA

ribonucleic acid

the human genome project

1990-2003, a international scientific research project, the worlds largest collaborative biological project aiming to work out the order of nucleotide base pairs that make up human DNA, it identified and mapped all of the genes of the human genome

What does DNA determine?

specific genetic makeup and physical features of an organism

What is DNA make of?

2 strands, each made by joining small molecules (polymer) in a double helix structure

What are proteins made of?

amino acids

What do genes code for?

the order of amino acid sequences, determines protein made

genome

entire genetic material that makes a human

benefits of studying the human genome

find diseases linked to specific genes, human migration patterns and inherited diseases

What can cause inherited variation?

choice of gene for a characteristic, fertilisation is random, mutation

sex chromosome

the 23rd pair of chromosomes, female is xx, male is xy, forms during reproduction

mitochondrial DNA

passed down by females

alleles

different forms of the same gene

dominant allele

represented as capital letter (eg. A)

recessive allele

represented as lowercase letter (eg. a)

recessive traits

only expressed if organism has both recessive alleles

genotype

a combination of alleles- the type of gene one has

phenotype

affect of alleles on characteristics- physical appearance

homozygous

same alleles- both recessive or both dominant (eg. AA or aa)

heterozygous

different alleles, one of recessive, one of dominant (eg. Aa)

punnet square/genetic cross

mutually exclusive event

when each event has no impact on a probability of a situation

DNA structure

double helix, polymer made of a monomer called ‘nucleotides’, contains pentose sugar (sugar with 5 carbons)

base pairing

adenine (A) with thymine (T), guanine (G) with cytosine (C)

codon/triplet code

each amino acid coding for by a sequence of 3 bases in a gene, etc. TCA- serine, GGG- glycine

mRNA

messenger RNA, single stranded DNA used to create protein chains

transcription

base sequence of the gene is copied into a complementary template molecule called messenger RNA (mRNA)

transcription process

DNA is unzipped, the free RNA nucleotide base sequence is copied onto a single stranded template called mRNA

translation

mRNA leaves nucleus attaches to ribosome, the ribosomes transfer RNA of tRNA complementary base pairs to the mRNA strand, tRNA is attached to amino acids which then link together in along chain to form a protein

proteinsynthesis

the process of transcription, then translation (making proteins)

mutation

a random change in DNA of an organism

characteristics of genetic mutations

rare, spontaneous, can happen on every gene, most mutations of have no effect on the final protein, some mutations can have a serious effect

serious effect of mutations

could change shape of protein, enzyme may no longer fit the substrate binding/active site or a structural protein may lose its strength

non-coding DNA

regions that doesn’t code for a protein, some regions of DNA determine whether a gene is switched on or off

expression

the process which genes are activated to produce a protein

polydactyly

when a baby is born with more than 20 digits (digits are toes and fingers)

cystic fibrosis

genetic disorder where the mucus is too thick and sticky, affecting many organs of the body, particularly the respiratory system and digestion

causes of polydactyly

caused by a faulty allele- dominant allele is faulty (P), and normal allele is recessive (p)

causes of cystic fibrosis

caused by faulty alleles, faulty allele is recessive (n), normal allele is dominant (N)

embryo screening

genetic tests showing if a baby carries a faulty allele during pregnancy for inherited disorders, they an also be screened before implanted in IVF

types of embryo screening

amniocentesis, chronic villus sampling (CVS)

amniocentesis

removing and testing a small sample of cells from the amniotic fluid (fluid surrounding the unborn baby in the womb in the uterus) by using a needle

when is amniocentesis offered?

only offered if there is a higher chance of baby having genetic conditions

amniocentesis procedure

occurs roughly 15-20 weeks, with a 0.5-1% risk of miscarriage from it

chorionic villus sampling (CVS)

removing and testing a small sample of cells from the placenta using a needle or foreceps

chorionic villus sampling (CVS) procedure

usually described as uncomfortable rather than painful- may experience cramps similar to period pains, procedure occurs roughly 11 to 18 weeks, miscarriage risk greater than 2% (>2%)

Reasons for embryo screening

reduces overall suffering- fewer people with health problems, saves lots of money later on treating the disorder

reasons against genetic disorders

implies genetic disorders are immoral, may screen for other traits in the future (eg. eye colour, sex, etc.)

variation

differences in characteristics of individuals in a population

inherited variation

differences between organisms that are a result of the genes you inherit from your parents

genetic variation

basic characteristics of every individual are because of the genes inherited from parents, mix of genes from mother and father, some only determined by genes (eg. blood type)

environmental variation

when some of the characteristics of an organism are altered by factors in the environment

examples of environmental variation

weight, pierced ears, tattoos, strength

continuous variation

gradual changes usually presented through a bar graph

discontinuous variation

stepped variation- set groups, also presented through bar graphs

detrimental

to affect negatively

Who came up with the theory of natural selection?

Charles Darwin (1.), Albert Russel Wallace (2.)

Darwin’s theory of evolution

species will show variation in their features as a result of the gene they inherit or natural mutation- makes some members of species more suitable to the environment, are better competitors, meaning they will survive and pass on genes that made them suitable to their environment

Darwin’s theory of evolution shortened

variation in species, advantageous alleles/characteristics more likely to survive and pass on to offspring via reproduction, offspring inherit beneficial alleles allowing them to outcompete

What did Darwin study to come up with theory of evolution?

giant tortoises, flinches and marine iguanas

artificial selection/selective breeding

process where humans breed plants or animals for particular genetic charecteristics

selective breeding writing frame

parents with desired characteristics chosen and bred together, alleles for the desired characteristics are passed to offspring, offspring with desired characteristics are bred together, repeated over many generations

genetic engineering

modifying an animals genome, genes from one organism is transferred to a different organism to result in a desired characteristic

Uses of GM organisms

disease resistant crops, golden rice, gm foods, producing insulin, cotton

how is insulin produced through gm?

extracted from pigs and cattle

GM foods examples

pest resistant maize, tomatoes, weedkiller resistant soya, golden rice- vitamin A to children in developing countries

Gene therapy

trying to cure inherited diseases from faulty genes

how does gene therapy work?

giving a person the non-faulty version of the genes, difficult as faulty gene is in all 100 trillion cells of the body

gene therapy procedure

transferring genes at early stage of development as it is passed on to other cells

cloning

creating offspring genetically identical to parents

plant cloning methods

tissue culture, plant cuttings

animal cloning methods

embryo transplant, adult cell cloning

plant cuttings

taking a cutting from a plant with desirable traits, dipped into hormone powder and put in clear bag to grow as a new plant with genetics identical to parent

plant cutting process

small length of stem cut, ends of the cut stem dipped into hormone coating powder, stem placed into stone pot with compost, covered with a transparent plastic bag, cuttings taken from that plant to grow another clone

tissue culture

small amount of plant tissue from a desirable plant cut off from original plant, tissue grows on agar jelly containing nutrients, aseptic technique used, genetically identical to parents

micropropagation

tissue culturing

embryo cloning

zygote cell formed from fertilisation of sperm and egg, blastocyst (ball of cells) is split apart and each new cell divides into a new ball of cells, ball of cells placed into surrogates and identical clones produced, generally done via cultural insemination/IVF

blastocyst

ball of cells from the zygote

zygote

fertilised cell

Gregor Mendel

father of genetics, studied pea plant and called alleles ‘hereditary units’, had no knowledge of DNA and chromosomes

Mendel’s findings

yellow pods were dominant over green, purple flowers were dominant over white flowers

Jean-Baptise Lamarck’s theory of evolution

suggested that any changes that occurred to an organism during their lifetime were passed to their offspring

flaws with Lamarck’s theory of evolution

only beneficial characteristics passed down, offspring having different charecterisitics

Differences between Lamarck’s theory and Darwin’s

Lamarck thought environmental variation traits could be passed down to offspring, Darwin believed the better adapted variation would be passed down as they could outcompete competition, Lamarck thought inheritance was through environmental changes, Darwin believed theory of evolution happened over many generations, Lamarck believed theory of evolution happened over one lifetime, Lamarck thought inherited characteristics could change over a lifetime, Darwin thought inherited characteristics cannot change in a lifetime

Why did people challenge Darwin?

god made all animals and plants on earth, insufficient evidence at the time, mechanism of inheritance and variation not until 50 years later

species

a group of organisms which share similar characteristics and which breed together to produce fertile offspring