Year 10 Biology

Cells and Organelle

• All living organisms are made up of cells

• Cells are the building blocks for life

Plant Cells vs Animal Cells

• Different Shapes

• Plant cells contain:

  • Cell walls

  • Chloroplasts

  • Larger Vacuoles

DNA (Deoxyribonucleic Acid)

• Carries genetic information determining the structure of cells and the way if functions

• Chemical code that the cell uses to produce proteins enzymes

• Found in both the mitochondria and the nucleus

• A polymer - a substance made up of a large number of small substances joined together

• Nucleotides

  • Make up DNA

  • Monomers - the smallest base units of a substance

  • Made up of a phosphate group, a sugar and a nitrogen base

• 4 Nitrogenous Bases

  • Adenine (A)

  • Thymine (T)

  • Guanine (G)

  • Cytosine (C)

    • A and T can only bond

    • C and G can only bond

• Protein Synthesis

  • Order of base pairing represents a code for making proteins

• Nucleotides form a ladder (double helix structure)

  • Sugar and Phosphate form the uprights

  • Nitrogenous bases form the rungs

• Watson and Crick were the two scientists who finalised this model

• Replication

• Chromosomes consist of DNA coiled around a protein (Histone)

• Chromosomes can consist of 1 or 2 strands of DNA

• The strand is called a chromatid

• Cells divide to replace old/dead/damaged cells and create new ones so organisms can grow

• Cell Division

  • New cells created are called Daughter cells and they need to have an exact copy of DNA from the Parent cell

    • DNA Replication is the first step of cell division and it ensures inherited information is passed on unchanged when new cells are formed

• The 2 linked chains of DNA molecules separate or unzip and this is controlled by an enzyme called DNA helicase

• Unzipped DNA molecule now has the bases exposed and they serve as a template for the nucleotides that will form the new half

• DNA polymerase move along the exposed strands and adds complementary nucleotides to each nucleotide in each existing strand

  

Mitosis

• the process of division of the nucleus of a cell in which the two daughter nuclei have the same number and type of chromosome as the parent nucleus

• makes daughter cells, which have identical copies of parent cell DNA

• imperative for growth and repair of the body

• happens for the first 22 pairs of chromosomes

  • before mitosis happens DNA replication takes place

  • interphase happens next, which is also not apart of Mitosis, the replicated DNA coils up forming chromosomes

4 Stages of Mitosis

• Prophase

• Metaphase

• Anaphase

• Telophase

Prophase

• centrioles become visible and migrate to opposite poles, producing spindles which grow towards the chromosome

• the nuclear membrane breaks down and the chromosomes become visible and they move to the centre of the cell

Metaphase

• the chromosomes create a line on the cell equator and the spindle fibres attach to the centromere of each chromosomes

Anaphase

• the spindle fibres retract back to the centrioles, separating the chromosomes into chromatids, pulling them to the poles of the cell

Telophase

• nuclear membrane reforms and spindle fibres breakdown

Cytokinesis

• the cell membrane and cytoplasm splits into two new cells

This leaves you with 2 exact replicas of the parent cell

Meiosis

• Diploid cells

  • a body cell contains 2(set/pair) of chromosomes

  • referred as 2n with n= number of different chromosomes

• Haploid cells (half)

  • in a gamete (sperm/egg cell) there is a haploid number of chromosomes

  • referred as n

  • amount of sets

• Process of cell division that produces gametes (sperm/ova)

• Gametes have half the amount on chromosomes that a body cell has

• Homologous Chromosomes

  • pairs of chromosomes that are identical in size/shape/genes

  • each member influences the same characteristics

• Aim of Meiosis

  • to produce haploid cells from diploid body cells

DNA Replication happens making 4 strands of DNA instead of 2 and then Interphase happen.

Meiosis 1:

Practically the same a Mitosis but is different Prophase 1

• Prophase 1

  • Crossing over between chromatid pairs happens changing the genetic make-up

• Metaphase 1

• Anaphase 1

• Telophase 1

• Cytokinesis 1

Meiosis 2:

Is the same as Mitosis

Summary:

Meiosis is a type of cell division used to produce the gametes. It has 2 rounds of division used to create 4 haploid cells. The daughter cells are GENETICALLY DIFFERENT.

Genes and Alleles

• Karyotype

  • the full set of chromosomes in a cell

  • in humans, the karyotype of a normal cell shows 46 chromosomes in 23 pairs

  • the 1st 22 pairs are autosomal

  • the 23rd pair are sex chromosomes

  • males have an X and a Y chromosomes

  • females have 2 X chromosomes

• Inherited Traits

  • a trait is a distinguishing quality or characteristic, typically one belonging to a person

• Gregor Mendel

  • father of genetics

  • worked on pea plants and concluded how genetics work, genes exist in pairs (one from each parent) and they can separate and form pairs again in the next generation

• Genes

  • a sequence within the DNA which codes for the production of a protein and this determines a trait

  • difference between genes is the order of nitrogenous bases

• Alleles

  • an alternative form/variation of a gene

  • the different possibilities for a given trait

  • each chromosome contains alleles, or different variations of the same gene

Chromosomes pair up as Homologous Pairs

• they’re the same shape/size

• carry genes controlling the same traits

Monohybrid Crosses

• Dominant and Recessive

  • a dominant allele will mask the trait of a recessive allele (represented by capital letter)

  • a recessive allele will only be expressed if a dominant allele is not present (represented by lower case letter)

  • e.g. T= curly, t= straight

  • Tt or TT = curly

  • tt = straight

• Genotype

  • genetic make up of an organism; the gene (or allele) combination an organism has

  • e.g. Tt, tt, TT

• Phenotype

  • physical characteristic of an organism; the way the organism looks

  • e.g. curly hair or straight hair

• Homozygous

  • 2 identical alleles for a trait (dominant or recessive)

  • e.g. TT or tt

• Heterozygous

  • has 2 different alleles for trait (dominant)

  • e.g. Tt

2 plants or animals, which differ at only one gene are bred together

• Punnet square/monohybrid crosses

  • diagram showing the gene combinations that might result from a genetic cross

  • used to calculate the probability of inheriting a particular trait

    • Rules

      • down key identifying alleles letters represent

      • write down parents pheno/genotypes

      • draw punnet square

      • complete cross

Sex Linked Traits/Characteristics

• The Y chromosome is very small compared to the X chromosome

• Y chromosomes doesn’t have the same number of genes in it as the X

• most of the genes in the x chromosome, will not have a matching allele in males

• the pattern of inheritance is different in males and females

• characteristics affected by the genes on your x chromosome are called sex-linked characteristics or x-linked characteristics

• Hemizygous

  • if a gene is only on the x chromosome, then males only have the one allele. this is referred to as being hemizygous for that gene.

• Red/Green colour blind

  • ability to discriminate controlled by a gene located in the x chromosome

  • individuals unable to distinguish have the recessive allele of this gene

  • more common in males then females

• A colour blind male mates with a female homozygous for a regular vision kids

Pedigrees

• Show the pattern of inheritance of a particular trait within a family

  • symbols

    

  • conventions

    • always included a title which indicates the trait and its made of inheritance

    • roman numerals indicate the generation

    • numbers represent the individuals

Modes of Inheritance

• what you need to know

  • whether the trait is dominant or recessive

  • whether the trait is autosomal or sex-linked

    • look for 2 parents without the trait that have a child with the trait (recessive)

    • If there is none it is dominant

    • If recessive look at the sexes affected. If prodominantly in males it is probably sex linked if equal between sexes probably autosomal

AUTOSOMAL RECESSIVE:

·      Equal chance of both sexes being affected; this tells you it is autosomal

·      An affected female does not have an affected father; this tells you it is autosomal

·      Each affected individual has normal parents; this tells you it is recessive

·      If both parents have condition, ALL of the offspring will be affected; this tells you it is recessive

·      Affected individuals must be homozygous recessive (eg rr). These are the shaded individuals.

AUTOSOMAL DOMINANT:

·      Equal chance of both sexes being affected; this tells you it is autosomal

·      Each affected individual has at least one affected parent; this tells you it is dominant

·      About ½ of the offspring of affected individuals have the condition; this tells you it is dominant

·      An unaffected individual cannot transmit an affected allele.

Unaffected individuals must be homozygous recessive (eg. rr). These are the unshaded individuals.

 SEX-LINKED RECESSIVE:

·      Affected individuals are usually male; this tells you it is most likely sex-linked

·      An affected female MUST have an affected father; this tells you it is sex-linked

·      Sons of the affected male (X^rY) and normal female (X^RX^R) are normal

·      Two parents that do not show the condition can have affected offspring; this tells you it is recessive

·      Females are generally carriers (X^RX^r) and thus do not show symptoms of the condition.

SEX-LINKED DOMINANT:

·      Affected individuals are usually female; this tells you it is most likely sex-linked

·      An affected male will pass it on to all his daughters and none of his sons. this tells you it is sex-linked dominant

·      A female with the trait may pass it on to both her sons and daughters.

·      Every affected person has at least one affected parent. this tells you it is dominant

·      Females are generally carriers (X^RX^r) and thus do show symptoms of the condition.

Mutations

A change in the nucleotide sequence of the DNA of the organism.

It’s random

Can be influenced by mutagens (environmental or external factor that causes a mutation):

• radiation

• UV light

• some chemicals (asbestos, tobacco)

• viruses

More likely to happen in DNA replication or meiosis.

• Types of Mutation

  • Gene Mutation: involves an error in a singular nucleotide base and can disrupt a gene or a sequence

  • Chromosomal Mutations: involve an error in a group of nucleotide bases, disrupting gene/gene sequence

• Gene Mutation Types

  • Substitution/Point: A pair is substituted for another

  • Frameshift: A base pair is added or deleted. This is more impactful as it’s changing the whole code by moving it up or down by one.

• Chromosomal Abnormality: different amount of chromosomes due to more or less

Natural Selection

Species - a group of organisms in which its members can produce fertile offspring

Population - a group of the same species in a location. all the different types of genes in the population is known as the gene pool

• Changes in gene pools

  • An allele is an alternative form of a gene (e.g. allele for black hair or allele for blonde hair)

  • Mutations, migration pressure, environmental factors are all reasons the frequency of an allele can change over time

  • E.g. allele frequency for the dark skin will increase in the frog population if it helps with camouflage on the logs.

Evolution - the genetic change in characteristics of a species over generations

Natural selection - the change in proportion of a particular genotype of a species over many generations due to environmental selection of a particular phenotype

• Natural Selection

  • Driving force behind evolution

  • Process where an environmental factor acts on a population and results in some organisms in one species having more off spring than others

• Selective agents/pressures'

  • The environmental factor that acts on the population

  • Biotic Factors (living)

    • Predation

    • Bacterial Infection

    • Competition

  • Abiotic Factors (non-living)

    • Temperature

    • Water

    • Soil nutrients

    • Fire

• Survival of the Fittest

  • in every population there is variation (natural differences) due to individuals having different genes

  • the fittest or most well adapted individuals have a better chance at survival and therefore reproduce

  • these individuals have a survival advantage

Speciation

The process where one species is separated into two different species or more different species

• Steps to Speciation

  • Variation

  • Isolation

  • Selection

Evidence for Evolution

• Fossil Record

  • shows intermediate species in an evolutionary lineage

  • shows how more complex species developed from simpler ones over time

• Comparative Embryonic Analysis

  • embryos of different species look similar to each other due to a shared common ancestor

• Comparative Anatomy

  • different species show similar structural organisation because they share a common ancestor (e.g. pentadactyl limb)

• DNA and Protein Evidence

  • species have similar genes or amino acids sequences because they share common ancestors

  • the closer related a species is the more amino acids sequences/genes they have in common