b5 - Genes, inheritance and selection

whats a gamete

reproductive cells (egg in female and sperm in males)

whats a chromosome

a long,thin molecule of DNA

whats a gene

A short section of DNA that codes for a protein, and therefore contribute to a characteristic.

whats an allele

Different forms of the same gene- can be called variants

whats a dominant allele

only one copy of it is needed for it to be expressed

whats a recessive allele

Two copies are needed for it to be expressed

what does it mean if an organism is homozygous

a genotype where the 2 alleles for the characteristic are the same (AA) or (aa)

what does it mean if an organism is heterozygous

a genotype where the 2 alleles needed for the characteristic are different (Aa)

whats a genotype

a collection of all the genes an organism has

whats a phenotype

The visible characteristics in the individual, e.g. eye colour

whats a genome

entire genetic material of an organism

whats discontinuous variation

variation that produces distinct categories (e.g eye colour or blood groups)

whats continuous variation

variation that cannot be places into distinct categories and creates a spectrum (e.g. height and weight)

what 2 things can variation be as a result of

1. genetics - variation is caused by differences in the genotype ( the genetic information)

2. environmental- conditions in which it lives

what causes variation

mutations in the gentic code

what does mutation mean

the sequence of DNA bases in the gene is changed which produces a genetic variant

whats the effect of mutation on the phenotype

most have no effect on the phenotype, some influence phenotype and a very few determine phenotype

why do some mutations only have a small influence on the organisms phenotype

• some characteristics e.g. eye colour are controlled by more than one gene

• a mutation in one of the genes may change the eye colour a but but the difference wont be huge

describe how a mutation in a coding DNA sequence could be detrimental

• the mutations may change the sequence of amino acids in the protein which will change its structure

• this may affect the protein, particularly in specific molecules like enzymes and antibodies

whats an example of when a mutation has a dramatic affect on the phenotype

• cystic fibrosis

• variant deletes the bases that controls the movement of salt and water in and out of cells properly

• leads to excess mucus production in lungs + digestive system

whats sexual reproduction

where genetic information from two organisms (mother and father) combine to produce offspring which are genetically different to either parent

sexual reproduction causes genetically __________ cells

different

whats a haploid cell

a cell that only has half the normal amount of genetic material

whats a diploid cell

a cell with the full number of chromosome (genetic material) - 46 chromosomes ( 23 pairs)

how many divisions are their in meiosis

2

how many cells does meiosis produce

4 haploid cells which are all genetically different from each other

where does meiosis occur

in sex organs - testes in males and ovaries for females

whats the process of meiosis

• chromosomes double to create x shaped chromosomes

• line up in random male and female pairs

• splits down the middle and pairs are pulled apart

• x shaped chromosomes pulled apart

• produces 4 gamete cells

give 1 advantage and disadvantage of sexual reproduction

advantage - introduces variation

disadvantage - it is slower and produces a limited amount of offspring

how are dominant alleles represented in a punnet square

using uppercase letters

how are recessive alleles represented in a punnet square

use lowercase version of the same letter as the dominant allele

what are the chromosomes that determines the sex

males : have an x and a y chromosome - y chromosome causes male characteristics

females : have 2 x chromosomes - lack of y chromosome causes female characteristics

whats asexual reproduction

• only 1 parent so offspring genetically identical to that parent

• happens by mitosis

• the new cell has exactly the same genetic information as the parent cell

• bacteria, some plants and animals reproduce asexually

give 1 advantage and 1 disadvantage of asexual reproduction

advantage - it produces a lot of offspring quickly

disadvantage - it does not introduce variation so all offspring are susceptible to the same environmental pressures as the parents

what 3 advancements have improved classification

• use of microscopes

• studies of biochemistry

• DNA evidence

how has DNA sequencing helped improve classification

• Studies of DNA sequences of different species show that the more similar the base sequences in the DNA of two species, the more closely related those two species are (and the more recent in time their common ancestor is)

  • Classification based on this information is called molecular phylogeny

what are the 2 types of classification

1. artificial - using observable features

2. natural - using evolutionary relationships

whats artificial classification

• used comparisons of observable and non-evolutionary features to group organisms

• Observable characteristics include things like whether they give birth to live young or lay eggs etc

• The less scientific nature of these methods means they are not considered to be the best way of classifying organisms

whats natural classification systems

• is based on evolutionary relationships between organisms

• Organisms are categorised using information about common ancestors and common structural features

• ceated by carl linnaeus

• He named organisms in Latin using the binomial system

• categorises organisms based on their structure and characteristics

• he created 7 different groups

  1. kingdom

  2. phylum

  3. class

  4. order

  5. family

  6. genus

  7. species

whats the binomial naming system

every species has a binomial name made up of 2 parts: the genus name and the species name

what are the 2 rules in the binomial naming system

1. both names should be written in italics

2. all letters should be lower case except the first letter of the genus name (‘Homo sapiens’)

what are the 3 advantages of using the binomial naming system

1. each species has a unique name which avoids confusion

2. allows scientists from different parts of the world to discuss species

3. can show how closely related organisms are ( as many related organisms often have the same genus name )

whats the process of natural selection

• populations are naturally varied die to random genetic mutations

• some genetic variants make characteristics that are better suited to a particular environment (advantageous phenotype)

• these organisms survive and reproduce passing on the successful genes

whats evolution

a change in the inherited characteristics of a population over time, through a process of natural selection

what affects the speed at which a species evolves

how quickly it reproduces because the inherited characteristics are passed on to future generations more quickly

how can evolution create new species

• a species phenotype changes so much that an entirely new species if formed

• happens when two populations of species are separated with a physical barrier

• conditions on each side of the barrier will be slightly different so the phenotype that will be beneficial will be different for each population

whats are 2 pieces of evidence for evolution

1. fossils

2. antobiotic resistance

how can fossils be used to see evolution

• is any trace if animals/ plants that lived a long time ago

• can tell us about what organisms looked like

• by arranging fossils in chronological order, we can see the gradual changed in organisms

how does antibiotic resistance happen

• bacteria can sometimes develop random mutations i their DNA which can cause the bacteria to become resistant to the antibiotic

• when antibiotic is used, all bacteria with resistance survive and the rest are killed

• the population containing the resistant bacteria then begins to grow