B6- Inheritance, variation and evolution Flashcards Preview

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Flashcards in B6- Inheritance, variation and evolution Deck (51):

What is DNA and where is it found?

DNA is deoxyribonucleic acid: genetic information.


Describe how genetic information is arranged and where it is found.

An organism is composed of many cells, each containing a nucleus. Within this are 23 homologous pairs of chromosomes (in humans, excluding gametes), made of coiled DNA. Arranged along chromosomes are sections of DNA called genes.


Describe the structure of DNA.

-DNA is a double helix, making it a polymer.
-Information is stored as a code, made of 4 chemical bases.
-These are Adenine, guanine, cytosine and thymine (A, G, T and C).
-The bases are arranged in pairs, in the combinations A+T, G+T.
-Arranged along a phosphate backbone.


What is the purpose of bases?

These code for a gene.


What does a gene code for?

Genes tell a cell in what order to arrange particular sequence of amino acids, which make a certain protein.


What results from DNA determining the proteins a cell produces?

This determines the type of cell it is.


What is the term used to describe all the genetic information in an organism?

The genome.


Why is it important that scientists now understand the human genome?

-It allows the identification of genes linked to disease. This would progress the treatment of inherited disease.
-All modern humans descend from a common ancestor in Africa; as people migrated, differences developed in genomes. Scientists can learn about movement of populations through investigating the genome.


What is sexual reproduction?

Involves the fusion of male and female gametes. Offspring contain a mixture of their 2 parents' genes and are therefore genetically different to their parents. This causes variation.


What is asexual reproduction?

Involves only one parent, so the offspring are genetically identical to its parent. Happens through mitosis- daughter cells have the same DNA as parent cells so they are clones. There is no variation in offspring.


What organisms reproduce asexually?

Bacteria and some plants and animals.


What is meiosis?

The process by which diploid cells undergo 2 cell divisions to become gametes- haploid cells.


How many chromosomes to gametes have and why?

23, so that, when they fuse, the product has 46 chromosomes, like a regular cell.


Where does meiosis happen in humans?

In the reproductive organs, testes and ovaries.


What are the stages of meiosis?

1. The cell duplicates its DNA.
2. Chromosomes arrange themselves into pairs of two which line up at the centre.
3. Maternal and paternal chromosomes swap genes 9first example of variation).
4. The pairs are pulled apart and two cells are formed, each with a copy of each chromosome.
5. Chromosomes line up at the centre of each cell.
6. Spindle fibres pull apart the arms of chromosomes.
7. A second division results in 4 gametes with single sets of chromosomes, each genetically different due to the random shuffling of chromosomes.


What are diploid cells?

Contain a full set (46) of chromosomes.


What are haploid cells?

Contain half a set (23) of chromosomes.


What term describes a cell that contains half a set (23) of chromosomes?



What term describes a cell that contains a full set (46) of chromosomes?



What is a phenotype?

The traits an organism has.


What is an allele?

A gene version. A gene is eye colour but an allele is blue eyes.


What pair of chromosomes determines sex, and how?

The 23rd pair, which is XX for females and XY for males.


Some characteristics are controlled by a single characteristic, but most are controlled by...

several genes interacting.


What is the word for when an organism has two of the same alleles for a particular gene?



What is the word for when an organism has two different alleles for a particular gene?



The combination of alleles an organism has is referred to as...

the genotype.


What is a phenotype?

The traits an organism has.


What do genetic diagrams show?

The possible alleles of offspring.


What does a recessive allele mean?

Two of these same alleles must be present for the organism to have this trait.


What does a dominant allele mean?

At least one of this allele must be present for the organism to have this trait.


What are haploid cells?

They contain half a set (23) of chromosomes.


What are diploid cells?

They contain a full set (46) of chromosomes.


___ cells contain a full set (46) of chromosomes.



___ contain half a set (23) of chromosomes.

Haploid (Haploid, Half: H)


What is selective breeding?

When humans artificially select plants and animals to breed in order to keep genes for particular characteristics in the population.


Give 3 examples of selective breeding.

1. Animals being bred for leaner meat/better milk.
2. Crops with resistance to disease or that are easier to harvest.
3. Dogs with a good sense of smell.


What is the main drawback of selective breeding?

The "best" animals or plants are bred over many generations, which reduces the gene pool (the number of alleles in a population). The population becomes closely related. This is inbreeding and is harmful because there's more chance of organisms inheriting genetic defects in a limited gene pool. Also, because there is little variation in the population, a new disease that can kill one can likely kill them all.


What is selective breeding also known as?

Artificial selection.


What is natural selection?

The natural process by which useful mutations cause certain organisms to reproduce more, passing down their useful characteristics. The species evolves over time.


What is the definition of a species?

A group of organisms which can interbreed to produce fertile offspring.


What is the theory of evolution?

All of today's species have evolved from simple life forms which started to develop over three billion years ago.


Who came up with the theory of natural selection?

Charles Darwin.


What is natural selection caused by?

Mutations in the genome.


What are mutations caused by?

They can occur naturally over time or be caused by background radiation or chemicals.


How did Darwin develop his theory of natural selection?

He knew organisms in a species show variation in their characteristics (phenotypic variation) and that they have to compete for limited resources in an ecosystem. He concluded that those with characteristics most suited to the environment would be more successful competitors and would reproduce more- survival of the fittest.


What later discovery supported Darwin's theory?

Genetics showed that genetic variants give rise to phenotypes which may be beneficial.


What is speciation?

Natural selection can cause phenotypes to change so much that a new species is formed. Populations of a species become reproductively isolated.


What does it mean to be reproductively isolated?

Organisms cannot interbreed to produce fertile offspring.


Why does extinction happen? Give 5 reasons.

1. The environment changes too quickly for a species to adapt. 2. A new predator kills all the organisms. 3. A new disease wipes out a species. 4. A catastrophic event, like a natural disaster, kills a species. 5. A species is unable to compete with another for resources.


What are 4 similarities between natural and artificial selection?

1. Species have adapted to become more suited to a purpose. 2. This is caused by mutations in the genome. 3. They both happen over many generations. 4. They both rely on variation.


What are 3 differences between natural and artificial selection?

Natural selection is ...natural, and artificial selection is artificial. Natural selection results in phenotypes suited to an environment while selective breeding results in a phenotype beneficial to humans- for example, bacteria resistant crops. Selective breeding is also quicker because the gene pool is being reduced as only selected individuals of a population are interbred.