B5 Genes, inheritance + selection Flashcards
What is the genome?
-The entire genetic material of an organism.
-May influence the phenotype when interacting with its environment.
-Arranged as chromosomes and stored in the nucleus.
What is the phenotype?
The visual characteristics of an individual.
What is a chromosome?
Long, coiled up strand of DNA.
What is a gene?
A short section of DNA that codes for a protein and therefore controls / helps other genes control a characteristic.
What is variation?
The differences between individuals of the same species caused by genetic and environmental factors.
What are the 2 causes of variation?
-Inherited / genetic: offspring inherit characteristics from their parents.
-Environmental: characteristics are impacted by the individual’s surroundings.
Why don’t most mutations influence the phenotype?
Most DNA is non coding therefore mutations rarely cause a change in proteins.
What is a mutation?
-A random / spontaneous change in the base sequence / quantity of DNA which causes the alleles to change and therefore produces genetic variants.
-Can be harmful / neutral / beneficial.
What causes mutations?
Mutagens.
What are coding genes?
Genes in the coding region of DNA.
What is regulatory DNA?
Genes in the non-coding region of DNA.
How can mutations in coding regions of DNA alter the activity of the protein that the altered DNA is meant to code for?
Change the shape of the protein made and make the protein non-functional.
How can mutations in non coding regions of DNA still affect how genes are expressed?
By stopping the transcription of mRNA during protein synthesis and therefore stopping the production of the protein altogether.
What is a promoter?
An example of regulatory DNA which determines which gene will be expressed.
What are the 3 types of mutation?
-Insertion: When a nucleotide is added to the DNA sequence.
-Deletion: When a nucleotide is removed from the DNA sequence.
-Change: When the order of nucleotides is changed.
What is sexual reproduction?
A source of variation due to the offspring acquiring half of their genes from each parent.
What is asexual reproduction?
A form of reproduction that only requires a single parent and produces genetically identical offspring.
What are the advantages of sexual reproduction?
-Variation in offspring leads to adaptations in a species.
-Only some organisms in a population will contain the adaptations required to cope with an environmental pressure and these organisms can reproduce, allowing the population to continue.
What are the disadvantages of sexual reproduction?
-Requires 2 parents.
-Slower reproduction.
-Requires energy so not energy efficient.
What are the advantages of asexual reproduction?
-If the parent is well adapted to the area, the offspring will share an identical set of characteristics.
-Only one parent needed so don’t require partner / pollination.
-Faster reproduction so large numbers of offspring produced quickly.
What are the disadvantages of asexual reproduction?
Adverse changes to the environment may destroy the species as all the organisms are identical and therefore all will be affected.
What is meiosis?
A form of cell division that produces 4 haploid gametes that are genetically different, ensuring variation in a species.
How do cells in the reproductive organs form gametes?
They divide by meiosis.
What are gametes?
Sex cells which have half the number of chromosomes as they only have one copy of each chromosome.
What is a haploid cell?
Has 1 set of 23 chromosomes.
What is a diploid cell?
Has 2 sets of 23 chromosomes.
What is the process of meiosis?
- The cell makes copies of its chromosomes so it has double the amount of genetic information.
- The cell divides into 2 diploid cells, each with half the amount of chromosomes.
- Each cell divides into 2 again to produce 4 haploid cells altogether.
- These haploid cells are called gametes and are all genetically different from each other.
Why does meiosis result in 4 genetically different haploid cells?
The chromosomes are shuffled during the process, resulting in random chromosomes ending up in each of the 4 cells.
What are alleles?
Different forms of the same gene.
Why do humans have 2 alleles for each gene?
They inherit one allele from each parent.
What is the difference between a dominant allele and a recessive allele?
-Only 1 out of 2 alleles needs to be dominant for the dominant allele to be expressed and present in the phenotype.
-Both alleles need to be recessive for the recessive allele to be expressed and present in the phenotype.
What is homozygous?
When both inherited alleles are the exact same.
What is heterozygous?
When both inherited alleles are different.
What is the genotype?
The combination of alleles an individual has.
Why do alleles exist in pairs?
At the time of fertilisation, one is inherited from the sperm and one from the egg.
What are punnet squares?
Used to work out the chances of a trait being passed on.
How do chromosomes work?
-22 pairs of chromosomes control the characteristics and each of these pairs looks very similar.
-23rd pair carries sex determining genes and the 2 chromosomes can look different.
-1 sex chromosome goes into each gamete when cells undergo meiosis.
What are the sex chromosomes for a female?
XX
What are the sex chromosomes for a male?
XY
What was the work of Gregor Mendel?
-He worked in the monastery gardens and observed the characteristics passed on to the next generations in plants.
-He carried out breeding experiments on pea plants using different species and observed the offspring to see which characteristics they inherited.
What were Gregor Mendel’s conclusions?
-Offspring have some characteristics their parents have because they inherit hereditary units from each.
-One unit is received from each parent.
-Units can be dominant / recessive and can’t be mixed together.
When were chromosomes observed as part of cell division?
In the late 19th century.
When was it discovered that chromosomes and units have similar behaviours and why?
In the 20th century and due to units being the genes on the chromosomes.
When was the structure of DNA determined so that we could understand how genes worked?
1953
