Unit 2- Section 2 Genetics Flashcards
What is the structure of DNA?
Double helix structure, formed by two separate strands which are coiled together in a spiral. The strands are polynucleotides which are made up of long chains of nucleotides
What is the function of DNA?
DNA contains your genetic information, that’s all the instructions needed to grow and develop
What is the nucleotide structure?
Each nucleotide is made from a phosphate group, a pentode sugar and a nitrogenous base. The sugar in DNA molecules is a deoxyribose sugar, each nucleotide has the same sugar and phosphate but the bases differentiate.
What are the four possible bases?
Adenine, Thymine, Cytosine and Guanine.
How is the DNA molecule arranged?
Phosphate then sugar then base on the inside
What are polynucleotide strands and how do then join?
Many nucleotides join together to form the polynucleotide strands. The nucleotides join up between the phosphate group of one nucleotide and the sugar of another creating a sugar-phosphate backbone
Is does specific base pairing occur?
Two DNA polynucleotide strands join together by hydrogen bonds between the bases. Each base can only join with one particular partner- this is called specific base pairing.
What does adenine always pair with?
Thymine
What does guanine always pair with?
Cytosine
How can the structure of the DNA relate to the function?
The double helix makes it very stable and strong which means the DNA does into break down or get easily damaged. If it did then important information could be lost.
The DNA molecules are very long and coiled together very tight so that the genetic information can fit into a small space in the cells nucleus
DNA molecules have a paired structure, which makes it much easier to copy itself. This is called semi-conservative replication. It’s important for cell division and for passing on genetic information from generation to generation
How do eukaryotic cells store DNA?
They contain linear DNA molecules that exist as chromosomes. Thread like structures, each made of long molecule of DNA. The DNA molecule is very long so it can be coiled up and can fit into the nucleus. The molecule is wound around proteins. The proteins has also help to support the DNA. It then can be oiled up tightly to make a compact chromosome
How do prokaryotic cells store DNA?
Prokaryotes also carry DNA as chromosomes but the DNA molecule are shirt era and circular. The DNA isn’t wound around proteins, it condenses to fit in the cell by supercoiling
What are genes?
Genes are sections of DNA. They’re found on chromosomes. Genes code for proteins and they contain the instructions for making them
How can you make proteins using genes?
Proteins are made up of amino acids. Different proteins have a different number and order of amino acids. It’s the order of amino acids. It’s the order of nucleotides bases in that determines the order of amino acids in a particular protein. Each amino acid is coded for by a sequence of three bases called a triplet in a gene. Different sequences do bases code for different amino acids
What is the code in DNA?
Degenerate- this means that more than one base triplet can code for the same amino acid. That’s because there are more possible combinations of three bases than there are amino acids
What is non-coding DNA?
Genes in eukaryotic DNA contain sections that don’t code for amino acids. These sections of DNA are called introns and the do code for amino acids are called exams. Introns are removed during protein synthesis. Their purpose isn’t know.
Eukaryotic DNA also contains regions of multiple repeats outside of genes. These are DNA sequences that repeat over and over. These areas don’t code for amino acids either
How do genes develop?
DNA sequence determines the amino acid sequence—-proteins and enzymes are formed—-enzymes control metabolic pathways—–metabolic pathways help determine nature and development
Why do alleles code for different things?
The order of bases in each allele is slightly different
What are homologous pairs?
They are pairs do matching chromosomes
What are the chromosomes like in a homologous pair?
Both chromosomes are the same size and have the same genes although they could have different alleles. Alleles coding for the same characteristic will be sound at the same position on each chromosome.
What happens during gene mutations?
Mutations are changes in the base sequence of an organisms DNA. So mutations can produce new alleles of genes. A gene codes for a particular protein, so if the sequence of bases in a gene changes, a non-functional or different protein could be produced. All enzymes are proteins, if there is a mutation in a gene that codes for an enzyme, then that enzyme may not fold up properly so because the active site is he wrong shape it is a non-functional enzyme
What are gametes?
Sperm and egg cells. They have a haploid number of chromosomes which means that they have one copy of each chromosome. Normal body cells have the diploid number… 46 chromosomes
What happens during fertilisation?
Sperm cell (haploid nucleus) joins with the egg cell (haploid nucleus) to form an embryo (diploid zygote)
Gametes are different because of meiosis
What occurs during meiosis?
It’s a type of cell division
1) a diploid cell with 4 chromosomes are about to undergo meiosis
2) the DNA unravels and replicates so there are two copies of the chromosome, called chromatids
3) the DNA condenses to form double-armed chromosomes, made from two sister chromatids
4) the chromosomes arrange themselves into homologous pairs
5) meiosis 1- first division. The holo gouts pairs are separated, halving the chromosomes number
6) meiosis 2- the pairs of sister chromatids that make up each chromosome are separated
7) four haploid cells that are genetically different from each other are produced
What happens during chromatids crossing over?
During meiosis 1, homologous pairs of chromosomes come together and pair up. The chromatids twist around each other and bits of chromatids cross over. The chromatids still contain the same genes but now have a different combination of alleles, this results in genetic variation
What happens during independent segregation of chromosomes?
The four daughter cells formed from meiosis have completely different combinations of chromosomes. All your cells have a combination of chromosomes from your parents, half from your mum and half from your dad. When the tempered are produced, different combinations of those maternal and paternal chromosomes go into each cell. This is called independent segregation of the chromosomes and results in genetic variation
What is genetic diversity?
It’s all about variety in DNA, the DNA of different species varies a lot because members of different species have different genes. The more closely the species are the more DNA they will have in common. DNA within species varies because they have the same genes but different alleles. It’s the difference in alleles that creates genetic diversity.
Why is genetic diversity important?
Can help a population or species to survive. It means that if the environment changes, there are likely to be some organisms with the alleles that enable them to survive the new conditions
What are the factors that affect genetic diversity?
Mutations in DNA- forming new alleles
Gene flow- this is where different alleles move between populations when individuals from one population migrate into another and reproduce
What are the factors that decrease genetic diversity?
It can be decreased by a number of factors including genetic bottlenecks, the founder effect and selective breeding.
What is genetic bottlenecks?
A genetic bottleneck is an event that causes a big reduction in a population, when a large number of organisms within a populations die before reproducing. This reduces the number of different alleles in the gene pool and therefore reduces genetic diversity. The survivors reproduce and a larger population is creates from rom a few individuals.
What is the founder effect?
The founder effect describes what happens when just a few organisms from a population start a new colony. Only a small number of organisms contribute their alleles to the gene pool, so genetic diversity is reduced. There is more inbreeding in the new population, which can lead to a huger incidence of genetic disease.
Why can the founder effect occur?
As a result of migration leading to the geographical separation or if a new colony is separated from the original population for another reason, such as religion.
What is selective breeding?
Changes in genetic diversity aren’t just brought about by natural events like bottlenecks and migration. selective breeding of plants and animals by humans has resulted in reduced genetic diversity in some populations. Selective breeding involved humans selecting which domesticated animals or strains of plants reproduce together in order to produce useful characteristics
What does selective breeding lead to?
Reduction in genetic givers it’s, once an organism has the desired characteristics only that one type of organism will continue to be bred, so only similar organisms with similar traits and therefore similar alleles are bred together. It results in a type of genetic bottleneck as it reduced the amount of alleles in the gene pool
What are the arguments for selective breeding?
1) it can produce high yielding animals and plants
2) it can be used to produce animals and plants that have increased resistance to disease. This means farmers have to use fewer drugs and pesticides
3) animals and plants could be bred to have increased tolerance of bad conditions
What are the arguments against selective breeding?
1) it can cause health problems
2) reduces genetic diversity which results in an increased incidence of genetic disease and an increased susceptibility to new diseases because of the lack of alleles in the population
