Genetics Flashcards
What is the diploid number? What is it in humans?
The total number of paired chromosomes, it is 46 in humans
What is a gamete?
A sex cell containing only one copy of each pair of chromosomes, the haploid number (23 in humans)
What are sex chromosomes in humans?
X and y
What are chromosomes?
Made of DNA wrapped around proteins
What is DNA? BONUS POINT!!! What does it stand for?????
A nucleic acid, it stands for dioxyribonucleic acid.
Describe the structure of DNA
A double helix, two polynucleotide strands held together by hydrogen bonds between base pairs.
What are the four different bases?
Guanine, adenine, cytosine, thymine.
What is complimentary base pairing?
A always pairs with T (think of TA, Talia Augustidis)
G always pairs with C (think Gloria Coles or Chloe Grabiner)
What is the triplet code?
3 bases are needed to code for one amino acid.
Describe the structure of a nucleotide
Circle = phosphate
Pentagon = dioxyribose sugar, has five carbons
And a base (hexagon)
What is the backbone of DNA
Sugar phosphate chain
What is a gene
A section of DNA that codes for a particular protein
What is an allele
A different form of gene
What is a genotype?
The genetic composition of an organism concerning the alleles of a particular gene e.g BB, bb, Bb
What is a phenotype?
The physical expression of the genotype of an organism e.g. Brown eyes, blue eyes
What is a dominant allele
Characteristic which will show up in the offspring even if only one of the alleles is inherited, written with a capital letter.
What is a recessive allele
Only expressed in the absence of a dominant allele, i.e. when both alleles are inherited. Written with a lower case letter
What does heterozygous mean?
When the two alleles for a particular gene on a pair of chromosomes are different.
What does homozygous mean?
When the two alleles for a particular gene on a pair of chromosomes are the same.
What would you do in a test cross?
Always breed the unknown genotype with a homozygous recessive and then look at the phenotype of the offspring. If the unknown genotype is a dominant homozygote, all the offspring will express the characteristic of the dominant allele. If the unknown genotype is a dominant heterozygote, the characteristic of the offspring will be a mixture of the dominant and recessive alleles.
What is codominance?
Two alleles which are both expressed in the phenotype of an organism. E.g co dominant inheritance of blood type or red and white flowers breeding to make pink.
What happens in DNA replication.
1: the polynucleotide strands of DNA separate
2: each strand acts as a template for the formation of a new strand of DNA
3: DNA polymerase (enzyme) assembles nucleotides into two new strands according to the base pairing rule (complementary base pairing)
4: two identical DNA molecules are formed - each contains a strand from the parent DNA and a new complementary strand
What is mitosis?
A type of cell division that produces two genetically identical daughter cells.
What is mitosis used for?
Cell repair and growth, cloning and asexual reproduction.
What is the process of mitosis?
1: chromosomes appear long and thin. DNA is replicated.
2: chromosomes appear shorter and fatter, each consisting of two sister chromatids.
3: chromosomes line up on the equator of the cell.
4: contraction of spindle fibres separate the chromatids.
5: chromosomes are pulled in opposite directions. Cytoplasm divides.
6: two new daughter cells with genetically identical information are produced.
What is meiosis?
A two stage process of cell division which reduces the number of chromosomes from the diploid parent cell to the haploid daughter cell, important for the formation of gametes.
What two things must the dividing cell do in meiosis?
1: it must copy each chromosome so that there is enough genetic material to be shared between four daughter cells.
2: it must divide twice in such a way that each daughter cell receives just one chromosome from each homologous pair.
What happens in the first division of meiosis?
1: before the cell starts to divide it replicates its DNA.
2: the chromosomes line up in pairs in the centre of the cell.
3: the homologous pairs are the pulled apart so each new cell has one copy of each chromosome. Some of the father’s chromosomes and some of the mother’s chromosomes go into each new cell.
4: each new cell will have a mixture of mothers and father chromosomes. Mixing up the genes like the creates genetic variation in the offspring.
What happens in the second division of meiosis?
1: the cells line up again in the centre of the cells.
2: the chromatids are separated and one chromatid from each chromosome ends up in each daughter cell.
3: you get four haploid gametes, each one has a single set of chromosomes. The gametes are genetically different.
NB: the fertilisation of gametes is random, this creates genetic variation.
What are variations?
Differences amongst individuals of the same species.
What are the causes of variation?
Genes and environment.
Uhhhm ok well let me think of this question. Environmental variation is much greater in plants. What are plants strongly affected by?
Sunlight
Water
Temperature
Mineral content of the soil
What is the most variation in animals due to?
BOTH!!!! Genes and environment e.g growth, health, intelligence, sporting ability.
What is discontinuous variation?
Distinct groups, no inbetweens. Always caused by genes. E.g. Blood groups, eye colour or lobed/unlobed ears.
What is continuous variation?
Not clear cut and is caused by genes, environment or both.
What is a mutation?
A spontaneous change in one of more of the nucleotides of a DNA.
Where can mutation happen?
In individual genes or in whole chromosomes.
What happens in gene mutation?
Sometimes, during DNA replication, mistakes are made and the wrong nucleotide is used. The result is a gene mutation and it can alter the sequence of bases in a gene. In turn, this can lead to the gene coding for the wrong protein.
What are the ways in which genetic mutation can occur?
Duplication, deletion, substitution and inversion.
What happens in duplication?
The nucleotide is inserted twice instead of once, therefore the whole gene is different and will now code for a different protein.
What is deletion?
On of the nucleotides is missed out, therefore the whole gene is different and will now code for a different protein.
What is substitution?
A different nucleotide is used. The triplet of bases In which the mutation occurs MAY code for a different amino acid and the structure of the protein molecule will be different. This MAY be enough to produce a significant alteration in the functioning in the protein or a total lack of function. But it MAY NOT because most amino acids have more than one code.
What is inversion?
The sequence of bases in a triplet is reversed. e.g. CTT instead of TTC. The effect is similar to substitution.
What is a mutagen? Give examples of two things that can cause mutation?
Any substance that causes mutation. Ionising radiation (x-Rays, gamma rays, alpha, beta, UV)
Chemicals (nitrous acid, chemicals in tobacco and mustard gas)
What are the types of mutations?
Most mutations are harmful, some mutations are neutral, few mutations are beneficial.
Give an example of harmful mutation
Mutations in the sex cells or the cells that divide to form sex cells, can be inherited e.g. Down’s syndrome.
What happens in mutations in body cells?
Mutations that occur in the body cells will only affect that particular cells. The cell could die and the mutation is lost. Or the mutant cell then divides and a group of cells containing the mutant gene is formed. They could also multiply uncontrollably and invade other parts of the body (cancer).
What happens in beneficial mutations for bacteria?
1: as a result of random mutations, bacteria can become resistant to antibiotics. These bacteria have an advantage over non resistant bacteria.
2: these bacteria will survive and reproduce, the gene will be passed onto the offspring. The offspring will be resistant and so the proportion of resistant types in this population will increase as this happens in each generation. This is an example of natural selection.
Why is mutations in bacteria a problem for people?
Because you can’t easily get rid of the bacteria with antibiotics and this can lead to infections being hard to control.
Mitosis vs. meiosis
Do chromosomes duplicate before division begins?
Mitosis: yes
Meiosis: yes
Mitosis vs. meiosis
How many cells are there?
Mitosis: one
Meiosis: two
Mitosis vs. meiosis
How many cells are formed in the process?
Mitosis: two
Meiosis: four
Mitosis vs. meiosis
Are the cells diploid or haploid?
Mitosis: diploid
Meiosis: haploid
Mitosis vs. meiosis
Is there genetic variation in the cells produced?
Mitosis: no
Meiosis: yes
Why does sexual reproduction result in genetic variation?
One main reason is there is a huge variation in the sex cells.
The other main reason is due to the random way fertilisation takes place. In humans, any one of the billions of sperm formed by a male in his life could potentially fertilise any one of the thousands of ova formed by a female.
How can variation in a species be environmental?
For example with plants:
• they may not all receive the same amount of water and mineral ions from the soul.
• they may not all receive the same about of light so some may not be able to photosynthesise as well as others.
• they may not all receive the same amount of carbon dioxide.
