SB3: genetics Flashcards
what is sexual reproduction?
-the joining of two sex cells, or gametes during fertilisation
what are the characteristics of
organisms produced by sexual reproduction?
organisms produced by sexual reproduction have two parents and are genetically similar to both but not identical to either
advantages of sexual reproduction
-produces variation in the offspring
-the species can adapt to new environments due to variation, which gives them a survival advantage
-a disease is less likely to affect all the individuals in a population
-humans can speed up natural selection through selective breeding
disadvantages of sexual reproduction
-time and energy are needed to find a mate
-it is not possible for an isolated individual
what is asexual reproduction?
only involves one parent so there is no joining of sex cells during fertilisation
what are the characteristics of organisms produced by asexual reproduction?
organisms produced by asexual reproduction are genetically identical to each other and their parent (clones)
advantages of asexual reproduction
-the population can increase rapidly when the conditions are favourable
-only one parent is needed
-more time and energy efficient as you don’t need a mate
-it is faster than sexual reproduction
disadvantages of asexual reproduction
-it does not lead to variation in a population
-the species may only be suited to one habitat
-disease may affect all the individuals in a population
how many chromosomes do gametes have?
23
how many chromosomes do humans have?
46 (23 pairs)
what are gametes?
sex cells
what are stem cells?
-stem cells are cells that can divide to produce many types of cel
-there are two kinds of stem cell; embryonic and adult stem cells
-only embryonic can develop into anything
what does mitosis create?
2 genetically identical diploid daughter cells
what does meiosis result in?
4 haploid daughter cells that are genetically different from one another
what does meiosis produce in animals and plants?
-sperm and egg cells in animals
-pollen and egg cells in plants
what are the stages of meiosis?
- the cell making gametes has a full set of chromosomes, they copy each other and stick together
- the cell splits into two. the new cells have half of the chromosomes (still a full set of DNA)
- each cell divide into 2 again and has 23 chromosomes
how many cell divisions occur in meiosis?
two
how many cell divisions occur in mitosis?
one
how many cells are produced in meiosis compared to mitosis?
meiosis - 4
mitosis - 2
where does mitosis occur?
stem cells
where does meiosis occur?
ovaries & testes
what is mitosis for?
growth and repair of cells
what is meiosis for?
production of gametes (sex cells)
does mitosis or meiosis create variation?
meiosis
what is DNA?
-the genetic material in the nucleus of a cell
-a polymer, made of nucleotides
what structure does DNA have?
-a double helix structure (formed when nucleotides join together, forming two strands)
-the double helix is held together by weak hydrogen bonding between complementary base pairs
-each base is connected to a deoxyribose sugar, the sugar is attached to a phosphate, these are the backbone of DNA
what does DNA stand for?
deoxyribonucleic acid
what is a nucleotide?
-made of a sugar and a phosphate group, with one of four different bases attached
what are the complementary base pairs and their hydrogen pairs?
adenine - thymine (2 hydrogen bonds)
cytosine - guanine (3 hydrogen bonds)
what are the parts of nucleotides?
-deoxyribose sugar
-bases
-phosphate
what is a gene?
-a small section of DNA in a chromosome
-each gene codes for a particular sequence of amino acids in order to make a specific protein
what is a genome?
one copy of all an organism’s DNA
what were the human genome projects aims?
-to work out the order or sequence of all the three billion base pairs in the human genome
-to identify all the genes
-to develop faster methods for sequencing DNA
did the HGP succeed?
the HGP used the DNA of several people to get a sort of average sequence, but each person has a unique sequence (unless they have an identical twin)
how can genomes be used in medicine?
-mapping of a person’s genome can help in predicting how likely they are to develop certain conditions
-scientists and doctors are also now beginning to use the information they have discovered in the HGP to help make more effective medicines as the effectiveness of medicines can be affected by variations in alleles
steps of extracting DNA from fruit:
- peel the skin from half a kiwi fruit and mash it up with a pestle and mortar
- mix a teaspoon of salt and small volume of washing up liquid into the fruit (detergent breaks down the cell membranes & nuclear membranes, causing the fruit cells to release their DNA/the salt causes the DNA to stick together)
- filter the mixture and retain only the filtrate
- pour ice cold ethanol onto the top of the filtrate (this causes the DNA to precipitate)
- extract the DNA
making proteins from amino acids
-the sequence of bases in the gene controls which amino acids are joined in order to make a specific new protein (or enzyme) molecule
-the proteins are then folded into their correct shape to make them functional
-each gene acts as a code, or set of instructions, for making a particular protein
making proteins from amino acids (steps)
-to enable genes to code for proteins, the bases A, T, G and C get together in triplets
-aach triplet of bases codes for one particular amino acid
-amino acids are made in the number and order dictated by the number and order of base triplets
-the amino acid molecules join together in a long polypeptide chain to make a protein molecule
-the number and sequence of amino acids determines which protein is produced
what are the stages of protein synthesis?
transcription: DNA bases are used to make a strand of rNA
translation: the bases are read 3 at a time and code for a specific amino acid to form a protein
what is tRNA?
an anticodon complementary to the codon on mRNA
what are the steps of transcription?
- an enzyme called DNA helicase attaches to the DNA (at a non coding region)
- the enzyme separates the DNA strands
- the enzyme moves along the strand and adds rNA bases (same as DNA but uracil rather than thymine)
- the nucleotides link together and form mRNA which leaves through the nucleus
- the DNA strands join again
what are the stages of translation?
- mRNA arrives at the ribosome
- the tRNA which has complementary anticodons lines up to make specific amino acid
- the ribosomes move along and join the amino acids made from the tRNA together, a polypeptide chain is made
- proteins are made from the polypeptide chains
do all parts of DNA code for proteins?
no, non-coding regions can switch genes on and off
how non coding regions affect phenotype?
-some regions of these non-coding DNA are not as good as binding to RNA polymerase
-this means the enzyme is less likely to bind and so less protein is produced
-if less protein is produce this can affect the phenotype of the organism
what is a mutation?
a change in a gene or chromosome
what are causes of mutation?
-ionising radiation
-chemical mutagen
do most mutations have an effect on an organism?
no
what happens if a mutation occurs in the non-coding region?
RNA can bind better or worse
what percentage is one part of a punnet square?
25%
pedigree analysis chart
a family tree diagram which show the inheritance of a genetic condition in a family
environmental variation
differences between organisms caused by environmental factors
continuous variation
variation that has no limit on the value that can occur within a population
discontinuous variation
variation that has distinct groups for organisms to belong to
what is a genotype?
a combination of alleles
what is a phenotype?
physical expression of genotype
what does heterozygous and homozygous mean?
heterozygous, different alleles (Hh) homozygous, the same alleles (HH, hh)
what are some facts about cystic fibrosis?
-recessive
-1 in 1600
-disorder of cell membrane
-thick mucus that causes blockages in air passages
what is x-linked inheritance?
a gene passed only through the X chromosomes
what is codominance?
when both alleles contribute to the phenotype
what chromosome do males have?
XY
what chromosomes do females have?
XX
what is a carrier?
someone who has one allele for a genetic disorder and can pass it one but doesn’t have it themselves
what is the function of DNA?
store genetic information that codes for proteins
dominant
an allele that is always expressed
recessive
an allele that is masked when a dominant allele is present
allele
different forms of a gene
zygote
fertilized egg
