Task 1 Flashcards
Importance of pedigrees
Pedigrees are valuable tools in genetic counseling as they allows for the pattern of inheritance to be traced through generations of a family.
What is incomplete dominance?
incomplete dominance a heterozygous individual blends the two traits
How does meiosis increase variation? why is this important?
meiosis purposefully introduces variation. Processes of crossing over, independent assortment and random segregation allow for combinations of different alleles, increasing variation in offspring and the wider population.
Genetic diversity (introduced by meiosis and sexual reproduction) is very important for the continuity of species, as mutation and variation are essential factors for survival and evolution.
When do Mendellian ratios not apply?
Sex-linked genes and co-dominant genes do not display the phenotype ratios predicted by Mendel’s laws.
How are the 23 chromosomes divided in terms of roles?
22 pairs of autosomes and 1 pair of sex chromosomes in humans
What do sex chromosome do?
Sex chromosomes carry genes that determine the sexual characteristics of a person and influence whether they are male or female
Female chromosome
Females = XX (homogametic)
Male chromosome
Males = XY (heterogametic)
Why do sex linkage characteristics occur?
Sex-linked traits are passed on the sex chromosome of an organisms. In humans, this means the X and Y chromosomes. During sexual reproduction, female offspring inherit one maternal X chromosome and one parental X chromosome (XX). Male offspring inherent one maternal X chromosome and one parental Y chromosomes (XY). If different genes are present on either the X or Y chromosomes, one sex will be more affected than the other due to this pattern of inheritance.
Mitosis
Mitosis: cell division resulting in two identical daughter cells, with the same number and kind of chromosomes as the parent cell.
Faults within the basic model of DNA
- Does not model major and minor groves (The major groove occurs where the backbones are far apart, the minor groove occurs where they are close together)
ASSESSING HOW GENES AND ENVIRONMENT AFFECT PHENOTYPIC EXPRESSION
An individual’s phenotype is a combination of environment and genetic expression.
o Nature vs. nurture debate
o Some variations are genetically inherited, others are influenced by environment
(and on a wide spectrum)
o Variations may arise as a result of interaction: GENES + ENVIRONMENT = PHENOTYPE
The appearance of an individual is not based solely on their genetic information. The environment of the organism also plays a part. Hydrangeas are plants that have different flower colour (pink or blue) depending on the pH of the soil they are grown in. in acidic soils (less than pH 5) hydrangeas are blue. In soils that have a pH greater than 7 they are pink. The pH has an effect on the availability of other ions in the soil and it is these ions that are responsible for the colour change. Another example of the influence of the environment on the appearance is the height of plants as genetically identical plants will grow to different heights if they are exposed to different growth conditions.
Genotype
- Genotype: the genome or genetic make-up of an organism
Phenotype
- Phenotype: the outward appearance of an organism, including observable traits, biochemistry, and physiology.
Gene
a section of DNA encoding a particular characteristic
Allele
alternative forms of a gene
Autosomal dominate
Autosomal dominate inheritance is when a trait is determined by the expression of a dominant allele. This means that the phenotype will always be expressed over the other the other allele inherited. In order to express the dominant phenotype, only one copy of an allele is necessary.
Autosomal recessive
Autosomal recessive inheritance describes the pattern of inheritance where two recessive alleles are required to be inherited in order for a trait to be phenotypically expressed. Individuals may be barriers of recessive traits, meaning they don’t exhibit them, butare bale to pass these traits onto offspring. Recessive traits may skip generations and generally are less prevalent in the population than autosomal dominant characteristics.
Co-dominance
when both alleles in a gene pair are fully expressed. Resulting in a third possible phenotype
Incomplete dominance: when an allele for a certain trait is not completely expressed over its paired allele. This results in the creation of a third possible phenotype which is a blended version of the phenotype of both alleles.
Incomplete dominance
Although both co-dominance and incomplete dominance are a result of co-expression of heterozygous alleles, incomplete dominance is different to co-dominance because it is a result of alleles not being fully expressed. Example of incomplete dominance include prink follows which are the result of cross-breeding red and white flowers.
Meiosis
Chromosomes line up in pairs during prophase 1
Crossing over occurs 🡪 variation as the chromosomes have swapped maternal and paternal alleles.
Metaphase 1 – chromosomes align in pairs in the middle of the cell. They do so independently of one another. This means various possible combinations of paternal and maternal chromosome alignment are possible.
Anaphase 1 – chromosomes separate
Telophase 1 – two daughter cells form. The chromosome number has been halved (started with double). Chromosome combinations in cells differ.
Crossing Over – During Prophase I
Before meiosis begins, the DNA is copied (interphase)
During Prophase 1, the chromosomes line up in pairs.
Crossing over or synapsis occurs – the arms of the chromosomes wrap around each other and the points where they meet are called chiasmata – at chiasmata the chromosomes break, exchanging genetic material between maternal and paternal chromosomes 🡪 variation occurring with new allele combinations.
Independent Assortment
Independent assortment describes how pairs of alleles separate independently from one another during gamete formation
According to independent assortment, the inheritance of one gene/trait is independent to the inheritance of any other gene/trait
Independent assortment is due to the random orientation of pairs of homologous chromosomes in meiosis I
Importance of DNA replication
DNA replication is important because it allows for identical copies of DNA (and hence genes) to be made, which is essential for cell replication.
mitosis importance (sumarrised)
- This process is essential for development and growth of organisms.
- It increases the number of cells in an organism, allowing for the development of a multicellular body
- Allows for old cells to be replaced and ensures that tissues continue to function
- For organisms like humans, mitosis allows for development to maturity, so genetic material can be passed through sexual reproduction
- In cases of asexual reproduction, mitosis creates the next generation of organisms
meiosis importance
- The combination of gametes during sexual reproduction creates new organisms, which have traits inherited from both parents
- Meiosis purposefully introduces variation (something that mitosis does not)
- The processes of crossing over, independent assortment and random segregation allow for different combinations of alleles, which increases variation
- Genetic diversity is very important for the continuation of species
Protein synthesis (summarised)
The DNA is unzipped and a complementary mRNA strand is transcribed. The mRNA moves to the ribosome where translation occurs. Each codon is matched to a tRNA molecule with a complementary anticodon and carries a specific amino acid. The amino acids are joined together to form a polypeptide/ protein.
Helicase
Unwinds the double stranded DNA molecule
Polymerase
Synthesis of DNA during replication; fetches nucleotides
Primase
Adds a RNA primer so that synthesis of DNA can start
Ligase
Joins newly synthesised DNA fragments
mitosis importance response
Mitosis (cell division) constantly occurs to enable growth and repair of tissues and organs. It ensures that new cells are identical to those they are replacing and that all genetic information is there. If a cell does not have the correct DNA code, it will not make the correct proteins. Since proteins affect the structure and function of cells, mitosis’s is necessary for the maintenance of normal bodily functions. i.e the maintenance of health. Mitosis also increases the immune response to a pathogen e.g. specific immune cells can reproduce via mitosis in response to exposure to an antigen.
Genetic Variation
Variation enables natural selection to occur and so enables the species to evolve over time. Genetic variation increases the chance of some organism will survive under adverse conditions e.g: when the environment changes. Those organisms with variations best suited to the environment will survive and reproduce. Hence they will pass their favourable adaptive features on to their offspring. Therefore, these characteristics will come to predominate in their population over time.
Transcription
- The process of turning genetic information stored in the DNA into a intermediary molecule mRNA.
1. RNA polymerase binds to a ‘promoter’, which signals the DNA to unwind, and allows the enzyme to read the bases.
2. The mRNA molecule is built, using complimentary bases.
3. mRNA detaches from the DNA strand.
Translation
- The process of turning information encoded as mRNA into a polypeptide chain.
1. mRNA attaches to a ribosome.
2. The ribosome matches the codon and anti-codons together.
3. A polypeptide bond is formed, and continues to grow as amino acids are added
4. Once a stop sequence is reached, the chain detaches and then folds.
Random segregation
in meiosis, pairs of homologous chromosomes split up randomly with half going to one gamete and the half to another. This causes variation in the offspring.
Mutations and their effect
Errors during replication lead to the insertion of the wrong base during copying of a strand. This is called a mutation. Mutations may be neutral if they occur in a non-coding area or may be beneficial or deleterious if they occur in a coding area. Mutations can lead to genetic disease or can provide the organisms with slightly different phenotype that may give it a selective advantage against other organisms.
role of genes
Genes regulate the cell cycle e.g. they control mitosis (need for growth and repair) and meiosis (need to produce gametes for reproduction). Genes control cell differentiation so cells with specialised roles to help maintain health are formed. Genes code for proteins that enable an organism to function properly, e.g. structural proteins, regulatory proteins for gene expression, enzymes for metabolism, antibodies in immune responses, etc.
proteins definition
proteins are large molecules with a particular shape that are composed of at least one poly[eptide. they are an essential component of living things as functional molecules (enzymes) and structural molecules e.g. histones in chromosomes
non coding sections
introns
removed in DNA replication
mutaution –> new alleles
one mutation could change one of the amino acids in a sequence that makes up a polypeptide. the new polypeptide may function in a different way giving rise to different characteristics or new alleles. in many other cases the resultant polypeptide does not function well.
causes of variation
variation is caused by mutations that can add to the pools of allels for a gene. it is further enchanted through crossing over, random segregation inmeiosis and the chance nature of fertilisation.
