patterns of inheritance Flashcards
KEY TERMS IN GENETICS-
what does each chromosome consist of?
what is a length of DNA that codes for a single polypeptide?
what is the position of a gene on a chromosome called?
what forms can a gene exist in?
different alleles of a gene have slightly different nucleotide sequences but?
-a long DNa molecule which codes for several different proteins
-a gene
-the position of a gene on a chromosome is its locus
-two or more different forms called alleles
-they still occupy the same locus (position) on the chromosome
VARIATION: PHENOTYPE
what is the phenotype?
what is phenotypic variation?
what is the complete phenotype?
-observable characteristics
-the difference in phenotypes between organisms of the same species: genetic, environmental or a combination of both
-determined by the expression of its genotype and the interaction of the environment on this
genetic factors-
how can genes have varying effects on an organisms phenotype?
what specifically?
for example?
-the phenotype may be affected by a single gene or by several genes and this effect may be large or small
-the different alleles an organism has at a single gene locus can determine the phenotype
-the F8 gene that codes for the blood-clotting protein factor VIII = the different alleles at the F8 gene locus dictate whether or not normal factor VIII is produced and whether the individual has the condition haemophilia
environmental factors-
examples of how different environments around the globe experience very different conditions:
how do these factors affect how organisms grow and develop?
•length of sunlight hours
•supply of nutrients
•availability of water
•temperature range
•oxygen levels
-eg. plants with a tall genotype growing in an environment that is depleted in minerals, sunlight and water will not be able to grow to their full potential size determined my genetics
examples of how the environment can affect phenotypic variation:
1?
2?
1- diet in animals
•the fruit fly is normally grey but there is a genetic mutant that is yellow
•if the larvae of normal grey flies are given a diet of silver salts, they develop a yellow colour due to an environmental factor = diet
2- growing conditions for plants = etiolation
•plants that are grown in the dark, or that can’t access enough magnesium become yellow, even though they should genetically be green
•plants that are grown in the dark my also develop long stems with small, curled leaves, even though they should develop normally
•known as etiolation
VARIATION: SEXUAL REPRODUCTION
what is genetic variation?
how is genetic variation caused?
what does this result in?
-the small differences in DNA base sequences between organisms within a species
•crossing over of non-sister chromatids during prophase 1 of meiosis
•independent assortment of homologous chromosomes during metaphase 1 of meiosis
•random fusion of gametes during fertilisation
•a new combination of alleles in a gamete or individuals
what happens during crossing over?
-non-sister chromatically exchange alleles
-meiosis 1, homologous chromosomes pair up and are in close proximity to each other
-the non-sister chromatids can cross over and get entangled
-these crossing points are called chiasmata
-the entanglement places stress on the DNA molecules
-causing a section of chromatid from one chromosome break and rejoin with the chromatid on the other chromosome
-results in a new combination of alleles on the two chromosomes
what happens during independent assortment?
-the production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle during metaphase 1
-resulting in different combinations of chromosomes in daughter cells = increases genetic variation between gametes
-each pair of chromosomes can be arranged with either chromosome on top, completely random, and the orientation of one homologous pairs along is independent
-homologous chromosomes are then separated and pulled apart to different poles
-the combination of alleles that end up in each daughter cell depends on how the pairs of homologous chromosomes were lined up
-there are 8 324 608 different combinations in humans
what happens during the random fusion of gametes?
-each gamete carries random, different alleles
-during fertilisation, any male gamete can fuse with any female gamete to form a zygote
-this random fusion of gametes at fertilisation creates genetic variation between zygotes as each with have a unique combination of alleles
Mutations?
-mutations can result in the generation of new alleles = it may be advantageous or disadvantages or have no effect on phenotype due to the genetic code being degenerate
PREDICTING INHERITANCE AND PATTERNS OF INHERITANCE-
what are monohybrid crosses/monogenic inheritance?
when two individuals sexually reproduce, this means there is an equal chance of what?
how do we present this information?
look at example-
-looks at how the alleles for a single gene are passed on from one generation to the next
-the zygote inheriting either allele from their parent
-by a punnet square, producing diagrams based on chance
explain what is meant by multiple alleles?
example?
look at table-
-many genes have more than two alleles
•however, a diploid individual will still only inherit two possible alleles
-human blood groups as there are three different alleles:
•Alleles IA and IB are codominant, but both are dominant to IO
•I, B or O represent the alleles
•IA results in production of antigen A in the blood
•IB results in the production of antigen B in the blood
•IO results in no antigens being produced in the blood
what is meant by codominance?
how is it written in a punnet square?
look at example-
-when both alleles can be expressed in the phenotype at the same time, eg. heterozygous will express both alleles in their phenotype
-geneotypes are represented using a capital letter for the gene and subscript letters for the alleles
PREDICTING INHERITANCE-
dihybrid crosses-
what are they?
how can they be used for example?
how to write this?
look at the example-
-look at how the alleles of two genes transfer across generations
-to show the inheritance of two different characteristics in an individual
-write the two alleles for one gene and then immediately after write the two alleles for the other gene
Phenotypic ratios-
LINKAGE- sex linkage
what does this mean?
so?
how can the presence of sex linkage be identified?
when a gene is sex-lined, what are the phenotypes?
in the case of a gene that causes a sex-linked disease?
look at example-
-sex-linked genes are only present on one sex chromosome and not the other
-so, the sex of the individual affects what alleles they pass on to their offspring through their gametes
-using pedigree diagrams and punnet squares
-the phenotypes are not spread evenly across the sexes
-one sex will be disproportionally affected
Phenotypic ratios-
LINKAGE- autosomal linkage
what is this?
meaning?
what does linkage between genes affect?
look at example of with and without linkage-
-when not all of the genes assort independently of one another during meiosis
-some genes that stay on the same chromosome display autosomal linkage and stay together in the original parental combination
-how parental alleles are passed on to offspring through gametes
Phenotypic ratios-
epistasis-
what is it?
in a standard dihybrid cross, what phenotypic ratio would we expect?
but, when epistasis occurs, what happens to the ratios?
look at the example-
-epistasis occurs when two genes on different chromosomes affect the same feature = one gene affects expression of another gene
- 9:3:3:1
-the ratios will differ from this, to=
9:3:4
12:3:1
9:7
13:3
predicting inheritance - chi-squared statistical test
look at example-
CONTINOUS VARIATION-
what is meant by the term variation-
what about when in relation to natural selection?
what is continuous variation?
so, when does continuous variation occur?
what does this mean?
-the differences that exist between at least two things eg. a level, amount, quantity or feature
-variation refers to the differences that exist between individuals of a species, referred to as intraspecific variation
-the differences between individuals of a species where the differences are quantitative (measurable)
-when there are quantitative differences in the phenotypes of individuals within a population for particular characteristics
that a range of values exist between two extremes within which the phenotype will fall eg, height of a human, as no distinct classes or categories exist
what is the genetic basis of continuous variation?
what are the 3 types of genetic influences?
-this type of variation is caused by an interaction between genetics and the environment,
genotype + environment = phenotype
•different alleles at a single locus have a small effect on the phenotype
•different genes can have the same effect on the phenotype and these add to gyro have an additive effect
•if a large number of genes have a combined effect on the phenotype then they are known as polygenes
DISCONTINUOUS VARIATION-
what is it?
so what do qualitative differences in phenotypes of individuals within a population give rise to?
example?
-the differences between individuals of a species where the differences are qualitative (categoric)
-discontinuous variation
-fall in discrete and distinguishable categories, usually with no intermediates and cannot be measured over a range eg blood group
what is the genetic basis of discontinuous variation?
at the genetic level, 3 types?
example?
look at comparison table on save my exams-
-this variation occurs solely to genetic factors, the environment has no direct effect
•different genes have different effects on the phenotype
•different alleles at a single gene locus have a large effect on the phenotype
•diploid organisms will inherit two alleles of each gene = can be the same or different alleles
-the different alleles at the F8 gene locus dictate whether or not normal blood-clotting protein FactorVIII is produced and whether the individual has haemophilia
FACTORS AFFECTING EVOLUTION-
what are the environmental factors that affect the chance of survival of an organism known as?
and what does this effect?
what are the different factors?
-selection pressures
-these selection pressures can have different effects on the allele frequencies of a population through natural selection
•stabilising selection
•direct selection
•genetic drift
•genetic bottleneck
•founder effect
what is stabilising selection?
meaning?
example?
-is natural selection that keeps allele frequencies relatively constant over generations
•things stay as they are unless there is a change in the environment
-human birth weights, as very low and very hight birth weights are selected against leading to the maintenance of the intermediate birth weights
