Patterns of inheritance (6) Flashcards
What is continuous variation?
This is when the individuals in a population vary within a range, there are no distinct categories.
What is discontinuous variation?
This is when there are two or more distinct categories, each individual falls into only one of these categories, there are no intermediates
What are alleles?
They are different versions of the same gene.
What process leads to variation in genotypes within a species?
Sexual reproduction leads to variation in genotypes within a species. Meiosis makes gametes with a unique assortment of alleles through crossing over and independent assortment of chromosomes. The random fusion of gametes during fertilizations also increases genetic variation in the offspring.
What is phenotypic variation?
The differences in genotype of organisms result in variations of phenotype, the characteristics displayed by an organism.
What are polygenic characteristics?
Inherited characteristics that show continuous variation are usually influenced by many genes.
What are monogenic characteristics?
Inherited characteristics that show discontinuous variation are usually influenced by only one gene.
What are the two factors that can affect variation?
- genes
- environment
How can both genes and the environment affect variation?
Genetic factors determine genotype and the characteristics an organism’s born with, but environmental factors can influence how some characteristics develop. Most phenotypic variation is caused by the combination of genotype and environmental factors. Phenotypic variation influenced by both usually shows continuous variation.
What is a gene?
A sequence of bases on a DNA molecule that codes for a protein which results in a characteristic.
What is an allele?
A different version of a gene
What is a genotype?
The alleles that an organism has
What is a phenotype?
The characteristics that the alleles produce
What does dominant mean?
An allele whose characteristic appears in the phenotype even when there is only one copy
What does recessive mean?
An allele whose characteristic only appears in the phenotype if two copies are present.
What does codominant mean?
Alleles that are both expressed in the phenotype
What is a locus?
It is the fixed position of a gene on a chromosome
What does homozygous mean?
It means that there are two copies of the same allele
What does heterozygous mean?
It means that there are two different alleles
What are monogenic crosses and monogenic inheritance?
Monogenic crosses show the likelihood of the different alleles of that gene being inherited by offspring of particular parents.
Monogenic inheritance is the inheritance of a characteristic controlled by a single gene.
What is a carrier?
It is a person carrying an allele which is not expressed in the phenotype but that can be passed on to offspring.
How is codominance and sickle cell anemia related?
- People who are homozygous for normal hemoglobin do not have the disease
- People who are homozygous for sickle hemoglobin do have the disease and all their red blood cells are sickle shaped.
- People who are heterozygous have an in between phenotype called the sickle cell trait where they have some normal hemoglobin and some sickle hemoglobin. The two alleles are codominant so are both expressed in the phenotype
What is a Punnett square?
It is a way of showing a genetic diagram and can be useful to predict the genotypes and phenotypes of offspring.
What is dihybrid inheritance and what are dihybrid crosses?
Dihybrid inheritance is the inheritance of two characteristics which are controlled by different genes.
A dihybrid cross is used to show how two different genes are inherited at the same time.
How can phenotypic ratios be predicted?
The phenotypic ratio is the ratio of different phenotypes in offspring. Genetic diagrams help you to predict the phenotypic rations in both generation 1 and 2 offspring.
What are some reasons that you won’t get the expected phenotypic ratio?
Sometimes the ratio will be unexpected due to sex linkage, autosomal linkage or epistasis.
What controls gender in mammals?
The genetic information for biological sex is carried on two sex chromosomes. In mammals, females have two x chromosomes and males have one x and one y chromosome.
What is a sex linked characteristic?
A characteristic is said to be sex linked when the allele that codes for it is located on a sex chromosome.
What is the difference between the X and Y chromosomes in mammals?
The Y chromosome is smaller than the X chromosome and carried fewer genes. So most genes on the sex chromosome are only carried on the X chromosome.
What are some exampled of genetic disorders caused by faulty alleles on the sex linked genes?
Color blindness and hemophilia. The faulty alleles for both these disorders are carried on the X chromosome so are called X linked disorders.
Why is it more likely for men to show recessive phenotypes for genes that are sex linked?
As males only have one X chromosome, they often only have one allele for sex linked genes. So because they only have one copy, they express the characteristic of this allele even if it is recessive.
What is an autosome?
An autosome is any chromosome that isn’t sex linked. Autosomal genes are the genes located on the autosome.
Why are genes on the same autosome linked?
Because they are on the same autosome they’ll stay together during the independent assortment of chromosome in meiosis I and their alleles will be passed onto offspring together. The only reason this won’t happen is if crossing over splits them up first.
What affects probability of expression of autosomal linkage?
The closer together the two genes on the autosome, the more closely they are said to be linked. This is because crossing over is less likely to split them up.
What is epistasis?
Many different genes can control the same characteristic, they interact to form the phenotype. This can be because the allele of one gene masks the expression of the alleles of other genes.
What is the chi squared test and when is it used?
The chi squared test is a statistical test that is used to see whether there is a statistically significant difference between observed vs expected results.
What is the chi squared equation?
χ² = Σ (Oi − Ei)² / Ei
How do you use your chi squared value in a hypothesis test?
If the x2 value is greater or equal to the critical value then there is a significant difference between observed and expected results.
How do you work out the degrees of freedom for the chi squared test?
number of classes - 1
