Genes and patterns of inheritance Flashcards
What is a gene?
Short sections of DNA that code for a particular polypeptide
What is an allele
A particular form of a gene
What is the gene locus?
The position of the gene on a locus
What is Mendels law of segregation?
Two alleles of the same gene separate during meiosis with only one entering each gamete
What is a genotype
Two alleles for a particular characteristic
What is a phenotype?
The outward appearance of the individual in terms of the trait under consideration
What is dominance?
In heterozygous condition the dominant allele will override the recessive allele
What is recessive?
The recessive allele will be dominated by the dominant allele
How do you do a test cross?
Cross the unknown individual with homozygous recessive and the ratio of phenotype will tell you the genotype of the unknown
What is co dominance?
1:2:1 ratio is observed when two heterozygote parents are crossed for a trait that displays co-dominance
What is observed for multiple alleles e.g. blood groups
blood groups shows 1:1:1:1
What is a ratio of 2:1 an example of
2:1 is an example of a lethal allelic combination. The offspring that have the lethal allelic combination will fail to develop as embryos and you will not see the phenotype. Only non lethal combinations will be able to be counted
what does it mean for a trait to be sex linked?
For a trait to be sex linked there is a close correlation between the trait and sex of the individual
Why do males generally have the disease
The Y chromosome is described as being genetically empty. The males only have one X chromosome so if they have the recessive allele they will have the disease. Females can have the recessive and the dominant and will therefore be a carrier for the disease
For a male baby to have the disease what must happen
The mother has to be a carrier as he inherits his X chromosome from his mother and Y from his father
What is a carrier
Someone who carries the allele but is phenotypically normal
What will happen if a sex linked disease is present in both parents and is dominant?
It will be seen in all offspring
For a pedigree diagram what indicates that it is :
- Autosomal recessive
- Autosomal dominant
- X-linked recessive
- X-linked dominant
- Will only appear in some generations as it is hidden in others (autosomal = equal numbers of male and female)
- Impossible to pass condition on without at least one parent having the trait (autosomal = equal male and female)
- More common in males but not present in all
- NOT mainly restricted to males. A Father will pass it to all of his daughters
What is dihybrid inheritance?
Investing two traits together e.g. height and shape of peas
What is 9:3:3:1
di hybrid inheritance
What is Mendels second law?
The law of independent assortment -
During the formation of gametes the segregation of the alleles of one gene is independent of the segregation of alleles of another gene
Where does mendels second law occur ?
Occurs at bivalents during metaphase 1
What are the two main types of ratios for dihybrid inheritance and how do they come about?
9:3:3:1 and 1:1:1:1
Their ratios are classified as dihybrid inheritance when each of the two genes involved has a dominant and recessive allele
What is independently inherited?
When the genes are on different chromosomes
What is polygenic inheritance, ratio
1:4:6:4:1
The additive effect of more than two genes. There is continuous variation
What is the 15:1 ratio an example of ?
Epistasis where only one of the two genes is necessary to produce a particular phenotype
What is the 9:3:3 ratio an example of ?
Epistasis with a lethal allele combination
What is epistasis?
Where one gene interferes with the expression of another
What is the 9:7 ratio
Epistasis where at least one dominant allele must be present in each gene. Two genes are necessary to produce a particular phenotype
what is 12:3:1
Dominant epistasis where one allele of a gene blocks the expression of both alleles of another gene
what is 9:3:4
Recessive epistasis where homozygous state of one gene blocks the expression of both alleles of another gene
What is epigenetics?
The role of the environment in affecting gene expression. Some genes can be turned off in the first place
Why is mendels research considered reliable?
Large number of replicates
