6.1.2- Patterns of Inheritance Flashcards
what is a gene?
a section of DNA that codes for a protein
what is an allele?
different forms of the same gene
what is a genotype?
the alleles an organism has
what is a phenotype?
the observable characteristics of an organism
what is the locus?
the position of a gene on a chromosome
what is a dominant allele?
the allele which exerts an affect on the phenotype of the heterozygote.
what is a recessive allele?
the allele which has no effect on the phenotype of the heterozygote
what does homozygous mean?
two identical alleles for a charcteristic
what does heterozygous mean?
two different alleles for a characteristic
what is variation?
the presence of differences between individuals, it can be continuous or discontinuous
what is continuous variation?
when there is a range of values between two extremes
eg- height
what is discontinuous variation?
when there are two or more distinct categories with no intermediates
eg- tongue rolling
what is monohydrid inheritance?
the inheritance of a single pair of alleles of a single gene
what are used to allow us to see the inheritance of genes and their alleles?
genetic diagrams, in particular a genetic cross
what are the 6 key steps when completing a genetic cross?
1- state the phenotype of both parents
2- state the genotype of both parents
3- state the gametes of both parents (circle the letter to show that the cell has gone through meiosis)
4- use a punnet square to show the random fusion of the gametes
5- state the proportion of each phenotype produced within offspring
6- state the corresponding phenotype for each genotype.
what can a test cross be used for?
to find out the genotype of a normal organism
what are the four blood groups and what alleles make these up?
blood group A= IAIA or IAIO, has A antigens on rbc
blood group B= IBIB or IBIO, has B antigens on rbc
blood group AB= IAIB, has A and B antigens on rbc
blood group O= IOIO, no antigens
what does codominant mean?
inheritance of alleles which both contribute to the phenotype if they both occur
eg- A and B are codominant and so when together, create the blood group AB
what number chromosome in humans is known as the sex chromosome and so genetically determines the sex of an individual?
the 23rd chromosome
when are characteristics sex linked?
if the gene that codes for it is found on one of the sex chromosomes
where are most of the sex-linked genes found?
on the X chromosome (found in both males and females)
how many alleles for sex-linked genes do females carry and why?
2, because they are XX
how many alleles for sex linked genes do males carry and why?
one (hemizygous), because they are XY
what are sex-linked genetic disorders caused by?
caused by recessive alleles
what are three examples of sex-linked genetic disorders?
-haemophilia
-Duchenne muscular dystrophy
-red-green colour blindness
why are males more likely to suffer from X-linked genetic disorders?
-if females carry a normal dominant allele on one X chromosome while the other X chromosome has a defective recessive allele, then they will be a carrier and not be affected
-however, as males only have one X chromosome, if the defective recessive gene is on this, it will affect the phenotype because it is the only allele of that gene present, and so they will suffer
what is a dihybrid cross?
It follows the inheritance of two genes located on different pairs of homologous chromosomes
what is unlinked dihybrid?
-the two gene loci are unlinked (carried on different chromosomes)
-the genes do not interact (they do not influence each others expression)
what is the common ratio used for unlinked dihydrid?
9 : 3 : 3 : 1
what is linkage dihybrid?
-genes for different characteristics that are present on the same chromosome are linked and inherited together
what does linkage do in terms of phenotypes?
it reduces the number of phenotypes resulting from a given genetic cross
what is the common ratio for linkage dihybrid?
3 : 1
what happens if the genes are linked and crossing over occurs?
the phenotypic ratio of the offspring will not follow a normal ratio for linked genes or unlinked genes
what are the offspring called that are produced due to crossing over and have different combinations of alleles than either parents?
recombinant offspring