7.1 inherited change Flashcards
what is the genotype?
- the genotype is the genetic constitution of an organism.
- it describes all the alleles that an organism contains.
what is the phenotype?
- the phenotype is the observable or biochemical characteristics of an organism.
- it is the result of the interaction between the expression of the genotype and the environment.
what is a gene?
a section of DNA (sequence of nucleotides) that codes for a particular polypeptide.
what is an allele?
one of the different forms of a gene.
explain what it means when alleles are referred to as ‘codominant’.
- alleles are referred to as ‘codominant’ when two alleles both contribute to an organism’s phenotype.
- this means that both alleles are equally dominant.
what is monohybrid inheritance?
the inheritance of a single gene.
state the law of segregation.
- in diploid organisms, characteristics are determined by alleles that occur in pairs.
- only one of each pair of alleles can be present in a single gamete.
what is dihybrid inheritance?
the inheritance of two characteristics, controlled by two different genes, located on two different chromosomes.
state the law of independent assortment.
each member of a pair of alleles may combine randomly with either of another pair.
explain why Mendel choose pea plants to experiment on.
Mendel chose pea plants to experiment on because they were easy to grow and possessed many contrasting features that could easily be observed.
explain the production of an enzyme for an organism that is homozygous for the first allele.
in organisms that are homozygous for the first allele, both alleles code for the enzyme that expresses the dominant characteristic.
explain the production of an enzyme for an organism that is homozygous for the other allele.
in organisms that are homozygous for the second allele, no enzyme is produced.
explain the production of an enzyme for an organism that is heterozygous.
in a heterozygous organism, both alleles code for an enzyme, so a combination of the phenotype for both alleles is expressed.
give the script that is used when writing for codominance.
superscript.
any gene that is carried on either the X or Y chromosome is described as what?
sex linked.
explain why characteristics that are controlled by recessive alleles on the non-homologous portion of the X chromosome appear more frequently in males.
because in males, there is no homologous portion on the Y chromosome that might contain the dominant allele, in the presence of which the recessive allele does not express itself.
an X-linked genetic disorder is caused by what?
a defective gene on the X chromosome.
give an example of an X-linked disorder in humans.
haemophilia.
give an example of one of a number of causes of haemophilia.
one of a number of causes of haemophilia is a recessive allele with an altered sequence of DNA nucleotide bases that codes for a faulty protein which does not function.
other than sex chromosomes, which are sex-linked, what are the remaining 22 chromosomes called?
autosomes.
describe ‘autosomal linkage’.
autosomal linkage refers to when two or more genes are carried on the same chromosome.
if two genes are heterozygous linked, how many combinations of alleles will be found in the gametes? how is this different from heterozygous unlinked?
heterozygous linked - two possible combinations of alleles in the gametes
heterozygous unlinked - four possible combinations of alleles in the gametes
when does epistasis arise?
epistasis arises when the allele of one gene affects or masks the expression of another in the phenotype.
give an example of another form of epistasis, other than gene masking.
- another form of epistasis is where genes act in sequence by determining the enzymes in a pathway.
- dominant alleles of each gene code for a functional enzyme, while recessive alleles code for a non-functional enzyme.
