M6 C20: patterns of inheritence Flashcards
how does variation occur?
mutations
why is variation important?
natural selection and evolution
what is chlorosis?
when leaves of plants look pale yellow due to cells not producing the right amount of chlorophyll
what is an effect of chlorosis?
reduces ability to make food in photosynthesis
what can cause chlorosis?
environmental factors such as:
lack of light
mineral deficiencies
virus infections
how can genetic factors contribute to animals body mass?
mutations in genes on chromosome 7 can cause fat deposition in the body to be altered causing more chance of weight gain
what are different versions of a gene called?
allele
what is a genotype?
genetic make-up of an organism
what is a phenotype?
observable characteristics of an organism
what is a modification?
when an environmental factors changes an phenotype of an organism
what is a dominant allele?
when present is always expressed
what is a recessive allele?
only expressed if 2 copies of it are present
what does homozygous mean?
two identical copies of an allele
what does heterozygous mean?
has 2 different alleles for a characteristic
what is continuous variation?
characteristic that can have any value within a range
what is the cause of continuous variation?
genetic and environmental
what is an example of continuous variation?
skin colour
animal mass
how is continuous variation genetically controlled?
polygenes- mutlipled genes
what is discontinuous variation?
characteristic that is only in discrete categories/ values
how is discontinuous variation genetically controlled?
one or 2 genes
what is the cause of discontinuous variation?
mostly genetic
what is an example of discontinuous variation?
blood group
what is monogenic inheritance?
inheritance of a single gene
what is codominance?
when 2 different occur for a gene, both of which are equally dominant
how can multiple genes code for a characteristic/
when there are more than 2 versions of a gene. however only 2 are present in an organism
what is a characteristic coded for by multiple alleles?
blood group
what are the co dominant and recessive alleles in blood groups?
Ia and Ib and dominant
Io is recessive
what is the 23rd pair of chromosomes?
the sex chromosomes
what is meant by sex linked characteristics?
determined by genes of the sex chromosome
how are males more likely to display sex linked characteristics?
Y chromosome is shorter, therefore an recessive allele on the X chromosome aren’t masked by a dominant allele on the Y chromosome so are expressed.
why are females less likely to display sex linked characteristics?
in females both X chromosomes are the same length so a recessive allele likely has a dominant allele on the other X chromosome
what are some examples of sex linked genetic disorders?
haemophillia
what will happen if a male inherits the recessive allele for a genetic disorder on his X chromosome/
it will be expressed and he will have the disorder as there is no dominant allele on the X chromosome to mask this
what are females called who carry the recessive allele on one of their X chromosomes?
known as carriers as they are hetrozygous for the recessive gene
may pass this gene on to their sons who could be affected
what is dihybrid inheritence?
inheritance of two different characteristics caused by two genes which may be located on different pairs of homologous chromosomes
why may the 9:3:3:1 ratio differ in offspring, when looking at dihybrid inheritence?
random fertilisation of gametes
if genes being studied are on the same chromosome these are known as linked genes, if no crossing over these are more likely to be inherited together
what are linked genes?
genes that are likely to be inherited together as 1 unit because they are physically close to one another on the same chromosome.
what is epistasis?
when one gene masks or suppresses the expression of another
what is recessive epistasis?
presence of two copies of the recessive allele at the first locus prevents the expression of another allele at a second locus.
what is dominant epistasis?
dominant allele masks the expression of both dominant and recessive alleles at another locus
what can a deviation from expected phenotypic ratios suggest?
genes are linked
epistatic genes
