7.1 Genetics Flashcards
define heterozygous
genotype with two different alleles at a particular locus
what does it mean for an allele to be dominant?
it is always expressed in the phenotype
what is a genotype?
the combination of alleles an organism contains
what does it mean for an organism to be diploid?
is has two copies of each chromosome
define codominant
both alleles for a gene in a heterozygous organism are expressed in the phenotype
what is a phenotype?
what characteristics an organism has as a result of its genes and the effect the environment has on them
define homozygous
genotype with two of the same allele at a particular locus
what is a monohybrid cross?
a diagram that shows the likelihood of two different alleles of a single gene being inherited by the offspring of two parents
what does it mean for an allele to be recessive?
it is only expressed in the phenotype if two copies are present (homozygous)
what does it mean for an organism to be haploid?
it only only has copy of each chromosome
what does it mean for a characteristic to be sex-linked?
the allele that codes for them are located on a sex chromosome
why are men more likely than females to show recessive phenotypes for characteristics that are sex-linked?
- the Y chromosome is shorter than the X chromosome and therefore carries fewer genes
- so most genes on the sex chromosomes are carried on the X chromosome
- males only have one X chromosome, so often just have one allele for sex-linked genes
- this means the characteristic will be expressed even if it’s recessive
what is an autosome?
any chromosome that isn’t a sex-chromosome
what combination of sex chromosomes do biological males have?
XY
what combination of sex chromosomes do biological females have?
XX
what evidence on a pedigree chart suggests that a characteristic in not sex-linked?
an unaffected father with an affected daughter
what evidence on a pedigree chart suggests that a characteristic is sex-linked?
only males are affected
define autosomal linkage
when two or more genes are positioned on the same autosome, they are unlikely to be separated by crossing over during meiosis, so are often inherited together
define dihybrid inheritance
the inheritance of two different genes that determine two phenotypes on two different chromosomes
define epistatis
the relationship between genes where the allele of one gene affects the expression of a different gene
define monohybrid inheritance
the inheritance of one gene
