inheritance Flashcards
chapter 7, unit 2 AOS 1
allele
different version of the same gene
genes
the information that is passed from parent to offspring that influences the structure,
physiology or behaviour of an organism
Genes are a sections of coding DNA that code for a specific protein in the body
Genes are given a name consisting of a group of up to 5 characters
genotype
the combination of alleles that code for a trait
In humans, we have 2 alleles for each gene - one allele from each parent
alleles are assigned a capital or lowercase letter to signify whether they are dominant or recessive
dominant alleles
the version of the gene that overpowers the recessive gene
Only one copy of a dominant allele is required for it to be expressed
recessive alleles
-versions of a gene that can skip generations and are overpowered by the dominant allele
-You need 2 copies of a recessive allele to show the trait it encodes. This means BOTH parents need to pass on the recessive gene.
homozygous
the alleles an organism has for a particular gene are identical
This can be either homozygous dominant (AA) or homozygous recessive (aa)
heterozygous
means that the alleles an organism has for a particular gene are different
This means the organism contains one dominant and one recessive allele (Aa)
phenotype
the expression (physical appearance) of a particular genotype
complete dominance
the dominant allele completely masks the recessive allele, complete dominance includes, homozygous dominant, homozygous recessive and heterozygous (AA,Aa,aa)
incomplete dominance
he traits blend in the heterozygote – creating a third phenotype e.g. Red + white = pink, alleles are represented by both capital letter e.g. PW
co dominance
he traits blend in the heterozygote – creating a third phenotype , alleles are represented by capital letters
di hybrid crosses
A dihybrid cross is a cross in which alleles of two different genes are involved.
The individuals in this type of cross can be either homozygous or heterozygous for each trait.
Four kinds of gametes are produced by each parent
pedigree chart
A record of a family and their genetic conditions
It is used to determine if a condition is dominant/recessive/x-linked
autosomal
Autosomal traits are carried on the autosomes (chromosomes 1-22) and can be dominant or recessive
sex linked
Sex-linked traits are carried on the X or Y chromosome and can also be dominant or recessive
sex linked traits
Males: XY – only inherit one copy of the X chromosome (from their mother)
Females: XX – inherit one copy of the X chromosome from their mother and one copy from their father
X-linked recessive traits – males who have the recessive allele on their X chromosome will ALWAYS express the recessive phenotype as they only have one X chromosome
X-linked dominant traits – females are affected more as they have two chances at inheriting the dominant allele
x- linked traits (haemophilia)
X-linked traits require a special notation
Haemophilia is an X-linked recessive trait –The alleles are written as follows:
Dominant: XH
Recessive: Xh
A male without hemophilia has the genotype: XHY
A male with hemophilia has the genotype: XhY
A female without haemophilia: XHXH or XHXh
A female with haemophilia: XhXh
X linked recessive
100% incidence of affected sons from and affected mother suggests x linked recessive
x linked dominant
100% incidence of affected daughters from an affected father suggests x linked dominance
y linked
only males are affected
autosomal dominant
autosomal reccesive
epigenetics
genes can be turned on or off depending on signals from the environment.
DNA methylation
prevents certain genes from being expressed. can be caused by , temperature, nutrient availability and radiation
polygenetics
A polygenic trait is a characteristic, such as height or skin color, that is influenced by two or more genes.
