Inheritance Flashcards
gene
section of DNA that codes for a specific polypeptide
genotype
genetic constitution of an organism. All the alleles an organism posesses.
gene pool
all alleles within an interbreeding population at a specific time
population
all individuals of the same species that occupy the same area/habitat at the same time
phenotype
the expression of its genetic constitution and the interaction with the environment
allele
different version of the same gene
- dom, codom or recessive
- alleles of same gene caused by mutation
multiple alleles
more than 2 alleles for the same gene. hierarchy of dominance.
locus
different alleles for the same gene are found at the same position on the homologous chromosome
homozygous
if two copies of gene are the same allele, homozygous
heterozygous
if two copies of a gene are different alleles
dominant allele
always expressed in the phenotype
recessive allele
only expressed in the phenotype if the genotype is homozygous
codominant alleles
equally expressed within the phenotype
diploid
somatic cells (ie: adult cells)
- two copies of a gene
haploid
only have one copy of a gene
eg: gametes
genetic crosses keys
“true-bred”/”pure-bred” = homozygous
P = parental generation
F1 = offspring of the generation
F2 = offspring of the F1 gen
expected offspring phenotype ratios from hetero parents
mono = 3:1
codom = 1:2:1
dihybrid = 9: 3: 3:1
epistasis = 9: 4: 3/ 15: 1/ 9:7
autosomal linkage = 3:1 (no cross) 4:4:1:1 (recombinant alleles)
dihybrid
two characteristics determined by genes found on different chromosomes
epistasis
expression of one gene is influenced by another gene
hardy weinberg equation
P + q =1
diploid: P^2 + 2Pq + q^2 = 1
ALWAYS find the recessive first
number divided by population size = q^2
what does the hardy weinberg equation predict?
the allelic frequency of a gene from one generation to the next will be constant, if there is no:
- migration
- mutation
- selection for a particular allele
- a large population
- random fertilisation of gametes
sex linked characteristics
- Y caries few non sex gene
- X carries sex gene and other body characteristics
- female needs two copies of a recessive allele for it to appear on phenotype, males only need 1
- mother- son inheritance, skip a gen
- if son affected, mother is not then not sex linked (if dominant allele)
- if daughter affected and father not, then not ressessive
linkage groups
set of genes on same chromosome that tends to be inherited together
state three causes of genetic variation
- mutation
- crossing over
- independent segregation
- random fusion of gametes
how do multiple alleles of a gene arise?
mutation
at different positions in the gene
in genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios. Suggest two reasons why.
- fertilisation of gametes is random
- small sample size
- epistasis
- crossing over
what is meant by a recessive allele?
only expressed when homozygous
define gene linkage
genes/loci on same chromosome
define epistasis
allele of one gene affects/masks the expression of another in the phenotype
rules for dom alleles
- affected offspring must have one affected parent
- unaffected parents = unaffected offspring
- if both affected and unaffected offspring, then heterozygous
rules for recessive alleles
unaffected offspring only hav
e unaffected parents
what is meant by the term phenotype
expression due to genetic constituion and interaction with the environment
EXPLAIN HOW asingle base sub causes a change in the structure of a polypeptide
change in sequence of amino acids
change in hydrogen/inic/disulfide bonds
alters 3 structure
