2.5 - inheritance Flashcards
what’s a gene
length of DNA on a chromosome that codes for the production of one or more polypeptide chains + functional RNA
define genotype
genetic constitution of an organism
define phenotype
expression of an organisms genetic constitution, combined with/ its interaction within the environment
what’s a locus
fixed position on a DNA molecules occupied by a gene
what’s an allele
different forms of particular gene, found at same locus on chromosome
single gene can have many alleles
define homozygous
having two identical alleles of a gene
e.g: FF or ff
define heterozygous
faving two different alleles of a gene
e.g: Ff
what’s a dominant allele
- allele always expressed
- represented w/ capital letter, e.g: F
what’s a recessive allele
- allele only expressed in absence of dominant allele, only expressed if 2 copies present
- represented w/ small letter, e.g f
what’s meant by codominant alleles
2 dominant alleles that both contribute to phenotype, either by showing blend on both characteristics, or characteristics appearing together
what’s an autosome
chromosome not an X or Y chromosome
what’s a sex chromosome
chromosome determining sex of an organisms
e.g: X + Y chromosomes in humans + other mammals
what’s the F1 generation
first generation of offspring resulting from cross of 2 individuals in parental generation
what’s the F2 generation
second generation of offspring resulting from cross of 2 individuals in F1 generation
define monohybrid inheritance
where one phenotype characteristic is controlled by a single gene
what’s mendels first law of inheritance
- law of segregation
- alleles separate randomly into gametes
- each parent passes one allele to their offspring
what’s mendels second law of inheritance
- law of independent assortment
- alleles of genes assortment independently of other genes during gamete formation
PKU is a recessive condition
two heterozygous parents have offspring
predict proportion of offspring that will have PKU
75% chance of normal phenotype
25% chance of PKU phenotype
what’s the purpose of a test cross
used to determine whether an individual w/ dominant trait is heterozygous or homozygous domiannt
describe how a test cross is carried out
- individual of unknown genotype bred w/ homozygous recessive individual
- offspring phenotypes observed to determine genotype of unknown individual
define dihybrid inheritance
determination of trait by inheritance of 2 genes
what does mendelian inheritance assume
genes involved aren’t linked
what’s meant by sex-linkage
- allele located on one of the sex chromosomes
- expression depends on sex of individual
give example of phenotype which shows sex-linkage
- haemophilia
- DMD
describe haemophilia
- X-liked recessive condition
- results in excessive bleeding + blood too slow to clot
describe DMD
- X-linked recessive condition
- characterised by muscle degeneration + weakness
why are haemophilia + DMD more common in males
they’re X-linked recessive conditions
males only inherit one X chromosome so are more likely to express the gene in their phenotype
what’s linkage
- two or more genes positioned on same autosome
- unlikely to be separated by crossing over during meiosis so often inherited together
what’s the chi squared test
statistical test used to determine whether difference between observed + expected data is due to chance or real effect
can be used to compare expected phenotypic ratios w/ observed ratios
hows a chi squared test performed
- make null hypothesis
- used mendelian ratios to calculate expected numbers
- calculate chi squared value using chi squared equation
- calculate degrees of freedom
- select appropriate significant level (usually 0.05)
- find critical value
- compare chi squared value w/ critical value
- accept or reject null hypothesis
how are degrees of freedom calculated
number of categories minus 1
if chi squared value is greater than or equal to critical value, is null hypothesis accepted or rejected
rejected
what is meant if null hypothesis is rejected
theres a significant difference between the observed + expected results
if chi squared value is less than critical value, is null hypothesis accepted or rejected
accepted
what is meant if null hypothesis is accepted
no significant difference between observed + expected results
results occurred due to chance
what’s a mutation
- alteration to volume, arrangement, or structure of DNA
- may affect single gene or whole chromosome
when do most mutations occur
- crossing over in prophase I
- non-disjunction in anaphase I + II
what’s a gene mutation
- change to at least one nucleotide base in DNA or arrangement of bases
- may occur spontaneously during DNA replication + can be beneficial, damaging, or neutral
give an example of condition caused by gene mutation
sickle cell anaemia
describe sickle cell anaemia
- recessive genetic disorder caused by substitution mutation on chromosome 11
- results in abnormal haemoglobin which distorts red blood cells
what’s a chromosome mutation
change in structure or number of chromosomes, affecting many genes
give an example of condition caused by a chromosome mutation
down syndrome
describe down syndrome
- genetic disorder characterised by delayed development + learning disabilities
- due to non-disjunction, affected individual possesses 3 copies of chromosome 21
what’s chromosome nondisjunction
failure of homologous chromosomes to separate in meiosis I or sister chromatids to separate in meiosis II
results in gametes w/ one extra or less chromosome than normal
what’s a mutagen
chemical, biological, or physical agent that increases rate of gene mutations above normal level
give examples of mutagens
- ionising radiation (gamma radiation, UV, X-rays)
- chemicals (e.g: polycyclic hydrocarbons)
what’s a carcinogen
type of mutagen that causes cancer
what’s an oncogene
mutations of proto-oncogenes that are activated continuously, resulting in uncontrolled cell division
define epigenetics
study of changes in gene expression that aren’t due to alterations in nucleotide base sequence of DNA
how can histone modification affect gene expression
- alteration of histones by addition of methyl, acetyl, or phosphate groups
- increases or decreases gene expression by causing histone to coil more tightly or loosely
how can DNA methylation affect gene expression
- addition of methyl (CH3) group to cytosine bases
- prevents recognition of bases, reducing gene expression
