patterns of inheritance and variation Flashcards
what is a gene
.a sequence of bases on DNA molecules that codes for a protein
.results in a characterisitc
what is a allele
different versions of the same gene that code for variants of a characteristic
e.g. B = brown eyes
b = blue eyes
what is a genotype
an organisms genetic makeup(alleles)
what is a phenotype
an organisms physical charateristics which are determined by its genotype and environment
what is a locus
specific position of a gene on a chromosome
what is homozygous
an organism with two identical alleles for a trait
TT or tt
what is heterozygous
an organism with two different alleles for a trait
Tt or tT
what is monohybrid(monogenic) inheritance
when one gene from parents are transmitted to their off-spring
how to use punnett squares
.they represent a monohybrid cross in a grid format
.state the phenotypes
.assign the genotypes of parents (e.g. homozygous dominant)
.state the gametes of the parents (G or g)
.use punnett square to show all possible genotypes
.state the proportion of each genotype as a ratio/percentage
.state the proportion of each phenotype
what is codominance
.when two different alleles are equally expressed in an organisms phenotype
(neither are dominant or recessive)
.leads to a phenotype which is a mix of both alleles
how to show codominance in genetic diagrams
.uppercase letter shows the gene e.g. C for colour for a trait
.superscript uppercase letter indicate alleles(C^W and C^R for white and red)
w
what are multiple alleles
genes that exist in more than two allelic forms
.increases phenotypic diversity
how are ABO blood groups considered as multiple alleles
.controlled by I gene
.alleles I^A and I^B are codominant
.allele I^O is recessive
inheritance of sex in humans
the 23rd pair of chromosome determines the sex of the person and differ between sexes
X is found in both
Y is found in males
female gamete contains XX
male gamete contain XY
what is sex linkage
.genes on the X and Y chromosomes are called sex-linked genes
.X carries majority of the genes as it is larger = makes most sex-linked genes X-linked
.this mean that recessive alleles on X chromosome appear more in male phenotype (e.g. X^h Y) as the Y allele cannot act as a dominant allele
facts about the inheritance of haemophilia
.mainly affects males as males dont have a second X chromosome to mask faulty allele
.dosen’t oftern affect females
.always inheritied from the mother in males
.mostly inheritied by carrier mothers
.affected fathers can only pass on to daughters
what is a dihybrid cross
shows the inheritance of two genes controlling separate characteristics
how can dihybrid cross help
.they determine if genes are linked
.locate genes on specific chromosomes
.calculated expected phenotypic ratios in subsequent generations
reasons for deviations from expected ratios
for random fertilisation:
.gamete fusion is a chance process
.small sample sixe can show skewed ratios
for linked genes:
.on the same chromosme so alleles are normally inherited together maintaining the parents original allele combinations in the offspring
.crossing over during meiosis could split the linked genes changing the allele combination
what is autosomal linkage
.autosomes are chromosomes that do not determine sex
.genes on the same autosome called linked genes and are normally inherited together in offspring rather than assorting independentaly
how do autosomal linkage diifer
.non-random association of alleles at different loci
.phenotypic ratios observed in dihybrid crosses are different from expected ones from independent assortment
.partental allele combinations are preserved across generations
how crossing over affects autosomal linkage
.crossing over can separate linked genes
.fewer recombinant offspring tend to be produced
.this indicates less genetic variation being introduced from crossing over for linked genes
.posibility of linked genes to be separated during crossing over is inversely proportional to how close they are on the chromosome
formula for recombination frequency
num of recombinant offspring/ total num of offspring
50% = no linkage
below 50% = some degree of autosomal linkage
lower frequency = close the genes are in the chromosome
criteria for using the chi-squared test (x^2)
.large sample size
.discrete data categories (e.g. heads or tails)
.use raw counts
.comparison of experimental and theortical results
steps for the chi squared test
.predict the expected phenotypic ratios among offspring
.conduct crosses and record the observed ratios
.calculate X^2 statistic
.compare the x^2 value to the critical value at a chosen probability level (5% or 0.05)
if x^2 is higher than critical value at chosen prob level = difference are not due to chance = reject null hypothesis
formula for Chi squared
sum of (O-E)^2/E
O = observed for each phenotype
E = expected for each phenotype
.df = num of phenotype - 1
p = 0.05
what is epistasis
.interaction between genes where one gene affects or masks the expression of another gene
what is a hypostatic gene
a gene which has its expression blocked
what is epistatic gene
gene whose alleles affect the expression of the hypostatic gene
recessive = epistatic gene must be homozygous recessive to block the hypostatic gene
dominant = can actively modify or block the expression of the hypostatic gene
