patterns of inheritance and variation Flashcards
how does sexual reproduction produce new combinations of alleles
crossing over (during meiosis)
independent assortment (during meiosis)
random fusion of gametes during fertilisation
what is continuous variation, give causes, how data is displayed and examples
a characteristic that has any value within a range
Causes: environment and genetics (usually several genes)
how is data displayed: line graph (quantitative data)
eg: body mass, height, blood glucose concentration
what is discontinuous variation, give causes, how data is displayed and example
a characteristic that has specific (discrete) values (within intermediate values)
Cause: genetics (1 or 2 genes)
how is data displayed: bar graph (usually qualitive data)
eg: blood groups, genetic diseases (i.e. someone has cystic fibrosis or not)
which of following statements represents continuous variation and which represents discontinuous variation (3 marks)
A: a characteristic controlled by 1 gene with 5 different alleles
B: quantitative data presented in a line graph
C: a persons lug capacity
A: discontinuous
B: continuous
C: continuous
identical twins are sometimes separated early in life and air raised in different environments. suggest how these sets of twins can be used to assess causes of variation in human population (3 marks)
genetics are controlled/ identical in twins,
relative influence of genetics and the environment can be analysed,
by monitoring differences that develop between the twins,
idea that a trait shows little variation between twins is likely to be largely determined by genetics (or reverse argument)
complete a genetic cross between a homozygous dominant male (F) and a homozygous recessive (f) female, cystic fibrosis caused by homozygous recessive alleles, what is the probability of offspring having cystic fibrosis
F,F ff
F and f gametes
100% chance of health (100%=Ff)
how do you write alleles for codominant alleles
one letter chosen to represent gene, 2 other letters in written in superscript to represent codominant alleles
give the offspring phenotypes and probability for blood group (codominant alleles) between group A and group B parents
I^b I^o= blood group B
I^A I^O=blood group A
25%: A
25%: B
25%: AB (I^A I^B)
25%: O (I^O I^O)
why are more genes found on the X chromosome
because its larger than Y chromosome
why are males more at risk to suffer sex-linked disease
because they inherit 1 X chromosomes, for recessive conditions, only 1 recessive allele would be required for them to inherit the disease
suggest why more X-linked traits exist than Y-linked traits (2 marks)
X chromosome is larger,
X chromosome contains more genes than the Y chromosome
what are the phenotype ratio of offspring for: Drosophila flies with red eyes (dominant R), recessive allele (r) are white eyes, normal wings (W) dominant allele, vestigial wings are recessive (w)
9: red eyes, normal wings
3: red eyes, vestigial wings
3: white eyes, normal wings
1: white eyes, vestigial wings
what does the chi-squared (x²) compare
actual offspring phenotypes against the expected phenotypic ratios against the expected phenotype ratios
what is autosomal linkage
2 genes that can be located on the same chromosome (non-sex)
what is epistasis
one gene that can affect the expression of another gene
2 genes are said to be linked when they are located on the same autosome, why is this important
linked allele combinations will be inherited together,
only crossing over during meiosis can separate linked allele combinations
the nearer the 2 genes are on a chromosome, the less likely they are to be separated during crossing over
describe recessive epistasis, give example
the epistatic gene (the gene doing the suppression) needs to be homozygous recessive to prevent the expression of other genes
flower colour in salvia
describe dominant epistasis, give example
the epistatic gene needs at least 1 dominant allele to prevent expression of the other gene
fruit colour in summer squash
what does O and E represent in chi-squared test
O= observed numbers
E= expected numbers
humans with red hair tend to have pale skin and green eyes, suggest a reason for this inherit pattern (2 marks)
(autosomal) linkage,
genes on the same chromosome,
allele combinations inherited together
suggest a likely molecular mechanism for
A: recessive epistasis
B: dominant epistasis
(4marks)
A:(epistatic gene produces) enzyme,
homozygous recessive genotype results in no enzyme production,
precursor molecule not converted
B: (epistatic gene produces) inhibitor/suppressor protein,
idea of modifies the other gene product,
affects/ AW transcription
describe stabilising as a form of selection, appearance and example with fur length
selection favours average phenotypes. Alleles that produce extreme traits are eliminated
mean population in the middle of preferred characteristic
mammals have fur length close to mean in an environment with a stable temperature, individuals with short or long fur are less likely to survive and reproduce, these alleles therefore eliminated
describe directional as a form of selection, appearance and example with fur length
occurs when environmental conditions change, selection favours individuals with extreme phenotypes
evolved population to the right or left of original population
fur length will increase if mean temperature decreases in environment, individuals with longer fur (ie those with more extreme phenotypes) will have higher survival rates, similarly mean fur length will decrease if environmental temp increases
what is a genetic drift
a random change in allele frequencies and its effects are more noticeable in small populations. Proportions of alleles in surviving population could be very different to those in original population
