Inheritance Flashcards
adhere to this booklet often to look at the practice questions
define gene
it is a sequence of DNA bases that codes for a specific polypeptide
where are the genes for particular traits found?
they will be found in the same location on the chromosomes (locus) in different individuals of the same species
what are the three main characteristics of a gene?
they can separate and combine
they can mutate
they code for the production of specific polypeptides
what does a diploid individual contain?
contains homologous pairs of chromosomes, one chromosome copy from their mother and one from their father
they therefore have two copies of each gene
define alleles
they are alternative forms of genes occupying a similar locus on homologous chromosomes
what are the three different allele combinations for any one gene?
heterozygous - having different alleles for a given gene (i.e. a dominant and a recessive allele are present together)
homozygous dominant - having two dominant alleles for a given gene
homozygous recessive - having two recessive alleles for a given gene
what is the gene pool?
all the alleles in a population at any one time are called the gene pool
define genotype
the genetic make-up of an individual; all of the alleles that they possess
define phenotype
the observable characteristics of an organism determined by the genotype
in the simplest situations, a particular characteristic is controlled by a single gene with two alleles
therefore, if an organism is homozygous dominant or heterozygous for a particular characteristic; the dominant allele will always be expressed in the phenotype
the phenotype for a homozygous recessive individual would be different
define monohybrid inheritance
it is the inheritance of a single gene, such as that controlling plant height or seed colour
describe Gregor Mendel’s investigation on pea plants
Mendel chose pairs of contrasting characteristics such as tall or dwarf plants, round or wrinkled seeds and yellow and green seeds
he was fortunate that his choice of characteristics were controlled by single genes and were clear cut and easy to tell apart
why are pea plants a useful choice for inheritance experiments?
they are easy to grow
can self or cross fertilise
can produce flowers and fruits in the same year
give the 5 instructions for genetic crosses
look at the parents: are they homozygous or heterozygous
choose suitable symbols for the alleles (unless already provided)
choose the first letter of the contrasting features if possible
use upper case for dominant and lower case for recessive
clearly label the parents; state their phenotypes, genotypes, and state the gametes produced by each
circle the gametes
remember there will only be one allele for a given gene in each gamete
draw a punnet square to cross the gametes
state the phenotypes and genotypes for the offspring results, with ratios
how would Mendel ensure that offspring produced were only from the parents above (page 5 in booklet)?
pollen transferred by hand - receiving flower could be in a bag to prevent further cross-pollination
remove anthers before they mature so no self-pollination
describe Mendel’s first ‘law of inheritance’
the characteristics of an organism are determined by (factors) alleles, which occur in pairs
only one allele of a pair is present in each gamete
describe continuous variation
the characteristic often has a range of values (usually the bell-shaped normal distribution curve)
controlled by a number of genes (polygenic), e.g. if height is influenced by two or more genes, then they have the potential to grow tall
environmental factors have an effect
describe discontinuous variation
the characteristic has distinct categories controlled by a single gene
environmental factors have no effect
state whether these following characteristics are continuous or discontinuous:
tongue rolling
ear lobes attached/unattached
skin colour
height
hair colour
blood type
(in order)
D
D
C
C
C
D
describe the ‘backcross’/test cross method
it is used in genetics to determine whether a particular dominant characteristic observed in an organism is caused by one or by two dominant alleles (heterozygous or homozygous dominant)
the unknown is always crossed with an individual displaying the recessive phenotype
describe pure breeding
two organisms of the same phenotype that, when bred together, produce offspring with the same phenotype (homozygous)
(example on page 8)
what is codominance?
(page 9 in booklet)
is a condition in which both alleles for a gene are expressed when present in a heterozygote
both alleles are written using a capital letter
what is incomplete codominance?
(page 9 in booklet)
where heterozygous individuals produce a phenotype intermediate of the parental phenotypes
the heterozygous condition is somewhere in between
both alleles are written using a capital letter
what is dihybrid inheritance?
(page 10 in booklet)
involves the inheritance of two unlinked genes (genes found on different chromosomes)
independent assortment of these genes produces recombinants (different allele combinations in the gametes)
describe Mendel’s second law (law of independent assortment)
either a pair of alleles may combine randomly with either of another pair
give two key terms of chi-squared
expected - based on ratios gained through genetic crosses
observed - actual ratios
describe the idea behind chi-squared
genetic crosses give expected offspring ratios
however, when the cross is actually carried out the ratio of offspring produced could be different
what does a chi-squared test work out?
if the expected ratio is significantly different from the observed ratio
define null hypothesis
there is no significant difference between the observed and the expected
describe the use of null hypothesis in chi-squared
if there is no significant difference between the observed and expected ratios then we accept our null hypothesis - any difference is down to chance
if there is a significant difference between the observed and the expected then we reject the null hypothesis - other factors must be having an influence
give the steps on how to use the chi-squared equation: χ² = Σ ((O - E)² / E)
(look at pages 14-15 in booklet)
equation can be solved using a table (sometimes you may need to add columns to the table)
once chi-squared value is worked out, we use the chi-squared table to work out if the value is significant or not
the value for the degrees of freedom is one less than the number of categories (i.e. phenotypes) we’ve used aka: no. of phenotypes - 1
we always compare our value to the value at the 5% significance level (shown usually as 0.05) unless the question says otherwise
if the chi-squared value is less than the value in the table, we accept the null hypothesis, therefore any difference is due to chance
if the chi-squared value is greater than the value in the table, we reject the null hypothesis, therefore other factors are influencing
what are the two types of chromosomes?
autosomes - any chromosome that is not a sex chromosome
sex chromosomes - a chromosome concerned in determining the sex of an organism, typically one of two kinds
in humans, they are similar in one sex (f) and dissimilar in the other (m)
out of the 23 pairs of chromosomes in humans, which are autosomes and which are sex chromosomes?
first 22 are autosomes
last pair are the sex chromosomes
