inheritance Flashcards
what is a mutagen
substances which increase the likelihood of a mutation occurring
when during the cell cycle is a DNA mutation most likely to occur
S phase (during DNA replication)
when during the cell cycle is a chromosomal mutation most likely to occur
mitosis/meiosis
or S phase
state 4 types of chromosomal mutation
duplication
deletion
inversion
translocation
3 points in meiosis where variation van arise
crossing over (prophase 1)
independent assortment (metaphase 1 and 2)
what is the phenotype of an organism influenced by
genes
environment
genetic factors affecting phenotype: MUTATIONS
what is a mutation
types
where do they occur
effects
mutations are random/spontaneous changes to the DNA
these can be point/substitution mutations which may be silent/missense/nonsense OR InDel mutations which lead to frameshift
usually mutations occur in somatic cells so are not inherited
mutations are neutral, beneficial or harmful
the chance of mutations occurring is increased by mutagens
mutations that occur during gamete formation (meiosis) are….
persistent (carried through many generations)
random (can influence selection of organisms)
what is non disjunction
type of chromosomal mutation
describe non disjunction
1 pair of chromosomes/ one of the sister chromatids fails to correctly separate, leaving 1 gamete with an extra chromosome
what are aneuploidy and polyploidy
types of chromosomal mutation
describe aneuploidy
diploid chromosome number is not an exact multiple of the haploid number so chromosomes fail to evenly separate
what is polyploidy
diploid gametes are fertilised by haploid/diploid gametes, increasing the variation in the phenotype
how does sexual reproduction lead to genetic variation within a species
crossing over during prophase 1 of meiosis
independent assortment of homologous chromosomes in metaphase 1 of meiosis
independent assortment of sister chromatids in metaphase 2 of meiosis
haploid gametes produced undergo random fertilisation with gametes derived from a random organism of the same species
describe crossing over in prophase 1
homologous chromosomes pair up/form bivalents
non-sister chromatids exchange DNA, creating new combinations of alleles
describe independent assortment in metaphase 1
homologous pairs randomly align/orientate at equator
creates new allele combinations
describe independent assortment in metaphase 2
sister chromatids randomly align/orientate at equator
creates new allele combinations
describe random fertilisation
any male gamete could fuse with any female gamete
any male organism could mate with any female organism
do environmental factors affect the phenotype or genotype
ONLY the phenotypes (not inherited)
examples of environment affecting phenotype
diet in animals
sunlight
lack of mineral ions
examples of environment affecting phenotype: diet in animals
overfed = becomes obese
underfed= becomes malnourished
examples of environment affecting phenotype: sunlight
humans use sunlight to produce additional melanin
plants turn yellow in dim light
examples of environment affecting phenotype: ;lack of mineral ions
plants turn yellow without magnesium
humans develop deficiencies e.g. scurvy without vitamin C
examples of variation caused solely by the environment
regional dialects
losing a limb or having a scar
examples of variation caused by the environment interacting w genes
- chlorotic plants
- human height
- E.coli (lac operon)
examples of variation caused by the environment interacting w genes: chlorotic plants
yellow in colour due to a lack of sunlight or minerals
examples of variation caused by the environment interacting w genes: human height
all humans are predisposed to a maximum height BUT factors like diet can influence this
examples of variation caused by the environment interacting w genes: E.coli
lac operon contains structural genes which can only be expressed hen there is insufficient glucose (environment)
describe continuous variation
can take any value within. range (has intermediate values)
is polygenic and significantly affected by environment
can be displayed on histogram or line graph
e.g. animal mass, skin colour
describe discontinuous variation
solely caused by genetic influences
e.g. blood group, sex
involves only discrete categories
presented on bar chart/ pie chart etc
what is monogenic (monohybrid) inheritance
single factor crosses where 1 gene controls 1 characteristic
what did Mendel conclude
features are inherited by offspring via gametes
each gamete contains 1 allele… alleles pair up at fertilisation
what is codominance
when both alleles of a gene in the genotype of a heterozygous individual contribute to the phenotype
neither allele completely dominates
examples of codominant inheritance
coat colour in shorthorn cattle (roan= red and white)
where can >2 alleles exist
more than 2 alleles can exist for a given gene but only 2 alleles can exist at a single locus at any one time ( one allele on each gene locus in a homologous pair)
what is multiple allele inheritance
a characteristic for which where are 3 or more alleles in the population’s gene pool
example of multiple alleles
human blood groups (inheritance of ABO)
A and B codominant and both dominant to O
what is sex determined by in humans
one of the 23 pairs of chromosomes (sex chromosomes)
what are the other 22 pairs (not sex chromosomes) called
autosomes
each autosomal pair is fully homologous (same length and contain same genes at same loci)
what are sex chromosomes in males
XY
what are sex chromosomes in females
XX
are X and Y chromosomes homologous
not fully homologous
what are sex-linked genes
characteristics determined by genes carried on the sex chromosomes
which of X and Y chromosomes are smaller
Y chromosome is much smaller than the X chromosome
what does smaller Y chromosome mean
there are a number of genes in the X chromosomes that males only have 1 copy of
this means that any characteristic caused by a recessive allele on the section of the X chromosome, which is missing in the Y chromosome, occurs more frequently in males
this is because many females will also have a dominant allele present in their cells
examples of sex-linked inheritance
haemophilia A
colourblindness
what is haemophilia A
inability of the blood to clot which leads to slow, persistent bleeding
what is haemophilia A caused by
mutation in the gene which codes for the production of Factor 8, a key blood clotting protein
the gene is located on the non-homologous part of the X chromosome (not on Y) and it is therefore sex-linked
why is colourblindness sex-linked
one of the genes involved in coding for a protein involved in colour vision is on the X chromosome, but not on the Y chromosome
a mutated allele of this gene may result in colourblindness: inability to distinguish between red and green
what are dihybrid crosses used to show
the inheritance of 2 different characteristics, caused by 2 genes, which may be located on different pairs of homologous chromosomes (UNLINKED)
each of these genes can have 2 or more alleles
what does the chi-squared test allow for
to compare the expected outcomes with the observed outcomes
it tests whether there is a significant difference between the 2
when is chi squared test used
when data is discrete/discontinuous
large sample size
we have a strong biological theory we use to predict the expected outcomes
data are raw counts (percentages and ratios cannot be used)
there are no ‘zero’ scores in the raw data
degrees of freedom chi squared
number of categories - 1
when are genes said to be linked
when they are carried on the same chromosome (ie same homologous pair)
what is a linkage group
all the genes carried on the same chromosome
these genes will be inherited together unless pieces of chromosomes break and rejoin onto a different chromosome (within the homologous pair) THIS OCCURS IN CROSSING OVER