topic 7:inheritance Flashcards
what are homologous chromosomes?
sperm and egg both contribute a set of chromosomes to offspring
known as homologous pairs because they carry the same genes
but are genetically different because of different alleles
total number of chromosomes
46(2n)
diploid
number of gametes in sperm and egg cells
haploid (n)
23
genotype
the genetic constitution of an organism
pheontype
the expression of the genetic constitution and its interaction with the environment
allele
a different form of the same gene
codes for a different version of the same characteristic
arise due to random mutations
dominant allele
always expressed in the phenotype
recessive allel
expressed in the phenotype only in the presence of another identical allele
homozygous
if an organism carries 2 identical copies of the same gene
e.g. AA,aa
heterozygous
if an individiual possess 2 different copies of the same gene
e.g. Aa
how are alleles represented?
using letters
capital letters represent dominant alleles
recessive for the same gene represented by lower case of same letter
what is monohybrid inheritance?
the inheritance of a single characteristic (gene) controlled by different alleles
ratio of phenotypes in monohybrid inheritance?
3:1 if heterozygotes are crossed
what is a Punnett square?
square grid to present results of genetic crosses by showing genotype of offspring
always draw circles round gametes
what is dihybrid inheritance?
inheritance of 2 characteristics(genes) controlled by different alleles located on different chromosomes
what are dihybrid crosses used for?
to investigate the simultaneous inheritance of 2 different characteristics
there is a pattern of offspring produced in dihybrid crosses, as there is in monohybrid inheritance. who first discovered these patterns?
Gregor Mendel in the 19th century
he was a monk famous for carrying out thousands of genetic crosses on pea plants
how do you write out the parental gametes in dihybrid inheritance?
one allele from each pair in each gamete
in organisms there are 2 copies of every gene, but the gametes will have one of the copies for every single gene
the ration of the F2 generation in any dihybrid cross
9:3:3:1
dominant:gene 1 d, gene 2 r: gene 1 r,gene 2 ;recessive
what is a test cross?
a method used to work out the unknown genotypes of individual organisms
when is a test cross carried out?
between an individual of unknown genotype showing a dominant phenotype and individual of recessive phenotype
what is codominance?
occurs when neither allele for a characteristic is recessive so they are Both expressed
what is incomplete or partial codominance?
an intermediate phenotype can be produced in some circumstances when the offspring is heterozygous for both dominant alleles
both are expressed
what does it mean to have multiple alleles?
different versions of the same gene on the same locus
more different alleles means more different phenotypes
what is sex-linked inheritance?
alleles for sex linked characteristics are located on the sex chromosomes
there are 23 pairs of chromosomes,22 are autosomes and the last 2 are the sex chromosomes
there are several characteristics coded for by alleles on these
the pattern of how these are inherited is sex-linked inheritacne
what gametes do females produced
all gametes will have x chromosome
what gametes do males produce
one X and one Y
half gametes with each
why are males more likely than females to show recessive phenotypes for sex linked genes?
males only have one X chromosome so often only have one allele for sex-linked genes
because they only have one copy, they express the characteristic of this allele even if its recessive
what are X linked conditions?
genetic diseases and conditions caused by faulty alleles located on the X chromosome
includes colourblindness and Haemophilia
why cant males be carriers of recessive conditions?
they only have one X chromosome so they either have it or don’t
when will a female be affected by a recessive condition?
if father is a recessive allele, and mother is a carrier of has it herself
if mother is affected, all sons will have it and daughters all be carriers
what is a pedigree chart?
an alternative method for presenting information about inheritance
genetic pedigree diagrams show how an inherited trait runs in a group of related individuals
what does a pedigree chart show?
genotypes and phenotypes in different generations
gives information on how allele are inherited
how do you answer a question including a pedigree chart?
- think of it like a puzzle
- work out genotypes you are sure of and write them down next to the individual
-this helps to identify patterns between parent and offspring
how are females represented in pedigree charts?
circles
how are males represented in pedigree charts?
squared
how are carriers/heterozygotes represented in pedigree charts?
shape will be half one colour, half other
how does a pedigree diagram show a recessive allele
if unaffected parents give rise to an affected individiual
what is autosomal linkage
if 2 or more genes are carried on the same autosome
autosomes are the remaining 22 chromosomes that arent sex linked
what are unlinked genes?
genes located on different chromosomes
linkage groups
a set of genes on different loci on the same gene that tend to be inherited together
except for crossing over
what happens to linked genes in meiosis?
assuming no crossing overall linked genes stay together during meiosis so pass into the gametes and offspring together and don’t segregate
what happens to genes on different chromosomes?
independent segregation can occur as genes are carried on different pairs of homologous chromosomes
what happens if crossing over occurs
variety of gametes increase
when is it easier for crossing over to occur?
when genes are far apart on a chromosome
when is it harder for crossing over to occur?
when different genes are close to each other
what does it mean if chromosomes are recombinant?
any point the genes have switched and have exchanges genetic material
why is the chi-squared test used?
to look at the differences between categorical variables in populations
basically, what you expect vs what you see
what is the null hypothesis?
the opposite of what you expect the experiment to show
it is rejected or accepted
conclusion from the result of the chi-squared test if it is LESS than the critical value
the chi-squared is less than the critical value which means there is a greater than 5% probability that the results occurred by chance
we can accept the null hypothesis
there is no significant difference between observed and expected
w
conclusion from the result of chi squared if it is GREATER than the critical value?
if it is greater than the critical value it means there is a less than 5% probability that results occurred by chance
reject null hypothesis
there is a significant difference between observed and expected
define epistasis
the influence of one gene on the expression of another
what does epistasis result in
a combination of genotypes in a hierarchy with each allele more dominant than another
leads to a variety of different phenotypes
