3.7.1 Inheritance Flashcards
What is a genotype?
The genetic make up on an organism. It describes ALL the alleles that an organism has.
What is an allele?
A different version of the same gene
What is a gene?
Short section of DNA made up of nucleotide bases, which codes for a specific order of amino acids which makes a protein.
What is a phenotype?
Observable characteristics due to environment and genetic makeup
What is a homologous pair?
A pair of chromosomes - maternal and paternal. Also known as a bivalent
What is a recessive allele?
An allele whereby you need 2 copies of it (homozygous) to express that characteristic. Its not expressed if the dominant allele is present.
What is a dominant allele?
You only need ONE copy of this allele to express this characterisitic
Homozygous dominant means?
Two dominant alleles present (in the genotype)
Homozygous recessive means?
Two recessive alleles present (in the genotype)
Heterozygous means?
One recessive and one dominant allele present (in the genotype)
A codominant allele is?
Where both alleles contribute/expressed in the phenotype
What are multiple alleles?
Where you have more than two alleles for a particular gene
In a diploid organism (human) how many chromosome pairs are there?
23
In meiosis what happens to the diploid number?
It becomes haploid - halves
Characteristics are determined by your allele combinations, how many alleles for each characteristics end up in the gamete?
1
Pure breeding plants are said to be
Homozygous
If there are 30 boys and 15 girls what is the ratio?
2:1
Why are actual ratios observed often not exactly the same as theoretical ratios in genetics?
Because fertilisation of gametes occurs by chance - each time a gamete is fertilised, it is an independent event of what has gone before it. Also, can be due to crossing over
How can you try and get theoretical ratios to match observed/actual ratios?
Increase sample size so its more representative
If you were to perform a statistical test on Mendelian genetics and you where looking at observed and expected ratios - what test would you do and why?
Chi Squared - because you are comparing observed and expected values and determining if there is a statistical difference
Suppose you obtained a chi squared value of 5 and the critical value was 5.99 (2dof) - what can you conclude?
Because the chi squared value is SMALLER than the critical value - you accept the null hypothesis and there is greater than a 5% probability that the difference in the results are due to chance. There is no significant difference.
Suppose you obtained a chi squared value of 8 and the critical value was 5.99 (2dof) - what can you conclude?
Because the chi squared value is LARGER than the critical value - you reject the null hypothesis and there is less than a 5% probability that the difference in the results are due to chance. There is a significant difference.
What is the difference between monohybrid inheritance and dihybrid inheritance?
Monohybrid is the inheritance of a SINGLE gene, dihybrid is the inheritance of TWO genes (that are located on different chromosomes)
Give an examples of a characteristic that involves multiple alleles
Blood groups - IA, IB and IO
Identify the chromosomes that determine sex
Sex Chromosomes - X and Y
Female sex chromosomes are
XX
Male Sex Chromosomes are
XY
Which sex determines the sex of the child?
Males - as females always pass on a X in their gametes.
What are the criteria must be met to perform a chi squared test?
sample size is large (20+), data falls into catergories (green, yellow), compare experimental observations with theoretical ones (expected)
When performing a statistical test what must you always state before you carry the test out?
Null hypothesis - this states that there is ‘no significant difference’….
What is are autosomes?
The 22 pairs of chromosomes (not the sex chromosomes)
What is meant by autosomal linkage?
This is the situation where two (or more) genes are carried on the SAME chromosome
For autosomal linkage genetic crosses, what do we have to assume?
That there is no crossing over, therefore all the genes remain together during meiosis
What is epistasis?
This is when the allele of one genes affects or masks the expression of another allele in the phenotype.
If the ratio of 9:3:3:1 is not achieved when the individuals of the F1 generation are crossed what does this suggest about inheritance?
It is NOT your typical dihybrid cross and there is some other explanation - e.g. epistasis, linkage
locus is
position on a chromsome
a carrier is
a person carrying an allele not expressed in the phenotype
what does diploid mean?
having 2 sets of chromosomes (pairs)
what does haploid mean?
having 1 set of each chromosome
dominant alleles are represented by using…
a capital letter
recessive alleles are represented by using …
lower case letter
monohybrid inheritance looks at..
the inheritance of a characteristic controlled by a single gene
In blood groups which allele is recessive?
O
In blood groups which alleles are codominant?
A and B
A person with an A and a B allele for blood group would have what blood type?
AB
A person who inherits a B allele off one parent and an O allele off another would have what blood type?
B
dihybrid inheritance looks at
the inheritance of 2 genes located on separate chromosomes
In a monohybrid cross what phenotypic ratios do you get in the F2 generation?
3:1
In a dihybrid cross what phenotypic ratios do you get in the F2 generation?
9:3:3:1
In a codominant cross what phenotypic ratios do you get in the F2 generation?
1:2:1
Sometimes you do not get expected phenotypic ratios because of …
sex linkage, autosomal linkage, epistasis, small sample size
Name a sex linked condition
haemophilia, colour blindness
A characteristic is said to be sex linked when..
its carried on the sex chromosome
How can you tell from looking at the family tree if a condition is sex linked?
males will only be affected
Why are males more likely to express recessive traits of sex linked conditions
only have 1 copy of X - so a recessive trait would be expressed
How are the X and Y chromosomes different?
X bigger (more genes), Y smaller (fewer genes)
no homologous portion on the Y
During autosomal linkage what happens?
genes are inherited together
When might genes that are on the same chromosome NOT be inherited together?
if crossing over during meiosis 1 has occurred
The closer together 2 genes are the more closely linked they are - why?
because cross over is less likely to split them up
what does the null hypothesis always start with?
there is no significant difference….
If 2 genes are said to be linked what does this mean?
they are on the same chromosome
a gene pool is
ll the alleles (of all of the genes) in a population
what is meant by the genome
all the DNA in a cell/organism
