Unit 6 - Patterns of Inheritance Flashcards
Genotype
Allele combinations possessed by an organism leading to specific phenotypes
Discontinuous variation
Qualitative differences Clearly distinguishable categories (categorical) Monogenic inheritance One/two genes An allele has a large effect
Continuous variation
Quantitative differences Phenotypic diff have a wide range of variation in a pop. (sig affected by environment) Each allele has a small effect Polygenic inheritance Large number of diff genes involved
Monogenic inheritance
One gene w/ 2 or more alleles
Codominant inheritance
Involves more than one dominant allele
Example of multiple allele genetic cross
Blood group
I A
I B
I O
3 ways genetic variation arises from sexual reproduction
IA of homologous chromosomes (M1)
Crossing over
IA of sister chromatids (M2)
random fertilisation of gametes
23rd pair of chromosomes
characteristics
Only pair that varies in shape and size
X - v. large and doesn’t carry genes involved in sexual development
Y - V. small, no genetic info, but carries gene that causes formation of male embryos
Sex linked genes
Characteristics determined by genes carried on X and Y
Why do sex-linked genes affect males
Y is much smaller so only has one copy of the gene, if recessive allele is found on X but no D allele on Y, male will express the recessive trait (usually condition)
Most females will have a D allele present on the 2nd X chromosome so are either normal or a carrier
Examples of sex-linked conditions
Haemophilia - blood clots v. slowly due to a lack of protein blood clotting factor
Red-green colour blindness
Dihybrid cross
Used to show inheritance of 2 diff characteristics, 2 genes at diff loci, >2 alleles on each
Expected results of a heterozygous dihybrid cross
9:3:3:1
Why may the actual ratio vary from expected
Fertilisation is random
If there is no crossing over, alleles for 2 characteristics will be inherited together if on same chromosome
Autosome
Any chromosome that is not a sex chromosome
Autosomal linkage
2 separate genes are found on the same autosome
Represented by diff letters
Linked genes are inherited together so offspring usually show same combination as parents (certain gametes are more common)
What may prevent linked genes from being inherited together
If they’re separated by chiasmata
Recombinant offspring
Offspring w/ a diff combination of alleles to either parent
Closer genes are located on a chromosome …
Less likely to be separated during crossing over –> fewer recombinant offspring
Recombination frequency
Measure of amont of crossing over that occurs in meoisis
indicating level of linkage
Calculating recombinant frequency
No of recombinant offspring/ total no. of offspring
50% recombination frequency means what
No linkage, genes on separate chromosomes
<50% recombination frequency
Gene linkage and IA has been hindered
Signifies autosomal linkage
Linked genes are inherited together
Crossing over produces few recombinant offspring
Homozygous
Has identical alleles on both chromosome
H0 in chi squared means what
There is no sig. difference between expected and observed values
Degrees of freedom in chi squared
No. of categories - 1
Epistasis
Interaction of genes at diff loci
Genes masking the expression of other genes (not alleles)
Gene regulaion is a example w. reg . genes controlling structural genes
When can epistasis be seen
Multistep reactions
Hypostatic
Gene affected by another gene
Cause the phenotype
Epistatic gene
Gene that affects the expression of another gene; can happen as a result of dominant or recessive alleles
Antagonistic epistasis also called what
Dominant and recessive epistasis