3.7 Genetics, populations, evolution and ecosystems Flashcards
What is the genotype?
The genetic constitution of an organism
What is the phenotype?
The expression of the genetic constitution and its interaction with the environment
In a diploid organism, the alleles at a specific locus may be either…
Homozygous or heterozygous
Define Homozygous alles
Both alleles at a specific locus on each homologus chromosomes are the same
Define Heterozygous alleles
Both alleles at a specific locus on each homologous chromosome are different
Alleles can be what?
Dominant
Recessive
Codominat
Define a dominant allele
The allele that is expressed in the phenotype in a heterozygous state
Define a Recessive allele
The allele that isnt expressed in the phenotype in a heterozygous state. Only expressed if homozygous recessive
Define a codominate allele
Both alleles for same gene in heterozygous organism contribute to phenotype
What is used to represent a dominant allele
Capital Letter
What is used to represent a recessive allele
Lowercase letter
What are monohybrid crosses used for?
Inheritance of one characteristic controlled by a single gene
What is the common ratio for monohybrid crosses?
3:1
What are dihyrbid crosses used for?
The inheritance of two different characteristics controlled by two different characteristics
What is the common ratio for dihyrbid crosses?
9:3:3:1
When do you use codominace crosses?
Both alleles in heterozygous individuals contribute to the phenotype
What is the common ratio for comindance ratio?
1:2:1
When are crosses involving multiple alleles used?
When a gene may have more than two alleles
What is an example of multiple allele crossing?
Inheritance of human blood groups
When is a gene “sex-linked”?
If its locus is on the sex-chromosomes, X and Y
What properties are ideal for a organism used to study genetic crosses?
A large number of eggs
Small size so reduced costs to store
Easy to identify
Short generation times → reproduce quicker so faster results
Why may the observed ratios calculated not be the same as the expected ratios in inheritance?
Fertilisation is random
Selection advantage or disadvantage
Why are males more likely to express a recessive allele carried on the X-chromosome than females?
Only 1 copy of the gene/allele
Cant be heterozygous
Are males or females more likely to carry genetic disorders?
Males - only have two options:
Healthy - X^HY
Disease - X^h Y
( H - healthy, h - Disease )
When do we use autosomal linkage?
When two genes are carried on the same autosome ( non-sex linked chromosome)
Explain ‘Autosomal Linkage’
Genes on same chromosome so stay together during independent segregation of chromosomes in M1
Linked genes pass into gamete and inherited together
Reduction of possible genotypes in offspring (more offspring with parents genotypes and phenotypes)
Closer together on autosome = more closely linked → crossing over less likely to split
When do we use crosses involving epistasis?
The interaction of non-linked genes where one masks the expression of the other
