7 Genetics... : 17 Inherited Change Flashcards
What is the genotype?
Definition
The genetic constitution of an organism.
What is the phenotype?
Definition
The expression of the genetic constitution and its interaction with the environment.
What types of alleles are there?
Regarding how they present in the phenotype.
Dominant, recessive, codominant.
There may be many alleles of a single gene.
In a diploid organism, what may the alleles at a specific locus be?
What combinations are there?
Homozygous or heterozygous.
What is monohybrid inheritance?
The inheritance of a characteristic controlled by a single gene.
What ratio from a Punnet square do you expect with monohybrid inheritance?
3 (dominant):1(recessive)
What is the law of segregation?
In diploid organisms, characteristics are determined by alleles that occur in pairs. Therefore, only one of each pair of alleles can be present in a single gamete.
What is dihybrid inheritance?
Definition
The inheritance of two characteristics determined by two different genes located on different chromosomes.
What ratio from a Punnet square do you expect from dihybrid inheritance?
9:3:3:1
What is the law of independent assortment?
Each member of a pair of alleles may combine randomly with either of another pair.
What is codominance?
Definition
Both alleles are expressed in the phenotype.
What ratio from a Punnet square would you expect from codominance?
No definite answer, maybe 1:2:1.
But if the ratio isn’t 3:1 or 9:3:3:1, consider codominance.
What are multiple alleles?
Definition
When there are more than two alleles of the same gene.
Which type of antibody do each of the blood groups form?
A - forms anti-B antibodies.
B - forms anti-A antibodies.
AB - forms neither antibodies.
O - forms both antibodies.
Which type of antigen do each of the blood groups produce?
I^A - antigen A.
I^B - antigen B.
I^O - neither antigen.
What is a sex-linked characteristic?
When the allele that codes for it is located on a sex chromosome.
Why are males more likely to express recessive phenotypes for sex-linked genes?
The Y chromosome is shorter so carries fewer genes. Most genes on the sex chromosomes are carried by the X chromosome (X-linked genes).
Males only have one X chromosome so only carry one allele for sex-linked genes. Therefore they express the characteristic if the allele is recessive.
They only need to inherit one recessive X allele to express it.
What are autosomal chromosomes?
Chromosomes that aren’t sex chromosomes.
Why are autosomal genes linked?
Genes on the same autosome are linked.
Because they’re on the same autosome, they’ll stay together during independent segregation of chromosomes and their alleles will be passed on to offspring together. (assuming crossing-over doesn’t split them up).
What does it mean if two genes on an autosome are closer together?
They are more closely linked because crossing over is less likely to split them up.
What ratio from a Punnet square would you expect with autosomal linkage?
Because the two autosomally-linked alleles are inherited together, there’s a higher proportion of offspring that injerit their parents’ heterozygous genotype.
Therefore, the phenotypic ratio will be different from expected.
e.g. a dihybrid cross would probably end up with 9:3:3:1 but with autosomally-linked alleles, the ratio could be more like 3:1.
What is epistasis?
Definition
The allele of one gene masks the expression of the alleles of other genes.
What is likely to be the phenotypic ratio in a dihybrid cross involving a recessive epistatic allele?
9:3:4
What is likely to be the phenotypic ratio in a dihybrid cross involving a dominant epistatic allele?
12:3:1
