Modified Mendelian Patterns + Sex-Linked Flashcards
Define what is the pattern if heterozygotes of a dominant allele that is black and a recessive allele that is white are grey.
This is incomplete dominance. The dominant allele does not completely hide the recessive one, thus the phenotype of both alleles are expressed in something like an intermediate between the two.
Give examples of incomplete dominance.
Pink flowers, calico cats, oval shape
What symbol should we use to identify the recessive allele in a co-dominant pair?
We need to use a ‘ instead of a small letter because otherwise it would imply a dominance, which there is not in the case of co-dominance.
Define what is the pattern if heterozygotes of a red haired horse and an black haired horse breeding are roan.
This is co-dominance. None of the allele is truly dominant on the other one. Thus, both alleles are fully expresses in the heterozygote offsprings. Erminette chickens are also like that,
What pattern has fractions over 3?
Lethal recessiveness because there is the complete homozygous recessive that cannot live, so we do not count it. Some combinations of alleles can cause the death of an individual. It is usually a recessive allele, but some dominant lethal can occur.
What is the difference between a dominant lethal and a recessive lethal?
The dominant lethal will usually be able to survive a few years before dying and in some cases be able to reproduce.
What if a gene can influence or hide the expression of another gene at another loci?
This is epistasis. For example, there can be the color of the hair. However, if you are bald, you won,t have hair.
What is sex-linked inheritance?
It happens on sex-determining chromosomes (not autosomes). The homologous sex chromosomes differ in size and shape. In humans, they are X and Y. A female will have all of ova with 1 X. In males, 1/2 sperm have 1 X and 1/2 sperm have 1 Y. Some genes only appear on the X…. so if the recessive is in a male, it will be activated more likely.
Which individuals have more X-linked traits?
Males because they only need to have one recessive on the X for it to be expressed.
How can we determine the sex of an offspring? (humans)
XX is female, XY is male. the male will thus pass a Y to all his sons and a X to all his daughters. They do not pass any X to the sons because in this case they would not be sons anymore.
Since a male needs to pass a Y to his sons for them to be sons, with aren’t there more females than males in society?
It does not happen because the combinations of alleles in gametes occur randomly, so you have 1/2 the chances to have a Y in the sperm.
Why do we say that men are hemizygous?
They only have one X-linked allele
What are examples of human X-linked traits?
red-green color blindness, Duchene’s muscular dystrophy, Hemophilia, Male-pattern baldness
What is dosage compensation?
You only need one X chromosome to function, so females inactivate one of the X chromosomes of the embryo but not the same X is inactivated in all cells. So some cats can have orange sports and some blacks depending on which orange gene is activated in which part of its fur.
