Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Sex determination is the biological process that determines the development of sexual characteristics in an organism, primarily governed by sex chromosomes (allosomes).
Male Heterogamety: A system where the male produces two different types of gametes. Examples include the type (Humans, ) and the type (Grasshoppers).
In type, males have one and one chromosome plus autosomes (), represented as . Females have two chromosomes, represented as .
In type, males possess only one chromosome (), while females possess two (). The presence of only one determines the male sex.
Female Heterogamety: A system where the female produces two different types of gametes. Example includes the type found in birds. Females are and males are .
Haplodiploid Sex Determination: Observed in honey bees. Males (drones) develop from unfertilized eggs via parthenogenesis and are haploid (). Females (queens/workers) develop from fertilized eggs and are diploid ().
In humans, the chromosome carries the (Sex-determining Region Y) gene, which triggers the development of male gonads. In the absence of , the embryo develops as a female.
📐Formulae
💡Examples
Problem 1:
In a cross between a male grasshopper and a female grasshopper, determine the chromosomal composition of the offspring and the sex ratio.
Solution:
The male is and the female is . Gametes from male: carry , carry no sex chromosome (). Gametes from female: carry . Offspring: (Female) and (Male).
Explanation:
This is an example of male heterogamety where the sperm determines the sex of the offspring based on the presence or absence of the chromosome.
Problem 2:
If a honey bee drone has chromosomes, how many chromosomes will the worker bees and the queen have?
Solution:
Worker bees and queens are females, which are diploid (). Since the drone is haploid (), the females will have chromosomes.
Explanation:
Honey bees follow a haplodiploid system where males are produced from unfertilized eggs () and females from fertilized eggs ().
Problem 3:
A couple has 3 daughters. What is the probability that their fourth child will be a son?
Solution:
The probability is or .
Explanation:
In every pregnancy, the segregation of and chromosomes from the father occurs independently. The fusion of an -carrying egg with either an -carrying sperm () or a -carrying sperm () always has a theoretical ratio of regardless of previous outcomes.