Related Experiment Video
Updated: Jul 19, 2026

Determining the Egg Fertilization Rate of Bemisia tabaci Using a Cytogenetic Technique
Published on: April 1, 2019
Sex ratio at birth, polygyny, and fertility: a cross-national study
1Nbarber@IME.net
Abstract:
The sex ratio at birth may reflect frequency of intercourse that affects the timing of conception. If so, cross-national variation in polygyny and fertility might account for country differences in secondary sex ratios. Consistent with the timing of intercourse hypothesis, the birth sex ratios of 148 countries declined with total fertility rates and polygyny intensity, and increased with contraception use in correlational analysis. Regression analysis confirmed that polygyny was a negative predictor of the sex ratio (and contraception was a positive predictor), with level of economic development and mother's age controlled, but the effects disappeared with total fertility added to the equation. The sex ratio evidently declines with increases in fertility because more children are born at a later birth order when frequency of intercourse is lower.
Related Concept Videos
The Ratio of X Chromosome to Autosomes
Normal male Drosophila has a ratio of one X chromosome to two sets of autosomes. In contrast, normal female Drosophila...
Testing a Claim about Population Proportion
There are two methods of testing a claim about a population proportion: (1) Using the sample proportion from the data where a binomial distribution is approximated to the normal distribution and (2) Using the binomial probabilities calculated from the data.
The first method uses normal distribution as an approximation to the binomial distribution. The requirements are as follows: sample size is large...
Chi-square Analysis
The chi-square test was developed by Pearson in 1990.
The first step of performing a Chi-square analysis is to establish a null hypothesis, which assumes that there is no real...
Trihybrid Crosses
Some of Mendel’s crosses examined three pairs of contrasting characteristics. Such a cross is called a trihybrid cross. A trihybrid cross is a combination of three individual monohybrid crosses. For example, plant height (tall vs. short), seed shape (round vs. wrinkled), and seed color (yellow vs. green).
The F1 generation plants of a trihybrid cross are heterozygous for all three traits and produce eight gametes. Upon self-fertilization, these gametes have an equal chance to...
Natural Selection and Mating Preferences
Females, due to their biological roles in conception, pregnancy, and nursing, inherently...
Infertility in Males

