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Twin studies[ edit ] A number of twin studies have attempted to compare the relative importance of genetics and environment in the determination of sexual orientation. Self reported zygositysexual attraction, fantasy and behaviours were assessed by questionnaire and zygosity was serologically checked when in doubt.
Other researchers support biological causes for both men and women's sexual orientation. Women showed a statistically non-significant trend to weaker influence of hereditary effects, while men showed no effect of shared environmental effects. The use of all adult twins in Sweden was designed to address the criticism of volunteer studies, in which a potential bias towards participation by gay twins may Biology genetics notes the results; Biometric modeling revealed that, in men, genetic effects explained.
Corresponding estimates among women were. Although wide confidence intervals suggest cautious interpretation, the results are consistent with moderate, primarily genetic, familial effects, and moderate to large effects of the nonshared environment social and biological on same-sex sexual behavior.
Nonetheless, it is possible to conclude that, given the difference in sexuality in so many sets of identical twins, sexual orientation cannot be attributed solely to genetic factors.
Gringas and Chen describe a number of mechanisms which can lead to differences between monozygotic twinsthe most relevant here being chorionicity and amniocity. Monoamniotic twins share a hormonal environment, but can suffer from the 'twin to twin transfusion syndrome' in which one twin is "relatively stuffed with blood and the other exsanguinated".
In Dean Hamer and colleagues published findings from a linkage analysis of a sample of 76 gay brothers and their families. Gay brothers who showed this maternal pedigree were then tested for X chromosome linkage, using twenty-two markers on the X chromosome to test for similar alleles.
This was popularly dubbed the "gay gene" in the media, causing significant controversy. In the full sample they did not find linkage to Xq Significant linkage was also detected in the pericentromeric region of chromosome 8, overlapping with one of the regions detected in the Hamer lab's previous genomewide study.
The authors concluded that "our findings, taken in context with previous work, suggest that genetic variation in each of these regions contributes to development of the important psychological trait of male sexual orientation". Female sexual orientation does not seem to be linked to Xq28,   though it does appear moderately heritable.
In a study population composed of more than participants, Ellis et al. They also found that "unusually high" proportions of homosexual males and homosexual females were Rh negative in comparison to heterosexuals.
As both blood type and Rh factor are genetically inherited traits controlled by alleles located on chromosome 9 and chromosome 1 respectively, the study indicates a potential link between genes on autosomes and homosexuality. In the common fruit fly Drosophila melanogasterthe complete pathway of sexual differentiation of the brain and the behaviors it controls is well established in both males and females, providing a concise model of biologically controlled courtship.
Without the gene, the mice exhibited masculine sexual behavior and attraction toward urine of other female mice. Those mice who retained the gene fucose mutarotase FucM were attracted to male mice. According to Dean Hamer and Michael Bailey, genetic aspects are only one of the multiple causes of homosexuality.
The research consisted of 1, homosexual men and 1, heterosexual men. Levay's research suggested that the hypothalamus of gay men is different from straight men. The researchers found another gene, named "thyroid stimulating hormone receptor" TSHR on chromosome 14 which dna sequence is different also for gay men.Principles of Genetics Mendel’s studies have provided scientists with the basis for mathematically predicting the probabilities of genotypes and phenotypes in the offspring of a genetic cross.
But not all genetic observations can be explained and predicted based on Mendelian genetics. IB Biology notes on Membranes. Membranes Draw and label a diagram to show the structure of membranes.. Figure - Annotated drawing of a cell membrane. Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes..
Phospholipid molecules make up the cell membrane and are hydrophilic (attracted to water) as well as. Page lists activities and worksheets related to a unit on genetics and heredity, designed for high school level biology, worksheets are printable. A biology resource site for teachers and students which includes lesson plans, student handouts, powerpoint presentations and laboratory investigations.
Molecular genetics is the field of biology that studies the structure and function of genes at a molecular level and thus employs methods of both molecular biology and genetics. The study of chromosomes and gene expression of an organism can give insight into heredity, genetic variation, and kaja-net.com is useful in the study of developmental biology and in understanding and treating.
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