Genetic sex determination, Slides of International Law

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Sex

Determinatio

n

John Angelo Q. Escuadro

Contents Introduction

• Definition of Sex Determination
• Importance of Understanding Sex Determunation Sex determination Systems
• Genetic sex determination (GSD)
• Environmental Sex Determination(ESD)
• Maternal Sex Determination (MSD)
• Mixed Sex Determination Disorders •^ Disorders of sex development Conclusion •^ Video recap

Introduction In mammals, including humans, the most common form of sex determination is based on sex chromosomes. Typically, males have one X and one Y chromosome (XY), while females have two X chromosomes (XX). The presence or absence of the Y chromosome determines whether an individual develops as male or female.

Introduction In some species, such as birds, reptiles, and some fish, sex determination can be influenced by environmental factors, such as temperature. In these cases, the sex of the organism is not determined by its genetic makeup but rather by external conditions during

Genetic Sex Determination (GSD) Genetic sex determination system is also recognized as genotypic sex determination, and the development of an individual as male or female is triggered by the presence or absence of one or more genes or chromosomal segment or the entire chromosomal complement. These gene/s or chromosome/s is responsible for the primary and secondary sexual characters associated with each sex. Indeed, genes responsible for the development of male or female sex are located on a single pair of

Genetic Sex Determination (GSD) In both sexes, they occur distinctly and are characterized by specific genes or by a different allelic constitution at homologous loci. The evolution of separate sexes (male and female) is the result of the evolution of anisogamy that is, sexual reproduction by the fusion of dissimilar gametes. The hermaphroditism/gynandromorphism (male or female sex organs within an individual) is common phenomenon in most of flowering plants (more than 90%), whereas it is a very rare phenomenon in

Chromosomal SDS In chromosomal sex determination systems, male and female individuals differ from each other by either in morphology or in a number of one pair of chromosomes these are known as sex chromosomes or allosomes or heterochromosomes, which are dissimilar to the normal chromosomes (autosomes). On the basis of structure, there are two types of sex chromosomes such as: i) homomorphic —both X and Y chromosomes are structurally similar and ii) heteromorphic —both X and Y chromosomes are distinct morphologically. In diploid species, where male or female individual produces different types of gametes is known as heterogametic sex , whereas individual producing similar kind of gametes is known as homogametic sex.

S.N.

Chromosomal mechanism Male Female Example (Animals) Example (Plants)

XX (female) and XY (male) Heterogametic (XY) Homogametic (XX) Humans, mice, Diptera, Hemiptera, Coleoptera, most common in animals Asparagus, Spinach, Hemp, White Campion, Sorrel, Humulus

XX (male) and XY (female) or ZZ and ZY system Homogametic (XX) Heterogametic (XY) Birds, silkworm Maidenhair tree, California poplar, Wild strawberry

XX (female) and X0 (male) Heterogametic (X0) Homogametic (XX) Grasshopper, protenor, Orthopteran insects

X0 (female) and XX (male) Homogametic (XX) Heterogametic (X0) Insects such as Fumea

Genic Sex Determination Sex determination is governed by separate genes or alleles present on specific locus of the chromosomes of both males and females. In this system, sex determination is in control of distinct alleles rather than sex chromosomes; therefore, such a system may also refer to as a multiple allele sex determination system. In case of polygenic sex determination system, a set of the factors (genes) distributed on several chromosomes were involved and have masculinizing or feminism effects and collectively,

Genic Sex Determination Genic balance theory (GBT) was given by Calvin Blackman Bridges (1921) for sex determination in Drosophila melanogaster (2n = 2x = 8). In Drosophila , instead of XY sex chromosome, sex is determined by the genic balance or sex index ratio between X-chromosomes and autosome genomes (sets). Sex index ratio = No. of X chromosomes X No. of autosomal sets A In Drosophila, Y chromosome is heterochromatic. Thus, it is not active in sex determination. However, gene for male fertility is located on Y chromosome and Y chromosome also plays a major role in spermatogenesis and development of male reproductive organ. Hence, Y chromosome is essential for restoring male fertility. The gene of femaleness is located on X-chromosome and gene associated with

Haplodiploidy Haplodiploidy is most commonly used in insects of Order-Hymenoptera (honey bees, ants, and wasps) and Thysanoptera (thrips) for sex determination. Sex determination takes place by sets of chromosomes of an individual receives. Two sets of chromosomes (diploid) tend to female and one set (haploid) tends to male sex formation. For example, in honey bee male individual ( i.e. , drone) formed from unfertilized egg cells ( i.e. , haploid). Thus, male develops from the process of parthenogenesis and called as arrhenotoky (where haploid egg cell develops males rather than females through parthenogenesis). However, female (queen and worker bees) develops from diploid egg cells ( i.e. , fertilized egg cell).

Haplodiploidy Byes and coworkers cloned complementary sex-determining ( cds ) locus in the Apis meliifera and proved that this gene is responsible for sex determination cascade of honeybees. Interestingly, firstly, in haplodiploidy system male has no father and cannot have son but it has grandfather and can have grandson. If there is only one queen in a hive, then the relatedness between workers will be ¾ rather than ½, which is common between siblings in other sex determination systems. Thus, it shows more eusocial behavior of honey bees. Secondly, there will be rapid elimination of recessive lethal and deleterious alleles from the population due to haploid genomic nature of males, while dominant lethal and deleterious alleles will be removed every time of their occurrence because of their phenotypic expression in each stage

Unshuffle the words: “lodipalophidy” Answer: haplodiploidy —Halt! —

Who is he? -Calvin Bridges