IV-Genes, environment and inheritance. 1- Understand the respective conditions i

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IV-Genes, environment and inheritance. 1- Understand the respective conditions in which there are deviations from Mendelian genetics 2- Understand extranuclear inheritance. 3- Understand the importance of sexual reproduction in evolution. 4- Understand the genetics of sex determination in human. 5- Understand the genetics of sex determination in other animals covered in this chapter a. Platypus; b. Snakes and birds; c. Mole voles. 6- Understand environmental sex determination in the species covered in this chapter. a. Marine tubeworms b. Bonellia; c. Flatworms; d. Alligators c. Tropical reef fish. 7- Understand the influence of the environment on the phenotype. V- Types of natural selection 3- Understand the stages of life at which natural selection can act. 4- Understand the importance of both differential survival and differential reproductive s success in the evolutionary theory Understand the different types of selection. a. Stabilizing selection; b. Directional selection; c. Disruptive selection; d. Canalization; c. Sexual selection; f. Group selection; 5- i. Altruism ii. Kin selection; ili. Eusociality; VI-Natural selection, phenotypes and genotypes tion of species (the Red Queen hypothesis) 8- Understand the importance of co-evolu 9- Understand the effect of developmental constraints on evolution. 10-Understand the concept of phenotypic plasticity and its importance in 11- Understand genetic assimilation. 12- Understand balance polymorphism: a. Heterozygous advantage b. Bastesian mimicry c. Müllerian mimicry

Explanation / Answer

IV

1. In some cases, expression of the dominant gene is incomplete or partial. Thus, in a cross involving such genes, there is incomplete dominance.

2. Extranuclear inheritance or cytoplasmic inheritanceis the transmission of genes that occur outside the nucleus. It is found in most eukaryotes and is commonly known to occur in cytoplasmic organelles such as mitochondria and chloroplasts or from cellular parasites like viruses or bacteria.

3. Consequently, a sexually reproducing parent transfers only 50 percent of its genetic material to each offspring. However, scientists agree that the most important advantage of sexual reproduction is the variation produced by the continual recombination of sex cells to create unique individuals.

4. It is the Y chromosome that is essential for the development of the male reproductive organs, and with no Y chromosome, an embryo will develop into a female.

5. Mammal XY and reptile ZW systems evolved independently from a common ancestor. Nearly all vertebrates have separate males and females, but sex is determined in different ways. Many fish and reptile species use an environmental cue, commonly temperature, to trigger male-determination (environmental sex determination or temperature sex determination). In other fish and reptile species, as well as in all amphibians, birds, snakes and mammals, sex is genetically determined (genetic sex determination). Amongst species using genetic sex determination, some are male heterogametic that is, the male is heterozygous at a sex determining locus while others are female heterogametic. Male heterogametic species have XX females and XY males, whereas female heterogametic species have ZW females and ZZ males

6. In many species, sex determination is genetic: males and females have different alleles or even different genes that specify their sexual morphology. In animals this is often accompanied by chromosomal differences, generally through combinations of XY, ZW, XO, ZO chromosomes, or haplodiploidy.

7.Phenotype is the observable physical or biochemical characteristics of an individual organism, determined by both genetic make-up andenvironmental influences, for example, height, weight and skin colour.

V. Types of natural selection

3. Natural selection can act on any heritable phenotypic trait, and selective pressure can be produced by any aspect of the environment, including sexual selection and competition with members of the same or other species.

4. This process of differential survival and reproduction is known as natural selection. Non-genetic changes that occur during an organism's life span, such as increases in muscle mass due to exercise and diet, cannot be passed on to the next generation. The term "differential reproductive success" refers to the difference between individuals in a given generation and how many offspring they are able to leave.

5. a) Stabilizing selection: Stabilizing selection is the opposite of disruptive selection. Instead of favoring individuals with extreme phenotypes, it favors the intermediate variants. It reduces phenotypic variation and maintains the status quo.

b) Directional selection: In population genetics, directional selection is a mode of naturalselection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype.

c) Disruptive selection: Disruptive selection, also called diversifying selection, describes changes in population genetics in which extreme values for a trait are favored over intermediate values. In this case, the variance of the trait increases and the population is divided into two distinct groups.

d) Canalization: Canalisation (genetics), a measure of the ability of a genotype to produce the same phenotype regardless of variability of its environment.

e) Sexual slection: natural selection arising through preference by one sex for certain characteristics in individuals of the other sex.

f) Group Selection: Group selection refers to the idea that naturalselection sometimes acts on whole groups of organisms, favoring some groups over others, leading to the evolution of traits that are group-advantageous

Altruism: - disinterested and selfless concern for the well-being of others.

Kin-Selection:- natural selection in which an apparently disadvantageous characteristic (especially altruistic behaviour) increases in the population due to increased survival of individuals genetically related to those possessing the characteristic

Eusocial: denoting social organisms (e.g. the honeybee) in which a single female or caste produces the offspring and non-reproductive individuals cooperate in caring for the young.

VI Natural selection, phenotypes and genotypes

8. Two Types of Coevolution. Coevolution is common among organisms participating in a mutual interaction. In mutualism, both the organisms benefit from each other. When coevolution occurs among mutually benefiting species, it is called mutualistic coevolution

9. Developmental constraints (defined as biases on the production of variant phenotypes or limitations on phenotypic variability caused by the structure, character, composition, or dynamics of the developmentalsystem) undoubtedly play a significant role in evolution.

10. Plasticity is usually thought to be an evolutionary adaptation to environmental variation that is reasonably predictable and occurs within the lifespan of an individual organism, as it allows individuals to 'fit' their phenotype to different environments.

11. Genetic assimilation is a process by which a phenotype originally produced in response to an environmental condition, such as exposure to a teratogen, later becomes genetically encoded via artificial selection or natural selection.

12. Balanced polymorphism is a situation in which two different versions of a gene are maintained in a population of organisms because individuals carrying both versions are better able to survive than those who have two copies of either version alone.

Heterozygous Advantage: A heterozygote advantage describes the case in which the heterozygousgenotype has a higher relative fitness than either the homozygous dominant or homozygous recessive genotype. A well-established case of heterozygote advantage is that of the gene involved in sickle cell anaemia.

Batesian Mimicry: Batesian mimicry is a form of mimicry where a harmless species has evolved to imitate the warning signals of a harmful species directed at a predator of them both. It is named after the English naturalist Henry Walter Bates, after his work on butterflies in the rainforests of Brazil.

Mullerian Mimicry: Mullerian mimicry is a natural phenomenon in which two or more distasteful species, that may or may not be closely related and share one or more common predators, have come to mimic each other's warning signals

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