Question

4. From a research paper: “Although sexual reproduction has proven to be highly successful, parthenogenetic all-female populations occur frequently in certain taxa, including the whiptail lizards of the genus Aspidoscelis.”

1. “True parthenogenesis, characterized by the complete absence of male contributions, has been described for various species of reptiles, including whiptail lizards, geckos, blind snakes, and rock lizards.” In your own words, define “parthenogenesis.”

2. Several observations suggest that two closely-related, sexually-reproducing species of lizards interbred to produce the (new) parthenogenetic species. In addition, for these parthenogenetic lizards, heterozygosity across the genome is preserved between generations.

i. Using your understanding of genetics, define “heterozygosity across the genome” (which is a new term for us).

ii. Explain how “hybridization between individuals from distinct species can explain the initially high degree of heterozygosity across the genome.” Hint: Consider whether the alleles contributed by the two ancestral species were likely to be the same or different.

3. “The mechanism that underlies clonal reproduction and fixed heterozygosity has been the topic of much speculation. Most variations of the meiotic program that would produce diploid oocytes by skipping a division or by fusion of a haploid oocyte with a polar body cannot account for fixed heterozygosity unless recombination between homologues is suppressed. On the basis of the exclusion of alternative models and the observation of large numbers of chromosomes in two oocytes from Aspidoscelis uniparens, premeiotic endoreplication of chromosomes was proposed as the most likely mechanism to produce mature oocytes that carry the complete complement of somatic chromosomes and maintain heterozygosity.”

In the above excerpt from the research paper, the authors address three different hypotheses that could explain how a diploid parthenogenetic organism could produce diploid “eggs.” In your own words, what are the three hypotheses?

i. Hypothesis 1:

ii. Hypothesis 2:

iii. Hypothesis 3:

4. Which, if any, of the three hypotheses would preserve heterozygosity across the genome?

Answer 1

Answer: definition of parthenogenesis ---

"Parthenogenesis is a phenomenon of reproduction where embryo developed directly from egg or ovum without performing fertilisation . "

I) Answer:- definition heterozyogosity across the genome --" heterozyogosity across the genome refers to the condition of genetic variation which denotes the degree of variation among nucleotide sequence present in chromosome within same individual obtained from parents ."

II) Answer:- " hybridization between individuals from distinct species can explain the high degree of heterzygousity across the genome" . This is because an individual shows heterozyogosity within their own genomoe sequence obtained from parents itself ( though both parents are from same species) and if the hybridization is done between different species then there is more difference in their nucleotide sequences as their species differ and when they are hybridised they will show higher degree of heterozyogosity across the genome in produced offspring.