AP BIO UNIT 5 FRQ

(d) A student claims that if the animal producing the spermatozoa has a mutation in a mitochondrial gene, the probability that any offspring will inherit the mutation is zero. Provide evidence to support this claim.

Mitochondrial DNA is inherited from the maternal side. The mitochondria from the sperm cell including their DNA are degrade after fertilization.

(a) If a particular gene is located on the Z chromosome of this lizard species, describe why a lizard with a ZW genotype has a greater probability of expressing the recessive phenotype for the trait than a lizard with the ZZ genotype does.

If there is no dominant allele for a trait present on a homologous chromosome to mask the recessive allele, the recessive phenotype will be expressed. In this case, the gene is located on the Z chromosome. In an individual with a ZW genotype (female) there is no homologous Z partner, meaning whatever allele is present on the solitary Z chromosome will be expressed.

(c) For each cross, describe whether genetics or temperature determines the sex of progeny produced from eggs incubated at 35°C. For each cross, describe whether genetics or temperature determines the sex of progeny produced from eggs incubated at 24°C.

ZW females X ZZ males at 24°CHalf of the progeny are female. This is likely determined by genetics, as there is a 50/50 chance that the offspring inherit Z or W from mother, and always Z from fatherZZ females X ZZ males at 24°CNone of the progeny are female. This is determined by genetics and temperature, as there are no W chromosomes to pass on to the offspring, meaning all offspring will always be ZZ. At this temperature, that means no ZZ females are produced.ZW females X ZZ males at 35°CAlmost all of the progeny are female. This is likely temperature dependent, because there is equal possibility genetically that offspring could be male or female (inherit W or Z). However, the proportions are different between 24 and 36C, suggesting higher temperatures influence the sex determination. At higher temperatures, ZW and ZZ individuals develop into femalesZZ females X ZZ males at 35°CAlmost all of the progeny are female. This is likely temperature dependent, because there is equal possibility genetically that offspring could be male or female (inherit W or Z). However, at higher temperatures, ZZ offspring develop into females over males.

(d) Predict the effect of increasing global temperatures on the continued presence of the W chromosome in this species of lizard. Scientists claim that, in this species, the Wchromosome is unimportant in sex determination. Instead, proteins that are encoded by a gene or genes on the Z chromosome, and that are maximally expressed only at certain temperatures, are responsible for determining whether embryos will develop as females or males. Use the data to support this claim.

At temperatures over 33C, there is a sharp shift towards female sex of XX individuals rather than males. The W chromosome determines a female, but is not required to do so. Increasing temperatures can also produce females. Therefore, the presence of the W chromosome will likely reduce or even disappear entirely, and the species could just rely on temperature to determine sex.This is supported by the data showing that the presence of the W chromosome is not at all required to develop into a female. If you look at the ZZ x ZZ crosses, you can get all males or or females or a mix completely dependent on temperature, without a W chromosome in sight.

(b) Using the template, construct an appropriately labeled graph, including error bars, to represent the data in Table 1. Based on the data, compare the ZZm×ZWf crosses and the ZZm×ZZf crosses to determine whether there is a significant difference between the two crosses in the fraction of female progeny produced at 24°C, 32°C, and 36°C.

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(a) Describe the process in meiosis that ensures that both maternal and paternal chromosomes are passed on to each spermatozoon.

Meiosis is a type of cell division in which the ploidy of the organism reduces to half in the daughter cells. Meiosis produces 4 daughter cells from 1 parent cell with a different combination of the genetic material but haploid chromosomes. The meiosis process takes place in two stages in which during the first stage, the homologous chromosomes separate reducing the chromosome number to half that is from diploid chromosomes of parents to haploid in daughter. Since the process of meiosis form haploid gametes in both male and female therefore after fertilization restores the diploid chromosomes of the parent cell and form a diploid structure.

(c) In some instances, meiosis of a primary spermatocyte with six chromosomes results in two spermatozoa that contain four chromosomes and two spermatozoa that contain two chromosomes. Predict the most likely cause.

Nondisjunction, it occurs when chromosomes do not align and separate properly prior to the formation of daughter cells, during meiosis I or II. This means that some gametes are missing some chromosomes, and other gametes have extra chromosomes. This is usually lethal, however, some genetic disorders in humans are caused by chromosome nondisjunction. For example, Down's syndrome is caused when the original gamete has an extra copy of chromosome 21, meaning the individual contains 3 copies of chromosome 21.

(b) Explain why the genetic content of individual chromosomes in a spermatozoon most likely differs from the genetic content of individual chromosomes in a primary spermatocyte.

The spermatozoon is a mature cell with having haploid (N) number of chromosome while primary spermatocytes are immature cell with having diploid (2N) number of chromosomes.Spermatozoon - It is the term used to describe the motile mature sex cell of the male organism. These cells have a haploid (N) number of chromosomes. Spermatozoon has one or more swimming flagella with a head-on anterior side. This cell is ready to fertilize with the female egg cell to produce a zygote.Primary spermatocytes - This is a diploid cell having a 2N number of chromosomes. Primary spermatocyte refers to the cell before the process of Meiosis I. After Meiosis I secondary spermatocytes are produced which have half the number of chromosomes.