Ap Biology Chapter 13

What is crossing over?

Crossing over, genetic rearrangement between nonsister chromatids, occurs during this stage.

What is the life cycle of protists and fungi?

Most fungi and some protists have a third type of life cycle. ○ Gametes fuse to form a zygote, which is the only diploid phase. ○ The zygote undergoes meiosis to produce haploid cells. ○ These haploid cells divide by mitosis to form either unicellular daughter cells or a haploid multicellular adult organism. ○ The haploid adult produces gametes by mitosis. ○ The only diploid stage in these species is a single-celled zygote.

What is a gamete?

A gamete with a single chromosome set is a haploid cell, abbreviated as n. Any sexually reproducing species has characteristic haploid and diploid numbers of chromosomes. ○ For humans, the haploid number of chromosomes is 23 (n = 23), and the diploid number is 46 (2n = 46).

What is a life cycle?

A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism. ○ A life cycle starts at the conception of an organism and continues until the organism produces its own offspring.

What is a zygote?

After fertilization (fusion of a sperm cell and an ovum), genes from both parents are present in the nucleus of the fertilized egg, or zygote.

What is the alignment of hollows on the metaphase plate?

Alignment of homologs on the metaphase plate o During metaphase I of meiosis, pairs of homologous chromosomes (rather than individual chromosomes, as in mitosis) line up on the metaphase plate.

What is an individual that reproduces asexually?

An individual that reproduces asexually gives rise to a clone, a group of genetically identical individuals. ○ Members of a clone may be genetically different as a result of mutation.

What happens as a person develops from a zygote to a sexually mature adult?

As a person develops from a zygote to a sexually mature adult, mitosis generates all the somatic cells of the body. ○ Each somatic cell contains a full diploid set of chromosomes.

What happens at metaphase 2?

At metaphase II, nonidentical sister chromatids sort independently from one another, further increasing the number of genetic types of daughter cells that are formed by meiosis.

What did charles Darwin realize the importance of?

Charles Darwin recognized the importance of genetic variation in evolution. ○ A population evolves through the differential reproductive success of its variant members. ○ Those individuals best suited to the local environment leave the most offspring, transmitting their genes in the process. ○ This natural selection results in adaptation, the accumulation of favorable genetic variations in a specific environment.

What does crossing over produces? What happend in a single crossing over event?

Crossing over produces recombinant chromosomes, which combine genes inherited from each parent. ○ Crossing over begins very early in prophase I, as homologous chromosomes pair loosely along their lengths. ○ Each gene on one homolog is aligned precisely with the corresponding gene on the other homolog. ○ In a single crossover event, specific proteins orchestrate an exchange of the corresponding segments of two nonsister chromatids—one maternal and one paternal chromatid of a homologous pair. ○ In crossing over, homologous portions of two nonsister chromatids trade places. ○ As a result, individual chromosomes carry genes derived from two different parents. ○ For humans, this occurs an average of one to three times per chromosome pair.

What happens in crossing over by combining DNA?

Crossing over, by combining DNA inherited from two parents into a single chromosome, is an important source of genetic variation.

What is attached n meiosis 1 ?

During meiosis I, the sister chromatids are attached along their lengths by protein complexes called cohesins. In mitosis, enzymes remove the cohesins to allow the sister chromatids to move to opposite poles of the cell at the end of metaphase.

What does each chromosome have?

Each chromosome has hundreds or thousands of genes, each at a specific location, or locus, along the length of the chromosome.

What does each zygote have a uniqueness of?

Each zygote has a unique genetic identity. All three mechanisms reshuffle the various genes carried by individual members of a population.

What does every living species have?

Every living species has a characteristic number of chromosomes. ○ Humans have 46 chromosomes in almost all of their cells. Each chromosome consists of a single DNA molecule associated with various proteins.

What happens in fertilization and meiosis alternate?

Fertilization and meiosis alternate in all sexual life cycles. The timing of meiosis and fertilization varies among species. These variations can be grouped into three main types of life cycles. Most animals, including humans, have the first type of life cycle, in which gametes are the only haploid cells. ○ Gametes do not divide but fuse to form a diploid zygote that divides by mitosis to produce a multicellular diploid organism.

What does fertilization restore?

Fertilization restores the diploid condition by combining two haploid sets of chromosomes.

What are gametes?

Gametes, which develop in the gonads (testes or ovaries), are not produced by mitosis. ○ If gametes were produced by mitosis, the fusion of gametes would produce offspring with four sets of chromosomes after one generation, eight after a second, and so on.

What are genes ? What is genetic info?

Genes are segments of DNA. Genetic information is transmitted as specific sequences of the four deoxyribonucleotides in DNA. ○ This process is analogous to the symbolic information of language, in which words and sentences are translated into mental images. ○ Cells translate genetic "sentences" into freckles and other features that have no resemblance to genes.

What is genetics?

Genetics is the scientific study of heredity and hereditary variation.

What happens if the environment changes?

If the environment changes or a population moves to a new environment, new genetic combinations that work best in the new conditions will produce more offspring, and these genes will increase. ○ Formerly favored genes will decrease.

What is a karyotype?

Images of the 46 human chromosomes can be arranged in pairs in order of size to produce a karyotype display. ○ The two chromosomes in a pair have the same length, centromere position, and staining pattern. ○ These homologous chromosome pairs carry genes that control the same inherited characters.

What happens in asexual reproduction?

In asexual reproduction, a single individual is the sole parent to donate genes to its offspring. ○ Single-celled eukaryotes can reproduce asexually by mitotic cell division to produce two genetically identical daughter cells.

What are the 2 chromosomes of a homologous chromosomes/

In contrast, the two chromosomes of a homologous pair are individual chromosomes that were inherited from different parents. ○ Homologous chromosomes appear to be alike, but they may have different versions of genes, called alleles, at corresponding loci.

What is essential in humans and most other organisms?

In humans and most other organisms, crossing over may be essential for the lining up of homologous chromosomes during metaphase I. ○ Chiasmata hold homologs together as the spindle forms in meiosis I.

What happens in a somatic cell?

In humans, each somatic cell (all cells other than the sperm or ovum) has 46 chromosomes. Each chromosome can be distinguished by its size, position of the centromere, and pattern of staining with certain dyes.

How is sister chromatid cohesion is released ?

In meiosis, sister chromatid cohesion is released in two steps. ○ In metaphase I, homologs are held together by cohesion between sister chromatid arms in regions where DNA has been exchanged. ○ In anaphase I, cohesins are cleaved along the arms, allowing homologs to separate. ○ In anaphase II, cohesins are cleaved at the centromeres, allowing chromatids to separate.

what happens in meiosis?

In meiosis, there are two consecutive cell divisions, meiosis I and meiosis II, resulting in four daughter cells. ○ The first division, meiosis I, separates homologous chromosomes. ○ The second division, meiosis II, separates sister chromatids. ○ The four daughter cells at the end of meiosis have only half as many chromosomes as the original parent cell.

What are reproductive cells?

In plants and animals, reproductive cells called gametes transmit genes from one generation to the next.

What happens in sexual reproduction?

In sexual reproduction, two parents produce offspring that have unique combinations of genes inherited from the two parents. ○ Unlike a clone, offspring produced by sexual reproduction vary genetically from their siblings and their parents.

What is the independent assortment of chromosomes?

Independent assortment of chromosomes contributes to genetic variability due to the random orientation of homologous pairs of chromosomes at the metaphase plate during meiosis I. Each homologous pair of chromosomes segregates independently of every other homologous pair during metaphase I. ○ Therefore, the first meiotic division results in independent assortment of maternal and paternal chromosomes into daughter cells.

Where do gametes undergo the process of meiosis?

Instead, gametes undergo the process of meiosis, in which the chromosome number is halved. ○ Human sperm or ova have a haploid set of 23 different chromosomes, one from each homologous pair.

What is meiosis 1 for? What is the mechasm of serpsrating

Meiosis I is a reductional division because it halves the number of chromosome sets from two (the diploid state) to one (the haploid state). In contrast, meiosis II is an equational division. The mechanism for separating sister chromatids is virtually identical in both meiosis II and mitosis. The molecular basis of chromosome behavior during meiosis continues to be a focus of intense research interest.

What is meiosis 1 preceded by?

Meiosis I is preceded by interphase, in which the chromosomes are replicated to form sister chromatids. ○ The two genetically identical sister chromatids make up one replicated chromosome. ○ The sister chromatids are closely associated all along their length. This association is called sister chromatid cohesion.

What is the goal of meiosis

Meiosis halves the total number of chromosomes, reducing the number of sets of chromosomes from two (diploid) to one (haploid), with each daughter cell receiving one set. Mitosis conserves the number of chromosome sets. Meiosis produces cells that differ genetically from the parent cell and from each other. Mitosis produces daughter cells that are genetically identical to the parent cell and to each other.

What are mutations?

Mutations are the original source of genetic diversity.

how do offspring differ?

Offspring differ somewhat from their parents and siblings, which demonstrates variation.

What happens Once different versions of genes arise through mutation?

Once different versions of genes arise through mutation, reshuffling of alleles during meiosis and fertilization produce offspring with their own unique set of traits.

What do parents endow to offspring?

Parents endow their offspring with coded information in the form of genes.

What is the life cycle of some algae and algae?

Plants and some algae have a second type of life cycle called alternation of generations. ○ This life cycle includes two multicellular stages, one haploid and one diploid. ○ The multicellular diploid stage is called the sporophyte. ○ Meiosis in the sporophyte produces haploid spores. ○ Unlike a gamete, a haploid spore doesn't fuse with another cell but rather divides by mitosis to form a multicellular haploid gametophyte stage. ○ Gametes produced via mitosis by the gametophyte fuse to form the zygote, which grows into the sporophyte by mitosis. ○ In this type of life cycle, the sporophyte generation produces a gametophyte as its offspring, and the gametophyte generation produces the next sporophyte generation.

What are sperm cells have a set of?

Sperm cells or ova (gametes) have only one set of chromosomes—22 autosomes and an X (in an ovum) or 22 autosomes and an X or a Y (in a sperm cell).

What happens in synapsis and crossing over?

Synapsis and crossing over o During prophase I, replicated homologs pair up and become physically connected along their lengths by a zipper-like protein structure, the synaptonemal complex, in a process called synapsis.

What is the fertilized egg?

The fertilized egg (zygote) is diploid because it contains two haploid sets of chromosomes bearing genes from the maternal and paternal family lines.

Where does the human life cycle begin?

The human life cycle begins when a haploid sperm cell fuses with a haploid ovum. ○ The union of these gametes, culminating in the fusion of their nuclei, is fertilization.

What is the number of chromosomes represented by?

The number of chromosomes in a single set is represented by n. Any cell with two sets of chromosomes is called a diploid cell and has a diploid number of chromosomes, abbreviated as 2n.

What is the number of cobinatiojns possible?

The number of combinations possible when chromosomes assort independently into gametes is 2n, where n is the haploid number of the organism. ○ If n = 3, there are 23 = 8 possible combinations. ○ For humans with n = 23, there are 223, or more than 8 million possible combinations of chromosomes.

What is the occurrence of homologus pairs?

The occurrence of homologous pairs of chromosomes is a consequence of sexual reproduction. ○ We inherit one chromosome of each homologous pair from each parent. ○ The 46 chromosomes in each somatic cell are two sets of 23, a maternal set (from your mother) and a paternal set (from your father).

What are autosomes?

The other 22 pairs of chromosomes are called autosomes.

What is the random nature of fertilization?

The random nature of fertilization adds to the genetic variation arising from meiosis.

What is the transmission of ratis/

The transmission of traits from one generation to the next is called heredity or inheritance.

What are th 2 event unique to mitosis?

Three events unique to meiosis occur during meiosis I: Synapsis and crossing over Alignment of homologs on the metaphase plate Separation of homologs

What are the 3 mechanisms thea contribute to genetic variation?

Three mechanisms contribute to genetic variation arising from sexual reproduction: independent assortment of chromosomes, crossing over, and random fertilization.

What are the 2 distinct sex chromosome?

Two distinct sex chromosomes, the X and the Y, are an exception to the general pattern of homologous chromosomes in human somatic cells. ○ The pattern of inheritance of the sex chromosomes determines an individual's sex. ○ Human females have a homologous pair of X chromosomes (XX); males have one X and one Y chromosome (XY). ○ Most of the genes carried on the X chromosome are not found on the tiny Y chromosome, which has genes that are not found on the X chromosome. ○ Only small parts of the X and Y chromosomes are homologous.

What is the separation of the homologs?

eparation of homologs o During anaphase I of meiosis, the replicated chromosomes of each homologous pair move toward opposite poles, while the sister chromatids of each replicated chromosome remain attached. o In anaphase of mitosis, the sister chromatids separate.

What follows the disassembly of the synaptomel complex?

following disassembly of the synaptonemal complex in late prophase, the two homologs pull apart slightly but remain connected by at least one X- shaped region called a chiasma (plural, chiasmata). o Synapsis and crossing over do not occur during mitosis.