Chapter 6 biology review

chromosomes and meiosis
6.1
in the reproductive organs (ovaries testes)
where are germ cells located in the human body?
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autosomes directly affect only body, where as sex chromosomes directly affect the sexual characteristics of an organism
what is the difference between an autosome and a sex chromosome?
diploid; the combination of 23 chromosomes from the mother and 23 from the father restores the diploid number of chromosomes (46)
is the cell results from fertilization a haploid or diploid cell? Explain.
mitosis occurs throughout an organism’s lifetime throughout many cells of the entire body, compared to meiosis, which only occurs at certain times and only in the reproductive organs
does mitosis or meiosis occur more frequently in the body? explain your answer.
no, females do not have the Y chromosome, and they are able to survive.
do you think the Y chromosome contains genes that are critical for an organism’s survival? Explain your reasoning.
if the ends of two chromosomes stick together, the chromosomes will not separate correctly during meiosis. one of the resulting gametes will have an extra chromosome, and the other will be missing a chromosome
the ends of DNA molecules from telomeres that help keep ends of chromosomes from sticking to each other. why might this be especially important to germ cells, which go through meiosis and make haploid gametes?
somatic cell
cell that makes up all of the body tissues and organs, except gametes
somatic cell
gamete (germ cell)
sex cell ; an egg or sperm cell, that contains DNA that can passed to your offspring
gamete (germ cell)
homologous chromosome
chromosomes that have the same length, appearance, and copies of genes, although the alleles may differ
homologous chromosome
autosome
chromosomes that contains genes for characteristics not directly related to the sex of an organism
autosome
chromosome that directly controls the development of sexual characteristics, humans have two very different chromosomes X and Y, XX = F, XY= M, 23 pair of chromosomes, X=larger, contains numerous genes, including many that are unrelated to sexual characteristics, Y= contains genes that direct the development of tests and other male traits, smallest and carries the fewest genes
sex chromosome
process by which two gametes fuse and offspring that are a genetic mixture of both parents are produced
sexual reproduction
fusion of an egg and sperm cell
fertilization
diploid
cell that has two copies of each chromosome, one from an egg one from a sperm, chromosome # is 46
diploid
haploid
cell that has only one copy of each chromosome
haploid
meiosis
form of nuclear division that divides a diploid cell into haploid cells; important in forming gametes for sexual reproduction, forms genetically unique cells, only occurs at certain points in an organisms life
meiosis
somatic and germ(gametes)
two major cell groups
humans have 46- pairs of 23, identical to each other(unless a mutation has occurred), 23 from each of your parents.
each species has a characteristic # of chromosomes per cell
conditions of having 4 copies of each chromosome (4n) , found in plants, rare in animals
tetraploidy
process of meiosis
6.2
homologous chromosomes: same genes but have different versions of them; sister chromatids; copies of each other, produced by DNA replication
how do homologous chromosomes differ from sister chromatids?
an egg needs to provide the nutrients and building blocks for life to begin; a sperm only needs to reach the egg and deliver its DNA, so it is streamlined and small
explain why an egg is so much larger than a sperm cell?
genetic diversity would not increase because the maternal and paternal chromosomes would not arrange in new combinations.
I f, during metaphase 1, all 23 maternal chromosomes lined up on one side of the cell, would genetic diversity increase? explain.
meiosis 1:begins with diploid cell, homologous chromosomes separate; meiosis 2: begins with two haploid cells, sister chromatids separate
list the key differences between meiosis 1 and 2
mitosis: chromosomes are duplicated and the copies are separated, one for each cell gets half of each other, each new cell gets half of each homologous pair.
both mitosis and meiosis are types of nuclear division, but they result in different cell types. describe how the steps of meiosis 1 differ from those of mitosis
Gametogenesis
process by which gametes are produced through the combination of meiosis and other maturational changes
Gametogenesis
haploid cell produced during meiosis in the female of many species; these cells have little more than DNA and eventually disintegrate
Polar body
Sperm
male gamete, contains 22 autosomes and 1 sex chromosome, X or Y
Sperm
Mendel and heredity
6.3
sister chromosome
sister chromosome
homologous chromosome: two separate chromosomes, one from each parent, similar to each other; same length & carry same amount of genes. not copies of each other though, each half is a duplicated chromosome called a chromatid, together the two chromatids are sister chromatids
homologous chromosome vs. sister chromatids
meiosis - DNA has already been copied, divides homologous pair, producing two haploids
4 stages of meiosis
1. prophase 1
2. metaphase 1
3. anaphase 1
4. telophase 1
meiosis – DNA has already been copied, divides homologous pair, producing two haploids
prophase 1
nuclear membrane breaks down, centrosomes and centrioles move to opposite sides, spindle fibers start to assemble, duplicated chromosomes condense and homologous chromosomes pair up precisely: gene for gene down there entire length. sex chromosomes pair up, some regions of there DNA pair up as well
prophase 1
metaphase 1
homologous chromosomes are lined up on cell’s equator by spindle fibers, result is 23 chromosomes (some from each parent), this arrangement mixes up the chromosomal combinations and maintains genetic diversity
metaphase 1
anaphase 1
homologous chromosome pairs separate and move to apposite sides of the cell, sister chromatids remain connected.
anaphase 1
telophase 1
membrane forms again in some species, spindle fibers break down, cytokinesis, result is two cells that have unique combinations of 23 duplicated chromosomes from both parents
telophase 1
meiosis 2
divides sister chromatids, results in undoubled chromosomes.
meiosis 2
prophase 2
nuclear membrane breaks down, centromeres and centrioles move to opposite sides of the cell, spindle fibers assemble
prophase 2
metaphase 2
spindle fibers align the 23 chromosomes at the cell’s equator, sister chromosomes are still attached
metaphase 2
anaphase 2
sister chromatids are pulled apart and moved to opposite sides of the cell
anaphase 2
telophase 2
nuclear membrane forms, spindle fibers break down, cytokinesis. result is 4 haploid cells with a combination of genes from both parents
telophase 2
– meiosis has 2 cell divisions, mitosis only one
– in meiosis homologous chromosomes pair up on cell’s equator, in mitosis homologous chromosomes never pair up
– in anaphase 1 of meiosis sister chromatids are still paired, in anaphase in mitosis, sister chromatids are separated
– meiosis results in a haploid cell, mitosis results in a diploid
– meiosis has two cell divisions, mitosis only one
meiosis vs. mitosis
gametogenesis
sperm formation starts with a round cell and ends by making a stream lined cell that can move rapidly, DNA is packed tightly and most of the cytoplasm is lost
gametogenesis
Egg
female gamete, contains 22 autosomes and 1 sex chromosome, always X
Egg
careful observation can lead to consolations even though the underlining reason or mechanism behind the phenomenon is unknown
Mendel had no understanding of DNA as genetic material, yet he was able to correctly predict how traits were passed between generations. what does Mendel’s work in genetics show about the value of scientific observation?
Self pollination of purebred plants always yield the same traits, so Mendel could be sure that any changes he saw were the result of the crosses he made
Why is it important that Mendel began with purebred plants ?
The units of color ( purple and white) were both individually present. They had neither blended tighter nor vanished.
Mendel saw purple flowers in the f1 generation, but both purple and white flowers in the f2. How did thus help him see that traits are inherited as discrete units?
Probably not, because by experimenting with multiple traits, he could see that the ratio of dominant to recessive traits in monohybrid crosses was always 3:1
If Mendel had examined only one trait, do you think he would have developed the law of segregation? Explain.
Mendel observed the inheritance of certain either – or – traits were inherited over generations without becoming diluted. He hypothesized that he could answer this question by selectively breeding specific types of plants and observing the offspring.
You have learned that scientific thinking involves observing, forming hypothesis, testing hypotheses, and analyzing data. Use examples from Mendel’s scientific process to show how his work fit this pattern.
Trait
characteristic that is inherited
Trait
study of the heredity patterns and variations or organisms
Genetics
type of organism whose ancestors are genetically uniform
Pure bred
mating of two organisms
Cross
Mendel’s first law, stating that (1) organisms inherit two copies of genes, one from each parent, and (2) organisms only donate one copy of each gene in their gametes because the genes separate during gamete formation
Law of segregation
says that allele distribution during meiosis is random
law of independent assortment
condition of having more than the typical number of toes of fingers, dominant gene= if one of your parents have it you will have it
polydactyly
studied genetics of pea plants, father of genetics, studied the probability of genes, revealed the basics of genetic factors,
Gregor Mendel
Traits, genes, and alleles
6.4
All have something to do with a particular segment of DNA, of nucleotides. A gene is a region of DNA, a series of nucleotides that code for a protein. It can come in different forms, called alleles, that code for the same general type if information but the specifics vary. The locus tells were a particular gene or allele is located on a chromosome.
How are the terms gene, locus, and allele related
The only way a phenotype or genotype can be recessive is if both alleles are recessive
Explain why an organism’s genotype my be homozygous dominant, homozygous recessive, or heterozygous, but never heterozygous recessive
Locus; on chromosome 2 at the same locus
Suppose you are studying a fruit fly’s DNA and you discover a gene for antennae length on chromosome 2. What word would describe it’s location, and where would it be found in other fruit flies’ DNA
The recessive allele
If a recessive allele helps an organism reproduce, but the dominant allele hinders reproduction, which will be common in population?
The persons genotype is cc. If a disease of other trait is recessive, a person must have two recessive alleles for the trait to be expressed
Cystic fibrosis is a recessive disease that causes the production of abnormally thick, life- threatening mucus alleles for the trait to be expressed.
specific region of DNA that codes for a particular protein
Gene
any of the alternate forms of a gene that occurs at a specific place on a chromosome
Allele
all of an organism’s genetic material
Genome
characteristic of having two of the same alleles at the same locus of sister chromatids, TT or tt
Homozygous
collection of all of an organism’s genetic information that codes for traits
Genotype
characteristic of having two different alleles that appear at the same locus of sister chromatids, Tt
Heterozygous
collection of all an organism’s physical characteristics
Phenotype
allele that is expressed when two different alleles are present in an organism’s genotype
Dominant
allele that is not expressed unless two copies are present in an organism’s genotype
Recessive
punnett square
punnett square
traits and probability
6.5
all of the possible allele combinations of offspring resulting from a cross
what do the grid boxes in a punnett square represent?
multiple genotypes can cause the same phenotype. for example, the homozygous dominant genotype and the heterozygous genotype yield the same phenotype in simple dominant- recessive cases.
why does the expected genotype ratio often differ from the expected phenotypic ratio resulting from a monohybrid cross?
Mendel was able to observe that the inheritance of one trait did not influence the inheritance of the second trait.
how did Mendel’s dihybrid crosses help him develop his second law?
cross the two plants together. if the off spring are tall: short in a 3:1 ratio, the unknown plant is heterozygous, Tt. if all the offspring are tall, the unknown plant is homozygous dominant, TT
if you are working with two tall pea plants and know that one is Tt, how could you determine the genotype of the other plant?
all Y (yellow): 3:1, heterozygous, R:r ( round: wrinkled)
what would be the phenotypic ratios of the offspring resulting from the cross; YYRr * YyRr?
the recessive condition could be advantageous for survival in some way, or the dominant condition could be disadvantageous.
you have seen that one-quarter of offspring resulting from two heterozygous parents are homozygous recessive. yet for some genes, the recessive allele is more common in the population. Explain why this might be.
model for predicting all possible genotypes resulting from a cross, or mating
Punnett square
cross, or mating, between organisms that involves only pair of contrasting traits
Monohybrid cross
cross between an organisms with an organism with a recessive phenotype
Test cross
cross, or mating, between organisms involving two pairs of contrasting traits
Dihybrid cross
Mendel’s second law, stating that allele pairs separate from one another during gamete formation
law of independent assortment
likelihood that a particular event will happen
Probability
meiosis and genetic variation
6.6
each egg and sperm already have a mixture of chromosomes from both parents due to the independent assortment of chromosomes. since any sperm could potentially fertilize any egg, the potential allele combinations are numerous even for simple organisms.
briefly explain how sexual reproduction generates new allele combinations in the offspring
crossing over makes new combinations of maternal and paternal genes. in this way, an egg or a sperm not only receives a unique combination of the maternal and paternal chromosomes, but those chromosomes themselves become a unique patchwork of maternal and paternal genes.
how does crossing over contribute to genetic diversity?
Not necessarily. The gametes that you inherited from you parents could have contained more chromosomes from one of their parents than the other.
you know that you get half your DNA from your mom, half from your dad. does this mean you got one-quarter of your DNA from each of your grandparents? Explain your reasoning.
cross two organisms purebred for the two traits coded for by genes. Then cross the F1 generation. the more often the traits are inherited together, the closer the genes are on the chromosome.
suppose you know two genes exist on the same chromosome. how could you determine whether they are located close to each other?
no, sister chromatids are identical to each other, so an exchange of DNA segments would be meaningless.
mitosis creates daughter cells that are genetically identical to the parent cell. if crossing over occurred between sister chromatids during mitosis, would it increase genetic diversity? Explain.
exchange of chromosome segments between homologous chromosomes during meiosis 1
Crossing over
tendency for genes located close together on the same chromosome to be inherited together.
Genetic linkage
review
meiosis reduces the amount of chromosomes in the cell
diploid -> haploid
the word meiosis comes from the Greek word meaning “to diminish” or to make less. how does the words origin relate to its meaning?
a haploid cell contains one copy of chromosomes and a diploid cell contains two copies of chromosomes
the word haploid comes from the Greek word haplous which means single. The word diploid comes from the Greek word diplous which means double. Explain how these two terms meanings relate to their origins
a homologous cell has the same genes and a homozygous contains one trait
the Greek prefix homo means one and the same, how does this relate to the words homologous and homozygous
4
a fruit fly diploid cells with 8 chromosomes. explain how many chromosomes are in its haploid gametes.
genotype is the alleles
phenotype is physical expression
both make up an organism genetically
describe a similarity and a difference between genotype and phenotype
in crossing over sister chromatids exchange parts of them selves and at the end you have mixed chromosomes.
how does crossing over during meiosis 1 increase genetic diversity?
homologous genes has two of the same alleles on eon each chromosome of the homologous chromosome
how does the homozygous condition differ from the heterozygous condition? in your answer, use the terms gene, homologous chromosome, and allele.
it would double the amount of chromosomes as the last generation
consider a species with a 2n, or diploid. chromosome number of 4. if gametes were formed by mitosis, rather than meiosis. what would happen to the chromosome number of the offspring of these organisms over generations? explain.
no, because somatic cells are body cells, the mutation would have to be in the germ cells, the ones that get passed on
could a mutation in one of an individuals somatic cells be passed on to the individuals offspring? Explain your answer
smooth petals are dominant, parents are both heterozygous
imagine that you are studying the trait of flower petal shape in a species of plant. petal shape is determined by a single gene with two alleles. you make a cross of two plants with unknown genotypes, both with smooth petals, and get the following f1, offspring phenotypes: 23 wrinkled and 77 smooth. what conclusions can you draw about the inheritance of this trait? in your answer, include the probable genotypes of each parent, and indicate which allele is likely dominant.
diploid, it has two copies of the chromosomes
is the above cell diploid or haploid? explain.
law of independent assortment
in a particular species of butterfly, the genes for two different traits, antenna shape and antenna color, are located on the same chromosome. as a result crosses between these butterflies do not obey one of Mendel’s laws. Which law does not apply, and why?
what stage of meiosis is shown above? defend your answer.
metaphase, the chromosome are lined up at the equator of the cell
what stage of meiosis is shown above? defend your answer.
squirrel, porpoise, human, potato
list the organisms in the above graph, in order form least to most possible chromosome combination.
there are fewer chromosomes in squirrels then potatoes.
what can you infer from the graph about the number of homologous chromosome in squirrels compared to potatoes?
independent assortment, crossing over
look again at the picture of the egg and sperm cells on the chapter opener. each of these sperm cells is genetically unique. what are the sources of variation that make each one different from the others?
C, each parent contributes one set of chromosome to each offspring
researchers crossed two types of mice together. type A and type B. in the resulting offspring, half of the DNA for specifying traits comes from type A and half comes from type B. Why?
C, it reduces the number of chromosomes in each resulting gamete by half
unlike cells that divide by meiosis undergo two cell divisions. What is the significance of this second cell division to sexual reproduction
D, in a sex cell that undergoes fertilization
a mutation occurs in a gene on chromosome 3, which is shown above. this mutation could be passed along to offspring if it occurs-
A, 0
in peas, the gene for green pod color (G) is dominant to the gene for yellow pod color (g). the gene for round shaped peas(R) is dominant to wrinkled-shaped peas (r). if a plant that is homozygous dominant for both genes is crossed with a plant that is heterozygous for both genes. what is the probability that the offspring will have yellow pods and round peas?
if the process of meiosis shown here proceeds normally, how many chromosomes will cells A,B,C and D have ?
A, 2 each
if the process of meiosis shown here proceeds normally, how many chromosomes will cells A,B,C and D have ?
the influence of the environment on an organism
epigenetics
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