chapter 6 biology review

6.4

Traits, genes, and alleles

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 haploid cell contains one copy of chromosomes and a diploid cell contains two copies of chromosomes

the Greek prefix homo means one and the same, how does this relate to the words homologous and homozygous

a homologous cell has the same genes and a homozygous contains one trait

what would be the phenotypic ratios of the offspring resulting from the cross; YYRr * YyRr?

all Y (yellow): 3:1, heterozygous, R:r ( round: wrinkled)

Genome

all of an organism's genetic material

what do the grid boxes in a punnett square represent?

all of the possible allele combinations of offspring resulting from a cross

Dominant

allele that is expressed when two different alleles are present in an organism's genotype

Recessive

allele that is not expressed unless two copies are present in an organism's genotype

explain why an egg is so much larger than a sperm cell?

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

Allele

any of the alternate forms of a gene that occurs at a specific place on a chromosome

what is the difference between an autosome and a sex chromosome?

autosomes directly affect only body, where as sex chromosomes directly affect the sexual characteristics of an organism

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?

careful observation can lead to consolations even though the underlining reason or mechanism behind the phenomenon is unknown

haploid

cell that has only one copy of each chromosome

diploid

cell that has two copies of each chromosome, one from an egg one from a sperm, chromosome # is 46

somatic cell

cell that makes up all of the body tissues and organs, except gametes

Heterozygous

characteristic of having two different alleles that appear at the same locus of sister chromatids, Tt

Homozygous

characteristic of having two of the same alleles at the same locus of sister chromatids, TT or tt

Trait

characteristic that is inherited

sex chromosome

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

6.1

chromosomes and meiosis

autosome

chromosomes that contains genes for characteristics not directly related to the sex of an organism

homologous chromosome

chromosomes that have the same length, appearance, and copies of genes, although the alleles may differ

Phenotype

collection of all an organism's physical characteristics

Genotype

collection of all of an organism's genetic information that codes for traits

polydactyly

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

tetraploidy

conditions of having 4 copies of each chromosome (4n) , found in plants, rare in animals

Test cross

cross between an organisms with an organism with a recessive phenotype

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?

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

suppose you know two genes exist on the same chromosome. how could you determine whether they are located close to each other?

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.

Dihybrid cross

cross, or mating, between organisms involving two pairs of contrasting traits

Monohybrid cross

cross, or mating, between organisms that involves only pair of contrasting traits

how does crossing over contribute to genetic diversity?

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.

is the cell results from fertilization a haploid or diploid cell? Explain.

diploid; the combination of 23 chromosomes from the mother and 23 from the father restores the diploid number of chromosomes (46)

meiosis 2

divides sister chromatids, results in undoubled chromosomes.

briefly explain how sexual reproduction generates new allele combinations in the offspring

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.

Crossing over

exchange of chromosome segments between homologous chromosomes during meiosis 1

Egg

female gamete, contains 22 autosomes and 1 sex chromosome, always X

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

fertilization

fusion of an egg and sperm cell

I f, during metaphase 1, all 23 maternal chromosomes lined up on one side of the cell, would genetic diversity increase? explain.

genetic diversity would not increase because the maternal and paternal chromosomes would not arrange in new combinations.

Polar body

haploid cell produced during meiosis in the female of many species; these cells have little more than DNA and eventually disintegrate

anaphase 1

homologous chromosome pairs separate and move to apposite sides of the cell, sister chromatids remain connected.

homologous chromosome vs. sister chromatids

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

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

how do homologous chromosomes differ from sister chromatids?

homologous chromosomes: same genes but have different versions of them; sister chromatids; copies of each other, produced by DNA replication

each species has a characteristic # of chromosomes per cell

humans have 46- pairs of 23, identical to each other(unless a mutation has occurred), 23 from each of your parents.

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?

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

where are germ cells located in the human body?

in the reproductive organs (ovaries testes)

Probability

likelihood that a particular event will happen

Sperm

male gamete, contains 22 autosomes and 1 sex chromosome, X or Y

Cross

mating of two organisms

list the key differences between meiosis 1 and 2

meiosis 1:begins with diploid cell, homologous chromosomes separate; meiosis 2: begins with two haploid cells, sister chromatids separate

6.6

meiosis and genetic variation

the word meiosis comes from the Greek word meaning "to diminish" or to make less. how does the words origin relate to its meaning?

meiosis reduces the amount of chromosomes in the cell diploid -> haploid

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

does mitosis or meiosis occur more frequently in the body? explain your answer.

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

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

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.

Punnett square

model for predicting all possible genotypes resulting from a cross, or mating

why does the expected genotype ratio often differ from the expected phenotypic ratio resulting from a monohybrid cross?

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.

do you think the Y chromosome contains genes that are critical for an organism's survival? Explain your reasoning.

no, females do not have the Y chromosome, and they are able to survive.

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.

no, sister chromatids are identical to each other, so an exchange of DNA segments would be meaningless.

prophase 2

nuclear membrane breaks down, centromeres and centrioles move to opposite sides of the cell, spindle fibers assemble

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

telophase 2

nuclear membrane forms, spindle fibers break down, cytokinesis. result is 4 haploid cells with a combination of genes from both parents

Gametogenesis

process by which gametes are produced through the combination of meiosis and other maturational changes

sexual reproduction

process by which two gametes fuse and offspring that are a genetic mixture of both parents are produced

6.2

process of meiosis

law of independent assortment

says that allele distribution during meiosis is random

gamete (germ cell)

sex cell ; an egg or sperm cell, that contains DNA that can passed to your offspring

anaphase 2

sister chromatids are pulled apart and moved to opposite sides of the cell

two major cell groups

somatic and germ(gametes)

Gene

specific region of DNA that codes for a particular protein

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

metaphase 2

spindle fibers align the 23 chromosomes at the cell's equator, sister chromosomes are still attached

Gregor Mendel

studied genetics of pea plants, father of genetics, studied the probability of genes, revealed the basics of genetic factors,

Genetics

study of the heredity patterns and variations or organisms

Genetic linkage

tendency for genes located close together on the same chromosome to be inherited together.

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.

the recessive condition could be advantageous for survival in some way, or the dominant condition could be disadvantageous.

6.5

traits and probability

Pure bred

type of organism whose ancestors are genetically uniform

meiosis vs. mitosis

- 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

a fruit fly diploid cells with 8 chromosomes. explain how many chromosomes are in its haploid gametes.

4

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

How are the terms gene, locus, and allele related

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.

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

Locus; on chromosome 2 at the same locus

6.3

Mendel and heredity

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.

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.

how did Mendel's dihybrid crosses help him develop his second law?

Mendel was able to observe that the inheritance of one trait did not influence the inheritance of the second trait.

Law of segregation

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 independent assortment

Mendel's second law, stating that allele pairs separate from one another during gamete formation

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.

Not necessarily. The gametes that you inherited from you parents could have contained more chromosomes from one of their parents than the other.

If Mendel had examined only one trait, do you think he would have developed the law of segregation? Explain.

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

Why is it important that Mendel began with purebred plants ?

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

Explain why an organism's genotype my be homozygous dominant, homozygous recessive, or heterozygous, but never heterozygous recessive

The only way a phenotype or genotype can be recessive is if both alleles are recessive

Cystic fibrosis is a recessive disease that causes the production of abnormally thick, life- threatening mucus alleles for the trait to be expressed.

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

If a recessive allele helps an organism reproduce, but the dominant allele hinders reproduction, which will be common in population?

The recessive allele

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?

The units of color ( purple and white) were both individually present. They had neither blended tighter nor vanished.